In people with high myopia (refractive error -6 diopters or worse) new blood vessels can grow under the retina of the eye (choroidal neovascularisation). For decades laser coagulation has been used to destroy lesions that are not central. This review found one small study, including 70 participants, which compared laser photocoagulation with no treatment for people with this disease. This study was inadequately reported and analysed, although it suggested a benefit with photocoagulation during the first two years of follow up. Another small study compared three laser wavelengths to achieve photocoagulation of the lesion, but actually had very little power to demonstrate a difference between them as only 27 participants were included. Therefore, despite its widespread use for many years, the amount of benefit achieved with photocoagulation and the possibility that it is maintained over the years remains unknown. Furthermore, these and other studies suggest that the enlargement of the laser scar could be a potentially vision-threatening long-term complication after two years, since it may cause the gradual occurrence of a blind spot in the centre of the visual field due to progressive atrophy of the retina.
Despite its use over several years the effectiveness of laser photocoagulation for myopic CNV has not been established. Although there was a suggestion of short-term effectiveness in one small study on non-subfoveal CNV the results were potentially biased. Observational studies suggest that the enlargement of the atrophic laser scar after laser treatment of non-subfoveal CNV could be a potentially vision-threatening long-term complication, even in eyes free of CNV recurrence.
Pathologic myopia is usually defined as the need for a spectacle correction of -6 diopters or higher. Choroidal neovascularisation (CNV) is the most commonly occurring cause of visual loss in people with pathologic myopia. In myopic macular degeneration the occurrence of newly formed vessels in the macula often leads to a fibrotic pigmented scar causing a blind spot in the centre of the visual field.
The primary objective of this review was to examine the effects of laser photocoagulation for CNV associated with pathologic myopia. A secondary objective was to compare the effects of different photocoagulation techniques.
We searched the Cochrane Controlled Trials Register (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register) in The Cochrane Library (Issue 1, 2007), MEDLINE (1966 to March 2007), EMBASE (1980 to March 2007), LILACS (March 2007) and reference lists of identified trial reports.
We included randomised controlled trials comparing photocoagulation with observation or comparing different photocoagulation techniques in people with CNV associated with myopia of -6 diopters or higher.
Two authors independently assessed the search results for eligibility.
Two studies were included that enrolled people with CNV located at 100 microns or more from the foveal centre. One study compared photocoagulation with observation. At the final examination, 16/35 participants randomised to photocoagulation versus 31/35 randomised to observation had visual acuity of 20/100 or worse after six to 48 months. The second study randomised 27 eyes (26 participants) to photocoagulation with three laser wavelengths (nine eyes per group). The number of eyes losing two or more lines was two (577 nm), three (590 nm) and three (620 nm) after three to 17 months. In both studies comparisons were made using outcomes assessed at the final examination. As the final examination took place at different follow-up times it was difficult to interpret the findings and it was impossible to extract data for further analyses.