Should Concern For Snuff-Out Phenomenon Deter Ophthalmologists From Glaucoma Surgery In Patients With Advanced Glaucoma?

Abstract

Introduction: Snuff-out phenomenon, an irreversible unexplained loss of central vision in eyes with advanced glaucoma following filtration surgery, is a source of concern for ophthalmologists managing advanced glaucoma patients requiring filtration surgery.¹ This concern could deter the ophthalmologist from offering trabeculectomy to patients with advanced glaucoma who need surgery. Most glaucoma patients in Sub-Saharan Africa present at the advanced stage of the disease with poor medication adherence driven by prohibitive cost.^2,3 With advancements in glaucoma filtration surgeries, controversies have arisen as to the actual existence of this phenomenon.¹ This study sought to determine the prevalence of snuff-out phenomenon among glaucoma patients with advanced glaucoma who have had trabeculectomy.

Methods: This was a descriptive cross-sectional study of consenting consecutive glaucoma patients who received trabeculectomy+mitomycin C (MMC) surgery at The Eye Specialists Hospital, Enugu Nigeria between 2021 and 2023. Inclusion criteria included consenting patients with mean deviation on Humphrey visual field of -12dB or worse who had a pre-operative visual acuity better than 6/60. Excluded from the study were patients who had MD better than -12dB, preoperative visual acuity of 6/60 or worseand those who withheld consent for the study. Patients who had explainable causes of loss of vision as a complication of the surgery were included in the study. They were however excluded from the definition of snuff out syndrome. Snuffout was defined as decrease in visual acuity to counting fingers or worse, persisting till 3- months post-surgery after other causes of reduction in vision had been excluded.⁴  Data was collated and analysed using SPSS version 23. Comparisons between means were done using T-test or Analysis of Variance (ANOVA). P value <0.05 was considered statistically significant.

Results: A total of 79 eyes of 72 patientswere studied comprising of 45 (62.5%) males and 27 (37.5%) females aged 15- 84 years; mean age 61.4±14.1 years. Fifty-five eyes of 50 patients underwent only trabeculectomy +MMC, 17 eyes of 15persons had combined small incision cataract surgery and trabeculectomy +MMC while 7 eyes of 7 patients had combined phacoemulsification and trabeculectomy +MMC. Forty-four (55.7%) were right eyes while 35 (44.3%) were left eyes.Mean preoperative and post-operative mean deviation scores were -22.9± 3.7dB and -22.9 ± 6.8dB respectively.
At 3 months no eye, 0(0.0%) had snuff out phenomenon (Table 1). Two (2.5%) eyes that had visual acuities of counting finger at 3 months postop had developed cataract and were excluded from the definition of snuff-out phenomenon. One (1.3%) patient who underwent phacoemulsification +Trabeculectomy had VA <3/60 at 1 month but vision had improved at 3 months. Four (5.1%) patients that underwent combined small incision cataract surgery and trabeculectomy+MMC had VA <3/60 on the first postoperative day buthad improvement in their vision at 3 months post-op. There was no statistically significant difference in mean logMAR VA across procedure groups before and after Surgery; ANOVA F value =1.269, p= 0.287 (Table 2).

Conclusion: Results of this study indicate that snuffout phenomenon is rare among our patients. This finding is encouraging, considering the high prevalence of glaucoma in our environment and the frequently late presentation of our patients with advanced glaucoma.⁶ A study in India,⁷ and others in Greece⁸ and Turkey⁹ similarly reported no case of snuff-out phenomenon in their patients. A cause of significant reduction in vision identified in a few post-trabeculectomy patients in this study was development of cataract. This study suggests that concern for snuff-out phenomenon should not deter ophthalmologists from offering surgery to patients with advanced glaucoma.