Role of Early Radial Optic Neurotomy in Central Retinal Vein Occlusion

Early histologic and functional study of radial optic neurotomy outcomes in normal rat eyes

BACKGROUND

Radial optic neurotomy (RON) has been proposed as a treatment for central retinal vein occlusion. However, it is still under debate whether RON would be an adequate treatment or a dangerous procedure, and persuasive animal studies are lacking. The aim of this study was to analyze the early histologic and functional outcomes of RON in normal rat eyes.

METHODS

Radial optic neurotomy was performed by cutting into the optic nerve edge at the nasal hemisphere, while the contralateral eye underwent a sham procedure. The retinal function was assessed by scotopic electroretinography, and the visual pathway was assessed by flash visual evoked potentials. Intraocular pressure was assessed with a tonometer, the pupillary light reflex was measured after exposing eyes to a 30-second light flash, whereas the optic nerve head structure was examined by histologic analysis.

RESULTS

In normal rat eyes, RON provoked minor histologic alterations at the optic nerve head level and a transient decrease in the electroretinography. No changes in visual evoked potentials, intraocular pressure, and pupillary light reflex were observed in rat eyes submitted to RON.

CONCLUSION

To our knowledge, this is the first study describing the early histopathologic and functional consequences of RON in normal rat eyes.

Intravitreal bevacizumab (avastin) in the treatment of macular edema associated with perfused retinal vein occlusion

PURPOSE

To evaluate the efficacy and safety of intravitreal bevacizumab (Avastin) injection in patients with macular edema (ME) secondary to retinal vein occlusive diseases.

METHODS

A prospective, interventional cases series study was conducted in patients with ME secondary to perfused retinal vein occlusions (RVOs), who were treated with intravitreal bevacizumab (2.5 mg per injection in a volume of 0.1 mL). Patients underwent complete ophthalmic evaluation, including Snellen visual acuity, optical coherence tomography (OCT), and fluorescein angiography (FA) at baseline, 1 month, and 3 months after the first injection and at the final visit.

RESULTS

Twenty-five patients (25 eyes) received intravitreal bevacizumab injections. The mean follow-up time was 6.5 months. Mean Snellen visual acuity improved from 20/125 at baseline to 20/74 at 1 month, 20/69 at 3 months, and 20/57 at the last follow-up (P < 0.01). Five of the 25 eyes (20%) had vision gain of >3 lines. The mean central 1 mm macular thickness was 422 microm at baseline and decreased to 263, 333, and 239 microm at 1 month, 3 months, and the last follow-up, respectively. Recurrent macular edema with a rebound increase of central retinal thickness was observed 3 months after the first injection, and improved after repeated bevacizumab injections. Patients received an average of 2 injections (range 1-3). FA showed no evidence of increased nonperfusion avascular area. No adverse ocular or systemic events were observed following injections.

CONCLUSIONS

The observed anatomic and visual acuity improvements after intravitreal bevacizumab injection demonstrate that bevacizumab is a useful adjunctive treatment for ME secondary to RVO without safety concerns in a short term. However, repeated injections are needed to maintain visual improvement. Long-term study is warranted to assess the long-term efficacy and safety.

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.

VISUAL FIELD DEFECTS AFTER RADIAL OPTIC NEUROTOMY FOR CENTRAL RETINAL VEIN OCCLUSION

PURPOSE

Surgical decompression of the vein in central retinal vein occlusion (CRVO) by radial optic neurotomy (RON) was recently proposed as being surgically feasible, safe, and beneficial. The effect of RON on the visual field has not been systematically reported, although possible visual field defects are expected due to iatrogenic cutting of the optic nerve fibers. The authors report the results of visual field testing in patients who underwent RON at the Tel Aviv Medical Center.

METHODS

Twelve consecutive patients (8 men, mean age of all patients 68 years) with nonperfused or indeterminate CRVO whose initial visual acuity (VA) was < or =20/400 underwent RON. Nine of these patients were able to perform visual field tests at 6 months post-RON and their visual field results are presented.

RESULTS

: VA improved by > or =3 lines in 5 patients (42%). Three (25%) patients had a final VA of > or =20/200 and another had a final VA > or =20/50. Fundus and VA improvement were relatively slow. Two patients had clearing of the intraretinal blood, resolution of the venous dilation, and improved VA at the 2-month follow-up visit. Temporal visual field defects consisting of temporal ones that could be correlated to the site of the RON incision were detected in five out of the nine patients who were able to perform visual field tests. No temporal visual field defects were found in the remaining four patients, and three other patients were unable to perform visual field tests due to inability to identify the largest target size.

CONCLUSION

VA improvement in 5 of 12 patients with ischemic or indeterminate CRVO following RON may be better than the natural history of CRVO. The risk of visual field defects may, however, be heightened by possibly cutting off blood supply to the optic nerve head and possible damage to nerve fibers in the optic nerve head, both inherent to the surgical procedure and both likely to produce visual loss.