The Relationship Between Binocular Imbalance and Myopic Shift in Unoperated Eyes After Unilateral SMILE and tPRK.

Purpose: The purpose of this study was to investigate the relationship between binocular imbalance and myopic shift in unoperated eyes after unilateral small incision lenticule extraction (SMILE) and transepithelial photorefractive keratectomy (tPRK) procedures.

Methods: This study included 51 participants who had undergone unilateral SMILE (n = 28) or tPRK (n = 23) for at least 3 months. The participants were categorized into stable and myopic shift groups based on the difference between preoperative and postoperative spherical equivalent refractive (SER) errors of unoperated eyes. Psychophysical tests were conducted only at the postoperative follow-up point. Spatial sensory eye dominance was determined by analyzing a binocular orientation combination task at spatial frequencies of 1 and 6 cycles per degree (c/d). A rotating cylinder generated a spontaneous Pulfrich phenomenon to determine the interocular delay at spatial frequencies of 0.95 and 2.95 c/d.

Results: The logrBP in the myopic shift group was significantly more negative than in the stable group at 1 c/d (P < 0.01) and 6 c/d (P < 0.01). And logrBP correlated with the difference between preoperative and postoperative SER of the unoperated eye at 1 c/d (rs = 0.513, P < 0.001) and 6 c/d (rs = 0.504, P < 0.001). In the myopic shift group, logrBP was more negative at 6 c/d than at 1 c/d (P = 0.013), but not in the stable group.

Conclusions: Patients who experience myopic shift in the unoperated eye after unilateral SMILE or tPRK tend to have stronger sensory eye dominance in that eye, with a more pronounced dominance at higher spatial frequencies.