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101 Cards in this Set
- Front
- Back
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effects of UV radiation on ocular tissue
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1. photokeratitis
2. pterygia 3. pinguecula 4. climate droplet keratopathy 5. cataract 6. retina (aphakia)ef |
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% reflected = (equation)
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((n'-n)^2/(n'+n)^2)I
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what are the symptoms for computer vision syndrome
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1. headaches
2. blurred near vision 3. accommodative facility problems 4. diplopia 5. eyestrain 6. glare sensitivity 7. eye irritation 8. neck, back and shoulder pain |
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transmission formula
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Tu= T1 x T2 x T3
transmission through lens system is product of individual transmissions |
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computer vision syndrome
what are some case Hx that you would ask? |
1. type of computer work and nature of visual demand
2. duration on computer work 3. position and work distance from computer 4. lighting sources and their locations in workspace 5. nature, severity, and freq of symptoms associated with computer work |
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computer vision syndrome
what are the main criteria that you have to correct |
1. correct even marginal refractive errors
2. give presbyopes special Rx 3. watch for dry eye 4. watch for glare 5. look for OMD 6. improve patients work environment |
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computer vision syndrome
when correcting refractive error, what should you take into consideration |
1. correct even low amounts or hyperopia and astigmatism
2. correct patients with PSEUDOMYOPIA and ACCOMMODATIVE INSUFFICIENCY with plus lenses |
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computer vision syndrome
presbyopic considerations |
1. patient may require special Rx for computer use
2. segmented bifocals need to be fit higher than typical lower limbus 3. PALs with wider intermediate zones 4. computer glasses -SV intermediate Rx -Bifocal with top portion for intermediate -PAL with wide intermediate zone |
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computer vision syndrome
watch for dry eye |
1. common in contact lens wearers
2. blink rate typically reduced in computer use 3. recommend artificial tears combined with frequent breaks 4. consider lowering screen height slightly |
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computer vision syndrome
glare |
1. especially a problem with older patients
2. use glare filter 3. even new monitors can produce glare 4. improper lighting may create problems 5. AR coating DO NOT eliminate reflections from monitors |
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what are the two main causes of broken lenses
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1. ROCKS (25%)
2. SPORTS (18%) -mainly basketball and baseball (swimming) |
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8 ways to deal with vertical imbalance
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1. lowering distance OC
2. single vision lenses for reading only 3. dissimilar bifocal seg 4. compensated bifocal seg 5. prism seg 6. slab off prism 7. fresnel press on prism 8. contact lenses |
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what material should you use in industrial safety eyewear
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POLYCARBONATE is the only lens material that can adequately resist the high energy impact of both large and small objects
90% of injuries caused by small objects moving really fast |
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relationship in eikonic lens design
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1. decrease mag of more plus lens (flatter/thinner)
2. increase mag of more minus lens (steeper/thicker) |
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knapps law
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1. fit axial ametropes with SPECTACLES
2. fit refractive ametrope with CONTACT LENSES estimating aniseikonia 1% per diopter of anisometropia |
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what are the difference between non industrial eye injuries and industrial
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non industrial
1. typically large objects 2. slow velocity industrial 1. typically object size less than 6mm 2. high velocity |
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field of view in relation to high plus lenses
what happens to FOV in aphakia?? |
1. decrease in peripheral and macular field of view in aphakia
2. decrease in MACULAR is GREATER 3. creates RING SCOTOMA |
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what is the difference between peripheral and macular FOV in aphakia?
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peripheral FOV
-FOV of steadily fixating eye subtended at the entrance pupil macular FOV: -FOV for the moving eye subtended by the center of rotation |
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Aphakia Lenses
lens aberrations? |
1. lenses greater than +8.00D, either oblique astigmatism or curvature of image can be eliminated by using aspheric surfaces
2. both cannot be eliminated using one set of curves 3. aspheric experience PINCUSHION effect |
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lenticular design
adv/disadv |
1. make the optical portion smaller that has the high Rx
2. decrease weight 3. decrease thickness 4. decrease FOV |
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what are the cosmetic problems with high minus lens
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1. thick edges
2. minification of eyes by observers 3. multiple ring effects |
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what are the issues with high plus lenses
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1. increased ocular rotations
2. increased lens aberrations 3. distortion 4. magnified eyes 5. motion of objects in FOV 6. increases the demand for convergence |
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what are the FOUR type of magnifications
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1. relative distance magnifcation
2. relative size magnification 3. angular magnification 4. projection magnification |
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what is relative distance magnifications?
examples and devices? |
mag that results from decreasing the distance of the object from the eye
bringing something closer MICROSCOPES and PLUS LENS |
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what is relative size magnifications?
examples and devices? |
magnification created by increasing the size of the object, but keeping the distance at its original spot
large print books, magazines and newpapers does not increase demand for accommodation |
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what is projection magnifications?
examples and devices? |
magnification resulting from optical or electronic enlargement of image on screen, used in combination with RDM
CCTV, really big print on TVs |
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what is angular magnifications?
examples and devices? |
magnification produced by an optical system
compares the apparent increase in the size of an object seen through the optical system with the size of the object seen WITHOUT the optical system afocal telescopes |
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what are the advantage and disadvantage of GALILEAN telescope
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1. Shorter than Kepler
2. Lighter than Kepler 3. Erect Image |
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what are the advantage and disadvantage of KEPLERIAN telescope
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1. Better image quality than Galiean
2. Greater FOV than Galilean 3. Higher Magnification than Galiliean 4. Need Image Erecting Prism for use in low vision |
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what are the optics of the Galilean vs the Keplerian
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Galilean:
1. Objective: PLUS 2. Eyepiece: MINUS 3. ERECT IMAGE Keplerian: 1. Objective: PLUS 2. Eyepiece: PLUS 3. IMAGE INVERSE |
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how are telescopes used by UNCORRECTED AMETROPES
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Magnification for an afocal telescope assumes patient is emmetropic or corrected to emmetropia
myopes: decrease mag in galilean increase mag in kepler hyperopes: increase mag in galilean decrease mag in kepler |
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what is the definition of an afocal telescope
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an optical system that provides angular magnification without a change in vergence
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telescope length in respect to refractive error and magnification
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1. separation is INCREASED for uncorrected HYPEROPE
2. separation is DECREASED for uncorrected MYOPE 3. for a given mag, galilean is SMALLER than keplerian |
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what are the difference between microscope lenses vs telemicroscope
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1. microscopic lenses offer larger FOV
2. telemicroscopes offer longer, more comfortable reading distance |
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what is a reading cap?
what determines the power of the reading cap? |
1. reading cap is a Plus Lens placed in front of an afocal telescope so that PARALLEL light enters the afocal telescope
2. power of the reading cap depends on the working distance +2.50D = 40cm +5.00D = 20cm |
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hand magnifiers
how do you increase field of view |
FOV increases as the magnifier is brought closer to the eye
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hand magnifiers
when the object is at the primary focal plane of the magnifier...what happens if you change the eye to lens distance |
changing eye to lens distance does not affect the magnification
AFFECTS THE FIELD OF VIEW |
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hand magnifiers
what happens to accommodation when the object is AT THE PRIMARY FOCAL PLANE of the magnifier inside the focal plane?? |
NO ACCOMMODATION
when object lies inside the focal length of the magnifier, either ACCOMMODATION or an ADD is required |
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why are contact lenses considered thick lens
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the steep curvature of a contact lens creates errors when using the approximate power formula
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base curve of contact lenses
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1. its the concave surface of a contact lens
2. selected for physiological, fitting and comfort considerations 3. base curves of a rigid lens has optical significance |
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tints:
trouble with glare from road surface |
Polarized Lenses
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tints:
problem with glare from overhead fluorescent lights |
Pink(85%T)
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tints:
light too bright when studying at the beach |
Gray Tint(20%T)
UV coating |
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tints:
trouble driving in fog and haze |
Yellow Tint
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tints:
exposure to high levels of IR radiation |
Therminon
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contact lense base curves in respects to keratometry
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base curve is generally close to radius of cornea
1. On K: CL BCR = K reading 2. Steeper than K: CL BCR = steeper than K reading 3. Flatter than K: CL BCR = flatter than K |
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what is the exploded method of CL/Eye optical system
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assumes that there is a layer of air between the contact lens and the tear layer and also between the tear layer and the cornea
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what are the refractions of concern when dealing the the exploded method
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Fc + Ft = Rx
1. Fc= contact len in air 2. Ft= tear lens in air |
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Soft Contact Lens in respect to Keratometry
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1. SCL ARE ALL "ON K" FITS
2. Soft contact lens conform to the shape of the cornea 3. there is no tear lens since the tear layer is thin and has no power |
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residual astigmatism in respects to soft contacts lens
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1. spherical soft CLs DO NOT correct either corneal or internal astigmatism
2. ALL refractive astigmatism will be residual astigmatism RA=TA |
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how would you correct astigmatism less than -0.75 with SCL?
when is cylinder most important to be correct? |
1. for astigmatism less than -0.75, USE SPHERICAL EQ.
2. the lower the sphere power, the more critical that the cyl power be correct |
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when do you use soft toric contact lenses
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1. when TA is greater than -0.75D
2. preferable to rigids when TA is not equal to corneal astigmatism |
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what FIVE methods are used to stabilize the lenses and prevent rotation
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1. prism ballasting
2. thin zones 3. eccentric lenticulation 4. truncation 5. combo of all the above |
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what happens when a soft toric CL rotates but is stable
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the axis of the cylinder correction can be altered to provide good vision
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what two methods is used to determine new cyl axis on a rotated soft toric contact lens
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1. LARS (Left Add, Right Subtract)
2. SCOR (Sphero Cylinder Over Refraction) - requires obliquely crossed cylinder problem |
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LARS EXAMPLE
M: -1.50-2.00X180 1. right contact lens rotates 10 degrees nasally 2. from examiner POV, RIGHT ROTATION |
right subtract
new cyl axis = 180-10=170 |
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what are two important things to note about LARS
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1. cyl axis of the manifest refraction is adjusted for the amount of lens rotation, NOT THE AXIS OF THE TRIAL LENS
2. when a lens with the cyl axis compensated for rotation is placed on the eye, we expect to see the same amount of rotation as with the original lens |
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in summary what is the SCOR method
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combination of two obliquely crossed cylinders:
1. Trial Lens Rx 2. Over Refraction the resultant is the required CL Rx |
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RIGID CONTACT LENS:
relate power and kerotometry |
1. ON K = tear lens does not contribute power
2. STEEPER than K = the tear lens is PLUS powered 3. FLATTER than K = the tear lens is MINUS powered |
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what should you NOT do when fitting RIGID CL
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1. change the corneal curvature
2. flex significantly on the eye - flexure is dependent on lens material and thickness |
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when are spherical rigid lens used in astigmatism
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cyl power: 2.50 - 3.00
1. as long as the spherical rigid lens maintains its curvature, it will correct all the CORNEAL astigmatism 2. it will NOT correct INTERNAL (LENTICULAR) astigmatism |
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what are RIGID TORIC CONTACT LENS used
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1. 3.00+ of cyl
2. when cyl is greater than 3.00D, fit with toric back surface to improve the fit 3. lenses will be unstable and may flex on the eye |
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what must you do you compensate for RIGID CONTACT LENS that are NOT ON K
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1. steepening the BC yields a PLUS tear lens,
- so MINUS power must be added to compensate 2. flattening the BC yields a MINUS tear lens, - so PLUS power must be added to compensate |
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curvature change in relation to dioptric change in rigid contact lenses
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amount of power added is 0.50D per 0.1mm of curvature change
ex: 1. steepened 0.15 = +0.75 2. flattened 0.15 = -0.75 |
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what is residual astigmatism
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the astigmatism present with a spherical contact lens on the eye
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what are FOUR causes of RESIDUAL ASTIGMATISM
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1. posterior corneal astigmatism
2. foveal displacement 3. crystalline lens astigmatism 4. crystalline lens obliquity |
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total astigmatism is equal to...
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TA = CA + RA
CA: corneal astigmatism RA: residual astigmatism |
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what are TWO rigid contact lenses with BACK TORIC SURFACES
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1. front sphere/back toric
2. bitoric (front toric/back toric) |
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what are indications of front toric rigid contact lens
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front toric/back sphere
1. used when most or all of astigmatism is internal 2. used when spherical rigid lens would result in excessive residual astigmatism |
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how does rigid bifocal contact lenses achieve add power
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incorporating a region that varies either:
1. in index of refraction 2. in radius of curvature |
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in rigid bifocal contacts lenses add power is equal to...
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the add power is equal to the difference in BACK surface interface powers of the near and distance portions:
F(ADD)= F2(near) - F2(distance) |
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advantages and disadvantages of...
distance CL w/ near spec Rx |
Advantages
1. Best Vision at distance and near 2. No loss of depth perception Disadvantages 1. Near Rx can be inconvenient 2. Cosmetic Issues |
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what is the ideal patient for...
distance CL w/ near spec Rx |
1. Requires best VA distance and near
2. Not worried about cosmetic appearance of reading Rx 3. Not prone to misplacing things |
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how should you fit monovision
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1. Dominant Eye: Fit with Distance Rx
2. Non Dominant Eye: Fit with Near Rx |
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advantages and disadvantages of...
Monovision |
Advantages
1. Use standard contact lenses (many options including toric lenses) 2. Better Distance and Near vision than most multifocal contact lenses 3. No glasses to lose Disadvantages 1. Can decrease depth perception |
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what is the ideal patient for...
Monovision |
1. Equal demands for distance and near vision
2. Adaptable, optimistic personality 3. Early presbyopes currently wearing contact lenses 4. Reads in positions other than downgaze |
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how should you fit modified monovision
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1. Dominant Eye: Distance contact lens
2. Non Dominant Eye: Multifocal CL |
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advantages and disadvantages of...
modified monovision |
Advantages
1. Better depth perception than monovision 2. Less adaptation than monovision Disadvantages 1. Vision not as good as with monovision |
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ideal patients for...
modified monovision |
1. Not as adaptable as required for monovision
2. Monovision failure |
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what is a diffractive bifocal contact lens
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1. Distance Vision: Refraction
2. Near Vision: Diffraction Entire lens contains distance power |
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what is a soft multifocal contact lens
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Simultaneous vision causes a reduction in both distance and near vision compared to best spectacle correction.
successful fitting = 20/happy concept |
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bifocal CL type in relation to...
on eye vs in the air dioptric power |
SAME:
1. one piece front surface 2. fused back surface 3. fused front surface DIFFERENT: 1. one piece BACK surface |
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what are FOUR contraindications of soft (hydrogel) CL
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1. Extreme Sensitivity
2. Extreme Dry Eye 3. Allergies 4. History of Microbial Keratitis |
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what are THREE contraindications of rigid CL
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1. Sensitivity
2. Dusty Environment 3. Extreme Dry Eye |
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in respect to rigid CL,
HYDROGEL SCL are BETTER for what TWO conditions |
1. dusty environments
2. dry eye due to MGD |
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in respect so soft CL,
RIGID CL are BETTER for what TWO conditions |
1. pts with decreased tear productions (low Shirmers)
2. better for patients with irregular astigmatism/corneal distortion |
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what do you use when you have a pt with...
1. manifest astigmatism greater than 0.75D 2. NO corneal astigmatism |
1. toric hydrogel lenses
2. front toric rigid lenses |
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what do you use when you have a pt with...
corneal astigmatism and manifest astigmatism are UNEQUAL |
TORICS!!!
soft or rigid |
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what do you use when you have a pt with...
NO corneal astigmatism NO manifest astigmatism |
1. spherical hydrogel lenses
2. spherical rigid lenses |
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what corneal astimatism and manifest astigmatism is EQUAL...
when should you use SPHERICAL RIGID LENSES |
1. up to 2.50-3.00D corneal astigmatism
2. greater than 2.50-3.00 use TORIC BACK SURFACE |
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when corneal astimatism and manifest astigmatism is EQUAL...
when should you use HYDROGEL LENSES |
1. astigmatism less than 0.75-1.00
(may use spherical hydrogel with spherical equivalent) 2. astigmatism greater than 0.75-1.00 (use toric hydrogel lenses) |
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rigid or soft...what provides better vision
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RIGIDS!!!
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rigid or soft...
what are better for bifocal optics |
RIGIDS!!!
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presbyopic contact lenses...
provides better vision |
distance contact lenses with reading glasses
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presbyopic contact lenses
best distance and near vision without spectacles |
monovision
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presbyopic contact lenses
better depth perception than monovision |
modified monovision
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what are the magnification effect of contacts lenses
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1. myope, a contact lens provides a larger retinal image
2. hyperope, a contact lens provides a smaller retinal image |
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compared to an EMMETROPE how does spetacle lenses effect accommodative demand in myopes? hyperopes?
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MYOPE, spectacles REDUCE the accommodative demand
HYPEROPE, spectacles INCREASE the accommodative demand |
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when compared to spectacle lenses...how does contact lenses effect accommodative demand in myopes? hyperopes?
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1. Myope with contact lenses has INCREASED accommodative demand
2. Hyperope with contact lenses has DECREASED accommodative demand |
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in respects to prismatic effect...what type of patient is disadvantaged when switch from spectacles to contact lenses
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EXOPHORIC MYOPES
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field of view in respects to contact lenses
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Most patients appreciate a greater field of view with contact lenses because the macular field of view is not limited by the spectacle frame
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