Pitfalls in the Use of Stereoacuity in the Diagnosis of Nonorganic Visual Loss

Abstract

Purpose: The Titmus Stereotest (Stereo Optical Co., Inc., Chicago, IL) has been used to estimate visual acuity (VA) in the evaluation of nonorganic visual loss. Previous 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 nonorganic visual loss. The purpose of this study was to evaluate the relationship between Titmus stereoacuity and minimal VA based on a real-world testing environment.

Design: Cross-sectional observational study.

Participants: All patients treated at the authors' neuro-ophthalmology service between April 25, 2014, and July 31, 2014.

Methods: All subjects underwent routine neuro-ophthalmic examination, including Titmus stereoacuity measurements. A compound Bayesian logit-lognormal model accounting for heteroscedasticity was used to determine 95% and 99% prediction intervals of the worse eye's near VA based on stereoacuity. Logarithm of the minimum angle of resolution VA and log stereoacuity were analyzed.

Main outcome measures: Titmus stereoacuity and worse eye VA.

Results: Of 561 patients, 364 subjects 11 to 91 years of age were included. Titmus stereoacuity was associated positively with VA: 9 circles correct (40 seconds of arc) indicated VA of at least 20/40 with 95% confidence and VA of at least 20/79 with 99% confidence; 6 circles correct (80 seconds of arc) indicated VA of at least 20/62 and 20/180, respectively; and 4 circles correct (140 seconds of arc) indicated VA of at least 20/110 and 20/570, respectively.

Conclusions: When fully accounting for individual variation and the full spectrum of neuro-ophthalmic diseases affecting VA, stereoacuity remains associated with VA, but previous commonly used VA estimates based on stereoacuity overestimated VA. Our results more accurately predict minimum VA from Titmus stereoacuity and should be used preferentially when evaluating patients with suspected nonorganic visual loss. We demonstrated that Titmus stereoacuity cannot definitively establish normal VA, and therefore can suggest, but not fully establish, the diagnosis of nonorganic visual loss.

Figure 1

Exclusion Criteria of the 561 included subjects. After exclusions for missing data, cognitive issues, suspected non-organic visual loss, the presence of a heterotropia or history of strabismus/amblyopia, and a “zero” score on the Titmus test, a total of 364 subjects remained for analysis.

Figure 2

Graphical depiction of worst eye near visual acuity (log scale) as a function of measured Titmus stereoacuity (log scale of circle score). Darkest blue line represents median visual acuity, medium blue line represents 95^th prediction interval, and light blue line represents 99^th prediction interval. Dots represent individual subjects and are jittered on the x-axis for visualization purposes.