Senuri Karunaratne, BSc, OD
Pathological myopia is characterized by excessive and progressive elongation of the globe leading to impaired vision and blindness. A common complication of pathological myopia is choroidal neovascularisation, also referred to as myopic CNV. Recognizing a lack of clarity surrounding the epidemiology of pathological myopia, myopic CNV, and its impact upon vision, Wong et al., 2014, conducted a systematic review involving 38 studies. In conducting the systematic review, it was apparent that there was a lack of consistency in defining pathological myopia.
The review found the prevalence of pathological myopia to be similar between various population groups. Studies from Asia showed a prevalence of 0.9 percent to 3.1 percent (per individual), while non-Asian-based studies, such as the Blue Mountains Eye Study (BMES), showed a prevalence of 1.2 percent (per individual). Interestingly, the incidence of low vision and blindness as a result of pathological myopia was much greater in studies from China and Japan (12.2 percent – 27.4 percent) compared to European studies (5.8 percent and 7.8 percent). However, despite the apparent correlation between pathological myopia and Asia, the systematic review identified the requirement for further research to confirm this association. Overall, across six studies, pathological myopia was ranked as the first, second, and third most frequent cause of blindness.
Secondary to pathological myopia was myopic CNV. This involved the abnormal growth of blood vessels below the retinal pigmented epithelium, leading to a significant deterioration of central vision and the development of central scotomas. Reflecting on the prevalence of pathological myopia, the prevalence of myopic CNV was greater in Asian populations (11.3 percent) compared to non-Asian populations (5.2 percent). The review also revealed that the incidence of bilateral myopic CNV was 14 percent, with the incidence of developing myopic CNV increasing to 34.8 percent in those with a pre-existing diagnosis of myopic CNV, compared to those without (6.1 percent).
The impact of pathological myopia upon vision, quantified as best corrected visual acuity letter scores, was 39 in those with pathological myopia, compared to 49 in those without (BMES). Similarly, the Beijing Eye study showed a letter score of 41 in those with pathological myopia, as opposed to 57. Considering the longitudinal impact of pathological myopia upon vision, a mean progressive deterioration in letter score from 49 to 19 was observed over 11 years.
Therefore, the primary risk factors for pathological myopia were identified as greater axial length and age. Studies also described evidence of a genetic association with the discovery of 9 chromosomal loci. Prognostically, the older the age of onset of pathological myopia, the location of myopic CNV (subfoveal versus juxtafoveal), and the duration of haemorrhaging from myopic CNV, all contributed to poorer visual outcomes.
All in all, despite the limitations of a lack of consistency in defining pathological myopia in the literature and the limited research, the systematic review highlighted the prevalence and the significant impact of the condition on vision. The review concluded that the condition should be a target for new treatment strategies.
Epidemiology and Disease Burden of Pathologic Myopia and Myopic Choroidal Neovascularization: An Evidence-Based Systematic Review
Tien Y. Wong, Alberto Ferreira, Rowena Hughes, Gemma Carter, Paul Mitchell
Purpose: To summarize the epidemiology of pathologic myopia and myopic choroidal neovascularization (CNV) and their impact on vision.
Design: Systematic literature review of all English-language studies evaluating the epidemiology and visual burden of pathologic myopia or myopic CNV.
Methods: PubMed and EMBASE were searched with no time limits using predefined search strings for English-language studies evaluating the epidemiology and visual burden of pathologic myopia and myopic CNV.
Results: In total, 39 relevant publications were identified. Population-based studies reported pathologic myopia to be the first to third most frequent cause of blindness. The prevalence of pathologic myopia was reported to be 0.9 percent-3.1 percent, and the prevalence of visual impairment attributable to pathologic myopia ranged from 0.1 percent-0.5 percent (European studies) and from 0.2 percent-1.4 percent (Asian studies). The prevalence of CNV in individuals with pathologic myopia was reported to be 5.2 percent-11.3 percent and was bilateral in approximately 15 percent of patients. All studies of visual outcome in patients with myopic CNV (duration ranging from less than three months to 21.5 years) reported deterioration in best-corrected visual acuity over time. Older age, subfoveal CNV location, and larger baseline lesion size were predictors of worse visual outcomes.
Conclusions: Pathologic myopia is an important cause of vision loss worldwide, affecting up to 3 percent of the population. Of these, a substantial proportion of patients develop myopic CNV, which mostly causes a significant progressive decrease in visual acuity. This condition should therefore be a target for new treatment strategies.
Wong, T. Y., Ferreira, A., Hughes, R., Carter, G., & Mitchell, P. (2014). Epidemiology and disease burden of pathologic myopia and myopic choroidal neovascularization: an evidence-based systematic review. American Journal of Ophthalmology, 157(1), 9-25.