How to keep your cornea safe

The cornea, a highly transparent tissue of the eye, often goes unnoticed because it allows light to pass through. The eyes derive their colour from the iris, a circular diaphragm within the eye, and not the cornea. Measuring 11-12 mm in diameter, the cornea is shaped like a watch glass and sits in front of the eyeball, focusing reflected light from external objects onto the retina.

The cornea is not merely a refracting lens; it is a highly complex, living, avascular tissue that remains transparent due to a single layer of tiny cellular pumps lining its rear, which removes any water that may enter it. Despite the protection offered by blinking eyelids, there is always a risk of corneal injury. Thanks to its highest density of nerve endings in the body, copious tears effectively wash away any foreign bodies on it.

However, this is not always the case. Specific activities, the most notable of which are crop harvesting or engaging in industrial or sporting activities without protective eyewear, may result in seemingly minor abrasions which remove the protective epithelial layer of the cornea. Abrasions make the cornea vulnerable to bacterial or fungal invasion, leading to corneal ulceration, a blinding disorder.

Bacterial corneal ulcers cause severe eye pain and redness and follow a highly aggressive course. If not promptly treated, these can quickly lead to corneal perforation. Fungal corneal ulcers are more prevalent in agrarian economies, such as those found in India. Dr Arunaloke Chakrabarti and colleagues from the PGI, Chandigarh, studied 2,500 patients over a seven-year period and discovered that in the post-monsoon season, men, especially those with diabetes and dry eyes, who sustained seemingly minor injuries from mud, vegetable matter, insects, or even animal tails, were at risk of developing fungal corneal ulcers.

Fungal ulcers exhibit a slow onset and are comparatively less symptomatic, which can delay their diagnosis and treatment. The inadvertent use of corticosteroid drops makes identification highly challenging, even for specialists.

Exposure to corticosteroid drops can also lead to disastrous consequences for herpes virus corneal ulcers. These viruses typically lie dormant, but can get active under psychological or physical stress, and travel down the corneal nerves, causing infection. Although antiviral therapy is quite effective, diagnosis is often delayed, and nearly half of those affected continue to experience recurrences.

Fungal ulcers require prolonged treatment with antifungal agents and may take several weeks to heal. Dr Amit Gupta and Dr Anchal Thakur from the PGI, Chandigarh, have utilised intracameral liposomal Amphotericin B, an antifungal agent, in cases of severe, recalcitrant fungal corneal ulcers, leading to faster healing.

Evidence is accumulating globally, including at PGI, that bacterial and fungal corneal infections heal more rapidly if, in addition to standard antimicrobial agents, riboflavin drops are applied to the corneal ulcer and activated with UV-A light. The UV light is commonly utilised for the sterilisation of air and water.

Corneal ulcers related to contact lens use are more prevalent in high-income regions and are increasingly reported among the urban youth population in India. Freshwater amoeba parasites, such as Acanthamoeba, cause most cases. They are typically acquired from homemade contact lens solutions, non-sterile water used for cleaning lenses, or swimming while wearing contact lenses without safety goggles. Acanthamoeba infection leads to the destruction of the corneal nerves and is extremely painful. Diagnosing it is highly challenging, and treatment is equally difficult. In the past, contaminated contact solutions have resulted in disastrous fungal infections in several countries. This infection is entirely preventable. Single-use disposable contact lenses are strongly recommended.

There is an ongoing silent epidemic of corneal blindness in India, with the incidence of corneal ulcers at 113 per 100,000, more than 10 times that of the western world. According to Maj Gen (Dr) JKS Parihar, a corneal transplant expert, 1.3 million people in India are corneally blind in both eyes, and 10.6 million in one eye, accounting for one-fourth of the bilateral and half of the unilateral corneal blindness worldwide.

Although the onset of a corneal ulcer is signalled by pain, redness, and watering, most patients report it after a considerable delay. Even when successfully treated, an ulcer leaves behind an opaque scar that prevents adequate light from entering the eye. The scarred cornea requires a transplant with a corneal button harvested from a recently deceased donor. Of the nearly 50,000 corneas harvested annually in India, only half can be used for corneal transplants.

In a widely acclaimed report 25 years ago, Dr Madan Upadhyay from Kathmandu successfully prevented corneal ulceration in 96 per cent of individuals with corneal abrasions in a rural community by applying an antibiotic ointment three times daily for three days. It was most effective when initiated within 18 hours of the injury. Dr Prashant Garg from Hyderabad and his collaborators from Sheffield, UK, also found it to be the most cost-effective strategy.

— The writer is an Emeritus Professor, PGI, Chandigarh

Protective measures

— Always wear safety glasses while practising agricultural and other outdoor activities to prevent unnecessary corneal injury that can lead to blindness.

— Avoid touching and rubbing the eyes with dirty hands or a soiled cloth at all costs.