Redefinition of high myopia: the relationship of axial length measurement to myopic pathology and its relevance to cataract surgery.

Owing to growing confusion over the true incidence of RD in HM after cataract surgery, a new definition for HM has been formulated based on measurement of axial length. Of 38 noncataractous phakic eyes with treated RD, 45% were found to have axial lengths more than 1 mm longer than would be expected from the eye's refraction. Of 180 moderate to highly myopic eyes examined 2 years after extracapsular extraction with lens implantation, 2 were found to have developed RD. Using the historic definition for HM by refraction (spectacle equivalent of -6.0 dptr or more), the incidence of RD was found to be 1/62 eyes (1.6%) but using the improved definition of axial length 26.5 mm or more, the incidence was found to be 2/49 eyes (4.1%). Both these studies suggested that axial length, in addition to myopic pathology, is a factor associated with RD and that a definition of HM based on axial length is more appropriate than that based on refraction.