1. Amblyopia Dx

How can VEP be used to Dx/monitor amblyopia?

Latency >> Relates to PHYSIOLOGY i.e. how fast signal is transmitted; integrity of visual pathway/axons; P-100 wave should be about 100 ms --Pathway lesions tell us about latency Amplitude >> relates to ANATOMY i.e. number of axons available to conduct signal; measured in µV; should be roughly 10 µV --VA reflected by amplitude Uses: -Visual prognosis in amblyopia -MS -GLC -Optic Neuritis -Alzheimers *Checkerboard pattern can be used to get VA; flash VEP for to see if any signal being transmitted at all. If VA is very reduced on VEP, may need to consider underlying disease.

T/F: Binocularity develops once there's a preference for the fovea in infants, and infants must devlop a preference to use the fovea.

True. Eyes wandering before 6 mos is normal, but after 6 mos or constant turn are concerns.

What is laser interferometry? Why is it useful in the Dx of amblyopia?

-Grating acuity via laser projected onto retina -Bypasses need for accurate accommodation -Helps estimate VA when assessing pts with cataracts or macular degeneration -Can also give an idea of prognosis of Tx of functional amblyopia >> can over-estimate VA *Potential Acuity Meter = similar >> projects acuity chart directly onto the retina

List some important characteristics of strabismic ambylopia

1. Deviation must be early (< 7 yo) & usually constant, unilateral, at near or far --Possible with intermittent/alternating, but less likely and lower severity 2. Abnormal binocular interaction >> suppression/inhibition of deviating eye 3. Pronounced monocular spatial distortion 4. Moderate to large EF typical and/or suppression ---EF 0.5 to 1.75º, to as large as 10º 5. VA varies widely ---Typical = 20/60 to 20/100 ---Ranges from 20/25 to 20/1000 (better for intermittent/alternating, worse for mixed mech)

List six characteristics of isometropic amblyopia.

1. Less common than aniso and strab 2. VA better than aniso (20/30 - 20/70) 3. Minimal EF -- maybe bilateral unsteadiness 4. Little to no monocular spatial distortion 5. No asymmetry of binocular interaction 6. Can resolve with full spec Rx over a few mos

What accommodative issues is amblyopia associated with?

1. Low gain 2. Decrease in slope of accommodative stimulus/response curve i.e. larger lag 3. Decrease in acc. amp 4. Decrease in peak velocity of AR 5. Increase in depth of focus >> might seem like a good thing, but it actually makes them less sensitive to blur which makes things more difficult when refracted 6. Difficulty accommodating and relaxing acc. *These results also found in fellow sound eye, eyes previously Tx to 20/20 acuity, and nonamblyopic (but strabismic) eyes. ALL ISSUES CAN BE HELPED WITH VT.

List four important characteristics of anisometopic amblyopia.

1. Most common cause of amblyopia 2. Usually moderate >> 20/40 - 20/100 3. Small EF if present 4. Little to no monocular spatial distortion

How does amblyopia affect contrast sensitivity in the context of taking VAs/reading/schoolwork etc.?

1. When they're eccentrically fixating i.e. letters aren't fixated with the fovea, the contours of the letters aren't crisp. The contrast appears lower. 2. When a letter/word is flanked by other letters/words, the surrounded word/letter can appear lower contrast because of an inhibitory effect of surrounding letters 3. When pt with EF is looking at words/lines of letters etc. they may perceive words/letters as being unevenly spaced and bunched up closer to fixation.

Most amblyopic pts tend to fixate with a point within 5º of the fovea. How will this affect VA?

1º results in 20/30 VA and every additional 1º, loses 1 line of VA.

What level of acuity would you expect in mild amblyopia?

20/25-20/40

What level of VA would you expect in moderate amblyopia?

20/40-20/100

For normal and amblyopic eyes, CS peaks at ________ cycles per degree.

4 cycles per degree *Amblyopic CS basically same level as normal VA pt, maybe with slight disadvantage at higher SFs. Issue = perception of the gratings. Often perceive their orientation, but at higher SFs, the way they perceive them is abnormal.

Strabismus is present in ~_____% of the population.

5% *Actually becomes more prevalent with age.

What is suppression?

All or part of ocular image of one eye is prevented from contributing to binocular perception. *Generally small D or dumbbell-shaped. Two options >> suppress or develop ARC. Suppression longterm is what causes amblyopia.

Which types of amblyopia has the best and worst visual prognosis?

Best = isometropic Worst = deprivational

Why is important to determine the age of onset of a strabismus?

Constant, unilateral strabismus present before 6 yo will almost always be accompanied by amblyopia. *NB: If the strab appears constant on CT but they have no amblyopia, the pt must have alternating fixation.

What is a MARS Chart Test? How is it conducted?

Contrast Sensitivity Testing -50 cm -BCVA -Stop testing at two incorrect responses -Note log value of highest correct in each row -Subtract 0.04 for any wrong answer -Compare to age-expected norms

What is the "just noticeable difference"? How is it helpful to consider when refracting pts with amblyopia or disease?

Differences in power just perceptible to pt >> good rule of thumb is the JND will correspond to the denominator of the Snellen fraction of the pt's VA divided by 100 Example: -VA = 20/100 >> 1.00D -VA = 20/50 >> 0.50D -VA = 20/25 >> 0.25D

How can you estimate what someone's VA will be if they have EF?

EF in pd!

What CHx details might make you more suspicious of amblyopia? A. Birth trauma, prematurity, distress B. Serious illness with fever C. Head injury D. Previous Tx for amblyopia E. FamHx of amblyopia F. All of the above

F. *For previous Tx, be sure to ask what type, when, compliance, results? If poor results with previous Tx, prognosis likely not great.

Congenital amblyopia

Failure of development of normal visual pathways e.g. from hereditary anomalies or congenital anomalies. Characteristics: -Present from birth & generally bilateral -Unsteady fixation — jerk or pendular nystagmus = common -20/40 to 20/60 VAs = common though can be as bad as 20/200 -Associated with >> nystagmus, bilateral high RE, color VA defects, general motor defects, albinism *Not real amblyopia = organic amblyopia.

T/F: When checking VAs of an amblyopic pt the type of VA chart makes no difference.

False.

T/F: For amblyopic pts the sensitivity of the peripheral retina is greater than the fovea.

False. *Sensitivity is reduced overall across the retina, but the fovea is still the most sensitive point.

T/F: Eccentric fixation is a good prognostic indicator for amblyopic pts.

False. BAD. Don't want pts to have EF.

T/F: For an amblyopic pt, telling them to really focus on a target works well.

False. Better off telling them to. "hold" rather than to fixate; telling them to focus results in more saccadic intrusions, while telling them to hold results in fewer.

An amblyopic pt has this Rx: +4.50 -5.00 x 180 You show them gratings oriented at 90º and at 180º to check VA. Which grating will have worse VA?

Lines oriented vertically will be worse. Higher-powered meridian at 180º; horizontal meridian focuses vertical images, so 90º gratings will be worse.

What is an example of monocular spatial distortion? Who has this issue?

Mono spatial distortion ONLY affects strabismic amblyopes!!! Example: Asking pt to bisect a line or center a dot between two other dots. Or on z-axis, XTs tend to over-estimate distances and ETs tend to under-estimate.

List the most common to least common causes of amblyopia.

Most common Anisometropia Mixed mechanism Strabismic Isoametropia Deprivational Least common *Overall, 2% prevalence (range of 1-6%).

List the anisometropic amblyogenic factors.

Myopia > 3.00D Hyperopia > 1.00D Astigmatism > 1.50D

List the isometropic amblyogenic factors.

Myopia > 8.00D Hyperopia > 5.00D Astigmatism > 2.50D

You are doing an MIT test on a pt's amblyopic eye (OD). She sees the haidinger brush to the left. What type of EF does she have?

Nasal EF

Nutritional amblyopia

Not true amblyopia — central VA impairment caused by malnutrition e.g. B vitamins or from heavy smoking/alcohol Characterized by: -Gradual loss of VA -Unsteady central fixation +/- jerk nystagmus -Bilateral, symmetrical central/centrocecal scotoma -ONH pallor -Poor overall appearance *NOT REAL AMBLYOPIA = ORGANIC AM.

What are the risk factors of amblyopia?

Premature birth CP Low birth weight (≤ 1500 g) Hx strab surgery Developmental/cognitive disability FamHx high RE, strab, amblyopia

You are testing a 30 yo pt's CS with the MARS chart. The chart reads log CS 0.88/contrast 0.132. What does this mean?

Pt's log CS = 0.88; they can see targets at 13.2% contrast, but not below this. Normal for their age-range is 1.72 to 1.96. Corresponds to "severe".

What other aspects of vision does amblyopia affect besides VA?

-CS -binocularity -OM skillz -Accommodative skillz -Contour interaction & crowding sensitivity -Processing speed -Early childhood development & fine motor skillz

How is neutral density filter testing done?

-Dark adapt x 15 mins -Patch amblyopic eye -Filter rotated over dominant eye until DISTANCE BCVA is reduced to 20/40 -Move patch to amblyopic eye -Take VA with filter over amblyopic eye with the same setting -Compare VA with filter to without filter Functional = Reduced VA 1-2 lines, same, or better VA with amblyopic eye. Nonfunctional = Drastic reduction in VA > 2 lines.

How is the Haidinger Brush Test performed?

-EF Test -Test distance 40 cm -MONOCULAR -Cobalt blue filter over tested eye or directly in the MIT -Ask pt to look at the dot/target -Ask where brush is in relation to dot If pt can't appreciate the brush: -High plus lens (e.g. +10/+20) -Extra layer of blue filter e.g. blue gls -Pt moves further away -Reduce room illumination *Piece of cellophane can be placed over blue filter >> pt should report reversal of direction of propellor

What findings might make you think a pt may have EF?

-poor VAs with no strabismus found on CT (subclinical tropia) -Lack of RDS -Anomalous result on 4 BO prism test

Do pts with amblyopia have trouble with eye movements? Explain

1. Increased saccade latency 2. Increased drift 3. Abnormal pursuits >> large saccadic pursuits & variable/low gain 4. Reduce vergence

What three tests can you do to detect EF?

1. Visuoscopy 2. Haidinger brush/MIT 3. Afterimage transfer test

A pt has 1º of EF. How many pds is this?

1º = 1.75 pd 1 pd = 0.57º

What level of VA would you expect in severe amblyopia?

20/100 - 20/400

How is visuoscopy performed?

= Most SENSITIVE & RELIABLE test of EF How to: -Dim lighting, sustained visuoscopy x 30 secs -Ask pt to look in center of target -MONOCULAR test -Perform on nonamblyopic eye first -Move the target and ask the pt to fixate again *Determine the type, direction, magnitude, stability, percent foveation, and localization of fixation

What leads to the appearance of the Haidinger brush?

Entoptic phenomenon caused by interaction of linearly polarized/dichroism of xanthophyll pigment at the macula lutea.

T/F: Nonamblyopic pts have better visual acuity in the dark compared to amblyopes.

True.

T/F: Any level of amblyopia can affect general development, BV, academic performance, athletic ability, and pt's ability to have occupation requiring acuity requirements.

True. ANY level

T/F: Amblyopic & nonamblyopic pts have comparable VFs.

True. Amblyopes have slightly decreased peripheral sensitivity, but overall hill of vision is the same.

T/F: Ambylopia is a functional loss of vision.

True. The visual pathways are formed & intact at birth. Amblyopia occurs when there is aberrant visual input that affects the development of vision during critical period. E.g. Ametropia, strabismus, form deprivation, combination *Remember Dr. Pola & Sedgwick's lectures talking about how visual skills change & develop throughout the critical period. Normal vision development is foundation for these skills.

T/F: Pts with ARC often have single vision, normal spatial judgments and eye movements.

True. *When you cover one eye, strabismic eye swings in and VA at fovea is still 20/20. All these reasons make it a fairly good adaptation to have.

T/F: Object fall on nasal retina will appear to be more temporal.

True. And vice versa. Fall on temporal retina, appears more central.

What should you document when you're doing visuoscopy?

Type = Central or eccentric fixation Direction = Which part of the retina does the pt use to fixate? Percent foveation = Observe for 30 secs; how often the pt uses fovea Localization = Visual direction pt associates with straight ahead i.e. ask if pt sees target straight ahead; move the target onto the fovea and ask if it's straight ahead. Typically eccentric localization. Magnitude = count reticles on the target for displacement in pd

What is anomalous retinal correspondence?

ARC = BINOCULAR condition in which the foveas are no longer corresponding points i.e. info from one fovea is re-wired to correspond to a nonfoveal point in the other eye. *Suppression scotoma surround fovea and extends to anomalous point. ONLY IN PTS WITH STRABISMUS, typically from a very young age. May also have EF.

What is eccentric fixation?

Adaptation common in strab and aniso (80%) = anomaly of MONOCULAR fixation in which time-averaged position of the fovea is off the object of regard. *Under MONO conditions amblyopic eye fixates objects using nonfoveal point even though fovea is intact. *NB: Suppression scotoma around fovea.

What is contour interaction?

Adjacent contours have an affect on VA -- amount of visual info becomes visually confusing. Crowding is related. At 2 MAR >> MAXIMUM contour interaction (20/40 and smaller). Beyond 5 MAR >> no contour interaction (20/100 and larger). *NB: Can be an issue for both amblyopia and dyslexia. Recommend larger worksheets/font size.

How can the slope of the Flom Chart give you more info about whether a pt may have functional or organic/pathology-related etiology?

Gradual slope = gradual slow of line tells you it's likely amblyopia because they lose a few here and there before VA becomes very poor Steep slope = More likely organic amblyopia or pathology because VA just drops off

How are saccades in ambylopic pts different from normal pts?

Greater latency (longer time to get going) Amp appears to be roughly the same

What additional tests are helpful to do in Dxing ambylopia?

Have to r/o disease first!!! -Keratometry/OPD/topography >> helpful to determine astigmatism magnitude and axis when subjective responses are poor -Refraction +/- cyclo >> Need to take care of blur caused by RE first! Remember to make changes that correspond to the pt's JND -Amsler Grid >> r/o macular pathology within central 10º -Color Vision >> R/o cone dystrophy, macular disease (particularly B/Y defects), and ONH disease (R/G defects) -DFE -OCT -ERG >> r/o rod-cone dystrophies; will be abnormal when a large area of retina is impaired functionally *have to have large area of retina not functioning properly to get abnormal ERG -Laser interferometry -VEP

Why is neutral density filter testing done?

Help determine if VA loss is 2º functional amblyopia or disease/damage.

An amblyopic pt has this Rx: -2.00 -4.25 x 180 You show them gratings oriented at 90º and at 180º to check VA. Which grating will have worse VA?

Horizontally oriented lines will have more reduced VA. *For all of these types of questions, need to think of the power cross and which meridian has more RE. Remember that the horizontal meridian focuses vertical lines and vice versa.

How is Brock Afterimage Transfer Testing done?

How to: -MONOCULAR test of EF -Testing distance = 1 meter -Light flashed to one eye while other eye is occluded >> after image seen in both eyes -Patch eye, flash up to 3x, quickly switch patch, look at cm number line -Ask pt to look at zero on number line >> where is the after image? If pt has difficulty seeing afterimage: -Blink eyes quickly -Flicker rooms lights -Use TBIT -Wave hand *Goal is to break suppression Magnitude of EF? -1 cm displacement = 1 pd at 1 m

What is the purpose of 2.2x telescope testing? What does it tell you?

Purpose = Gives idea of prognosis of amblyopia s/p Tx. Expect 2 line VA improvement by telescope alone. How does it help? -Reduces FOV -Allows more accurate localization & fixation -Compensates for inaccuracies of accommodation & or RE What can it tell us? Better than 2 line improvement with telescope = good prognosis Two line improvement = poor prognosis How is it done? Check BCVA without telescope Give pt large letter and have them focus the telescope with their dominant eye Pt reads chart with better seeing eye through telescope Reads chart with scope with amblyopic eye

Define diplopia

Similar images falling on noncorresponding points on the retina e.g. falling on fovea of one eye and nonfoveal point in another eye. They're interpreted by the brain as being in different places. *Pt experiences diplopia unless they suppress nondominant eye or develop ARC.

Which cards may be helpful in a low vision context?

Single Tumbling E Card Grating Acuity Card Basic Vision Card

Which type of amblyopia produces the most EF and monocular spatial distortion?

Strabismic

What is the Snell-Sterling Efficiency value?

Tells us about visual efficiency based on MAR. MAR of 1' = 100% efficiency For every 1' they lose, it's a 0.83 loss in visual efficiency. Vis. efficiency, binocularity, and peripheral vision combine to give an overall picture of visual fxn for assessment of disability.

What is the current definition of amblyopia?

Unilateral or bilateral condition in which BCVA is < 20/20 in the absence of structural or patholgical anomalies but with the presence of one or more of the following conditions before 6 yo: -High amblyogenic aniso or iso ametropia -ET or XT -Stimulus Deprivation/image degradation *Neurological condition in which brain suppresses one eye due to unequal or incompatible visual signals leading to poor development of VA in affected eye. LONGTERM SUPPRESSION is what leads to development of amblyopia. NB: Amblyopia doesn't cause frank damage to visual system — it leads to adaptations.

What is the Flom Chart aka the Psychometric chart?

VA chart that controls for contour interactions. Acuity from 20/277 to 20/9 (21 levels) Endpoint = 2 or less correct for 2 lines Chance line at 5 correct Where curve crosses chance line = VA

Toxic Amblyopia

VA loss 2º to toxins, most commonly lead. Also: methyl alcohol, quinine and endogenous auto-immune disorders and infections. Characterized by : -Sudden onset -Unsteady, non-central fixation -Dense central scotoma *NOT REAL AMBLYOPIA

What is organic amblyopia? Is it true amblyopia?

Visual pathway doesn't develop 2º prenatal structural defects or from insult to fully developed pathway Examples: -Nutritional -Toxic -Congenital *Think of this as actual structural/physical damage or defects, while in amblyopia there are functional issues instead.

What are some considerations for when you're checking VA on an amblyopic pt?

Want chart with confusable optotypes Snellen chart letters = not very confusable, but good crowding Landolt C and Sloan Chart = more confusable Options for kids: Lea gratings, Teller Cards, Cardiff Cards HOTV, Allen card, Lea Symbols >> Lea = most confusable How to proceed: Start with full chart, then single line, then single letter if trouble, then PH *Better acuity with less clutter tells you there's BETTER PROGNOSIS

How can you determine the type and magnitude of EF in Haidinger Brush Testing?

What type of EF is it? *Toward the nose = nasal *Toward the ear = temporal *Up = superior *Down = inferior Magnitude: -4mm displacement = 1 pd at 40 cm test dist.

Define confusion

dissimilar images falling on corresponding points e.g. two different images falling on the fovea appear to occupy the same space even though they don't really. *Recent onset strab will have both diplopia & confusion.

Nasal EF is typically associated with...

esophoria/tropia

Temporal EF is typically associated with ...

exophoria/tropia

You are doing MIT testing on a pt's amblyopic eye (OS). She sees the haidinger brush to the left. What type of EF is this?

temporal EF Haidinger brush should be straight ahead if they're fixating with the fovea!