Acute retinal arterial obstruction presents as central retinal artery (CRA) obstruction in 57% cases, branch retinal obstruction in 38% and cilioretinal artery obstruction in 5%. It may be related to known preexisting systemic disease or may be an initial manifestation of previously undiagnosed systemic abnormality. In young adults with retinal artery occlusion, associated etiological factors are more often obscure and diverse. Hemi-central retinal artery occlusion (Hemi-CRAO) is an extremely uncommon clinical entity that has hardly been described in the literature. Hereby, we describe systemic and ophthalmologic characteristics of four patients ranging between 22 and 36 years of age, who presented with hemi-central retinal artery occlusion.
A 26-year-old gentleman presented with sudden, partial visual field loss in right eye. He had a prosthetic mitral valve implanted, 14 years back. Vision was 20/20 in both eyes. Anterior segment was essentially normal. Right fundus [Fig. 1] showed two central retinal artery hemi-trunks instead of main central artery [Fig. 2]. Supero-temporal arteriolar attenuation was noted; upper hemi-trunk was shorter. Retinal pigment epithelial alteration was noted; foveal reflex was dull. Left eye was normal. Findings of fundus fluorescein angiography (FFA) [Fig. 3], visual field examination [Fig. 4], optical coherence tomogram (OCT) [Fig. 5], multifocal electroretinogram (mfERG) [Fig. 6] and color Doppler study of right eye [Fig. 7] are summarized in Table 1. A summary of systemic investigations and treatment is included in Table 2. A cardiology consult was sought; patient was advised to continue current treatment [Table 2] with regular follow-up.
A 36-year-old gentleman reported with sudden visual loss in left eye. He had a similar problem two months back with spontaneous improvement, for which he did not seek any treatment. Vision was 20/20 in right eye and no perception of light in left. Anterior segment examination was normal. Right eye was normal. Left fundus revealed patchy areas of retinal edema over posterior pole and bifurcated central retinal artery [Figs. 8 and 9]. Generalized arteriolar attenuation, box-carring of vessels and cherry red spot at fovea were seen. Treatment was initiated immediately [Table 2]. However, fundus appearance remained same. He was referred to the physician. Next day, the patient reported perception of light in that eye. A platelet-fibrin embolus could be made out in infero-temporal arcade. Findings of FFA [Fig. 10 a and b], visual field examination [Fig. 11], ERG [Fig. 12] and color Doppler study of the right eye are summarized in Table 1. A summary of systemic investigations and treatment is included in Table 2. Five days later, vision recovered to 20/125. On the tenth day, it improved to 20/40 and after six months it was 20/20. The patient also had regular follow-ups with the hematologist and cardiologist.
A 28-year-old lady reported with sudden, painless visual loss in right eye since five days. Diagnosed to have systemic hypertension, rheumatic mitral valve regurgitation and chorea, she was under treatment for the same [Table 2]. Vision was 20/60 in the right eye and 20/20 in the left. Anterior segment examination was unremarkable. Right fundus revealed retinal edema involving superior half, sparing fovea with no embolus [Fig. 13 and 14]. Left eye was normal. Findings of FFA [Fig. 15], multifocal ERG [Fig. 16] and color Doppler study of the right eye [Fig. 17] are summarized in Table 1. A summary of systemic investigations and treatment is included in Table 2. The patient was detected to have Factor V Leiden mutation (Real time Polymerase Chain Reaction, RT PCR) and was also advised a regular follow-up with cardiologist and hematologist.
A 22-year-old young man, a known case of congenital heart disease, reported with decreased vision in left eye since two days. Vision was 20/20 in both eyes. Anterior segment examination was essentially normal. Right fundus was normal. Left fundus revealed retinal edema involving superior half, sparing fovea with no embolus [Fig. 18]. Findings of FFA [Fig. 19], ERG [Fig. 20], visual field examination [Fig. 21] and color Doppler study of the right eye [Fig. 22] are summarized in Table 1. A summary of systemic investigations and treatment is included in Table 2. Diagnosed to have Eisenmenger syndrome, the probable cause of vascular occlusion was paradoxical embolism through ventricular septal defect. At six weeks review, retinal edema had reduced with no evidence of anterior segment neovascularisation.
CRA commonly originates as a separate stem from the first part of the ophthalmic artery and usually divides into two branches at the disc, each of which further bifurcates into temporal and nasal divisions. Anatomical variations of branching patterns are known. Reports describe a case with two CRAs running independently up to the optic disc and joining at the optic disc to form a loop, from the summit of which arose terminal branches that followed the usual course. However, this anatomical arrangement was not seen in any of our cases. Singh and Dass also describe a branch of CRA originating from behind the lamina cribrosa that supplied the supero-medial part of the retina but this was more of a ‘branching’ than a ‘bifurcation’.
On entering the eye, CRA loses the elastic lamina and has a prominent muscularis as it bifurcates at the optic disc. These histological changes distinguish retinal arteries from muscular arteries of the same size in other tissues. Additionally, the unusually developed muscularis may allow greater constriction of the vessels in response to chemical and pressure changes. These histological changes coupled with the pre-lamina cribrosa branching of CRA may make these hemi-trunks more ‘vulnerable’ to vascular occlusion, especially in subjects with systemic co-morbid conditions. Hence, hemi-CRAO may be a manifestation of a preexisting systemic condition or a harbinger of a hitherto undiagnosed systemic condition.
Thromboembolic events are the main culprits in the pathogenesis of retinal artery occlusions which can manifest as ‘Hemi-CRAO’ in a proximally bifurcated CRA. A sole report has described hemi-CRAO occurring in association with sexual activity and sildenafil citrate; a coincidental finding as mentioned by the author. In our series, Case 1 had an artificial mitral valve and was on anticoagulation therapy. Case 2 had polycythemia. Both are well documented etiological factors,[10–12] which lead to the devastating vascular episode. Genetic mutation in Factor V renders it resistant to anticoagulant effect of endogenous anticoagulant protein C. The most common of these mutations is called the Leiden mutation. Similar etiological factor was reported in a 25-year-old woman with multiple bilateral retinal arteriolar occlusion and in a 33-year-old lady with branch retinal vein occlusion. Case 3 had Leiden mutation. There have been isolated case reports of ocular ischemic features in association with Eisenmenger’s syndrome. However, its manifestation as hemi-CRAO (Case 4 in our series) is reported as first of its kind. All patients in this unique case series were young, had angiographic evidence of hemi-CRAO owing to proximal, pre-lamina cribrosal branching pattern of CRA (confirmed by color Doppler) and also had remarkable visual recovery of 20/60 or better.
To conclude, unusual pre-lamina cribrosa (extraocular) branching pattern of central retinal artery coupled with the unique histological features of the retinal arterioles (hemi-trunks) may predispose to the development of ‘hemi-central retinal artery occlusion’ in young adults with underlying systemic conditions. However, further histopathological studies are required to understand this clinical entity better.
Dr. V Suresh, Director, Mediscan Imaging, Chennai for the Doppler imaging.
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