Snake Venom Ophthalmia – A Debilitating Eye Condition

Sanjukta Jana, Optometry Intern

LVPEI, Bhubaneshwar, India

 

Snake venom ophthalmia is a rare and potentially debilitating eye condition caused by the introduction of venom from venomous snakes into the eye. Venomous snakes produce complex venom, which they deliver through their fangs to immobilise prey or defend against predators. While most venomous creatures reserve their venom for self-defence, exercising extreme caution and respecting their spatial boundaries is crucial to avoid accidental exposure. ⁽¹⁾

Venomous snakes, such as spitting cobras, possess the ability to project venom into the eyes of their victims, potentially inducing temporary or permanent blindness. The venom itself contains a diverse array of toxins, including:

• Neurotoxins
• Cytotoxins
• Phospholipases
• Cardiotoxins ⁽¹⁾

The cardiotoxins present in snake venom exhibit proteolytic properties, leading to conjunctival chemosis and corneal erosions. The severity of ocular effects resulting from snake venom exposure is directly correlated with the duration of contact between the venom and the ocular surface. Prompt medical attention is essential in the event of snake venom exposure to mitigate potential damage and ensure optimal treatment outcomes. ⁽¹⁾

Figure 1: Showing Duvernoy’s and Nuchal gland
[ https://www.mdpi.com/2072-6651/12/9/576 ]

Few snake species can spit venom from Duvernoy’s gland while irritated or threatened, whereas few species conduct a toxin spray from their nuchal gland. After a toxin spray attack, the eyes are most often affected, causing inflammatory responses mostly in the anterior segment of the eye (hyperaemia, uveitis, corneal erosion, pseudo hypopyon, iris atrophy). Ocular complications in the posterior segment are often observed after snake bites (mostly in limbs from which venomous toxins circulate in the host body and reach the eye). ⁽²⁾

Due to the enriched retinal vascular network, toxins reach the site and cause symptoms like CRAO, and macular infarction. Most snakes discharge venom into victims via fang hooks. Usually, cobras respond to moving faces and not to hands and can spit venom. Cobras perform rapid cephalic oscillations to correlate with the target’s frequency to hit at least one eye of an aggressor. ⁽²⁾

Some snakes possess a nuchal gland that stores venomous fluid. These snakes consume poisonous prey and conserve the obtained poison in their cervical gland – to be utilised later as a defensive mechanism.

Snake venom injection has been noticed to cause ocular morbidity, including local swelling, proptosis, and exposure keratopathy.

Pathophysiology of venom-induced ocular complications:

• In venom spit ophthalmia, the cornea is the first tissue exposed to venom. Severe stromal oedema associated with uveitis results from the intrinsic release of histamine and acetylcholine. Due to neurotoxins in venom, abnormal pupillary reactions are triggered, associated with nerve paralysis. ⁽³⁾
• In viper venom injection-induced ocular complications, proteases, oxidases, and phospholipases induce retinal haemorrhages. Presynaptic toxins inhibit acetylcholine release from nerve terminals, causing motor nerve disorders. ⁽³⁾

Primary Management and Workup Procedure for Snake Venom Ophthalmia:

Primary Management:

1. Flush the eye: Immediately rinse the eye with copious amounts of water or saline solution to remove any remaining venom.
2. Topical antibiotics: Apply topical antibiotics to prevent secondary infection.
3. Pain management: Administer pain relief medication as needed.
4. Monitor vital signs: Closely monitor the patient’s vital signs, including temperature, pulse, and blood pressure.

Figure 2: Showing Corneal Erosions
[https://www.thepmfajournal.com/education/case-reports/post/recurrent-corneal-erosions-secondary-to-isotretinoin-use]

Workup Procedure:

1. Visual acuity test: Assess the patient’s visual acuity to determine the extent of vision loss. ⁽⁴⁾
2. Slit-lamp examination: Perform a slit-lamp examination to assess the anterior segment for signs of inflammation, haemorrhage, or venom-induced damage. ⁽⁴⁾
3. Fluorescein angiography: Conduct fluorescein angiography to evaluate retinal and choroidal perfusion. ⁽⁴⁾
4. Imaging studies: Consider imaging studies like ultrasound or CT scans to rule out orbital cellulitis or other complications. ⁽⁴⁾
5. Venom identification: Attempt to identify the species of snake, if possible, to guide treatment and anticipate potential systemic complications. ⁽⁴⁾
6. Systemic evaluation: Perform a thorough systemic evaluation to rule out systemic envenoming, including laboratory tests like complete blood count, coagulation profile, and renal function tests. ⁽⁴⁾
7. Consultation: Consult with an ophthalmologist and/or a medical toxicologist for further guidance and management. ⁽⁴⁾

Clinical notes:

Administer antivenom if indicated and available.

• Provide supportive care, including wound care and tetanus prophylaxis if necessary.
• Monitor for signs of systemic envenoming.

 

References:

1. Adhi, R. S., & Yen, K. Y. (2011). Snake venom ophthalmia. Brunei International Medical Journal, 7(6), 332-335.
2. Kasturiratne, A., et al. (2017). Snakebite-induced ocular complications: A review. Journal of Venomous Animals and Toxins, 23, 1-11. doi: 10.1186/s40409-017-0111-4
3. Kumar, A., et al. (2018). Ocular manifestations of viperine snakebite: A case series. Journal of Clinical Ophthalmology, 12(1), 43-47. doi: 10.4103/jco.jco_134_17
4. Mittal, R., et al. (2019). Management of ocular complications of snakebite. Indian Journal of Ophthalmology, 67(5), 631-636. doi: 10.4103/ijo.IJO_493_18