Visual Acuities Flashcards
4 testing methods for VA
minimum visible/detection acuity
minimum separable/ resolution
Vernier acuity (don’t use clinically)
Recognition acuity (snellen)
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.
Resolution acuity stimuli
Square wave, sine wave, checkerboard.
Can use with children or non-verbal pts.
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
Recognition acuity- landolt C
Child chooses between two images- one with broken C and one with circle. Forced preferential pattern.
Most common recognition acuity test
Snellen
Differences in cortical immaturities in children
Incomplete myelination of optic pathways
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
When does the foveal pit become more adult like?
17 months.
Foveal and cone immaturities in children
Short and stubby til age 4
less densely packed til age 4
Full development of foveal cone in children
4 years
If you cannot get monocular acuities, then what?
Test binocular but do other objective tests to assess: Ret, CT, health check
How to occlude babies eye?
Sticky patch, mom/dads hand.
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.
What do infants love to look at?
Faces
Babies should be able to make eye contact at ___ weeks
8
Babies should smile back at you at __ weeks
12
Heidi smile test
Screening device. 3 months. Not acuity test!
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.
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
How to document CSM
If pt fails C, S, or M, document it with a “u” or “N” in front of the letter.
CUSUM
Nystagmus with poor acuity (maintainence)
F&F. What is it and what is the technique?
Grosser measurement of fixation. Less advanced than CSM.
Technique: Pen light, monocular.
How to determine if there is a fixation problem using vertical prism?
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?
- 38 cpc to 0.23 cpc
- 20/2400 to 20/10
- 30 or 32 cpd= 20/20 but not really equal. Like comparing apples and steak dinner
- 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
- Pt must pay attention to stripes
- Pt must accommodate to stripes
- 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.
