Focal grid laser photocoagulation

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To characterize the severity of macular edema and for treatment guidelines, the term clinically significant macular edema (CSME) is defined: retinal thickening at or within 500^m of the foveal center, hard exudates at or within 500^m of the foveal center with adjacent retinal thickening, or retinal thickening greater than 1 disc diameter in size, within 1 disc diameter of the foveal center (ETDRS group, 1985, 1987a).

There is good evidence that focal laser treatment preserves vision in eyes with DME. The ETDRS randomized 1490 eyes with DME to receive focal laser treatment or observation (ETDRS group, 1985). Retreatment was applied at 4-month intervals if CSME persisted, one or more treatable lesions were identified, and the investigator believed these lesions were responsible for the edema (ETDRS group, 1987b). At 3 years, treatment significantly reduced moderate visual loss as compared with observations, with the greatest benefits in eyes with CSME (ETDRS group, 1987b)

Although focal laser photocoagulation reduces the risk of moderate visual loss by approximately 50%, approximately 12% of treated eyes still lose vision, many because of persistent DME (ETDRS group, 1985). Kim et al. assessed macular optical coherence tomography (OCT) findings of DME patients to determine whether specific OCT patterns are predictive of visual outcome after focal laser photocoagulation (Kim et al., 2009). DME was classified into four different OCT patterns, which are: diffuse retinal thickening, cystoids macular edema, serous retinal detachment, and vitreomacular interface abnormalities (Figure 1). In this study, eyes with diffuse retinal thickening achieved a greater visual acuity increase than eyes with other patterns.

It is unclear how focal retinal laser exerts its effects. One theory is that it improves oxygenation to the inner retina by eliminating highly oxygen-dependent photoreceptors (Gottfredsdottir et al., 1993; Stefansson, 2001). Another theory is that the laser reduces the retinal capillary area and thereby reduces leakage (Wilson et al., 1988). Other authors postulate that photocoagulation restores the outer blood-retinal barrier (Bresnick, 1983).

Focal Grid Laser

Fig. 1. Different patterns of diabetic macular edema by optical coherence tomography. (A) Diffuse retinal thickening appears as a sponge-like retinal swelling with areas of reduced intraretinal reflectivity. (B) Cystoid macular edema showing intraretinal cystoid spaces. (C) Serous retinal detachment showing shallow elevation of the retina, with an optically clear space between the retina and the retinal pigment epithelium. (D) Vitreomacular interface abnormalities showing a highly reflective band over the inner retinal surface and extending towards the optic nerve or peripherally.

Fig. 1. Different patterns of diabetic macular edema by optical coherence tomography. (A) Diffuse retinal thickening appears as a sponge-like retinal swelling with areas of reduced intraretinal reflectivity. (B) Cystoid macular edema showing intraretinal cystoid spaces. (C) Serous retinal detachment showing shallow elevation of the retina, with an optically clear space between the retina and the retinal pigment epithelium. (D) Vitreomacular interface abnormalities showing a highly reflective band over the inner retinal surface and extending towards the optic nerve or peripherally.

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