The eyes are a good place to look for signs of trouble brewing in the body. An eye check-up is, in fact, a relatively inexpensive way of doing so (a comprehensive check-up, which includes testing all parameters pertaining to the eye, costs Rs600-1,000 and takes about 30 minutes to an hour).

Rajeev Jain, eye surgeon and director of the Save Sight Centre in Delhi, says that even if you have 20/20 vision, you should pay a visit to an eyecare specialist at least once a year. The eyes are composed of different types of tissue and it is this unique feature that makes them susceptible to a wide variety of diseases, and provides insights into our bodies.

According to Dr Jain, almost every part of the eye can offer important clues to the diagnosis of disorders. Signs of a systemic disease may be evident on the outer surface of the eye (eyelids, conjunctiva and cornea), middle of the eye (iris) and back of the eye (retina). “It is important to catch these changes as the retinal blood vessels can eventually lead to blindness if left untreated," he adds.

■ Hypertension

High blood pressure (BP) is mostly asymptomatic, but an eye doctor may be able to detect it through a retina check. “We can see hypertension through the eyes because it gives retinal arteries a silver or copper hue that we call copper wiring," says Kenshuk Marwah, a consultant ophthalmologist at the Fortis Memorial Research Institute in Gurugram. “High BP is also related sometimes to muscle paralysis of the eyes," he adds.

■ Cholesterol

High cholesterol can trigger changes in the eye that are detectable—the condition shows up as yellowish deposits on the eyelids. “These yellowish spots are called xanthelasma," says Uma Malliah, senior consultant (ophthalmology), Apollo Hospitals, New Delhi. “If both these conditions are left untreated, they can cause blood vessels in the retina and throughout the body to harden, increasing the risk of heart attack or stroke," Dr Marwah adds. Dr Jain warns that sudden blackouts of vision could also be a sign of an underlying heart problem.

■ Cancer

According to Dr Jain, cancer can start in the eye or can spread to the eye. “Early detection and treatment of cancer in the eye can be vision-saving and, in some cases, life-saving," he says. Brain tumours may affect vision by causing swelling of the optic nerve—that is why doctors often suspect a brain tumour and advise a visit to a neurologist when they find an optic nerve swelling during an eye check-up.

■Thyroid issues

“If someone has protruding prominent eyeballs, this might be an indication that he is suffering from thyroid abnormalities, and needs to get tested," says Dr Marwah. Proptosis, as this profusion is called, may also indicate severe infection and inflammation in the body, adds Dr Malliah.

■ Diabetes

High blood sugar can clog or damage retinal blood vessels over time, rendering them weak and porous. Eye doctors can often spot this change. “Indeed, diabetes takes a big toll on the eyes in general and can lead to blindness in serious cases. It can lead to decreased vision due to cataracts and diabetic retinopathy," warns Dr Malliah.

■ Autoimmune disease

Autoimmune conditions like rheumatoid arthritis and ankylosing spondylitis can cause the body to attack healthy cells and tissues, leading to inflammation. This shows up as dry eyes, keratitis and uveitis, which causes pain, redness of eyes, and decreases vision, says Dr Malliah.

■ Extreme stress

Blisters in the eyeballs are symptomatic of a condition called central serous retinopathy (CSR), typically caused by excessive mental or emotional stress, which can tax the body so much that the retina starts leaking blister-forming fluid. “Usually, in this case, people have blurry vision or see wavy lines when trying to focus on a set point. In most cases, CSR can be alleviated by slashing stress levels," states Dr Marwah.

■ Neurological problems

While the annoying eyelid twitch you get from time to time likely signals fatigue, stress or sensitivity to caffeine, it could also be a sign of an underlying neurological disorder. According to Dr Jain, neurological diseases such as multiple sclerosis could show up as changes in eye movement, vision or the function of the optic nerve

Take care

When you should visit the eye doctor

At birth: To rule out any congenital eye disorders like cataract, glaucoma, etc.

After a year: To rule out any developmental disorders (e.g., cataract, squint, retinoblastoma)

4-6 years: To rule out refractive errors (need for spectacles), amblyopia (lazy eye), squint, etc. 

6-40 years: An eye check-up is important every 3-5 years

After 40: Every 1-2 years, to detect presbyopia, glaucoma, cataract, effects of any other disease.