It normally starts with the letter “E” and should end with a clear picture of your vision and eye health.
The standard eye test, one of medicines most enduring diagnostics, is designed to measure a range of functions and capabilities, but has matured since Dutch ophthalmologist Hermann Snellen devised his chart in 1862.
The familiar 11-line grid of letters in diminishing sizes – the Snellen Chart – still forms the foundation, but the eye test has become a sophisticated technological process that can define indicators of general health as well as visual acuity.
Clinicians recommend a check-up at least every two years so that variations in eye strength and health can be plotted against base readings taken from the first examination.
A patient will still be expected to go through the ritual of reading the chart with one eye at a time, however opticians now have a suite of technology and a battery of tests that can help predict not only the correct spectacles and contact lenses, but also the likelihood or presence of conditions, such as diabetes, high blood pressure and brain tumour.
“A thorough eye test may take up to 30 minutes and is an excellent MoT because it covers aspects of your health that have a huge impact on your life,” says Vicky O’Connor, an optometrist for Boots. “At the end you have a good idea of the health of the eye and of general health.
The thought of a test can cause apprehension, but your eyes are something you cannot check yourself
“None of us likes to think of our eyes changing because it can be a sign of ageing or simply an acknowledgement that our body isn’t working quite like it used to. The thought of a test can cause apprehension, but your eyes are something you cannot check yourself.”
Research has suggested that only 40 per cent of the population adheres to a regular cycle of eye examinations, and clinicians believe the “refuseniks” could be putting their eyesight and health at risk.
The core elements of a proficient eye test include a lifestyle assessment, pre-screening tests to measure eye pressure, visual field and a digital photograph of the back of the eye which provides more general health intelligence. There is also a bank of tests measuring changes in vision, eye function and eye health.
The initial tests are normally performed by a trained, but not medical, assistant before the optometrist, who does have a professional degree, continues with procedures that examine muscle control, clarity of vision, visual field, the balance of sight between the two eyes and overall health of the eye.
The pre-screening test trio is the new technology that enhances the more traditional charts, and following lights and tracking the lateral movement of the optician’s pen. All are performed with the patient seated and some with their head positioned by a chin rest.
The first test involves a gentle puff of air being directed at the eye to calculate its pressure. It flattens an area on the surface of the eye and an established scientific algorithm is used to determine levels with a range or readings bracketing a normal. Extremes can indicate glaucoma (too high) and an unseen injury (too low).
The visual fields test generates flashing dots of light which the patient has to acknowledge by either pressing a button or telling the assistant what they see, which gives a clear report on the range of vision.
Digital retinal photography then provides an orange-hued image of the back of the eye to reveal structures, such as blood vessels, arteries and vein composition, which carry more information about general health.
The optometrist also checks the ability of the eyes to work as a pair, monitors colour vision and depth perception. A crucial component of the process is the optometrist’s interpretation of the data from the technology, the lifestyle information and the results of the further tests.
“Eye examinations are important as they impact on our day-to-day lives, and our abilities to live and to work,” adds Ms O’Connor. “They should be done at least every two years so that it is possible to detect any changes in function and react accordingly.
“The patient should leave with a full understanding of what, and why, something has been recommended as a prescription and with any advice on next steps.
“People who don’t have eye tests miss an opportunity to detect many eye and general health problems when it may be early enough to address them.”
The comedic heritage of eye test is the TV stereotype of people with bottle-end glasses conversing with hatstands, but the eye test is now a potent screening exercise for both eyes and general health.
CONDITIONS TO LOOK OUT FOR
FACTFILE
AGE-RELATED MACULAR DEGENERATION (AMD)
A gradual loss of central vision caused by wear and tear, which is normally signalled by blurring, although the condition is not painful. It is the biggest cause of blindness in the UK and risks are increased by age, smoking and hereditary factors. There are two types – the slow-forming Dry AMD, due to damage to the macula from lack of nutrients or the build-up of waste products, for which there is no cure, and the more serious Wet AMD, caused by abnormal blood vessels, which can ruin vision in a matter of days.
DIABETIC RETINOPATHY
A common complication of diabetes, when high blood-sugar levels damage sensitive cells at the back of the eye which turn light into electrical signals for the brain to interpret. Controlling the diabetes reduces the risk, but some patients need surgery and can go blind.
GLAUCOMA
This refers to a group of conditions that develop when the drainage tubes within the eye become blocked. The build-up of fluid can damage the optic nerve and cloud the lens. It can be treated with eye drops, laser or other surgery, but damage cannot be reversed, so early diagnosis is essential.
CATARACTS
These cause the lens of the eye to become cloudy and restrict vision. Age is the principal cause, but poor diet, lifestyle and over-exposure to sunlight can accelerate the condition. They can be removed by routine surgery and more than ten million cataract operations are performed around the world each year.
FLOATERS
Tiny pieces of debris that become lodged in the eye’s structure which cast shadows over the retina and interfere with vision. They are associated with ageing and are formed by minute strands of collagen within the eye that have become detached.
