INTRODUCTION
Snakebites are common in tropical countries like India. Systemic complications following snakebite can be either neurological or hematological. Ocular involvement following snakebite is common. Posterior segment complications in the form of central retinal artery occlusion (CRAO), optic atrophy, vitreous hemorrhage, macular infarction, and tractional retinal detachment following snakebite have been reported in the literature.[1–5] We report a case of resolved CRAO with consecutive optic atrophy following the bite by Russell’s viper.
CASE REPORT
A 19-year-old female presented with sudden-onset painless loss of vision in the left eye (LE). There was a history of bite by Russell’s viper 2 months back. The past records stated that the patient was unconscious for a day following the snakebite and underwent treatment in the intensive care unit. She complained of loss of vision in LE after regaining consciousness. Her blood coagulation parameters were deranged (increased prothrombin time, decreased platelet count, and raised activated partial thromboplastin time). She had an acute renal failure with raised blood urea and serum creatinine. She had been treated with antisnake venom therapy and six sittings of hemodialysis. All blood parameters returned to normal levels 1 month after the incident. The patient did not have any ocular symptoms before snakebite.
On presentation, best-corrected visual acuity was 20/20, N6, and light perception positive in the right eye (RE) and LE, respectively. Anterior and posterior segment examinations were unremarkable in RE [Figure 1a]. Anterior segment examination of LE showed clear cornea, quiet anterior chamber, and clear lens. The pupil was fixed and dilated in LE. Posterior segment examination of LE showed clear vitreous, pale optic disc, sclerosed arterioles, and retinal pigment epithelium mottling in the macular area [Figure 1b]. Fundus fluorescein angiography of LE showed normal filling of the arteries and veins with an enlarged foveal avascular zone. Pruning of capillaries was evident in the macular area [Figure 2]. Time-domain optical coherence tomography of LE showed marked retinal thinning with loss of normal foveal contour [Figure 3]. Central retinal thickness in LE was 98 μ. Fundus fluorescein angiography study and optical coherence tomography scans of RE were within normal limits [Figures 2 and 3]. We diagnosed it as a case of resolved CRAO with consecutive optic atrophy in LE.
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Figure 1: (a) Color fundus photograph of the right eye showing normal retinal features. (b) Color fundus photograph of the left eye showing pale optic disc, sclerosis of arterioles, and pigmentary mottling in the macular area
Figure 2: (a) Late phase fundus fluorescein angiography image of the right eye showing complete filling of the retinal blood vessels and normal foveal avascular zone. (b) Late phase fundus fluorescein angiography image of the left eye showing complete filling of the major retinal blood vessels with the enlarged foveal avascular zone. Pruning of capillaries noted in the macular area (white arrow)
Figure 3: (a) Optical coherence tomography scan of the right eye showing normal foveal contour and thickness. (b) Optical coherence tomography scan of the left eye showing marked thinning of the retina and effacement of normal foveal dip
Poor visual prognosis was explained to the patient. The patient was asked to follow-up with her physician and advised regular ophthalmic check-ups.
DISCUSSION
Bites due to venomous snakes can lead to multi-organ involvement although ocular involvement is rare. The snake venom is a complex mixture of various polypeptides, proteins, inorganic compounds, and enzymes.[6] Snake venom can either affect the neurological or hematological system. In our case, the patient was bitten by hematotoxic viper and had systemic features of bleeding diathesis leading to end-organ dysfunction in the form of acute kidney failure.
CRAO following snakebite is a very rare complication. The possible etiology of CRAO can be the direct toxic effect of the snake venom causing toxic vasculitis leading to thrombosis.[1] Direct vasospasm induced by snake venom can be another cause of CRAO.[1] Our patient most likely developed disseminated intravascular coagulation with thrombus formation within the central retinal artery leading to its occlusion.
Acute CRAO presents with sudden-onset loss of vision in the affected eye. Retinal examination in acute CRAO usually reveals pale optic disc, retinal whitening due to ischemia, cherry red spot, cattle trucking in the retinal blood vessels, and arteriolar narrowing.[7] The retinal whitening tends to start resolving by the end of 1 week, and the retina regains its normal transparency by the end of 1 month.[7] Resolved cases of CRAO present with consecutive optic atrophy, arteriolar narrowing, and pigmentary changes in the macular area. Our patient presented to us 2 months following snakebite. By that time, all features of acute CRAO had resolved. Clinical findings of pale optic disc, pigmentary changes in the macula, and sclerosed arterioles helped us in making a diagnosis of CRAO in our case. Electrophysiological studies could have confirmed the diagnosis of CRAO and optic atrophy. Jalali et al.[4] have reported ERG findings in a 24-year-old male with CRAO following snakebite. Grossly reduced B-wave with electronegative pattern was noted in flash ERG. Flash visual evoked potential showed reduced amplitude and prolonged latency in the affected eye. Electrophysiological studies could not be conducted due to nonavailability of the machine in our center.
CONCLUSION
CRAO following snakebite is very rare. Acute CRAO can be easily diagnosed. Good clinical and multimodal examinations are needed to correctly diagnose a case of old CRAO. This case adds to the body of literature available on CRAO following snakebites.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
REFERENCES
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