High myopia is not only a refractive state; for many patients, it is a lifelong structural risk. Alongside myopic macular degeneration, optic nerve damage is one of the major sight-threatening complications of pathological myopia. Yet clinicians often face a difficult question: how worried should they be about a highly myopic optic nerve that looks normal today?
A new study in the British Journal of Ophthalmology attempts to bring numbers to that question. The study authors developed and validated equations to estimate the probability of high myopia-associated glaucomatous or glaucoma-like optic neuropathy (GLON) and non-glaucomatous optic neuropathy (NGON), using data from the Two-Continent Eye Study.
The analysis combined five population-based cohorts: the Beijing Eye Study, Ural Eye and Medical Study, Ural Very Old Study, Ural Children Eye Study, and Central India Eye and Medical Study. Together, these included 35,167 eyes from 17,996 individuals spanning ages six to 100 years. Participants underwent ophthalmic and medical assessment, including refractometry, ocular biometry, optic nerve and macular photography, OCT in four of the five cohorts, and perimetry in the adult cohorts.
The investigators distinguished between two forms of optic nerve damage. GLON was defined by characteristic glaucomatous or glaucoma-like optic nerve head abnormalities, such as abnormal neuroretinal rim shape, rim notching, and a vertical cup-to-disc ratio larger than the horizontal ratio. NGON, by contrast, was defined by a normal rim configuration but signs of optic atrophy, including rim pallor, reduced retinal nerve fibre layer visibility or thickness, and thin retinal arterioles, after excluding other evident causes.
Across the full cohort, GLON was present in 2.7 percent of eyes and NGON in 0.3 percent. Most GLON eyes had intraocular pressure of 21 mm Hg or below, underscoring the diagnostic complexity of glaucoma-like damage in highly myopic eyes.
The study population was randomly divided into development and validation subgroups. In the development cohort, GLON probability was driven by longer axial length, older age, Indian ethnicity, higher IOP, and the presence of NGON. NGON probability was associated with longer axial length, older age, myopic macular degeneration stage, GLON presence, and lower probability in Indian ethnicity.
Performance was strong: in the validation subgroup, the equations achieved areas under the receiver operating characteristic curve of 0.881 for GLON and 0.964 for NGON. For a non-Indian individual with axial length of 28 mm and IOP of 22 mm Hg, estimated GLON probability rose from 3.5 percent at age 30 to 60.2 percent at age 75; NGON probability rose from 3.4 percent to 16.4 percent. At axial length 30 mm, estimated GLON probability increased from 6.9 percent to 75.6 percent, while NGON rose from 28.2 percent to 68.4 percent.
However, the study authors emphasize that these equations offer rough estimates and are not definitive predictions. The data are cross-sectional rather than longitudinal, axial length was assumed to remain constant over time, and the model was not externally validated. Other potentially relevant factors, such as family history of glaucoma, were also not included.
Even so, the work offers a clinically useful framework. For highly myopic patients, particularly those with very long axial length, optic nerve risk is not static. A simple clinical-parameter-based score may help ophthalmologists to better communicate risk, guide monitoring intensity, and identify patients who warrant closer structural and functional follow-up.
