Quantification of functional retinal damage in branch retinal vein thromboses

Abstract

Branch retinal vein occlusion (BRVO) induces variable functional deficits depending on the grade of vascular occlusion and its localisation. Theses deficiences are not easily defined by visual acuity measurements. However, microperimetry offers topical mapping of retinal function, allowing precise documentation of the intensity and dimension of retinal functional loss in BRVO. Retinal sensitivity was examined using a Rodenstock Scanning Laser Ophthalmoscope (SLO). A standardized grading system of stimuli ranging from 0 to 32 dB was used to document the retinal threshold in three different areas: regions presenting vascular occlusion, the collateral edematous zone and adjacent areas with intact perfusion. Absolute and relative scotomas as well as the fixation behavior were studied. Forty-two patients with isolated BRVO within the vascular arcades were examined with microperimetry and angiography. At initial presentation with BRVO the retinal sensitivity in the area of occlusion on average diminished to 4.1 dB. In the collateral edematous zone retinal threshold was reduced to 21.5 dB; area with intact perfusion demonstrated a threshold of 23.2 dB. Within the occluded area itself defects of significantly differing intensity were found which only partially correlated with the angiographic evidence. Intense scotomas (0 dB) were observed in 59% of the eyes examined: angiographically nonperfused areas or extended intraretinal hemorrhage were present. Relative scotomas (12.1 dB) were seen in 19.1% and minimal, non-significant defects (19.5 dB) were documented in 21.4% of the BRVO. The level of angiographically documented leakage did not correlate with the functional deficits present in these two groups. Measurements performed after 6-8 weeks revealed noticeable spontaneous recovery of retinal sensitivity, unless an additional progressive closure occurred. The average functional improvement in the area of leakage found after laser therapy was less than the results shown in spontaneous resolution of edema. BRVO may lead to significant reductions of central and paracentral retinal function. Angiographically observed leakage is not always directly correlated to the magnitude of retinal sensitivity loss. As spontenous remission is frequent in one group and intact retinal function can be shown in areas of angiographic leakage, therapeutic interventions, e.g., laser treatment, should be carefully considered. Scanning laser ophthalmoscopy provides additional information for precise evaluation and follow-up of the retinal damage in BRVO.