Nonexudative Macular Neovascularization - A Systematic Review of Prevalence, Natural History, and Recent Insights from OCT Angiography

Purpose: To review the available literature on the prevalence, incidence, natural history, and exudative conversion rates of subclinical (treatment-naïve) nonexudative macular neovascularization (MNV) in patients with age-related macular degeneration (AMD).

Clinical relevance: Nonexudative MNV is now known to be more prevalent in patients with AMD than initially thought and is bringing new insights into both the natural history and management of this very prevalent disease.

Methods: We conducted a literature search on PubMed, Scopus, and Web of Science, along with a manual search, from January 2014 to June 2019. We included studies that used optical coherence tomography angiography (OCTA) as a primary diagnostic tool to evaluate subclinical (treatment-naïve), nonexudative, neovascular AMD.

Results: Of the 258 screened articles, 12 were included. The prevalence of subclinical nonexudative neovascular AMD in the fellow eyes of patients with unilateral exudative AMD ranged from 6.25% to 27%. Although these lesions were not associated with a significant decrease in visual acuity, the presence of nonexudative MNV seems to be an important predictor of exudative disease. Incidence of exudation in the reviewed studies ranged from 20% to 80% (follow-up 6 months to 2 years). There is some evidence that nonexudative MNV may slow down the growth of adjacent geographic atrophy (GA). As long as exudation does not occur, it appears that subclinical nonexudative MNV is not responsible for the deterioration of visual function.

Conclusions: Nonexudative MNV is an asymptomatic condition. Although nonexudative MNV seems to be a precursor for the formation of exudative neovascular AMD, there is evidence suggesting a protective effect in slowing the progression of GA. Early detection of nonexudative MNV before exudation develops should result in better monitoring of patients who are at high risk of conversion to exudative AMD. Though no controlled clinical trial has been performed to provide definitive recommendations, the authors of the studies included in this review agree that nonexudative lesions should not be treated until symptomatic exudation develops. Moreover, the existence of a nonexudative form of neovascular AMD would suggest that the term "neovascular AMD" should be preceded by either "exudative" or "nonexudative" when describing this neovascular stage of AMD.