Biomechanical Assessment of Radial Optic Neurotomy

Sequential multiple retinal vein occlusions and transient ischemic attack in MTHFR polymorphism and protein S deficiency

BACKGROUND

The C677T variant of the MTHFR (5,10-Methylenetetrahydrofolate reductase) gene is associated with increased susceptibility to homocystinuria (OMIM#236250), neural tube defects (OMIM#601634), schizophrenia (OMIM#181500), thromboembolism (OMIM#188050), and vascular diseases. Protein S deficiency is also associated with an increased risk of thromboembolism from reduced thrombin generation. In this report, we describe the case of a patient who presented with multiple retinal vein occlusions likely caused by an underlying combination of a homozygous MTHFR C677T variant and protein S deficiency.

METHODS

We performed 8 years of continuous ophthalmic follow-up of one patient diagnosed with central retinal vein occlusion. Peripheral blood was collected for metabolic evaluation and hypercoagulability assessment. Targeted gene sequencing was used for genetic diagnosis. Examination of the retinal vasculature was performed through dilated funduscopic examination, digital color fundus and ultrawide-field color fundus photography, spectral domain optical coherence tomography, and fluorescein angiography.

RESULTS

Sequential retinal vein occlusions and a transient ischemic attack were observed during the follow-up period. Targeted gene sequencing by PCR identified the homozygous MTHFR C677T variant. The metabolic profile indicated low-protein S activity, high levels of vitamin B6, and LDL cholesterol consistent with her hypercoagulable state. Prescription of low-dose aspirin and atorvastatin for hypercholesterolemia resulted in no further neovascularization, leakage, or vein occlusion.

CONCLUSION

Retinal vein occlusions associated with the MTHFR C677T variant and protein S deficiency may signal impending systemic thromboembolic episodes and warrant aggressive preventative measures.

Central Retinal Vein Occlusion: A Review of Current Evidence-based Treatment Options

A central retinal vein occlusion (CRVO) can induce an ischemic and hypoxic state with resulting sequelae of macular edema and neovascularization. Many treatment options have been studied. Our review aims to investigate the safety and efficacy of the multiple treatment options of CRVO. A PubMed and Cochrane literature search was performed. Well-controlled randomized clinical trials that demonstrated strong level 1 evidence-based on the rating scale developed by the British Centre for Evidence-Based Medicine were included. Seven clinical trials met inclusion criteria to be included in this review. These included studies that investigated the safety and efficacy of retinal photocoagulation (1 study), intravitreal steroid treatment (2 studies), and antivascular endothelial growth factor treatment (4 studies) for the treatment of CRVO. In addition, studies evaluating surgical treatment options for CRVO were also included. Many treatment modalities have been demonstrated to be safe and efficacious in the treatment of CRVO. These treatment options offer therapeutic benefits for patients and clinically superior visual acuity and perhaps the quality of life after suffering from a CRVO.

Ultrastructural analysis of the lamina cribrosa after radial optic neurotomy

Radial optic neurotomy (RON) has been proposed for alleviation of the "scleral outlet compartment syndrome" at the level of the lamina cribrosa, which is thought to play a pathoetiologic role in central retinal vein occlusion (CRVO). The aim of this study has been to analyze the ultrastructural alterations of the lamina cribrosa after RON to gain new insights in the underlying pathomechanical factors. Fifteen donor eyes underwent a standardized open-sky-vitrectomy and RON after removal of the anterior eye segment for keratoplasty. Using a microvitreoretinal blade, a radial incision was performed on the nasal hemisphere of the optic nerve head radial to the optic disc and parallel to the nerve fibre layer. The lamina cribrosa and the surrounding scleral ring were then prepared for light microscopy, scanning (SEM) and transmission electron microscopy (TEM). Ultrastructural analysis demonstrated that in 60% (n=9) of the evaluated cases the scleral ring was dissected completely and in 40% (n=6) only partially. The adjacent neuronal tissue to the dissection area showed only minimal injury. The central retinal vessels were not injured in all cases. Only complete incision of the circular ring of collagen fibrils surrounding the lamina cribrosa via RON resulted in effective relaxation of the scleral outlet and was achieved in 60% of all eyes under standardized conditions. In all cases the adjacent tissue showed only minimal injury. The high rate of incomplete dissection of the scleral outlet may be an explanation for the variable outcome seen in different studies on RON.

Radial optic neurotomy for central retinal vein occlusion: results of the Pan-American Collaborative Retina Study Group (PACORES)

OBJECTIVE

To evaluate the complications after radial optic neurotomy (RON) for central retinal vein occlusion (CRVO).

METHODS

Seventy-three consecutive patients (73 eyes) with CRVO who were treated with RON participated in a retrospective, uncontrolled, interventional, multicenter case series at 7 institutions from 6 countries.

RESULTS

In the ischemic CRVO group (n = 53), 32% of eyes had an improvement in best-corrected visual acuity (BCVA) (mean, 5.5 lines), 35.8% had worse BCVA (mean, 6.4 lines), and 32% had BCVA that remained the same after RON. In the nonischemic CRVO group (n = 20), 50% of eyes had an improvement in BCVA (mean, 6.5 lines), 15% had worse BCVA (mean, 4.3 lines), and 35% had BCVA that remained the same after RON. Complications occurred in 71.2% of cases, including cataract in 17 eyes (23.2%), vitreous hemorrhage in 16 eyes (20.5%), persistent macular edema in 15 eyes (20.5%), neovascular glaucoma in 7 eyes (9.5%), anterior segment neovascularization in 5 eyes (6.8%), retinal detachment in 3 eyes (4.1%), and phthisis bulbi, choroidovitreal neovascularization, central retinal artery perforation, and optic nerve atrophy in 1 eye (1.3%) each.

CONCLUSIONS

RON may improve visual acuity in some eyes with CRVO, but complications are common. In our series, surgery by itself did not seem to improve the outcome of CRVO when compared with its natural history.