Preservation of retinal sensitivity in central visual field after panretinal photocoagulation in diabetics

Effect of laser spot diameter on the reproducibility of visual field analysis in diabetic patients with upper temporal retinal vein occlusion

AIM

To evaluate the effect of the laser spot diameter on the reproducibility of the visual field analysis in diabetic patients with upper temporal retinal vein occlusion.

MATERIAL AND METHODS

Thirty-six eyes of 36 consecutive type-2 diabetes mellitus patients with upper temporal retinal vein occlusion who required sectoral retinal photocoagulation (SRP) treatment were enrolled for the study. Patients with a history of previous retinal laser photocoagulation, significant lenticular opacities and those whose perimetric test reliability criteria were low (fixation loss >20% and false-positive or false-negative responses >33%) were excluded from the study. SRP was applied to the upper temporal retinal quadrant. Nineteen eyes received SRP treatment with 500-mum laser spots (group 1) while the rest of the eyes (n = 17) received SRP with 300-microm laser spots (group 2). Patients underwent five consecutive visual field analyses, each on a different day during a 2-week period, both before and 6 weeks after SRP. The Humphrey field analyzer central 30-2 threshold test using SITA Standard strategy was applied for visual field testing.

RESULTS

The mean age of the patients in groups 1 and 2 were 58.6 +/- 6.7 and 59.1 +/- 7.1 years, respectively (p > 0.05). Pre-SRP mean retinal sensitivities of the lower nasal quadrant in groups 1 and 2 were not different statistically (p > 0.05). Post-SRP mean retinal sensitivity of the lower nasal quadrant was significantly higher in group 2 than group 1. Moreover, mean defect has been found to be lower in group 2 (p < 0.05). The coefficient of variation for pre-SRP retinal sensitivity measurements were 7.9 and 7.6% for groups 1 and 2, respectively (p > 0.05). The coefficient of variation for post-SRP retinal sensitivity measurements were 3.8 and 2.1% for groups 1 and 2, respectively (p < 0.05).

CONCLUSION

SRP treatment with 300-microm diameter laser spots may yield more reproducible visual field data than that with 500-mum diameter laser spots. Moreover, the improvement in the retinal sensitivity of the patients with branch retinal vein occlusion is more marked in case where 300-microm laser spots are used.

Macular function assessed with mfERG before and after panretinal photocoagulation in patients with proliferative diabetic retinopathy

PURPOSE

To examine macular function and its correlation to macular thickness before and after panretinal photocoagulation for proliferative retinopathy in diabetic patients.

METHODS

Ten diabetic patients (aged 57 +/- 10 years, diabetes duration 21 +/- 10 years) treated with panretinal photocoagulation outside the great vascular arcade underwent multifocal electroretinography (mfERG) and optical coherence tomography (OCT) before and 6 months after treatment. When focal treatment in the macular region was performed prior to panretinal photocoagulation the investigations took place 3 weeks after this treatment but before the panretinal photocoagulation. One eye per patient was examined. Amplitudes and implicit times of the mfERG response were analyzed within the four innermost (27 degrees) of the six concentric rings registered by the mfERG, which corresponds to the area measured by the OCT (psi 3.5 mm).

RESULTS

Visual acuity was similar before and after photocoagulation, 1.0; 0.7-1.0 (md, range) versus 1.0; 0.6-1.0 (md, range). The mean values of the ring average amplitudes were reduced in the first and second, third and fourth concentric rings from foveola after photocoagulation, p = 0.001, p = 0.011 and p = 0.004, respectively. No change was seen in implicit time after treatment. OCT values were similar before and after photocoagulation. There was no correlation between retinal thickness assessed with OCT and amplitudes measured by the mfERG.

CONCLUSION

In spite of unchanged values of retinal thickness and visual acuity, panretinal photocoagulation seems to cause a functional impairment in the adjacent untreated macula, shown by reduced amplitudes measured by the mfERG.