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309 Cards in this Set
- Front
- Back
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two basic forms of refractive surgery
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1. Keratorefractive procedures
2. Lenticular (scleral) procedures |
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keratorefractive procedures
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lasers
incisions thermal implants non-laser lamellar surgery |
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Lenticular (scleral) procedures
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1. secondary lenses
2. scleral relaxation or expansion |
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what group dictates the amount of RE allowed to correct with Refractive Surgery?
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FDA
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main two lasers used for refractive surgery
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1. LADAR vision by Alcon
2. Visx Star S4 |
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t/f approval ranges for refractive surgery differ for cusom (computer guided) and conventional (non-computer guided)
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true
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approved astigmatism ranges for AK (astigmatic keratectomy)
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ideal 0-3 (extend to 4)
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approved astig ranges for PRK
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ideal 0-4 (extend to 5)
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approved astig ranges for LASIK
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ideal 0-7 (extend to 9)
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approved RE ranges for LASIK
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+3 to -10 (extended +6 to -15)
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approved RE ranges for PRK
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-1 to -6 (extended +5 to -11)
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Blepharitis
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-must be managed prior to RS
-Acute, chronic, or involving conj -Erythema & lid ulceration -staph etiology |
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chronic bleph
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-must be managed prior to RS
-typically seen w/ concomitant meibomianitis -symptoms: burn, FBS, crusty lids in morning -Signs: fibrin collarette, thickening of lid margin, madarosis (loss of lashes) |
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blepharoconjunctivitis
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must be mngd prior to RS
Palpebral & bulbar hyperemia limbal papillae or phlyctenules |
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meibomian gland dysfxn (meibomianitis)
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Symptoms: fluctuating vision, burning, FBS
Signs: Foam in tear film, inspissated meibomian glands, hyperemia, lid margin thickening Corneal involvement: peripheral neo, pannus, epi erosions, marginal ulcer, phlyctenules -assoc w/ sebaceous gland dysfxn *trx preop w/ doxycycline or erythomycin/bacitracin |
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what org causes angular bleph?
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moraxella
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treatment of MGD
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doxycyline (avoid sun exposure) or erythromycin/bacitracin
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_____ is thought to be responsible for diffuse lamellar keratitis
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Meibomian secretions
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Acute Bacterial Keratitis
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causes by Strep, Micrococcaceae, pseudomonas aeruginosa, enterobacteriaceae
*epithelial keratitis -> edema (stromal infiltration) -> hypopyon *risk factors for developing acute bacterial keratitis: trauma, HSV, persisten epi defect |
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Acute bacterial conj
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*most commonly due Staph aureus & Strep Pneum.
*hx includes tearing, redness, mp discharge, crusty lids in morning *signs: purulent discharge, subconj hemorrhage, conj hyperemia, conj membrane formation Trx: gram pos AB (bacitracin) |
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trx of acute bacterial conj
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gram positive antibiotic (bacitracin)
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most common ocular surface orgs
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staph epidermidis
corynebacterium |
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chronic bacterial conj
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by defn, lasting > 3 weeks
most commonly due to staph au. can also be due to gram - orgs |
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three main etiological agents for viral keratitis & conj
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adenovirus
HSV HZV |
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Acute nonspecific follicular conj is caused by
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adenovirus
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acute nonspecific follicular conj...
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-adenovirus
-redness, watery discharge, irritation -CI for RS if active infection |
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EKC is caused by..
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adenovirus 8,19,37
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EKC
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adenovirus 8,19,37
bilateral extremely contagious itch, red, watery discharge, irritation, lids stuck shut in am, can lead to vision loss 80% pts have diffuse SPK & SEI *avoid topical steroids CI only if SEIs are present |
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t/f acute nonspecific follicular conj is a CI in RS
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only if active infection
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when is EKC considered a CI for RS?
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is SEIs are present
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PCF is caused by...
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adenovirus 3,4,7
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PCF
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-adenovirus 3,4,7
-bilateral & mild -redness, watery discharge, irritation, fever, pharyngitis, lympadenopathy -milder than EKC -corneal signs include mild SPK |
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what percent of pts of EKC show corneal signs of SPK and SEIs?
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80%
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HSV
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*corneal involvement ranges from diffuse SPK to dendritic keratitis
*Assoc w/ preauricular lymphadenopathy, mild papillary & follicular conj, uveitis -hx of HSV is a strong relative CI -oral acyclovir should be used is RS is decided to be done |
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HZV
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-Herpes zoster(shingles) or chix pox
-Keratitis includes stromal keratitis, corneal scarring, neo, neurotrophic keratitis **absolute CI for RS!!! |
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etiologies of dry eye/ K sicca
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age
dry env hormonal changes meds CLs bleph LASIK RA |
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hallmark signs of dry eye to evaluate in LASIK post op
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-telangiectasia (severed corneal nerves)
-meibomianitis |
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trx of evaporative dry eye
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Restasis (works on Tcells to hold Tcell #s down -which are responsible for inflamm rxns)
Lotemax (which keeps current Tcells under control while restasis inh new growth) Doxy (has an anti-inflamm component) |
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types of dry eye
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1. evaporative
2. tear-deficient (sjogrens & non-sjogrens) |
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evaporative dry eye is due to...
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-blepharitis
-rosacea & MGD -infrequent blinking -lid disorder (proptosis, ectropion, etc..) -ocular surface disease (trachoma, chm burns) -environment -meds ***quality prob, not a quantity prob!!! |
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will a punctal plug help evaporative dry eye
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no- the pt has enough tears, they're just bad quality tears
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Sjogrens syndrome
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-autoimmune disease (RA)
-affects all moisture producing glands -dry eye, dry mouth -specific antibodies that may be present: SS-A, SS-B, ANA, RF) |
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Non-sjogrens syndrome
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-lac gland dysfxn caused by various diseases (sarcoidosis, trachoma, vitamin A def, trauma, atopy)
-other etiologies: diabetes, CLs, age, previous herpetic infection) |
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why is dry eye a CI for LASIK?
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b/c the procedure cuts central corneal flap, cutting corneal nerves. The nerves can no longer detect eye is dry and so eye won't produce tears. Because LASIK causes eye to be more dry, a pt with pre-op dry eye would be much worse
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5 categories of allergic conj
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1. Seasonal allergic conj (SAC)
2. Perennial allergic conj (PAC) 3. Vernal keratoconj (VKC) 4. atopic keratoconj (AKC) 5. GPC |
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Seasonal allergic conj (SAC)
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*symptoms last for a defined period of time (spring, summer, fall)
*asymptomatic in winter *personal or family hx of atopic disease (rhinitis, asthma, dermatitis) *ITCHING,CONJ INJECTION, CHEMOSIS, LID EDEMA *Trx: Patanol, Pataday |
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Perennial Allergic Conj (PAC)
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*symptoms last all year
*pet dander, dust mite, cockroaches |
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what type of allergic conj is usually asymptomatic in the winter?
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seasonal allergic con
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what type of allergic conj is due to pet dander, roaches, and dust mites?
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perennial allergic conj
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does perennial allergic conj tend to be symptomatic during certain times of the year or the whole year?
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entire year
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Vernal Keratoconj (VKC)
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*bilateral conj inflamm
*personal or fam Hx of atopic disease *almost exclusively in warm weather climates *majority of pts have atopic disease (asthma, eczema, rhinitis) *ITCHING *photophobia, blepharospasm, tearing, FBS *signs common in cornea & conj without skin involvement *2 forms: limbal & palpebral |
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this type of allergic conj occurs almost exclusively in warm weather climates
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vernal keratoconj (VKC)
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Palpebral VKC
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*hallmark sign: giant papillae on superior tarsal conj w/out inferior involvemnt
(cobblestone appearance) *can cause mechanical ptosis *papillae produce a ropy, mucous discharge & a lot of eosinophils |
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Limbal VKC
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*dark-skinned pts
*gelatinous papillae on limbus *Horner-Trantas dots *shield ulcer *SPK *vernal pseudogerontoxon (resembles arcus) *keratoconus (due to eye rubbing) |
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what is the hallmark sign of palpebral VKC
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giant papillae on superior tarsal conj w/ out inferior involvement
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what type of VKC commonly occurs in dark-skinned pts?
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limbal VKC
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two types of VKC
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palpebral
limbal |
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atopic keratoconj (AKC)
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*bilateral
*strong assoc w/ atopic derm *common hereditary *onset in childhood *men > women *peak incidence 30-50yo *age range teen to 50 *symptoms regress w/ advancing age *Affects 3% popln; 25% of those affected have ocular involvement *Type I hypersensitivity *Similar to VKC *hx of dermatitis, asthma, rhinitis *no seasonal variation *itch, tearing, ropy discharge, burn, photophobia, decreased vision, SPK, epi defects, corneal scarring & thinning, keratoconus, cataracts, symblepharon (palpebral conj sticks to bulbar conj) |
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t/f atopic keratoconj usually varies depending on the season
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false - no seasonal variation
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GPC
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-immune-mediated inflamm disorder
-giant papillae w/ creamy white center -decreased CL tolerance, CL mvmnt, high riding CLs, itch, mucous discharge, blurred vision, conj injection *Diagnosis defn: papillae min diameter 0.3mm + symptoms *Other etiologies: ocular prosthesis (fake eye), extruding scleral buckle, exposed sutures, filter blebs |
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diagnosis defn of GPC
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minimum diameter papillae of 0.3mm + symptoms
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____% of Americans have a RE (excluding presbyopia)
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40%
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prevalence of hyperopia & myopia in N.America
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hyperopia 49%
myopia 29% |
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Microcornea
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*diameter <10mm (normal globe size)
*non-progressive *unilateral or bilateral *cornea usually flatter than normal (leading to hyperopia) *risk for narrow angle glaucoma |
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microphthalmos
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small eye (microcornea) & abnormal eye contents
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nanophthalmos
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small eye (microcornea) & normal eye contents
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megalocornea
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corneal diameter > or = 13mm, with normal thickenss & curvature
*non-progressive *Bilateral *symmetrical *90% male (X-link recessive) *assoc w/ ectopia lentis, phacodonesis (lens moves back and forth), iridodonesis (iris fluctuates back and forth) *Differential-buphthalmos from congenital glaucoma |
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Sclerocornea
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-scleralization of cornea
-cornea curve flat 20-35D -non-progressive -bilateral -symmetrical -assoc w/ cornea plana |
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Keratoconus
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*Ectasia
*bilateral *symmetrical *hx of eye rubbing *symptoms btw 16-25 *inferior steepening, Fleisher ring, Vogt's Striae *advanced cases - Munson's sign(visible protruding out of the lower lid in downgaze due to cone pushing the lid out *corneal hydrops (rupture of descemets leading to edema, scarring, reduced VA) *scarring many times caused by RGP wear due to central touch |
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Keratoglobus
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*bilateral
*progressive (anomaly is present at birth, but progresses) *entire cornea thins (vs. just inferior part in keratoconus) (cornea will be 1/3 to 1/5 normal thickness) *k readings of 50-60D *globular shape of cornea *corneal hydrops may present (ruptures of Descemet's) *excessive thinning can lead to corneal rupture *PKP (penetration keratoplasty) is needed |
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what does PKP stand for?
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penetration keratoplasty
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PMD -pellucid marginal degeneration
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*bilateral
*asymmetry *non-inflamm peripheral ectatic disorder *inferior band of thinning 1-2mm wide (4:00 to 8:00) *max corneal protrusion occurs superior rather than within the area of thinning (like keratoconus) ** irregular against-the-rule ** classic crab claw pattern on topography **inferior thinning |
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medicamentosa (some meds assoc with temporary myopia)
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*Isotretinoin (Accutane)
*Morphine *Prednisone *Sulfonamides *Tetracyclines |
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Two basic categories of CIs for RS
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1. Absolute CI (under no conditions should these pts have RS)
2. Relative CI (maybe after assessing risk to benefit ratio) |
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defn of absolute CI
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under no circumstances should these pts have RS performed
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defn of relative CI
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pts may be eligible for RS with careful consideration taking into account the risk to benefit ratio
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Ocular & Systemic diseases assoc with hyperopia
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microcornea
sclerocornea sublaxated lens angle-closure glaucoma choroidal folds nanophthalmos optic disc drusen non-arteritic anterior ischemia optic neuropathy |
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ocular & systemic diseases assoc with myopia
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megalocornea
posterior keratoconus keratoglobus PMD anterior lenticonus microspherophakia congenital microcornea primary open-angle glaucoma Macular degeneration lattice degeneration retinal detachment AIDS Wagners Stickler Marfan Down Diabetes mellitus cerebral palsy Weill-Marchesani |
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is systemic lupus erythematosus absolute or relative CI?
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absolute
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is RA an absolute or relative CI?
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absolute
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is polyarteritis nodosa an absolute or a relative CI?
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absolute
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is pregnancy an absolute or a relative CI?
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absolute
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is AIDS a relative or an absolute CI?
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absolute
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Ocular disorders that are an absolute CI
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*Keratoconus
*Moderate-severe Dry Eye (Stevens-Johnson, cicatricial pemphigoid) *chemical burns *irregular astigmatism *cataracts |
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is Stevens-Johnson dry eye absolute or relative CI
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absolute
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is cicatricial pemphigoid absolute or relative CI
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absolute
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are chemical burns an absolute or relative CI
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abosolute
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is keratoconus an absolute or a relative CI
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absolute
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is irregular astigmatism absolute or relative CI
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absolute
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is glaucoma an absolute or relative CI?
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relative
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why is glaucoma a relative CI?
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-IOP is increased with suction ring
-steroid responders may be difficult to mng post op |
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why might controlled diabetes be a relative CI
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reduced healing response
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is herpetic keratitis a relative or absolute CI
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relative
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is epi bm dystrophy (EBMD) or other corneal dystrophies recommended to do LASIK?
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no, relative CI; recommend PRK if anything at all
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preop eval RE stability...
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should be within 0.50D in at least 1-2 years
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What refraction element is mandatory on every RS preop eval?
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1% cyclo exam
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soft sph CLs should be removed _____ (time) prior to preop exam
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3-7 days
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soft toric CLs should be removed _____ (time) prior to preop exam
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7-10 days
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RGPs should be removed ____ (time) prior to preop exam
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2-3 weeks
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PMMA lenses should be removed ____ (time) prior to preop eval
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4-6 weeks
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corneal curvature (K's) that are not eligible for RS
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below 36D or above 48D (pre or post op)
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how do you determine post op K's (before you do the surgery?)
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flat K - (spec Rx x 0.7)
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corneal measurements of keratoconus suspects
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K's greater than 48D
> 3D of infererior steepening |
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should pupil sizes greater than 6.5mm be recommended for traditional(non-custom) or custom RS?
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custom
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what does wavefront technology measure?
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higher order aberrations (Zernicke)
- needed to determine custom laser settings |
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is the wavefront measurement used to determine custom or traditional settings?
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custom
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what must the corneal thickness (via pachymeter) be in order to qualify for RS?
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greater than 500 microns
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what is the required thickness of the stromal bed needed to do RS?
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250 microns
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when doing topography for a preop eval, do we typically look at the absolute scale or the relative scale?
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relative scale
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t/f corneal topography measusres corneal curvature as a 3-D image
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false; 2-D
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at every point on the cornea, there are two major curvatures measured by the topographer. they are...
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maximum curvature
minimum curvature |
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what is the difference btw the maximum curvature and the minimum curvature of the cornea a measure of?
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astigmatism
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most commonly used topographic maps:
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axial
tangential (meridional) |
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axial curvature used for topography
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average of the tangential curvature over an interval from the topographic center to the surface point along tangential planes
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tangentional (meridional) curvature used for topography
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uses equations for curves on the surface of the cornea along the tangential planes of intersection which is converted to diopters using the formula: 1-1.3375/r x 1000
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t/f a prolate cornea has better vision than an oblate cornea
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false - not proven to be true
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most popular instrument for elevation topography
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Orbscan by B&L - gives info on anterior float, posterior float, K's , corneal thickness
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Form Frust Keratoconus
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*20/20 VAs
*42D K's * posterior float of concern |
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t/f steeping of 3D or less in the inferior cornea is normal. Anything above this suspect keratoconus
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true
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anterior cornea best fit reference...
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8.33mm sphere (epithelial side)
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posterior cornea best fit reference...
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6.88mm sphere (endothelial side)
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is the epithelial (anterior) or the endothelial (posterior) side of the cornea steeper?
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the posterior endothelium
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posterior surface elevation topography is thought to be correlated in the early detection of...
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corneal ecstatic conditions
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when is a posterior float clinically significant?
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if we find 40 microns in the highest area
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two main types of aberrations
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1. chromatic - refractive index is a fxn of color or frequency
2. monochromatic |
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Monochromatic aberrations subgroups:
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A. Primary or lower order Abs
-spherical abs -coma -astigmatism -field curvature -distortion B.Higher Order Abberations -Secondary astigmatism |
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normal emmetropic eye is free of aberrations when the pupil diameter is...
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less than 2.5mm
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t/f an increase in pupil size results in an increase in retinal img quality
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false - quality decreases due to peripheral ray aberration
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what is wavefront aberrometry used for?
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to determine the optical aberrations of the eye
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how does wavefront aberrometry work?
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1.laser project a wavefront into eye
2.sensor detects reflected wave & compares it to an 'ideal' wave 3.aberrations are calculated & displayed on a 3-D map |
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Aberrations are classified as lower and higher... what are lower and what are higher?
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lower - myopia,hyperopia,astig
higher - glare,shadow,halo... |
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name two manufacturers of wavefront aberrometers
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1. VISX
2. Alcon LADARwave |
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Does LASIK & other refractive surgeries induce or fix optical aberrations?
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induces
(custom focuses on removing the higher orders, but not the lowers) |
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what does LASIK stand for?
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Laser Assisted in-Situ Keratomileusis
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what is the difference btw LASIK, LASEK, and PRK when considering the corneal flap?
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LASEK cuts flap a lot thinner than LASIK & the flap is cut off (not hinged)-then flap is put back on
PRK cuts of epi all together and doesn't replace it (it will grow back) |
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Two basic types of Microkeratomes
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Mechanical
Laser (femtosecond lasers; Intralase) |
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3 basic parts making up the mechanical microkeratome
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-peripheral part
-central unit -connections/accessories |
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which part of the mechanical microkeratome contains the suction ring, cutting head, and driving unit?
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the peripheral part
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the peripheral part of the mechanical microkeratome consists of...
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suction ring
cutting head driving unit |
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what part of the mechanical microkeratome determines the size of the flap (indirectly determining the size of the ablation zone)
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the suction ring (which is part of the peripheral part of the mechanical microkeratome)
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Suction ring of the mechanical microkeratome
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*determines size of flap (which indirectly determines size of ablation zone)
*applied to cornea (so central unit of the microkeratome can provide vacuum to draw the cornea into the ring, stabilizing the globe) |
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Cutting head of the mechanical microkeratome
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(part of the peripheral unit)
*consists of a plate (holds cutting head in place) *plate is separated from blade by a certain number of microns to determine thickness *Motorized drive unit moves the blade across the cornea, stopping about 3/4 of the way to create the hinge |
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Drive unit of the mechanical microkeratome
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(part of the peripheral unit)
*delivers energy to the motor (cutting head) *creates vacuum for ring (IOP can be raised to 60-70) |
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IOP is raised to _____ when creating a flap using the mechanical microkeratome
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60-70
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possible complications using the mechanical microkeratomes
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free caps
buttonhole caps epi erosion diffuse lamellar keratitis |
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thickness of flap cut with a mechanical microkeratome
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140-180 microns
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what must be done after the flap created by the mechanical microkeratome has been peeled back before ablation begins?
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must do pachymetry to see if there is enough stromal bed left!
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when creating the flap, is the IOP raised higher with the mechanical or the laser microkeratome?
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the mechanical (60-70)
(laser is only 30) |
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generic and brand name of the lasers microkeratomes
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femtosecond lasers (intralase)
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does the laser microkeratome use long or short pulses?
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ultra-short (10 ^ -15)
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what wavelength is used with the laser microkeratomes?
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1053 nm (IR) (cornea is transparent to IR)
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t/f cornea is transparent to IR
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true (this is good since laser microkeratomes use 1053 nm wavelengths which are IR)
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how do laser microkeratomes work?
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1. delivers ultrashort pulses of 1053nm IR waves (cornea is transparent to IR)
2. this causes molecular disruption due to anatomic ionization 3. results in vaporized matter in the form of cavitation bubbles, which separate the tissue |
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the corneal ring used with laser microkeratomes raises the iop to...
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30mmHg
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depth of the flap cut in laser microkeratome (& ideal depth used for intralase)
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potential cut 90-400 microns
optimal intralase = 110 mic. |
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advantages of laser over mechanical microkeratome methods
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1.better control of flap depth
2.hinge can be placed anywhere 3.size easily adjusted |
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disadavantages of laser over mechanical microkeratome
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-takes longer to heal due to cavitation bubbles
-more painful healing |
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what separates the corneal flap from the stroma in the case of the laser microkeratome?
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cavitation bubbles
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interactions btw the cornea & laser radiation are grouped into 4 types:
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1.absorption
2.transmission 3.reflection (little effect on cornea) 4.dispersion (litte effect on cornea) |
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effects of absorption & transmission on the cornea vary based on ...
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wavelength
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corneal transmission is maximal btw which wavelengths?
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btw 400-1600 (argon & YAG lasers) (longer wavelengths penetrate ('transmit') thru cornea; shorter waves don't)
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corneal absorption is the main effect when the wavelength is at...
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below 350nm (photoablation)
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match:
Absorption Transmission 400-1600 nm below 350nm photoablation Argon lasers YAG lasers |
transmission - btw 400-1600nm
& Argon/YAG lasers absorption - below 350nm & photoablation |
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do longer or shorter wavelengths penetrate thru the cornea?
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longer do (short don't)
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Effects of laser application applicable to RS is (transmission or absorption), more specifically ______.
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absorption - specifically photoablation (wavelengths under 350nm)
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Photoablation used for RS:
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-uses UV radiation
-very superficial due to very short wavelengths (below 350) -tissue is vaporized thru disruption of chem bonds secondary to photonic energy -"Flying Spot" excimer lasers reduce any thermal effect by having a very short pulse frequency & varying the distance btw spots allowing spots to "cool down" btw pulses. -thermal effect is not strong enough to cauterize tissue (therefore, bleeding occurs after application) |
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does photoablation use IR or UV radiation?
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UV (which is absorbed by cornea)
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what is the purpose of the 'flying spot' used with photoablation during RS?
|
flying spot excimer lasers reduce any thermal effect of the laser by having a very short pulse frequency & varying the distance btw spots allowing spots to 'cool down' btw pulses
|
|
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t/f the thermal effect of photoablation by excimer lasers is strong enough to cauterize tissues, so no bleeding will occur afterward
|
false - not strong enough, therefore we will see bleeding afterwards
|
|
|
three excimer beam delivery systems
|
1. full beam system
2. scanning slit delivery sys 3. flying spot delivery sys |
|
|
this type of excimer delivery system uses early generation lasers
|
full beam system
|
|
|
advantages & disadvantages of the full beam system
|
Adv: rapid trx & low sensitivity to decentering
Disadv: nearby thermal effects (worse for higher myopes b/c they are exposed to the laser longer during the RS) |
|
|
full beam system procedure
|
*produces shock wave responsible for central islands (portion of cornea which is less treated than other areas secondary to plume of ablated tissue) (plume cloud like atom bombs)
*a refractive mask or diaphragm must be used |
|
|
does a diaphragm or refractive mask need to be used with the full beam system, the scanning slit system, or the flying spot delivery system?
|
full beam system
scanning slit delivery |
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|
scanning slit delivery procedure
|
*a rectangular 10mm x 1mm beam is created by a diaphragm
*the beam is attached to a rotary device allowing the beam to 'scan' in many directions |
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advantage of the scanning slit delivery system
|
rapid treatment
low sensitivity to decentering |
|
|
what type of RE can be corrected using the scanning slit delivery sys?
|
all types of ametropia
|
|
|
what delivery system method is used for custom LASIK?
|
the flying spot delivery system
|
|
|
shape and size of the flying spot beam
|
circular and small (0.6-2.0mm)
|
|
|
in the flying spot delivery system, is the center of the beam or the periphery of the beam used the most?
|
center (most homogenous)
|
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t/f a diaphragm is needed in the flying spot delivery system
|
false
|
|
|
flying spot procedure
|
1.circular small center of the beam is used to ablate the tissue with many pulses while only removing a small amount of tissue per pulse
2.spots are separated to avoid thermal effects 3.eye tracking software is used (b/c sys is very sensitive to decentering) - camera records iris and IR detector determines eye mvmt. |
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advantages and disadvantages to the flying spot delivery system
|
Adv: able to produce asymmetric ablation profiles when coupled w/ topographers or wavefront analyzers
Disadv: very sensitive to decentering |
|
|
what is eye tracking software, why is it used, and with what delivery system?
|
-used in flying spot delivery systems b/c sys is very sensitive to decentering
-camera records iris and IR detector determines eye mvmt. -tracks in X and Y axes and cyclotorsion axes when pt lies down. |
|
|
surgical technique of LASIK for myopia
|
-suction ring is applied, increasing IOP to 60.
-ablation depth is important -traditional removes 15mic.; custom removes 20-40mic. -following surgery, cornea follows an oblate shape |
|
|
how much stroma is ablated in the traditional technique on a myopic eye?
|
15 microns
|
|
|
how much stroma is ablated in the custom technique on a myopic eye?
|
20 microns
|
|
|
how is the risk of corneal ectasia following ablation in a myopic eye minimized?
|
1. assuring a residual stromal bed of at least 250-300 microns (what's left)
2. Not doing RS on eyes w/ less than 500 mic total thickness 3. careful screening of those with asymmetrical corneal astigmatism (PMD & keratoconus) |
|
|
does LASIK on a myopic eye induce more or less positive spherical aberrations?
|
more
|
|
|
procedure of LASIK on hyperopic eye
|
1. peripheral cornea is flattened, therefore steepening central cornea
2. ablation zone is applied in an annular fashion 3. edge of optic zone is thinnest 4. transition zone must have additional ablation performed to "blend" the central steep area with the untouched periphery |
|
|
under what conditions are RS outcomes significantly better and more predictable in the hyperopic eye?
|
when the hyperopia is less than +4D (very unpredictable above 4, fairly unpredictable above 2)
|
|
|
corneal aberrations increase significantly after hyperopic LASIK...esp this type of aberration...
|
spherical aberrations (due to increase in prolate shape)
|
|
|
t/f surgically induced aberrations with traditional LASIK increase loss of contrast sensitivity
|
true - custom tries to reduce the loss
|
|
|
when are topography guided ablations used vs wavefront guided ablations
|
topo guided are used when aberrations are mainly caused from the corneal surface; wave guided used when aberrations are from all portions of the eye
|
|
|
which are more commonly used - topography guided or wavefront guided ablations?
|
wavefront
|
|
|
does the topography guided ablation follow axial, tangential, refractive, or elevations maps for the ablation?
|
elevation maps
|
|
|
topography guided ablations procedure
|
1.couped with a flying spot or scanning laser
2. a 3-D corneal view is acquired & the volume of tissue ablation is calculated 3. goal is to create an aspheric surface free of corneal aberrations (4. some units can remove epi (prk) as well as shape stromal bed) |
|
|
what type of laser is the topographer coupled with in topography guided ablations?
|
flying spot or scanning laser
|
|
|
what type of ablation technique is used when the aberrations are from all portions of the eye vs from just the corneal surface?
|
wavefront guided ablations
|
|
|
what is the goal of the topography guided ablations?
|
to create an aspheric surface free of corneal aberrations
|
|
|
what is the goal of wavefront guided ablations?
|
to create a close to "perfect eye" where monochromatic light would be free of aberrations and all light rays would come into focus on the fovea (ideally, the ablation would cancel the phase differences within the wavefront)
|
|
|
results of what custom technique show that the custom laser can reduce the induced higher-order aberrations associated with LASIK?
|
wavefront guided ablations
|
|
|
how do we cancel the phase differences in the case of wavefront guided ablation?
|
shorten optical path - use modulated acceleration of the slower waves - taking into account the cornea's refractive index
|
|
|
how is the thickness of the corneal tissue to be removed decided in the case of wavefront guided ablation?
|
the thickness of the corneal tissue to be removed is = length of the optical path difference x refractive index of the stroma
|
|
|
how do wavefront aberrometers measure the aberrations in wavefront guided ablations?
|
wavefront scanners measure the wavefront aberrations before flap is created and mathematically transfers the ablation pattern for use under the flap
|
|
|
Preop LASIK complications
|
1.SPK (secondary to allergic rxn to topical anesthetic) (anesth applied ot superior & inferior conj decreases chance of SPK)
2. epi defect from an allergic rxn to topical anesth |
|
|
Microkeratome complications (cutting the flap)
|
1.irregular/incomplete flap formation
2. free cap 3. button hole flap 4. corneal perforation 5. corneal epi defect 6. corenal bleeding 7. edematous flaps |
|
|
Irregular or Incomplete flap (microkeratome complications)
|
-microkeratome stops prior to creating a complete flap
-less than 1% -wait 3-6 mos before another attemp to cut flap |
|
|
Free Cap microkeratome complication
|
-microkeratome passes completely thru cornea
-less than 1% -procedure can procedd if exposed stroma is equal or larger than ablation zone -cap replaced in original position epi side up -sutures not necessary -bandage CL if epi is dmgd *"avoid hi-risk activities while eye heals" -can be due to a flat cornea (< 41D) or to insuff suction -using a larger suction ring will provide more corneal tissue |
|
|
Button hole Flap microkeratome complication
|
-occurs when Mkeratome blade comes to the surface of the cornea & returns underneath as flap is created
-worst outcome of flap complications in terms of BCVA -Provides channel for epi cell ingrowth -increased risk of subepi scar formation -if happens, abort procedure -can reattempt in 3-6 mos -due to steep corneas, low Ks, and eyes with previous RS |
|
|
Corneal perforation microkeratome complication
|
-human error in placement of the microkeratome
-difficult w/ newer keratomes -if occurs, suture with a 10-O Nylon suture |
|
|
Corneal epi defect microkeratome complication
|
-defect secondary to loose epi from excess anesthetic or to dry corneal surface (epi sticks to blade)
-epi should be replaced is possible -use bandage CL with topical Ab to prevent infection, provide pain control, & stabilize flap to prevent epi cell ingrowth ***mild dosing of topical NSAID can be used for pain (although this slows epi healing) (bid-tid x 2-3 days) -should rule out epi defect masquerade syndrome |
|
|
in the case of a corneal epi defect (due to a microkeratome complication), what can be used to mng pain?
|
***mild dosing of topical NSAID can be used for pain (although this slows epi healing) (bid-tid x 2-3days)
|
|
|
corneal bleeding (microkeratome complication)
|
occurs when microkeratome contacts limbal vessels during procedure
|
|
|
Edematous flap (microkeratome complication)
|
-due to excessive manipulation of the flap
-floating flap phenom may occur (flap decentration) -aggressive steroid use post-op can help reduce edema |
|
|
surgical eligibility: traditional ablation removes ____microns tissue; custom removes _____
|
traditional = 15 micronsD
custom = 20 microns/D |
|
|
guidelines of RE eligibility for RS
|
-1 to -9 (5D reg astig)
+1 to +3 (4D reg astig) |
|
|
corneal curvature values for RS eligibility
|
< 36 or > 48 not eligible
(for pre or post op) (to determine post op Ks: flat K - (spec Rx x 0.75) |
|
|
pupil size requirements for RS eligibility
|
if pupils greater than 6.5 mm, custom procedure recommended
|
|
|
the mechanical microkeratome creates a flap of _____
|
160 microns
|
|
|
Intralase creates a flap of _____
|
110 microns
|
|
|
minimum age of LASIK requirement
|
18
|
|
|
anesthesia used in LASIK
|
45 mins pre-op give 5-10mg oral sedation diazepam & 1-2 drops proparicaine
|
|
|
is a miotic agent used in LASIK pre-op?
|
no
|
|
|
trx in case of edematous flap
|
aggressive steroid to reduce edema
|
|
|
photoablation operative complications?
|
-central islands
-decentered ablation zone -flap wrinkling -interface debris |
|
|
central islands
|
-steep areas w/in ablated area
-classified by width in mm & height in diopters -symptoms-irregular astig,monoc diplopia,loss of BCVA,glare,ghosting -common 3-29% -Causes: plume dynamics, acoustic shock waves, temporal degradation of the laser, wound healing anomalies *typically spontaneously resolve |
|
|
how are central islands classified?
|
by width in mm and height in diopters
|
|
|
symptoms assoc with a central island
|
irregular astigmatism
monocular diplopia loss of BCVA glare ghosting |
|
|
% of cases of central islands
|
3-29%
|
|
|
steep areas of cornea within the ablated area due to a photoablation operative complication
|
central islands
|
|
|
proposed causes of a central island
|
-plume dynamics
-acoustic shock waves following laser corneal contact -temporal degradation of the laser -wound healing anomalies |
|
|
trx of a central island
|
typically spontaneously resolve
|
|
|
Decentered Ablation Zone
|
classified as mild (0-0.5mm), moderate (0.5-1.0) or severe (> 1.0mm)
-symptoms: Monocular diplopia,glare,halo -caused by eye drift or misaligned laser -topographic ablation is best option (wavefronts can't be acquired due to irregular corneal surface) -Alphagan P can be used to increase night vision quality (its a scotopic miotic - to reduce glare) |
|
|
how is a decentered ablation zone classified?
|
mild 0-0.5mm
moderate 0.5 - 1.0 mm severe > 1.00 mm |
|
|
symptoms of a decentered ablation zone
|
-monocular diplopia
-glare -halo |
|
|
what is the cause of a decentered ablation zone?
|
eye drift or misaligned laser
|
|
|
what is the trx or best option to trx a decentered ablation zone?
|
*topographic ablation (wavefronts can't be acquired due to irregular corneal surface)
*give Alphagan P for nighttime glare |
|
|
Flap Wrinkling
|
1.Intraoperative (surgeon)
-due to malpositioned flap -post surgical wrinkling will be detected immediately postop -mild wrinkles outside visual axis not always treated 2. Postoperatively (pt) -due to eye rubbing or excess eyelid pressure -may appear as fine fingerprints & best seen with indirect illum -mild wrinkles outside visual axis not always treated.(or dump steroids on it, or use a LASIK iron) |
|
|
Interface debris
|
*thought to be caused by:
-conj epi cells -skin epi cells -meibomian secretions -glove powder -debris from swabs -microkeratome blade fragments -ocular surface mucous *trx involves lifting flap & irrigating (or dump steroids on it if it's not in the pupil area) |
|
|
most common early postop complication
|
undercorrection of ametropia
|
|
|
rate of early postop complications
|
-about 3%
|
|
|
most common complication after retreatment for undercorrection
|
overcorrection
|
|
|
a dislogded flap is most commonly seen within _____ post op.
|
24 hrs
|
|
|
how long post op is a dislodged flap still susceptible?
|
2-3 mos
|
|
|
DLK is aka
|
sands of the sahara
|
|
|
t/f DLK is an infectious inflammation btw the flap and the stroma
|
false - sterile inflamm (clx show no bacterial or fungal growth)
|
|
|
DLK appears ______ days following surgery
|
1-3
|
|
|
what causes DLK?
|
allergic or toxic rxn to interface debris
|
|
|
symptoms of DLK
|
FBS
Photophobia Tearing Pain |
|
|
how can we differentiate btw SPK and DLK?
|
DLK is deep so will not stain. SLK is superficial, so will stain
|
|
|
Stage 1 DLK incidence
|
1 in 50
|
|
|
appearance of stage 1 DLK
|
white granular cells accumulate in peripheral interface - usually 1-3 days post op
|
|
|
trx of stage 1 DLK
|
1% prednisolone q1h - typically results in complete resolution
|
|
|
Stage 1 DLK
|
1:50
white cells in periphery 1-3 days post op 1% prednisolone q1h |
|
|
Stage 2 DLK
|
1:200
white cells spread diffusely 2-3 days post op 1% prednisolone q1h short, rapidly tapering course of oral methylprednisolone for 2-3 days (for max anti-inflamm) |
|
|
incidence of Stage 2 DLK
|
1 in 200
|
|
|
appearance of stage 2 DLK
|
white granular cells spread diffusely completely under flap
|
|
|
stage 2 DLk seen ____ days post op
|
2-3 days
|
|
|
treatment of stage 2 DLK
|
1% prednisolone q1h
short, rapidly tapering course of oral methylprednisolone for 2-3 days(for max anti-inflamm activity) |
|
|
stage 3 DLK
|
1 in 500
central clump of white, granular inflamm cells 2-3 days post op *main risk is release of inflamm mediators & collagenolytic enzymes from PMNs (can lead to stromal melting) Trx-lift flap, irrigate -may see endo folds due to edema trx-topical 4th gen fluoroquinolone ab & 1% prednisolone |
|
|
incidence of stage 3 DLK
|
1 in 500
|
|
|
appearance of stage 3 DLK
|
-central clumping of white, granular inflamm cells
-endo folds due to corneal edema |
|
|
stage 3 DLK seen ____ days post op
|
2-3 days
|
|
|
treatment of stage 3 DLK
|
*lift flap, obtain tissue for analysis, gently irrigate
*topical 4th gen fluoroquinolone ab *1% prednisolone |
|
|
main risk to cornea in stage 3 DLK
|
release of inflamm mediators & collagenolytic enzymes from aggregated PMNs - can lead to stromal melting
|
|
|
stage 4 DLK
|
1 in 5000
stromal melt resulting in permenanet abnormalities -resolved stromal melting will lead to scarring no matter what - leading to permanent vision loss |
|
|
incidence of stage 4 DLK
|
1 in 5000
|
|
|
stromal melting is seen stage ____ DLK
|
stage 4
|
|
|
most common causative org of bacterial keratitis
|
gram positive bacteria & mycobacteria
|
|
|
bacterial keratitis (risk 0.1 - 0.2%)
|
-most common is Gm + & mycobacteria
-symptoms: pain, photophobia, decreased VA, halos -signs: conj injection, ant chamber rxn, hypopyon in severe cases -4th gen fluoroquinolone qid x 4-5 days |
|
|
normal post op regiment
|
4th gen fluoroquinolone qid x 4-5 days
|
|
|
epithelial ingrowth
|
-epi cells grow beneath the flap creating a 'nest' of cells
- can lead to corneal melting in severe cases -typically detected w/in 1 month of surgery (incidence is 4.3%) -cause is poor flap adhesion or epi defect -symptoms: FBS,photophobia, glare -trx is recommended is cells are greater than 2 mm from flap edge -trx involves lifting flap & cells removed -flap should be monitored 1-2 wks after surgery, then at 1, 2, and 3 mos. -trx with steroids |
|
|
appearance of epi ingrowth
|
corneal epi cells grow beneath the flap creating a "nest" of cells
|
|
|
severe cases of epi ingrowth can lead to....
|
corneal melting
|
|
|
epi ingrowth is typically detected ______ postop (time)
|
within 1 month of surgery
|
|
|
cause of epi ingrowth
|
poor flap adhesion or epi defect
|
|
|
symptoms of epi ingrowth
|
FBS
photophobia glare |
|
|
treatment of epi ingrowth
|
-recommended if cells are greater than 2mm from flap edge
-lift flap & remove cells -trx with steroids |
|
|
Late post op complications
|
1.Regression
2.Iatrogenic Keratectasia 3.Night Vision complaints |
|
|
potential mechanisms for regression
|
-wound healing
-iatrogenic keratectasia -epi hyperplasia -lenticular nuclear sclerosis |
|
|
Iatrogenic keratectasia can occur ____ time post op
|
btw 1 wk to 2 years
|
|
|
how do we tell the difference btw keratectasia & a central island?
|
a central island tend to fade away within a few mos post op, keratectasia will progress
|
|
|
trx of iatrogenic keratectasia
|
take steroids for a year
corneal transplant intracorneal rings & eventually PK |
|
|
night vision complaints post op due to...
|
pupil size exceeding optic zone diameter, inc in sph aberration, decentered ablations, induced astigmatism
|
|
|
PRk stands for...
|
photorefractive keratectomy
|
|
|
prk uses ____ lasers at ___ nm
|
excimer, 193nm
|
|
|
RE approved for PRK
|
1 - 7 D myopia
|
|
|
regression of RE post op PRK happens how long after surgery
|
6-12 months
|
|
|
regression after prk is caused by...
|
stromal regeneration
epi hyperplasia |
|
|
typical amount of stroma removed during prk
|
70 mic
|
|
|
if more than 70 mics are removed during prk, what is applied to cornea to decrease haze formation?
|
mitomycin C (***)
|
|
|
Lasek stands for
|
laser assisted subepi keratectomy
|
|
|
adv of lasek over prk
|
decreased pain post op
reduced post op scarring faster recovery time |
|
|
post op mngmt after lasek
|
bandage CL used for 2-4 days to encourage epi healing
ab & steroid used qid 5-10 days |
|
|
Epi-Lasik stands for
|
epi laser in situ keratomileusis
|
|
|
is epi reapplied following prk?
|
no
|
|
|
is epi reapplied after Lasek?
|
yes
|
|
|
is epi reapplied after epi-lasik
|
yes
|
|
|
intracorneal rings will correct what range of RE?
|
myopia - 1.00 to -3.00
|
|
|
advantages of intracorneal rings
|
-removable
-don't create scarring |
|
|
Intacs (intracorneal rings) 0.25mm fix what RE?
|
-1.30 (range -1 to -1.6)
|
|
|
intacs (intracorneal rings) 0.30mm fix what RE?
|
-2.00 (range -1.75 to -2.25)
|
|
|
intacs (intracorneal rings) 0.35mm fix what RE?
|
-2.70 (range - 2.375 to -3.00)
|
|
|
intracorneal rings are placed vertically to correct...
|
keratoconus
|
|
|
intracorneal rings are placed horizontally to correct...
|
refractive error
|
|
|
how does radial keratotomy work?
|
by thinning out peripheral corenea, causing central cornea to bulge forward
|
|
|
following RK, you see a pt with 8 spoke like incisions...how would you record this finding?
|
8-incision keratotomy
|
|
|
t/f with RK, the higher the myopia, the more incisions made.
|
true
|
