Visual Acuities Flashcards by Emme Gilchrist

4 testing methods for VA

minimum visible/detection acuity
minimum separable/ resolution
Vernier acuity (don’t use clinically)
Recognition acuity (snellen)

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Detection acuity

Child states whether or not an object is present.
Similar to visual field. Can you detect the stimulus or not?
Not used much
Ex: Can you find the blue jellybean at different distances?
Problem: Not standardized. Hard to document/repeat/compare.

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Resolution acuity stimuli

Square wave, sine wave, checkerboard.

Can use with children or non-verbal pts.

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Vernier Acuity

The smallest area of misalignment that can be detected between two stimuli. Not used clinically, more experimental.

Could be two lines or two dots

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Recognition acuity- landolt C

Child chooses between two images- one with broken C and one with circle. Forced preferential pattern.

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Most common recognition acuity test

Snellen

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Differences in cortical immaturities in children

Incomplete myelination of optic pathways

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Limits of acuity testing in children. Why might they not have as good of vision?

Incomplete myelination 
Foveal and cone immaturities
-Short and stubby (4 yrs) 
-Less densely packed (3-4 years) 
Variable morphology of foveal pit

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When does the foveal pit become more adult like?

17 months.

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Foveal and cone immaturities in children

Short and stubby til age 4

less densely packed til age 4

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Full development of foveal cone in children

4 years

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If you cannot get monocular acuities, then what?

Test binocular but do other objective tests to assess: Ret, CT, health check

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How to occlude babies eye?

Sticky patch, mom/dads hand.

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What is more concerning?
Baby cries when OD and OS are covered
Baby cries when OD is covered, ok when OS is covered

Asymmetry is concerning.

Baby who cries about both eyes could mean they just don’t like eye being covered.

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What do infants love to look at?

Faces

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Babies should be able to make eye contact at ___ weeks

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Babies should smile back at you at __ weeks

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Heidi smile test

Screening device. 3 months. Not acuity test!

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CSM technique and what are you assessing?

Central, steady, maintained.
Use penlight and shine into pt’s monocular eye.
Gross assessment of fixation and acuity. Used by many peds ophthalmologists.

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What does CSM stand for?

Central:
Light is centered on pupil

Steady:
Eye is steady, no nystagmus

Maintained:
Can the eye follow a target? Ex: follow the pen light. Indicates acuity

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How to document CSM

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If pt fails C, S, or M, document it with a “u” or “N” in front of the letter.

CUSUM

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Nystagmus with poor acuity (maintainence)

F&F. What is it and what is the technique?

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Grosser measurement of fixation. Less advanced than CSM.

Technique: Pen light, monocular.

How to determine if there is a fixation problem using vertical prism?

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Have pt fixate at near object. Please 10pd BD or BU in front of 1 eye. Child should see double. If the child sees double, the eyes will move up and down between the images.

if they do not see double, suspect amblyopia or strabismus.

Resolution VA using stripes. What is 1 cycle

One black and one white stripe

Difference between higher and lower spatial frequencies

Thick stripes= low spatial frequencies= poorer VA | Thin stripes= High spatial frequencies= better VA

What distance should you be at for cycles per cm and cycles per degree to be equal?

55cm Closer= easier Farther= harder (Similar to normal acuity testing)

Teller Acuity Cards (TAC) Type of preferential looking - Range of cycles/cm - Range of snellen - What cpd "equals" 20/20 - Pt must be correct what percentage of the time?

1. 38 cpc to 0.23 cpc 2. 20/2400 to 20/10 3. 30 or 32 cpd= 20/20 but not really equal. Like comparing apples and steak dinner 4. 70-75% correct

Downside to preferential looking

Time consuming, not cheap Hard to keep child's attention Does not equate to snellen equivalent *Objectivity of examiner

In healthy infants, VA should steadily increase from __ to __

4 weeks to 1 year

At 1-2 months, expect what VA

1.3 cpd | 20/470 acuity at 55cm

At 6 months, expect what VA

5cpd | 20/100 acuity at 55cm

At what age should children have "adult vision"

3-5 years

Lea Paddles technique

Hold grey paddle over one with stripes. Separate paddles. See if child's gaze follows paddle with stripes. Make sure your face is covered!! Babies love to look at faces

Lea paddles distance

Typically calibrated for 57cm

Advantages and disadvantages to lea paddles

Advantage: Good cost and portable Disadvantage: No snellen equivalent (same as TAC), time consuming

OKN: what is it?

Involuntary eye movement induced by speed of motion of the visual field. Make sure the speed isn't too fast, or you will not elicit an OKN response.

What kind of nystagmus occurs in OKN?

Jerk. Smooth (slow) pursuit in direction of target with fast saccade bak. Natural phenom.

2 requirements to elicit OKN response

1. Pt must pay attention to stripes 2. Pt must accommodate to stripes 3. Target cannot be moving too fast

OKN test distance

40 cm. Want it to block pt's visual field.

Probably causes if pt does not have OKN response?

Pt could be blind Lesion in cortex, cerebellum, brainstem Cortical dysplasia (dysmorphia of brain) Cortical blindness

Is OKN foveal?

No. Deep central scotoma only reduces gain by 10-30%.

Is OKN affected by blur?

Not particularly. Can get a positive OKN response even with high refractive error. Doesn't tell you that they need glasses or not, tells us that they are getting visual input.

Can you determine VA based on OKN?

No. Doesn't tell you that they need glasses or not, tells us that they are getting visual input. Lets us know if the child can see anything. If child has OKN response, expect at LEAST 20/400 acuity.

If child has OKN response, expect at LEAST ____ acuity.

20/400

Infant response with binocular OKN

Strong and healthy (robust) response, regardless of direction.

1-2 month response to monocular OKN

Only show OKN response to temporal --> nasal motion. NOT nasal--> temporal. Due to cortical immaturities (myelin and pathways undeveloped).

When does monocular OKN become symmetrical for children?

5-6 months Could be as early as 3 months or as late as 24 months.

When might asymmetric OKN responses persist past 5-6 months?

If the pt has abnormal binocularity. Strabismus, anisometropia, unilateral congenital cataract.

If pt has no OKN response, what should you do next to determine if the pt can see?

Blink to startle: flick fingers at child's eyes. They should blink as a defense mechanism. Blink to light: Dark room. Shine BIO in child's eyes. They should blink.

Visual Acuities Flashcards

(50 cards)