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Kevin Sitko, Jason Peragallo, Samuel Bidot, Valerie Biousse, Nancy J. Newman, Beau B Bruce; Pitfalls in the Use of Stereopsis for the Diagnosis of Non-organic Visual Loss. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):554.
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© ARVO (1962-2015); The Authors (2016-present)
Titmus stereoacuity testing is used to estimate visual acuity (VA) in the diagnosis of non-organic visual loss (NOVL), but only predicts mean VA and doesn’t account for normal inter-subject variability. These predictions were derived from optical degradation of VA in normal subjects and may not account for the variability seen in patients with neuro-ophthalmic pathologies included in the differential diagnosis of NOVL. The purpose of this study was to evaluate the relationship between Titmus stereoacuity and minimal visual acuity based on a real-world testing environment.
All patients presenting to our service between 4/25/2014 and 6/26/2014 underwent routine neuro-ophthalmic examination, including Titmus stereoacuity measurements. A compound Bayesian logit-lognormal model accounting for heteroskedasticity was used to determine 95% and 99% prediction intervals of the worse eye’s near visual acuity (VA) based on stereoacuity. LogMAR acuity and log stereoacuity were analyzed.
Of 561 patients, 28 were excluded for missing stereoacuity or VA measurements, 4 for cognitive issues, 3 for suspected NOVL, and 119 for heterotropia or history of strabismus/amblyopia. Patients who correctly identified zero circles (43) were also excluded from the calculation. 364 subjects were analyzed [median age: 45-yo (range: 11-91); 258 (71%) women; median worse-eye VA 20/25; median Titmus: 7 circles correct]. Titmus stereoacuity was positively associated with VA: 9 circles correct (40 seconds of arc) indicated VA of at least 20/41 with 95% confidence and 20/88 with 99% confidence; 6 circles correct (80 seconds of arc): 20/63 and 20/197; and 4 circles correct (140 seconds of arc): 20/106 and 20/582, respectively.
When fully accounting for individual variation and the full spectrum of neuro-ophthalmic diseases affecting VA, stereoacuity remains associated with VA, but commonly-used VA estimates based on stereoacuity overestimate VA. Our results more accurately predict minimum VA from Titmus stereoacuity and should be preferentially used when evaluating patients with suspected non-organic visual loss. We demonstrate that Titmus stereoacuity cannot establish definitively normal VA, and therefore can only suggest, but not establish, the diagnosis of NOVL.
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