CaseWise 23

Retinal Nerve Fibre Layer Splaying – A Case Report

Dr. Chennamsetty Alekhya, Dr. Sarang Lambat, Dr. Vinay Nangia
Suraj Eye Institute, Nagpur, India

Introduction
Glaucoma, results in the death of retinal ganglion cells (RGC) and the degeneration of their axons. The loss of RGC axons in turn leads to a thinning of the retinal nerve fiber layer (RNFL). Retinal arteries coming from, and veins going to, the optic disc travel in the RNFL and contribute to it’s thickness1. Arrangement of blood vessels influence the RNFL thickness measured with OCT1. The double hump pattern was identified in the RNFL profile, where the humps fall on, or just adjacent to, major temporal blood vessels1. So, the location of the major temporal blood vessels is a good predictor of the variation in the RNFL thickness profile. There are 2 factors contributing to this correspondence. First, the blood vessels make a direct contribution to the OCT RNFL thickness1. Second, the arcuate fiber bundles, providing the major contribution to the hump, tend to travel with the major temporal blood vessels1.

Case Report
A male, 17 years of age, reported to us with the chief complaints of diminution of vision in right eye (RE) since 2 years. He had a BCVA of counting finger (CF) at 1 metre in RE and 6/6 in left eye (LE). Slit lamp biomicroscopy was within normal limits. Intraocular pressure was 18 mmHg in both eyes. Fundus examination showed combined hamartoma of retinal pigment epithelium in RE and LE was normal (Fig 1a, 1b). SDOCT of LE showed moderate RNFL thinning in temporal and inferotemporal quadrants, severe RNFL thinning in superotemporal quadrant with increase of RNFL thickness in superonasal and inferonasal quadrants suggesting RNFL splaying (Fig.2). RNFL splaying due to widening of angulation between superotemporal and inferotemporal vessels explains thinning of RNFL temporally in left eye.

Fig.1a – Fundus photo of right eye showing combined hamartoma of retinal pigment epithelium, 1b-left eye showing widening of angulation between superotemporal and inferotemporal vessels
Fig. 2: left eye SDOCT showed moderate RNFL thinning in temporal and inferotemporal quadrants; severe RNFL thinning in superotemporal quadrant; increase of RNFL thickness in superonasal and inferonasal quadrants suggesting RNFL splaying

Discussion
The location of the blood vessels may help predict the variations in the profiles of OCT RNFL thickness1. Here, in our case, arrangement of blood vessels may explain decrease in temporal RNFL thickness and increase in superonasal and inferonasal thickness, due to RNFL splaying in left eye. Splaying may occur due to widening of the angle between the major vascular arcades which in turn drag the RNFL along, leading to thinning in the macular area and thickening in the vertical quadrants. This can induce errors in assessment as it may show thinning in the temporal quadrants leading to incorrect diagnosis of glaucomatous or neurological RNFL loss.
Location of the major temporal blood vessels can help us to understand RNFL variation. A better understanding of the relationship between the distribution and angulation of the major blood vessels and the OCT RNFL thickness might lead to improved assessment of the RNFL.1

References

  1. Hood et al. Blood Vessel Contributions to Retinal Nerve Fiber Layer Thickness Profiles Measured With Optical Coherence Tomography. J glaucoma. 2008,Volume 17 doi: 10.1097/IJG. 0b013e3181629a02
  2. Xiulan Zhang et al. Nerve Fiber Layer splaying at vascular crossings.  Invest Ophthalmol Vis Sci.2002. PMID: 12091397 
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