Structural assessment of branch retinal vein occlusion using imaging techniques
Dr. Shashank Somani, Dr. Sarang Lambat, Dr. Prabhat Nangia, Dr. Vinay Nangia
Suraj Eye Institute, 559 New Colony, Nagpur
A female, 51 years of age, presented with diminution of vision in right eye since 3 months. Her best corrected visual acuity was counting fingers at 3 meters, N36 in right eye (RE) and 6/6, N6 in left eye (LE). Anterior segment examination was normal. Intraocular pressure recorded by Goldmann applanation tonometer was 11 mmHg in RE and 13 mmHg in LE.
The patient was advised Anti-VEGF injection for the right eye. On 1 month follow up the macular edema was reduced and the BCVA was 6/60 in the right eye and patient is under follow up.
Optical coherence tomography angiography (OCTA) is a new imaging modality that allows noninvasive visualisation of retinal blood flow without use of exogenous dyes. The layer-specific imaging capabilities of OCTA have the potential to simultaneously visualise both superficial and deep retinal capillaries by segmentation of each layer. In the normal human retina, the main branches of the central retinal artery and the central retinal vein lie horizontally within the retinal nerve fiber layer (RNFL). The arterial branches then supply a total of four (two superficial and two deep) layers of the capillary networks in the perifoveal region, that is, (1) the RNFL, (2) the retinal ganglion cell layer (GCL) and superficial portion of IPL, (3) the deep portion of IPL and superficial portion of inner nuclear layer (INL), and (4) the deep portion of INL. The SCP in the OCTA represents the retinal arterioles, venules, and capillary networks in the first through third of these. The DCP in the OCTA indicates the capillary networks at the deep portion of inner nuclear layer (INL) which seem to be important for nutritional and oxygen support of the synaptic connections responsible for transmission of visual signals. Hypo-perfusion in the DCP may cause acute nutritional deficiency in the synaptic connections, resulting in decreased VA.
In this case, macular OCT showed presence of significant edema and fluid filled spaces in the inner and outer retinal layers and photoreceptor loss in the fovea. On FFA there is a very small FAZ which was due to the presence of collaterals invading the FAZ. These collaterals were also present in the superficial and the deep capillary plexus of the OCT angiography. On SCP the size of FAZ in right eye was marginally larger than the that of left eye, however it was distorted, vertically elongated in shape, with reduced horizontal width. Whereas the size of FAZ on DCP was significantly larger in right eye as compared to the left eye. The difference in the area of right eye and left eye FAZ in SCP was 0.07mm2 and that on the DCP was 0.78mm2. The exact significance of a relatively smaller FAZ in the SCP versus that in the DCP is not well understood. It may be noted that vascular changes may be more signifiant in the DCP and or that the collateral vascular response may be more aggressive in the SCP. At the same time, we also keep in mind that sections of the SCP and DCP on OCTA in such patients pass through the fluid filled spaces that constitute the macular oedema and play a role in distorting the FAZ on OCTA. Findings on OCTA give a greater understanding of the vascular changes in venous occlusion. The OCT gives us a detailed view of the structural changes and enables us to plan further management and follow up of these subjects.
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Dr. Sarang Lambat
Suraj Eye Institute
Email – email@example.com