Stereopsis & Suppression

I. Stereopsis

A. Factors that effect stereopsis

Strabismus

Amblyopia

Blur (unilateral and bilateral)

Refractive error

Accommodative dysfunction

Fixation disparity

Vergence dysfunctions

Aniseikonia

Suppression

Luminance

Exposure duration

Retinal eccentricity

Practice (learning)

B. Characteristics of Stereopsis

40 seconds expected with local stereopsis

Try 20 sec for definitive statement

Booklet calibrated for 40 cms

Stereo Fly picture

Qualitative responses are important

Time of response

Movement of head or booklet

Crossed vs. uncrossed disparity

Esophoria

Stereopsis affected significantly

Exophoria

Stereopsis threshold can be better than predicted

C. Random dot (global) stereopsis

Very sensitive to binocular dysfunction

Better predictor of binocular dysfunction than local stereopsis

RDE

II. Suppression

A. Characteristics of Suppression

Found only in binocular dysfunctions

Competitive disadvantage of one eye

Corresponding points

Constant or intermittent

Unilateral or alternating

Central and/or peripheral (spatial zone)

Shallow or deep

Stimulus dependent

B. Clinical Responses

Detected:

Vergence tests

Phoria tests

Vectographic tests

    Suspected:

Reduced stereopsis

Anomalous findings (PRA, etc.)

Suppression in non-strabismus:

Foveal (central)

Intermittent, alternating

Constant (longer duration of dysfunction)

Purpose?:

Reduce demand for precise binocular alignment

Aniseikonia