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79 Cards in this Set
- Front
- Back
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What are 4 anatomical measurements that should be done? |
- Blink rate (12-15 is normal) - Horizontal visual iris diameter (HVID) - Palpebral aperture/lid position - Pupil diameter |
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Large cornea will require ___ sagittal height and a ___ lens, Small cornea will require a ___ lens |
higher/ steeper, flatter |
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Lid position is especially important for fitting __ |
RGP |
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The patient will report blurry if the pupil size is ___ than the OZD - this is not important in soft lenses because OZD is >__mm |
larger, 8mm |
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Contact lenses are usually not contraindicated in patients with ____ and ____ |
Entropion, trichiasis |
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Tear meniscus detects ____ and insufficient tear prism indicates ____ deficiency |
borderline DES, aqueous deficiency |
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What tests measures tear quality and tear quantity? |
- TBUT (Quality) - Schimer and Phenol Red (Quantity) |
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___ test is more irritating to the patient and must be done for 5 minutes |
Schimer Tear test |
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IF Schimer tear test is done without anesthesia, patient will feel the strip and this will cause ___ ___ IF Schimer tear test is done with anesthesia, this measures ___ ___ |
- Reflex tearing - Basal tear secretion |
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Phenol red is ___ irritating than Schimer test, done in 15 secs and more accurate |
less
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Keratometry is limited in that it measures only the first _-_mm of the cornea and measures the reflection of the light over the ____ ___ |
3-4mm, tear film |
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Topography measures ___ ___ and needed for speciality lenses |
corneal curvature |
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"left-over" astigmatism that is uncorrected by the lenses |
Calculated Residual Astigmatism (CRA) |
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CRA for RGPs = CRA for Soft CL = |
CRA = Refractive astigmatism - Corneal astigmatism (tear lens power) CRA = Refractive astigmatism |
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Whenever CRA is > -0.75, fitting a spherical RGP lens will compromise VA. Therefore, RGP CRAs larger than -0.75 are best corrected with ___ ____ |
soft lenses |
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IF CRA is small and x180, the flexure of a RGP may correct for the CRA or reduce it - lenses that flex are mostly lenses fitted ____ than K with __ center thickness - if at 090 meridian, flexure will make CRA ___ |
Steeper than K, thin center worse |
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Every time the corneal astigmatism is higher than the refractive astigmatism, the CRA for a RGP will be 90 degrees away from the ____ _ |
flattest K |
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Giant Cell Papillae (GPC) can occur in wha type of patients (3)? |
- CL wearer - Prosthetic eye - Cataract |
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If you have two patients with the same K’s but one has one with 12mm, one with 11.2mm cornea diameter. The patient with the sagittal height of ___ will most likely need a steeper base curve. |
12mm |
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What are the advantages of empirical fitting? (2) What is a disadvantage of empirical fitting? |
- Less chair time (initially) - Minimize lens contamination If doesn't fit must reorder and causes doubt |
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What are the advantages of diagnostic fitting? (3) What is a disadvantage of diagnostic fitting? |
- Confidence in fitting relationship - Fewer reorders - Better patient compliance Longer chair time |
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For positive lenses (hyperopes), we use _____(FTK/STK) BC or _____ (larger/smaller OZD)? |
STK, larger |
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Using steeper than K base curve or larger OZD for positive lenses will improve lens ____ |
centration |
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OAD/OZD average is? |
9.4/8.0 |
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Hyperopes or flat corneal curvature (flatter K's) should be fitted with ___/steeper than average OAD/OZD |
larger diameter (9.8/8.4) |
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Myopes or steeper corneal curvature (Higher K's) should be fitted with ___/flatter than average OAD/OZD |
smaller diameter (9.0/7.6) |
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Rule of thumb: Select OZD equal to the ____ in mm |
Base curve radius |
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Steep Fit: - Lens is ___ - ____ pooling - ____ touch - ____ edge clearance - movement? |
- tight - central pooling - mid-spheral touch - minimal edge clearance straight down because apex of cornea is inferior |
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Flat Fit: - Lens is ___ - ____ pooling - ____ touch - ____ edge clearance - movement? |
- loose - mid-peripheral pooling - central bearing or touch - excessive edge lift - lens decentration (inferior and laterally) |
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Soft lens have a polymer component which consists of (3) |
Pores, monomers, and is stable (can absorb water and expand) |
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What're the 3 FDA approved modalities? |
- Conventional (yearly) - Daily - Weakly/monthly |
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Soft lenses consist of ____ which allows chemical characteristics of the lens material to be created such as water content, refractive index, hardness, mechanical stress and oxygen permeability |
monomers |
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What are characteristics of soft lenses (8)? |
- Transparency - Tensile strength - Hardness/Stiffness - Ionic charge - Modulus of elasticity - Refractive index - Wettability - Water content |
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How much stretching force that can be applied is called? |
Tensile strength - usually very high (good durability) |
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The degree of flexibility of the material |
Hardness/Stiffness |
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The ____ flexible the material the better initial comfort. ____ materials retain their shape, so easier to insert and remove |
more, stiffer |
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Silicone hydrogel has ____ stiffness compared to hydrogel |
greater - patient will feel more when changing |
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Ability of a material to keep its shape when subject to stress |
Modulus of elasticity |
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Low modulus of elasticity = ___ resistant to stress High modulus of elasticity = ____ resistant to stress which one is better and why? |
- less
- more, hold their shape better and provide better VA feel more though (SH) |
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What type of relationship exists between refractive index and water content? |
As water content increases, refractive index decreases |
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The ability of the lids to pass tears over the lens when it blinks |
Wettability |
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____ aids in closure of the lid over the lens (improving comfort) creating a stable, even tear film |
Wettability |
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Wettability optimizes (3) |
- Comfort - VA - Deposit resistance |
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The higher the surface wettability = the ___ comfortable it is |
more |
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Molded and spin cast are ____ wettable/comfort able compared to lathe cut. - Lathe cut are polished so are more rubbery and therefore have ___ surface wettability. Needs to be treated |
more, less |
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What type of affect does ionic charge have on the lens? |
Affect solution compatibility or deposit formation |
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Material that have electric charge are said to be |
ionic (negative charge) |
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Ionic material are more reactive with solution that are _____ and make material ___ prone to deposit formation |
acidic, more |
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Materials electrically neutral are said to be |
non-ionic |
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Non-ionic material are ___ reactive to tear and ____ deposit resistant |
less, more |
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Amount of water that the material absorbs |
Water content |
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<4% water content are referred as _____ ≥4% content are referred as ____ |
hydrophobic (silicone, absorbs 0%) hydrophilic (hydrogel) |
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Increase in water content generally ____ the Dk value, _____ lens fragility, and may make the material ____ (more/less) prone to deposit formation |
increases, increases, more |
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Average water content is 45% of weight of lens is for _____ and >55% is for ____ |
daily's, extended wear |
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The higher the water content in hydrogel lenses, the ___ the Dk value, the ___ oxygen transmission. |
higher, more |
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(T/F) With silicone hydrogel, you can have VERY low water content but still have high oxygen transmission and permeability because silicone has very high permeability (~24%) |
True |
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Non-ionic, low water content |
Group 1 hydrogel |
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Non-ionic, high water content |
Group 2 |
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Ionic, low water content |
Group 3 |
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Ionic, high water content |
Group 4
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Which group has high quality (least prone to deposits) and is most expensive? |
Group 1 |
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Patient’s that are prone to damaging/soiling the lens and DES should use group? |
Group 1 |
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Dry eye patients (or borderline dry eye) can use group 1 lenses because they do not produce enough ____ necessary for a high water content lens. |
tears |
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DES or borderline DES can also use group ___ but those w/ reduced TBUT may have mucus, for example, that is attracted by an ionic lens so the lens will soil quickly |
3 |
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Highest probability of getting deposits and cheapest material |
Group 4 |
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Solid polymer that is grounded or cut with a diamond tool to give the curvature needed, can be used to cut higher power and cylinders/toric lenses (up to ~9D) |
Lathe cute |
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Liquid polymer used and takes form by centrifugal force |
Spin cast |
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Liquid polymer used and takes its form by "male and female", solidified with UV radiation |
Cast mold |
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Most comfortable lens construction to least comfortable |
Spin --> Cast --> Lathe - (Spin and cast more wettable) |
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Patients that are borderline dry eye, use ___ water content |
low |
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Do NOT want high water content in DES because if they have poor tear production, the lens will ___ and cause tightness and change in refraction |
dehydrate |
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Patients with seasonal allergies should use |
Group 1 or daily disposable lenses |
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What base curve should be used for average K's of 42-45.00? |
Medium BC: 8.6 or 8.7 |
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What base curve should be used for flatter K's of <42? |
Flatter BC: 8.8,8.9,9.0 |
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What base curve should be used for steeper K's of >45.00? |
Steeper BC: 8.3,8.4 |
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(T/F) Keratometric readings will predict lens fitting on soft lenses. |
False, For this reason you could select a medium base curve diagnostic lens and observe lens movement. |
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2 corneas that are 44.00, one is 11.5mm and the other is 12.5mm, - The larger the cornea (12.5mm), the higher the sagittal height of the cornea need = ____ lenses [averageis 11.8mm diameter cornea (HVID)] |
steeper |
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If lens doesn't move, select a ___ BC If lens moves too much, select a ___ BC Adequate movement = stay with BC selection |
Flatter, Steeper |
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What is adequate movement? |
0.5-1.0mm in primary gaze and 2.0mm in superior gaze |
