Peripheral eye length measurement techniques: a review.

Along with the rising myopia epidemic is the increasing interest in any ocular parameter that might inform understanding of myopia progression. The relationship between eye length and myopia has long been established but the recent interest in the central and peripheral retina, eye shape, retinal contour, and refractive error development is attracting more clinical and research interest in peripheral eye length measurements. Therefore, peripheral eye length measurements are an important step in the ongoing research involving the peripheral retina. Since the first measurement of peripheral eye length reported in 1991, many techniques and methods have been developed, which vary in many aspects. These techniques involve custom-built or modified commercially available instruments, with the use of off-axis targets and other considerations such as eye or head turn of the subject. The wide range of methods and instruments used for peripheral eye length measurements make it difficult to compare results and may account for some of the variations in the reported results. Specifications of the different methods are presented along with their advantages and disadvantages. Although researchers acknowledge a good agreement between the modified commercially available optical biometers for peripheral eye length measurement, the Lenstar LS 900 appears to offer better results. Nevertheless, the introduction to the market of an instrument specially designed for peripheral eye length might overcome the issues noted with other methods and could allow for more insights in future research involving the peripheral retina. Moreover, future studies may be able to track peripheral eye length changes and its relationship to the progression of myopia and find out if those changes are responsible for or correlated with important eye conditions.