The predictive value of optical coherence tomography after grid laser photocoagulation for diffuse diabetic macular oedema

PURPOSE: To assess the predictive value of optical coherence tomography (OCT) mapping of retinal thickness and intraretinal morphological changes after macular grid for diffuse diabetic macular oedema (DMO).

METHODS: We carried out a prospective, non-controlled, case series study, in which 28 consecutive eyes with previously untreated diffuse DMO underwent fundus photography and OCT at baseline and at 1, 3 and 6 months after treatment.

RESULTS: Macular photocoagulation was followed by a significant reduction in retinal thickness in the foveal centre (- 80 microm) and in the foveal subfield (- 65 microm) from baseline to 6 months (p < 0.01). The bulk of the reduction in retinal thickness and macular volume was manifest after 1 month. No significant change in retinal thickness occurred from 1 to 3 months or from 1 to 6 months in any macular subfield (p > 0.05). The relative decrease in retinal thickness at 6 months was highest in the foveal centre (- 22%), followed by the foveal region (- 18%), the inner parafoveal region (- 8%), and the outer parafoveal region (- 2%). Thus, the effect of photocoagulation on retinal thickness decreased with increasing eccentricity (p < 0.025). Overall, there was no statistically significant change in best corrected visual acuity (BCVA) between baseline and follow-up (p < 0.05), but changes in foveal subfield thickness and changes in VA were highly correlated (r = 0.66, p < 0.0001). Visual outcome (final BCVA) and final foveal subfield thickness at 6 months were correlated with the pattern of intraretinal morphological changes at baseline (Spearman's correlation coefficient r = - 0.41, p = 0.03 and r = 0.45, p = 0.02, respectively). In addition, visual outcome (final BCVA) and final foveal subfield thickness at 6 months were correlated with baseline foveal thickness (Spearman's correlation coefficient (r = - 0.37, p = 0.05 and r = 0.5, p = 0.01, respectively).

CONCLUSIONS: It seems that the 1-month time-point after macular laser treatment is a critical point for establishing the outcome of this modality of management of DMO. Baseline OCT mapping of intraretinal fluid accumulation patterns and foveal thickness can help to predict the final visual outcome and final foveal thickness, but not the absolute change in either of these parameters after macular laser therapy.