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Roly D. Megaw, Stephen A. Madill; A Method for Objectively Assessing Acuity Using Dynamic Random Dot Stereograms: A Pilot Study. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4791.
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© ARVO (1962-2015); The Authors (2016-present)
Various methods have been suggested for objectively assessing acuity, one example being Optokinetic Nystagmus (OKN). Although exponents of OKN claim some capacity to quantify acuity, the test is only really useful in differentiating between eyes with NPL and eyes with some acuity remaining. We decided to investigate whether the OKN stimulus could be improved to allow an objective quantitative assessment of acuity
Observational study. 2 dynamic Random Dot Stereograms (RDS) of 240x240 points were created. Both presented moving vertical strips to the observer when fused stereoscopically; one with strips scrolling to the left and one scrolling to the right. Batteries of 10 RDSs were created, with the order of left and right scrolling assigned using a random number table. 3 observers (with 6/6 acuity in both eyes) viewed the stimuli at 3 distances so that the component dots (3mm in height) described visual angle equivalents to Snellen 6/9, 6/12 and 6/24. These distances were 6.88m, 5.16m and 2.58m respectively. The observers’ vision was blurred with plus lenses to 6/6, 6/9, 6/12, 6/24 and 6/60. A different RDS battery at each of the 3 Snellen equivalent distances was presented for each of the induced acuities. Observers reported the perceived direction of strip movement using a 2 way forced choice protocol
A significant association was demonstrated between the observer's acuity and the ability to see RDSs of Snellen equivalents as good as the respective acuity (fisher's exact test; p=0.0005)
The pilot study demonstrates that when using dynamic Random Dot Stereograms of specific Snellen equivalents, observers will only perceive strip movement if their own acuity in both eyes is the same as or better than the Snellen equivalent of the stereogram. Generating an OKN response with stereograms could therefore allow a more quantitative assessment of acuity than a standard OKN stimulus. In the next phase of this study, subjects' verbal responses will be replaced by a masked observer recording the direction of induced OKN movements in response to presented stereograms. A correlation between the direction of OKN response and RDS strip movement may allow a protocol to be developed towards an objective test of visual acuity
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