Previous strabismus appearance studies using images from real face photographs could not preclude the effect of other facial landmarks, such as position and contour of brow, nose, and facial outline, from pure effect of ocular deviation itself. With conceptualized drawings of eyes, we simulated strabismus deviation and collected the responses of observers.
The experiments consisted of three sessions: (1) one-eye, (2) two-eye cornea, and (3) two-eyelid deviation simulations. On a monitor, eight different ocular deviations in increments of 6 prism diopters of horizontal or vertical deviations were simulated. Nine ophthalmology residents were asked to choose between esotropia and exotropia for horizontal simulations and hypotropia or hypertropia for vertical simulations. Psychometric function fitting was performed. Detection sensitivity, point of subjective equality, and 95% thresholds were calculated.
Between cornea and lid deviation simulations, there was no difference in 95% thresholds, points of subjective equality, and sensitivity (all p values > 0.10), reflecting that the relative location of cornea and lid was the determinant factor in recognizing ocular deviation. The sensitivities of vertical deviation simulations were higher than that of horizontal in two-eye cornea and lid comparisons (p values < 0.04) but not in one-eye (p value = 0.37).
Our results suggest that the appearance of strabismus depends not on the absolute ocular alignment but rather on the reciprocal relationship of cornea and lid margin. Vertical misalignment was more apparent than horizontal misalignment.