Purpose:
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.

Methods:
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.

Conclusions:
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.