Clinical Features and Natural Progression of Unilateral High Myopia in Adults: A Comparison Study

Abstract

Purpose: To investigate and compare the clinical characteristics of patients with unilateral high myopia (UHM) and bilateral high myopia (BHM) based on axial length (AL).

Design: A retrospective cohort study.

Participants: Adult patients diagnosed with UHM or BHM between March 2011 and August 2021.

Methods: Unilateral high myopia was defined as ≥26 mm AL in 1 eye and <26 mm in the other, with ≥2 mm difference. Bilateral high myopia was defined as ≥26 mm AL in both eyes, with ≤3 mm difference. In each patient, the eye with the longer AL was designated the "longer eye" and the other the "shorter eye." We analyzed differences in clinical features, including ophthalmic history, best-corrected visual acuity, ocular biometry, and myopic maculopathy grade. Myopic maculopathy was graded based on atrophy, traction, and neovascularization using a known method. Long-term features included treatments for myopic neovascular maculopathy and myopic tractional maculopathy and AL change over time.

Main outcome measures: Comparison of clinical characteristics between UHM and BHM groups.

Results: We analyzed 369 patients (79 with UHM and 290 with BHM) with a median follow-up period of 4.5 years. The UHM group had a higher proportion of women than the BHM group (88.8% vs. 76.2%, P = 0.025). Compared with longer eyes in the BHM group, those in the UHM group had worse best-corrected visual acuity (0.8 ± 0.6 vs. 0.6 ± 0.6 in logarithm of the minimum angle of resolution, P < 0.001) despite having shorter AL (29.1 ± 1.6 mm vs. 30.6 ± 1.9 mm, P < 0.001). In the analysis of AL changes, shorter eyes in the UHM group showed no elongation over time (0.014 mm/year, P = 0.12), unlike the longer eyes in UHM and both eyes in BHM (0.049-0.071 mm/year, P < 0.01).

Conclusions: Adult UHM patients mostly lacked associated environmental factors. The poorer visual acuity in the longer eyes of UHM patients, which cannot be explained by structural abnormalities, suggests that the interocular difference may have originated in early childhood. During the follow-up period, AL elongation and myopic complications occurred at similar rates in the longer eye of UHM and both eyes of BHM. Meanwhile, such changes were not observed in the shorter eye in UHM. Further investigation of the underlying mechanisms, such as the genetic factors contributing to this extreme asymmetry, is warranted.

Financial disclosures: The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Keywords: Bilateral high myopia; Myopic maculopathy; Ocular asymmetry; Unilateral high myopia.

Figure 1

Flow chart of the study population. AL = axial length.

Figure 2

Cumulative probability of first myopia-related treatment in treatment-naïve patients. The first treatments for MNM (A, B) and MTM (C, D) occurred consistently over time in longer eyes, with no significant difference between the 2 groups (A, C). Additionally, in certain cases, treatment became necessary over time in the shorter eyes of the BHM group. However, in the UHM group, no cases required treatment for MTM or MNM over time (B, D). BHM = bilateral high myopia; MNM = myopic neovascular maculopathy; MTM = myopic tractional maculopathy; UHM = unilateral high myopia.

Figure 3

The spaghetti plot of the axial length changes over time. Both eyes in the BHM group and the longer eye in the UHM group showed significant axial length elongation over time (A, B, C). However, the shorter eye in the UHM group did not show significant axial length elongation over time (D). The rate of axial length elongation was not significantly different between the longer eyes of the 2 groups (P = 0.09), but there was a significant difference between the shorter eyes (P < 0.01). BHM = bilateral high myopia; UHM = unilateral high myopia.