Midterm #2 Flashcards by laura Capelle

what might an esophoria at distance suggest?

hyperopia or an over-minused patient

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what might an exophoria at near suggest?

undercorrected myopia

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how do you get a spherical equivalent?

take half the cylinder power (keep sign) and add it to sphere power

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OD: -0.50 -1.00 x 180

what would the unaided VA be expected to be?

20/50 - about -1.00D of blur

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what is refractive hyperopia?

abnormal refractive power due to curvatures that are too flat (do not have enough power)

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what is axial hyperopia?

abnormal refractive power due to an axial length that is shorter than normal

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what is simple myopia?

most common type, no pathology, usually less than 6D, juvenile or adult onset

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what is degenerative myopia?

degenerative changes in posterior segment, retina is partially stretched away from disc, decreased BVA, myopic conus, and RD and glaucoma are common

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what is nocturnal myopia?

only occurs in dim illumination, increased accommodative response toward dark focus

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what is pseudomyopia?

inappropriate accommodative response, overstimulation or spasm

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what is induced myopia?

occurs with pharmaceutical agents, blood sugar changes, NS - temporary and reversible

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what two things change during emmetropization?

radii of cornea and lens (refractive) and length of eye (axial)

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what refractive power is the end result of emmetropization?

emmetropic or slightly hyperopic (acts as visual buffer)

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what do minus lenses induce during emmetropization?

induce hyperopic defocus - causing the eye to develop myopia

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what do plus lenses induce during emmetropization?

induce myopic defocus - causing the eye to develop hyperopia

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what part of the eye does myopia change in emmetropization?

sclera

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what part of the eye does hyperopia change in emmetropization?

choroid

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what are two influential factors for emmetropization?

image quality and neuronal interaction

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what are the best ways to control myopia?

bifocal, multifocal CL’s and orthokertatology

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why can’t you control myopia progression with myopic glasses?

the higher the lens power, the larger the peripheral defocus - eye grows until periphery is same defocus as center

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what is tonic convergence?

convergence maintained by the EOM tonus (phoria position)

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what is accommodative convergence?

occurs reflexively with stimulation of accommodation

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what is proximal (psychic) convergence?

due to awareness or impression of nearness of an object

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what is fusional vergence?

typically autonomic response to retinal disparity - when an image falls outside panum’s fusional area

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what is positive fusional vergence?

both eyes move in or converge

what is negative fusional vergence?

both eyes move out or diverge

what is vertical fusional vergence?

one eye moves up and the other moves down

what type of vergence is measured using BD prism?

supravergence

what do you measure infravergence with?

BU prism

what is the AC/A ratio?

the relationship between accommodative convergence (lateral phoria) and accommodation (usually 1 diopter)

how do you measure the gradient AC/A?

measure near lateral phoria (40cm), add +1.00 sphere, remeasure near lateral phoria = difference between two measurements : 1 diopter

what is Morgan's expected for AC/A?

4/1 (+/- 2)

what is Morgan's expected for distance lateral phoria?

1 exo (+/- 2)

what is Morgan's expected for near lateral phoria?

3 exo (+/- 3)

what is Morgan's expected for amplitudes?

``` ave = 18 - 1/3(age) min = 15 - 1/4(age) ```

what is Morgan's expected for FCC?

+0.50 (+/- 0.50)

what is Morgan's expected for NRA?

+2.00 (+/- 0.50)

what is Morgan's expected for PRA?

-2.37 (+/-1.00)

how do you calculate the convergence demand?

pd (prism diopters) = convergence demand | pd = PD(cm) x meter angle (1/test distance)

what are some symptoms of accommodative insufficiency?

blurry vision at near, discomfort/strain/fatigue with near work, difficulty with attention and concentration at near

what are some clinical signs of accommodative insufficiency?

esophoria at near, low accommodative amplitude, low PRA, will accept plus at near (any age)

what is the most common non-strabismic binocular condition?

convergence insufficiency

what are some clinical findings for convergence insufficiency?

normal distance lateral phoria and higher exophoria at near (more than 6pd), reduced NPC, low NRA and low AC/A

what type of ametropia is best corrected with CL's?

refractive ametropia

what type of ametropia is best corrected with spectacles?

axial ametropia

what can you use to correct for aniseikonia?

plano size lenses

what plano size lens could you use for 4% aniseikonia?

use 4% size lens over one eye to cancel (concave side towards eye to magnify)

what is the order of tests in the near testing suite?

FCC, NRA, PRA, phorias and vergences

what is the FCC testing?

evaluates the accommodative posture of a patient while viewing a near target under binocular conditions

what does it mean if the FCC is over +0.75 in pre-presbyopes?

the patient may be over-minused

what does it mean if the FCC is a minus number?

the patient has a lead of accommodation - may consider VT

what are the NRA and PRA testing?

accommodation under binocular conditions when total convergence demand is constant - how changes in accommodative convergence are compensated for by changes in fusional vergence

what 3 things happen when looking from distance to near?

convergence, accommodation, miosis

what are normal K readings?

44.00D

a patient has -1.75 x 180 astigmatism in the OD, what is the predicted refractive astigmatism (Javal's rule)?

-1.25 x 180

a patient has -2.50 x 090 astigmatism in the OD, what is the predicted refractive astigmatism (Javal's rule)?

-3.00 x 090

what is compound myopic astigmatism?

(CMA) myopic in both meridians

what is simple myopic astigmatism?

(SMA) myopic in one meridian and emmetropic in other

what is mixed astigmatism?

(mixed A) myopic in one meridian and hyperopic in other

what is compound hyperopic astigmatism?

(CHA) hyperopia in both meridians

what is simple hyperopic astigmatism?

(SHA) hyperopic in one meridian and emmetropic in other

what is manifest hyperopia?

measured by relaxation of accommodation with addition of plus lenses - detected dry refraction

what is latent hyperopia?

portion of total hyperopia compensated for by tonicity of ciliary muscle - revealed with wet refraction (wet - dry refraction = latent)

what is total hyperopia?

manifest + latent hyperopia or total will equal amount revealed with wet refraction

what is facultative hyperopia?

can be self-corrected with accommodation, uncorrected distance VA may be 20/20

what is absolute hyperopia?

cannot be overcome with accommodation - uncorrected distance VA will be worse than 20/20

what are the average powers for the cornea, lens and total eye power?

cornea = 43D lens = 17D total eye = 60D

what is the average axial length?

24mm

what are some symptoms of uncorrected astigmatism?

blur at distance and near, "ghost" images/diplopia, bothered by bright lights/glare, asthenopia, tearing

how can you check if your patient has true diplopia or astigmatism symptoms?

have the patient close one eye if the diplopia is still there monocular = lens/astigmastim (binocular = nerve palsy, stroke, DM changes)

why does the binocular balance work?

accommodation is consensual; the patient's accommodative responses of the eyes is always matched

what test answers the questions: where are the eyes focused when fixating a stationary near target? Is there a lag or lead of accommodation?

Fused Cross Cylinder Test (FCC)

what is an accommodative demand and how do you calculate it?

distance of blurred target in diopters - 40cm = (100/40) = 2.50D

if a target at 40 cm has an accommodative demand of 2.50D, but the patient accommodates 2.00D, do they have lead or lag?

lag of accommodation

what is the most important cue to accommodation?

blur or defocus (accommodative stimulus)

how much lag at near is normal?

+0.25 to +0.50 and increases with age

what type of convergence is active during the distance lateral phoria measurement?

tonic convergence

what types of convergence are involved when measuring the near lateral phoria?

tonic, accommodative and proximal convergences

which test do the eyes move instead of the image, phorias or vergences?

vergence (image moves in phorias)

what 3 things must the patient have in order to do the binocular balance?

1. vision is same in each eye 2. has accommodation 3. good enough VA's to notice small discrepancies in refraction