Post-Natal Vision Development

o Why difficult to study

Difficult patients

Racial / geographic differences

Malleability / rapid change in vision behavior

o Why important

Ability to predict normal from delayed vision development

Set a time course for intervention with Rx or orthoptics

Proper referral for developmental / neurological consult

GENERAL DEVELOPMENTAL MILESTONES

Developmental Milestones:

Visual Acuity Development In Infants

Development Of Refractive Error

10 Days To 3 Months

Cyclopleged: hyperopia (2.2D - 4.4 D); few myopes (25%)

Non-Cyclopleged: myopia (-7.00 to -.70) huge variance depending on exam protocol

Mohindra (dry) ret results

(-.70+/- .40D)

Astigmatism: (30%-50%) between 1-2 D

A/R tendencies for Caucasians; W/R for Asian populations

No associations with particular spherical refractive error

Magnitude decreases in first year of life

Howland et. al used isotropic retinoscopy (photorefraction)

scanned two meridians simultaneously

eliminates concern over rapid changes in accommodative response

Found similar results to above

Keratometry revealed that most astig. in infants was corneal

Development Of Refractive Error

10 Days To 3 Months

Anisometropia Common

Extremely Fluctuative in Longitudinal and Cross Sectional Studies

Difficult to Pinpoint Role in Amblyogenesis

Development Of Refractive Error

4 Months To 1 Year

Hyperopia Increases

Astigmatism Decreases

Anisometropia Fluctuates

Development Of Accommodation / Convergence

Accommodation: Two Problems For Neonate

Detection Of Blur: due to immaturity of retina/sensory processing

Attention: may be most prominent cause of poor skills in infants

DETECTION OF BLUR

1-2 Diopters Accurate

>3 Diopters Inaccurate

ROLE OF ATTENTION

Vast Improvement On Accuracy @ 2-4 Diopters When Alert

Development Of Accommodation / Convergence

Convergence: Three Months To Consist Bifoveation

Near target: Improvement @ 3 months to 15 Prism Diopters

high spatial frequencies best (5-10 c/deg)

Prism: No consistent response To 6 Months of Age

Development Of Oculomotor Control

Fixation times for infants decrease w/complex visual environments

Improve w/simple visual environments

When slip occurs, infants will refixate the target inaccurately (i.e. their attention is now elsewhere)

Monocular Saccades: balance of infant's immature sensory and motor systems with these very precise eye movements

Simple geometric target on black background:

Amplitude and latencies are very poor in infants

Accuracy degrades:

First saccade: significant undershoot

Followed by a series of corrective saccades

Monocular Saccades: cont.

Complex, realistic target contours on "natural" background:

Amplitude and latencies come close to adult levels!!

Accuracy improves:

First saccade: some inaccuracy

Few saccadic steps necessary for correction

Pursuits: failed to obtain consistent pursuits in infants ²3 months old: immature foveal development is culprit

More consistent by 5-6 weeks: driven by parafoveal regions

best to use slower moving (² 10 degrees/sec.) parafoveal targets

Too big: lose attention

Too small: hits immature fovea

dark background

Clinical Application For Young Infants

Use moderate size (3-5 degree) complex visual targets/backgrounds with saccade and pursuit testing

Maximize attention throughout test

Maximize ability to detect motion from background

Use moderate size (3-5 degree) simple targets on black background to test fixation

Minimize distraction from target