Optical signals of the peripheral retina control eye growth and associated myopia more than previously believed. Traditional thought held that the fovea must play the largest role in progression of refractive error because of its integral role in vision. However, recent research shows that the peripheral retina may be involved. In Rhesus monkeys, peripheral form deprivation and optically induced hyperopia lead to increased axial elongation and myopia. Furthermore, emmetropization occurs when the peripheral cue is removed, even after ablation of the central retina. Human myopes have relative hyperopic blur in the periphery, whereas emmetropes and hyperopes exhibit emmetropia or myopia in the retinal periphery. In fact, relative peripheral hyperopia precedes myopia onset by two years in children. This peripheral hyperopic blur may be a signal for myopic eye growth. Tracking the 3-dimensional shape of the eye through peripheral measurements could provide clues about how peripheral blur increases axial elongation. Understanding these optical signals and pathways could be valuable in ultimately determining how to manage or prevent myopia.
Research has focused on methods to stymie eye growth by inducing peripheral myopic defocus. It is therefore important to determine whether any change in peripheral eye length is greater than that which can be expected by measurement error alone. This study aims to determine the inter-occasion repeatability of peripheral axial length measurements using the IOLMaster in order to learn more about the growth of peripheral eye.
To assess the repeatability of the IOLMaster in measuring peripheral eye length, we performed five measurements of both non-cycloplegic and cycloplegic (two drops of 1% tropicamide) axial length in primary gaze and at gazes 20 degrees nasal, temporal, superior, and inferior. The same examiner repeated the measurements one week (± 2 days) later to assess how similar the measurements were from one week to the next, assuming that no significant eye growth would happen in that span of time.
A total of 30 subjects completed the study. The 95% limits of agreement (LoA) for the cycloplegic repeatability at each location were: central (-0.05, +0.07), nasal (-0.24, +0.23), temporal (-0.14, +0.12), superior (-0.11, +0.11), and inferior (-0.11, +0.11). The 95% LoA for the non-cycloplegic repeatability at each location were: central (-0.07, +0.06), nasal (-0.17, +0.17), temporal (-0.11, +0.09), superior (-0.27, +0.23), and inferior (-0.15, +0.13). In general, nasal measurements were the least repeatable of the peripheral locations. Neither cycloplegic nor non-cycloplegic measurements consistently provided better repeatability at all locations. However, cycloplegic measurements provide shorter eye lengths than non-cycloplegic measurements (p < 0.001). If peripheral eye length is to be measured over time, operators of the IOLMaster must be consistent in whether or not they use cycloplegic drops. Users of the IOLMaster can be confident that any change of 0.25 mm in peripheral eye length is due to a real change in the eye and not due to measurement error. Repeatability of the IOLMaster is quite good for tracking peripheral eye growth.