Optometry

Sherrol A. Reynolds

Jamie Althoff

A 76-year-old white female presented to our clinics for a comprehensive eye exam. Her ocular history was significant for a macular hole in the right eye and cataracts in both eyes. She was being closely followed by a vitreoretinal specialist but did not want eye surgery. Her health problems included hypertension, hypercholesterolemia and thyroid regulation for which she was taking medications.

Ocular exam revealed best-corrected visual acuity of 20/200 OD and 20/40 OS. There was no improvement on pinhole testing in either eye. Pupils were equal with no relative afferent pupillary defect. Ocular motilities and confrontation visual fields were unremarkable.

Fundus exam revealed unusual retinal vessels superior temporal to the optic disc and a macular hole in the right eye. Image: Reynolds SA

Slit lamp evaluation revealed moderate nuclear sclerotic cataract in both eyes. Intraocular pressures were 17 mm Hg OD and OS. Examination of the retina revealed unusual retinal vessels superior temporal to the optic disc and a macular hole in the right eye, contributing to the decreased vision in that eye. There was a choroidal nevus in the left eye.

What is your diagnosis?

The retinal finding may demonstrate retinal neovascularization, retinal collateral vessel, retinal arteriovenous malformations, intraretinal microvascular abnormalities (IRMA) or retinal vessel tortuosity.

Upon further questioning, the patient reported a history of a retinal hemorrhage in the right eye. Based on the additional information, the clinical characteristic and location of the vessels, it was concluded that the unusual vessels represented retinal collaterals caused by a prior vascular occlusion.

Collateral vessels play an important role in supplying oxygen to an organ when delivery by the normal vasculature has been compromised by disease. Henkind and Wise describe retinal collateral as dilated vessels that arise from the pre-existing capillary bed to join adjacent vessels.

Three types of vessel formation

Three types of collateral vessel formation can occur. The first and least commonly seen is the arterio-arteriolar (A-A) subtype, which develops after branch artery obstruction. The second is the veno-venular (V-V) subtype, which develops after vein obstruction. The third is the arteriovenous (A-V) subtype, which occurs when capillary bed obstruction results from diabetic retinopathy and long-standing glaucoma.

If there is no capillary bed obstruction, arteriovenous communication are called shunts, which may be a congenital variation in conditions such as racemose angioma, retinal angiomatosis and Coats’ disease, according to Landa and Rosen.

The formation of collaterals is an attempt to restore blood flow to an area of relative ischemia in cases of vascular occlusive events. Collateral channels usually form near or adjacent to areas of nonperfusion of the capillary bed. Ultimately, they assume a structure similar to the occluded vessels.

They may be observed several weeks to months after a vascular occlusion. They may be single or multiple and appear as normal small blood vessels connecting adjacent arterioles and venules or as small tortuous venous channels. Collaterals may recede if the occluded vessel becomes patent or they may assume the responsibility for blood flow to the affected area.

Collaterals are a frequent occurrence in branch retinal vein occlusion (BRVO). They typically occur across the horizontal raphe or in another location to bypass the blocked retinal segment. In patients with BRVO, the formation of collaterals has been observed to have a favorable effect on visual prognosis, according to Im and colleagues.

Retinochoroidal collaterals, also known as retinociliary or optociliary shunts or opticociliary anastomoses, can occur in a central retinal vein occlusion (CRVO). As with BRVO, Priluck and colleagues have suggested that the occurrence of collaterals after a CRVO is associated with an improved visual prognosis. Another variation of collateral at the optic nerve head occurs in chronic glaucoma cases in response to compromised nerve vascular perfusion.

FA may be necessary

Clinically, collateral vessels may resemble retinal neovascularization, so fluorescein angiography (FA) may be necessary. Neovascularization are thin-walled, fragile vessels that may be accompanied by fibrotic scaffolding. More importantly, neovascularization leaks on FA. Collateral vessels do not leak fluorescein, except in their earliest stages of development. Additionally, collaterals do not extend outside the retinal level in which they originate.

Although this patient did not have diabetes, it is important to mention that IRMA represent a variation of collateral formation in areas of nonperfusion in diabetic retinopathy. They are considered preneovascularization and may leak in the early phases of FA. A retinal consultation and FA are necessary.

Collateral formation can be beneficial to the health of the retina or optic nerve. Rapid collateralization can effectively avert total sensory retinal loss. On the other hand, collaterals may indicate a past or present retinal vascular event. Therefore, it becomes important to ascertain the underlying systemic cause and manage it appropriately.

In this case, the patient reported having a prior vascular event in the right eye and she has significant systemic risk factors. Also, a reported 10% of patients with a retinal-vein occlusion develop an occlusion in the other eye over time, according to Cugati and colleagues. It is important to closely monitor patients with collateral formation. Collaterals should not be treated by photocoagulation, which may lead to further retinal compromise.

References:

• Cugati S, et al. Ten-year incidence of retinal vein occlusion in an older population: The Blue Mountains Eye Study. Arch Ophthalmol. 2006;124:726-732.
• Henkind P, Wise GN. Retinal neovascularization, collaterals and vascular shunts. Br J Ophthalmol. 1974; 58:413.
• Im CY, et al. Collateral vessels in branch retinal vein occlusion. Korean J Ophthalmol. 2002;16:82–87.
• Landa G, Rosen RB. New patterns of retinal collateral circulation are exposed by a retinal functional imager (RFI). Br J Ophthalmol. 2010;94:54-58.
• Priluck IA, et al. Long-term follow-up of occlusion of the central retinal vein in young adults. Am J Ophthalmol. 1980;90:190–202.

• Jamie Althoff, OD, is an assistant professor at Nova Southeastern University College of Optometry. She can be reached at (954) 262-1432; jalthoff@nova.edu.
• Sherrol A. Reynolds OD, FAAO, is an associate professor at Nova. She can be reached at (954) 262-1442; sreynold@nova.edu.
• Edited by Leo P. Semes, OD, a professor of optometry at UAB and a PCON Editorial Board member. He may be reached at lsemes@uab.edu.