The utility of white-to-white distance in predicting myopia and its practical implications: a review
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Abstract
White-to-white (WTW) distance is one of the anterior segment metrics of the eye that has significant clinical implications and utility. Traditionally used as a diagnostic tool for congenital glaucoma, microcornea, and megalocornea, WTW distance has also been found to play an important role in planning and predicting successful outcomes for refractive cataract and implantable collamer lens (ICL) surgeries. For example, it has become a standard measurement utilized for calculating both the refractive power of intraocular lenses (IOL) for cataract surgeries, and ICL size. The goal of this thesis is to review 1) the various ways in which WTW distance is used in the clinical setting and 2) whether it has any correlation to the degree of myopia.
The current literature on WTW distance, including the various methods of measurement and its utility in clinical procedures is reviewed. Comparative evaluations of the various devices that can measure WTW distance show a generally good repeatability, with no gold standard for accurate measurement. Some argue that a manual measurement using a caliper at the slit lamp is the gold standard, but this method has been found to have high variability. Additionally, there is ongoing debate on whether WTW distance is sufficient for accurate ICL sizing and successful surgical outcomes. More recent data show alternative metrics such as sulcus-to-sulcus (STS) or angle-to-angle (ATA) diameter to be better predictors of accurate ICL sizes. Despite recent findings of better clinical outcomes using these internal ocular metrics for ICL surgery, whether they are cost effective and clinically significant enough to replace existing methods remains inconclusive.
WTW distance and degree of myopia from the patient database at Boston Vision was also analyzed. A pairwise p-test with Bonferroni correction of WTW distance in 107 eyes with no myopia, low myopia, or high myopia revealed that there was no strong correlation between WTW and degree of myopia (p > 0.05). However, the WTW distance was smaller in females than in males (mean difference -0.3245; p < 0.001), which confirmed findings from a previous study. Based on these preliminary findings, it doesn’t seem clear that a correlation between WTW distance and degree of myopia exists. While the practical implications of WTW have been widely assessed, additional studies and research using a large dataset should be performed to accurately evaluate the utility of WTW in predicting myopia.