Axial length as a predictor of myopic macular degeneration: a meta-analysis and clinical study

This study aims to investigate the relationship between axial length (AL) and the severity of myopic macular degeneration (MMD).

We conducted a comprehensive search of PubMed, Web of Science, and China National Knowledge Infrastructure (CNKI) databases from their inception until October 1, 2023, to identify population-based or hospital-based studies reporting AL across different grades of MMD. Only studies employing the International Photographic Classification and Grading System for Myopic Maculopathy (META-PM) were included. A meta-analysis was performed to assess the association between AL and MMD severity. To further validate our findings, we analyzed data from 395 eyes of 206 participants at Beijing Tongren Hospital, Capital Medical University.

The meta-analysis included 20 high-quality studies from seven countries, with 33822 patients studied. Information, including the study name, year of publication, country, sample size, basic demographic characteristics of the participants, AL of different grades of MMD, best corrected visual acuity (BCVA), and spherical equivalent (SE), was extracted. The meta-analysis revealed a significant overall increase in AL as MMD progressed from category C0 to C4 (P < 0.0001). AL exhibited a consistent increasing trend from categories C0 to C3; however, this trend appeared to level off between categories C3 and C4, with no further increase observed. This trend was confirmed by the distribution of our new dataset. A higher prevalence of MMD was significantly associated with longer AL (per 1 mm increase: OR, 1.90; 95% CI, 1.75-2.07; P < 0.001), older age (per 1-year increase: OR, 1.04; 95% CI, 1.02-1.05; P < 0.001), and female gender (OR, 1.89; 95% CI, 1.24-2.89; P < 0.01). Compared with C0, each 1 mm increase in AL was associated with an increasing likelihood of MMD progression, with ORs of 2.8 for C1, 3.6 for C2, 5.2 for C3, and 5.7 for C4. The increase in OR was more pronounced in later stages (C2-C3 and C3-C4) than in earlier transitions (C0-C1 and C1-C2). Similarly, the ORs for age increased significantly from C3 to C4, and the ORs for female gender increased progressively from C2 to C4.

The meta-analysis and new clinical study indicate a clear trend of increasing AL with advancing MMD severity from C0 to C4. However, the relationship between AL and MMD progression from C3 to C4 warrants further investigation. Additionally, older age and female gender are identified as risk factors for MMD progression.