Optic nerve head measurements using optical coherence tomography (OCT) following combined trabeculotomy with trabeculectomy in juvenile open-angle glaucoma

Juvenile open-angle glaucoma (JOAG) is a rare subset of open-angle glaucoma characterized by an early age of onset (5–40 years) and a high intraocular pressure (IOP) with autosomal dominant inheritance. The most definitive form of treatment for JOAG is surgical, which has been traditionally goniotomy or trabeculotomy. Primary combined trabeculotomy with trabeculectomy has better success rates in the Indian population.[1] Reversal of cupping following a marked reduction in IOP is generally considered to be an indicator of successful treatment in pediatric glaucoma. Longitudinal clinical data regarding cupping reversal in adults is conflicting as to whether it is a true indicator of reversal of functional damage by visual field testing. Although studies have been done to evaluate the success of IOP control, very few have been done to assess the structural and functional outcomes of CTT in JOAG. We conducted a prospective interventional study in 33 eyes of 27 JOAG patients to evaluate the changes in optic nerve head measurements, RNFL thickness, and macular thickness following CTT. Average RNFL thickness increased by 1.61 ± 5.39 μm during the third postoperative month and decreased by 0.12 ± 5.38 μm during the sixth postoperative month [Table 1 and Fig. 1]. Similarly, Wu et al.[2] in 2016 showed no significant change in RNFL thickness (P > 0.05) in the teenage group postoperatively. However, RNFL thickness was assessed using GDx VCC in that study. In contrast, Elgin et al.[3] compared optic disc parameters using HRT II after antiglaucoma treatment in JOAG and found that the mean RNFL at baseline was statistically significantly smaller (P = 0.016) than the value after treatment.Figure 1: Representative OCT images before and after combined trabeculotomy with trabeculectomyTable 1: Postoperative comparison of RNFL thickness, vertical cup: disc ratio, and RIM areaVisual field remains an important tool for assessing the stability of ongoing glaucomatous pathology in the optic nerve head. Though there are multiple theories explaining the reversal of cupping, the functional significance of this remains unknown. Gupta et al.[4] observed that mean deviation (MD) worsening was greater in eyes with higher long-term mean IOP and higher IOP fluctuations. In our study, we did not find any significant change in the MD values before and after surgery. Studies done previously have shown that after filtration surgery, when IOP returns to normal values, the cup: disc ratio (CDR) reduces postoperatively in congenital glaucoma. This is believed to be due to the possibility of infants’ optic nerves having stronger recovery capability, which heals to a certain extent once the stress on it is relieved. Furthermore, myriad theories have been proposed in the past to explain this particular phenomenon, which includes anterior movement of lamina cribrosa, shrinkage of the elastic scleral canal, hypertrophy, or proliferation of glial cells. The basis of many of these theories is the age-dependent elasticity of scleral tissue and hence younger eyes are more likely to have cupping reversal due to rebound anterior repositioning of posteriorly displaced lamina cribrosa after substantial IOP reduction.[5] Similarly, our study showed a statistically significant reduction in vertical CDR by 0.03 ± 0.06 μm and by 0.05 ± 0.08 μm during the third and sixth postoperative month, respectively, as well as increase in rim area by 0.15 ± 0.18 μm during the sixth month when compared to preoperative values [Table 1]. OCT has the potential to demonstrate improvement in optic nerve head parameters, with evident reversal of cupping following combined trabeculotomy with trabeculectomy in JOAG.