Stereopsis: are we assessing it in enough depth?

Abstract

The assessment of stereoacuity is an integral part of the ophthalmic assessment, with the responses used to inform clinical management decisions. Stereoacuity impacts on many aspects of life, but there are discrepancies reported where people without measurable stereoacuity report appreciating 3‐D vision. This could be due, in part, to the presentation of the stimuli. A literature review was undertaken to evaluate current assessment techniques, how they relate to patient outcomes, identify the limitations of current tests and discuss how they could be improved. Recent evidence has been collated on currently available tests, used commonly within vision clinics, with normative data provided allowing responses to the tests to be interpreted. The relevance of the results is evaluated in relation to a range of outcomes, where a reduced level of stereopsis has a negative impact on the ability of an individual to perform many tasks, and can lead to an increase in difficulty interacting in the world. Current tests are limited in the aspects of stereoacuity they assess and their ability to precisely measure stereopsis. The world is not static, yet clinical tests are limited to measuring static stereoacuity, even though higher grades of depth perception can be identified in the presence of changing depth. Presentation methods of stereoacuity tests have remained similar over time, with a limited number of disparity levels assessed. New assessment methods are becoming available that include automated staircase testing to present multiple levels of disparity using digital technology. Current clinical tests are limited in their presentation, and are poor at detecting/measuring stereoacuity in those with limited stereopsis. Given the relevance of the stereoacuity measurement to management choices and functional outcomes, new testing methods would be beneficial to fully assess stereoacuity, both static and dynamic.

Suppression Rather Than Visual Acuity Loss Limits Stereoacuity in Amblyopia

“…Stereopsis, the ability to perceive the depth of an object relative to an observer, arises from the binocular sensory fusion of slightly dissimilar retinal images that have horizontal disparity by virtue of the lateral separation of the two eyes. 1,2 Stereoacuity, reported in minutes or seconds of arc, describes the smallest horizontal disparity in binocular images that leads to the perception of depth in the observed stimulus. In observers with equal normal visual acuity and normal vision development, stereoacuity thresholds are typically of 20 to 40 seconds of arc.…”

“…In observers with equal normal visual acuity and normal vision development, stereoacuity thresholds are typically of 20 to 40 seconds of arc. [2][3][4] Stereoacuity will be worse when there are significant differences in the retinal images between eyes, that is, if the dichoptic images differ in contrast, size, or clarity. [5][6][7][8][9] Differences in retinal image clarity and size can occur if there is unequal refractive error (anisometropia) or ocular media obstruction from corneal or lens anomalies, with both blur and contrast differences known to degrade stereoacuity.…”

The prevalence and diagnosis of ‘stereoblindness’ in adults less than 60 years of age: a best evidence synthesis

“…The best way to show the presence of monocular cues in a stereotest is to determine whether observers can pass the test monocularly with a higher probability than chance. In the review presented here, we do not consider studies that simply assumed that patients with serious binocular dysfunctions are totally stereoblind because such patients may have residual stereovision …”

Congenital Nasolacrimal Duct Obstruction and the Visual System

“…Recovery of stereoacuity may require more vigorous treatment protocols in strabismic than in anisometropic amblyopia. Individuals with strabismic amblyopia have a very low probability of improvement with monocular training; however, they get on well with dichoptic training (promising new therapeutic approach to amblyopia, which employs simultaneous and separate stimulation of both eyes) than with monocular training and much better with direct stereo-training [72,73].…”