Dr. Nilufer Sayed Mohammed, Dr. Anthrayos C V Kakkanatt
BACKGROUND: A prospective observational clinical study of 95 snake bite patients admitted in Medical ICU, with the aim of finding the occurrence of ophthalmic manifestations in them.
RESULTS: The present study revealed the age group most affected as 51-60 (21%). Males (73%) were more affected. The type of snake most commonly involved is viper (53%). Bite to hospital time was less than 6 hours in 87% and between 6-12 hours in 13%. Coagulopathy (94.7%), acute renal failure (40%) and respiratory failure (7.3%) had a p value which was significant with relation to the type of snake. Out of the total 95 patients studied, 11 (11.6%) had ophthalmic manifestations. Initial examination showed ptosis and ophthalmoplegia in 4 (4.2%) patients. Anterior segment findings were present in 8 (8.4%). They had abnormal pupil and of which one patient had bilateral acute angle closure glaucoma. The p value was significant. Posterior segment finding was seen in only one patient (1.05%). The patient had vitritis in both eyes. On first follow up, there was one case with hyphaema (1.05%) and one with subconjunctival haemorrhage (1.05%). In posterior segment, there was one macular oedema (1.05%), one bilateral anterior ischaemic optic neuropathy (1.05%) and one bilateral central serous retinopathy (1.05%). Intraocular tension was raised in two (2.1%). No significant p value was present in these findings with relation to type of snake. On second follow up after a month, one had developed secondary glaucoma due to hyphaema, one patient had persisting central serous retinopathy and one patient who had AION.
CONCLUSION: Out of the 95 patients studied, 11 (11.6%) had ophthalmic manifestations following snake bite. This shows that ophthalmic manifestations can occur in poisonous snake bites, either due to the venom or the anti-venom received. Early detection can prevent development of further complications and improve the final visual outcome.
Snakes evoke an innate and primordial fear in humans. Snakebite is a common and dangerous environmental and occupation disease, especially in rural areas of tropical developing countries. The public health importance of snake bite has widely been neglected. This has led the WHO to include snakebite in the WHO’s list of neglected tropical diseases (1).
Two families of venomous snakes found in India are Elapidae and Viperidae. The Elapidae includes Cobra and Krait which is neurotoxic. Viperidae includes typical vipers and pit vipers which are mainly haemotoxic (1).
Most of the poisonous bites in India is by Cobra (Naja naja), Russell’s viper (Dabiola russelii), saw-scaled viper (Echis carinatus) and common krait (Bungarus caerulus). These are the ‘big four’ against which the Antivenom is manufactured.
Snake venom is rich in protein and peptide toxins which, due to evolutionary pressures have targeted specific tissue receptors. Anti-snake venom provides a specific lifesaving treatment.The systemic complications due to snakebite are well researched and documented. The venom mainly acts on the haematological and neurological system leading to coagulation defects, flaccid paralysis, renal failure and respiratory failure. This depends on the type of snake involved.
India has 81000 envenomations per year with 11000 deaths per year due to snake bite, the highest in the world (1, 2). The ophthalmic manifestations in snake bite though rare is a significant cause of morbidity. Ptosis and ophthalmoplegia are well known manifestations following bite of elapids. The reason for ophthalmic involvement could be due to the snake venom or the polyvalent antivenom as hypothesized by several authors (3, 4).
As there is a high disease burden due to snakebite, the ophthalmic manifestations though rare, should be carefully looked for in patients with envenomation. Most of the patients are systemically unstable at admission and the primary concern of the treating doctor is making the patient stable. Hence, the ophthalmic conditions are often missed as the patient may not be able to complaint or realise the visual symptoms. Herein, lays the need of the present study. The primary physician should be aware about the incidence of ocular complications as a result of venom from snakebite and that its early detection can prevent visual loss in most of the patients.
Only isolated case reports or case series of ophthalmic manifestations in snakebite has been published in literature so far. The present study is a significant one as it statistically analyses the occurrence of ophthalmic manifestations in snakebites with due importance on the type of poisonous snake involved.
AIM OF THE STUDY
To study the occurrence of ophthalmic manifestations in snake bite. As the snake venom has hemotoxic, neurotoxic and cytotoxic properties, it can affect the eye.
MATERIALS AND METHODS
A prospective observational clinical study of 95 patients admitted in Medical ICU. The study was conducted in a Medical college hospital in South India. All the patients were examined within first 24 hours of admission. The patients admitted in ICU had envenomation and hence anti-snake venom was received by all patients included in the study.
A detailed history was taken about the type of snake, time of injury, arrival at hospital. Also history was taken about any new onset defective vision or previous ophthalmic diseases or surgeries done. Most of the time history was taken from bystanders as the patient would be systemically unstable and unable to communicate properly. Written consent for examination was obtained from patient if possible or from their bystanders. Vision was checked using a portable Snellen’s chart. The patients underwent a basic ophthalmic examination using diffuse torch light. Pupils were examined, anterior depth was assessed, direct ophthalmoscopy and tonometry was also done. All the patients were examined again after 5 days for the first follow up. The patients who were stable were brought to the out-patient department of ophthalmology and were examined. Vision was recorded, slit lamp examination and dilated fundus examination was done. Intraocular tension was recorded. All patients were advised to come for a follow up one month later and were examined.
RESULTS AND DISCUSSION
- Age distribution
The present study reveals the age group most affected as 51-60 (21%), though 21-30 (18.9%) and 31-40 (20%) follow close behind.
Males (73%) were more affected than females (27%). This is consistent with the other epidemiological studies (5, 6). This is mainly due to the outdoor activities handled more commonly by males and hence the risk for a snake bite is increased.
- Type of snake involved
The type of snake most commonly involved is viper (52.6%), followed by unidentified snake (41%), cobra (5.3%) and krait (1%). This is similar to the findings of Kumar V et al (7) with their study in central Kerala showing that 90.4% had hemotoxic envenomation due to viper. Saravu et al (8) reported 74% involvement due to viper in their study in Manipal, Karnataka. Bhalla G et al (9) also reported 55.2% viperine snake bites in their study at a tertiary health center in Maharashtra. In contrast, studies from north India, by Jarwani et al (6) conducted in Gujarat, report cobra and krait as a major cause of snake bite. Similarly, Gautam P et al (10), reported neurotoxic bites were predominant in their study at Himachal Pradesh.
- Part of body bitten
Part of body bitten most commonly was lower extremities (98%). This is obviously due to the fact that most of the time snake bites occur when snakes are trodden upon unknowingly.
- Bite to hospital time
Bite to hospital time was less than 6 hours in 87% and between 6-12 hours in 13%. The time of reaching hospital is drastically decreased due to better transport and health care facilities and increased awareness about snakebite. This parameter is significant as any delay in getting emergency medical care further increases the damage caused by the venom.
- Systemic manifestations
In the present study, coagulopathy was present in 94.7% patients. Acute renal failure was present in 40% of the patients studied. This shows disparity with the study reported by Dharod M V et al (11), where coagulopathy was 40% and acute renal failure was 31%. But a point to be noted is that, they had a high number of neurotoxic snake bites (27%) included in their study. The high number in our study could be because all the patients included in the study had envenomation and majority of the bites were haemotoxic. Respiratory failure occurred in 7.3% of the patients.
Coagulopathy in relation to type of snake revealed a p value less than 0.001, suggesting that this feature is highly dependent on the type of snake involved. Coagulopathy was not seen in any of the patient bitten by cobra, as it is neurotoxic. Similarly, acute renal failure in relation to the type of snake showed a p value less than 0.001, confirming that this complication is dependent on the type of snake. Acute renal failure was not seen cobra bite. Respiratory failure also had a p value less than 0.001, showing significance. 80% of patients with cobra bite went in for respiratory failure.
- Initial examination
Initial examination revealed two patients with new onset defective vision. Nine patients could not be assessed for vision as they were drowsy.
Ptosis and ophthalmoplegia was seen in 4 (4.2%) patients. This is a common finding seen after bite by cobra and krait (12, 13). Extraocular muscles are seen to be affected early because of the special structure of fast twitch fibres and the nerve : muscle ratio being 1:5 to 1:10 when compared to skeletal muscle, that is 1:100. Ptosis and ophthalmoplegia was seen in 4 out of 6 patients of neurotoxic bites. The p value was less than 0.001 and hence significant with respect to the type of snake involved.
Anterior segment findings was seen in 8 (8.4%). Pupil was sluggish in these patients. Six out of the seven were bite by neurotoxic snake which explains the pupil involvement. One was a bite by viper. It might be a Russell’s viper which has mild neurotoxic effect also (14). This again had a p value less than 0.001 and therefore significant for the type of snake involved. One patient had mid dilated fixed pupil in both eyes with blurring of vision and shallow anterior chamber. She had a high IOP and was diagnosed as bilateral acute angle closure glaucoma. This complication of snakebite is often reported (3, 15).The mechanism was hypothesized as capillary damage causing ciliary body oedema leading to forward movement with pupillary block.
Posterior segment findings was seen in only one patient. This patient had vitritis in both eyes. This is the second patient who had new onset defective vision. Associated anterior uveitis might have been there, but slit lamp examination could not be done in the patient as he was sick and hence could not be documented. Inflammatory manifestation could not only be due to the venom, but also the anti-venom which can produce such a reaction (4). Further studies are required to know the exact mechanism involved.
- First follow-up
First follow up was done after 5 days in the out-patient department of ophthalmology. Out of the total patients, one patient was discharged against medical advice and one patient succumbed to death.
Four patients had defective vision (DV). In the anterior segment, there was one case with unilateral hyphaema (Grade 3) and one with subconjunctival haemorrhage in both eyes. Both can be explained by the haematological abnormalities caused by the snake venom of Viper. In the posterior segment, there was one case of bilateral macular oedema, one patient with bilateral central serous retinopathy and one patient with bilateral anterior ischaemic optic neuropathy. The macular oedema was seen in the patient who had vitritis on initial examination. Bilateral central serous retinopathy and bilateral anterior ischaemic optic neuropathy are being reported for the first time. Intraocular tension was raised in two, in the patient with hyphaema and in the patient with bilateral angle closure glaucoma. No significant p value was present in these findings with relation to the type of snake involved.
- Second follow-up
On second follow up after a month, there was defective vision in three patients. One had developed secondary open angle glaucoma in one eye probably due to the initial hyphaema, the other two were persisting central serous retinopathy and bilateral AION. Ten patients (10.8%) were lost to follow up.
LIMITATIONS OF THE STUDY
There was marked difficulty in detailed examination of patients on first visit, as most of them were in serious condition.
- A portable handheld slit lamp for examination of these patients might have picked up more ophthalmic manifestations.
- Difficulty in convincing patients to come for follow-up after one month, as late ocular manifestations like optic neuritis had been reported.
- As the study was conducted in Medical ICU, all patients had envenomation and hence received anti-snake venom. This study could not ascertain whether the ophthalmic manifestations seen like vitritis and bilateral central serous retinopathy were due to venom or the reaction to anti-venom.
Out of the 95 patients studied, 11 (11.6%) had ophthalmic manifestations in snake bite. This shows that ophthalmic manifestations can occur in poisonous snake bites, either due to the venom or the anti-venom received. As most of the patients will be in serious condition or unconscious, they will not be able to complaint or even realise the symptoms and hence the eye manifestations could be missed. Early detection can prevent development of further complications and improve the final visual outcome. Furthermore, the primary physician should be aware of the possibility of eye involvement and should refer to ophthalmologist or get a bedside consultation when required.
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