Sir,
In reply to the Letter to the Editor titled “Evaluation of retinal nerve fiber layer thickness after optic canal decompression,”[1] we would like to thank you for your keen interest in our article titled as “Navigation-guided optic canal decompression for traumatic optic neuropathy: Two case reports.”[2] However, we feel that it would be misleading to read this article as “Evaluation of retinal nerve fiber layer thickness after optic canal decompression,” since the original article solely emphasized the role of newly introduced and infrequently used navigation guided technology in the management of traumatic optic neuropathy (TON) by trans-caruncular orbital approach. In case one, it is erroneous to presume that retinal nerve fibre layer (RNFL) damage was more significant as compared to case 2 and also that the RNFL improvement would not be much after the surgery. Both the cases had different type of etiopathologenesis (case 1 direct TON and case 2 indirect TON) and different time of presentation and so cannot be compared in terms of outcome. We agree with the fact that maximum RNFL reduction occurs by 6 weeks but it does not guarantee that the intervention beyond 6 weeks will not result in improvement in RNFL. In fact, the optic chiasm decompression study by Moon et al.[3] found that average RNFL thickness improved significantly at 6 months compared to that seen at 3 months, from 74.78 ± 2.92 to 76.89 ± 4.02 μm in nine patients (P = 0.030) after intervention.
Furthermore, in case 2, average RNFL thickness at day 6 was 90 μm which is comparable to study by Hur et al.[4] with average RNFL thickness of 95.03 ± 5.93 μm at second week after trauma. It is also noteworthy that RNFL thickness reduced sequentially over the 6 months to 50.61 ± 5.99 μm in their study.
In our case, the average RNFL thickness has only reduced from 90 to 84 μm following intervention, which is quite less comparable to the study by Hur et al.[4](95.03 to 50.61 mm); however, there appeared to be a quadrantic improvement in the inferior nasal quadrant (preoperative 6–9 and postoperative 71) in Case 2.
As multiple factors can affect the signal strength of optical coherence tomography (OCT) scans in TON with absent light perception, so repeat OCT scans had been taken preoperatively to overcome the artifacts and the best possible has been taken for consideration.
The interpretation of the changes in the RNFL thickness during the natural course of the disease or improvement in the thickness after intervention in TON is quite complex and rarely explored area. Long-term randomized trials aiming at RNFL or ganglionic cell layer changes following intervention would probably expand our knowledge for the management of TON.
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Conflicts of interest
There are no conflicts of interest.
References
- 1.Sen S, Singh P, Saini P, Desai A. Comment on: Evaluation of retinal nerve fiber layer thickness after optic canal decompression. Indian J Ophthalmol. 2018;66:1658–9. doi: 10.4103/ijo.IJO_876_18. [DOI] [PMC free article] [PubMed] [Google Scholar]
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