Determining vertical fusion values from digital photographs of healthy eyes.

PURPOSE

To determine the mean difference of vertical corneal light reflex (VCLR) among healthy eyes via digital photography.

STUDY DESIGN

Retrospective study.

METHODS

The study enrolled 155, healthy eyes participants, 71 males and 84 females with a mean age of 14.7 years (range 12-19 years). The participants received complete eye examinations and 2 digital photographs were taken, with the flash on, while participants fixated their eyes on a near and a distant target. Two hundred and eighty qualified photographs were analyzed by Photo-Hirschberg testing using computer software. The vertical corneal light reflex ratio (VCLRR) was calculated as the distance of the corneal light reflex (CLR) to the inferior limbus or to the pupillary border divided by the horizontal corneal diameter, defined as VCLRR1 or VCLRR2. VCLRR was analyzed using Spearman's correlation.

RESULTS

The mean ± SD of horizontal corneal diameter in near and distance photographs was 11.47 ± 0.62 and 11.37 ± 0.58 mm, respectively. For correlation analysis, at 1 m fixation and 6 m fixation, the number of participants within an acceptable range of vertical fusion were 94.6% and 100% of participants. The 95th percentiles (estimated as the mean ± 1.64SD) in VCLRR1 between the two eyes at near and at distance fixation were 0.0316 and 0.0272, respectively; whereas the corresponding values for VCLRR2 were 0.0309 and 0.0240, respectively.

CONCLUSIONS

The normal range of the vertical corneal light reflex ratio suggests that the Photo-Hirschberg test could be used for screening vertical strabismus cases depending on iris pigment.