Hemi-central retinal artery occlusion in young adults

Amongst the clinical presentations of retinal artery occlusion, hemi-central retinal artery occlusion (Hemi-CRAO) is rarely described. This case series of four adults aged between 22 and 36 years attempts to describe the clinical profile, etiology and management of Hemi-CRAO. Case 1 had an artificial mitral valve implant. Polycythemia and malignant hypertension were noted in Case 2. The third patient had Leiden mutation while the fourth patient had Eisenmenger’s syndrome. Clinical examination and fundus fluorescein angiography revealed a bifurcated central retinal artery at emergence from the optic nerve head, in all cases. Color Doppler examination of the central retinal artery confirmed branching of the artery behind the lamina cribrosa. It is hypothesized that bifurcation of central retinal artery behind the lamina cribrosa may predispose these hemi-trunks to develop an acute occlusion if associated with underlying risk factors. The prognosis depends upon arterial recanalisation and etiology of the thromboembolic event.


Pukhraj Rishi, Ekta Rishi, Tarun Sharma, Sheshadri Mahajan
Amongst 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%. [1] 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. [2] 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.
Vol. 58 No. 5  ]. Generalized arteriolar attenuation, box-carring of vessels and cherry red spot at fovea were seen. Treatment was initiated immediately [ Table 2]. However, fundus appearance  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.

Case 3
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.
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.

Case 4
A 22-year-old young man, a known case of congenital heart Vol. 58 No. 5    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.

Discussion
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. [3] 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. [4] 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'. [5] 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. [6] 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. [7,8] A sole report has described hemi-CRAO occurring in association with sexual activity and sildenafil citrate; a coincidental finding as mentioned by the author. [9] 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][11][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. [13] Similar etiological factor was reported in a 25-year-old woman with multiple bilateral retinal arteriolar occlusion [14] and in a 33-year-old lady with branch retinal vein occlusion. [15] Case 3 had Leiden mutation. There have been isolated case reports of ocular ischemic features in association with Eisenmenger's syndrome. [16,17] 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 (hemitrunks) 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.