The refractive development of untreated eyes of rhesus monkeys varies according to the treatment received by their fellow eyes.

To determine the extent to which the visual experience of one eye may influence the refractive development of its fellow eye, we analyzed the data of untreated (UT) eyes of monkeys that received different types of unilateral pattern deprivation. Subjects were 15 juvenile rhesus monkeys, with five monkeys in each of three treatment groups: aphakic eyes with optical correction (AC), aphakic eyes with no correction (ANC), and eyes that were occluded with an opaque contact lens (OC). Under general anaesthesia, refractive error (D) was determined by cycloplegic retinoscopy and axial length (mm) was determined with A-scan ultrasonography. For measurements of refractive error of the UT eyes, there was a significant main effect of groups according to the treatment of the fellow eyes, F(2, 12) = 6.6. While UT eyes paired with AC fellow eyes (mean = +4.2 D) were significantly more hyperopic than the eyes of age-matched normal monkeys (mean = +2.4 D), t(25), = 2.5, UT eyes paired with OC fellow eyes (mean = -0.5 D) were significantly more myopic than the eyes of normal monkeys, t(25) = -9. UT eyes paired with ANC fellow eyes (mean = +1.9 D) were not significantly different from normal eyes. For measurements of axial length there was also a significant main effect of groups, F(2, 12) = 6.9. While UT eyes paired with AC fellow eyes (mean = 16.9 mm) were significantly shorter than the eyes of age-matched normal monkeys (mean = 17.5 mm), t(25) = 2.3, UT eyes paired with OC fellow eyes (mean = 18.1 mm) were significantly longer than the eyes of normal monkeys, t(25) = 2.3. UT eyes paired with ANC fellow eyes (mean = 17.5 mm) were not significantly different from the eyes of normal monkeys. The measurements of axial length and of refractive error of the UT eyes were also significantly correlated with one another, probably indicating that the differences in refractive error were due to differences in axial length, r = -0.8. The present data reveal that despite normal visual experience, UT eyes can have their refractive development altered, systematically, simply as a function of the type of pattern deprivation received by their fellow eyes. These data add to the growing evidence that there is an interocular mechanism that is active during emmetropization. As a consequence, future models of eye growth will need to consider both: (1) the direct influence of visual input on the growing eye; as well as (2) the indirect influence coming from the fellow eye.