Ophthalmology

Eye Test

Introduction to Eye Test

An eye test is performed by an ophthalmologist (a medical specialist who deals with eyes) or an optometrist. It consists of a series of tests to assess your vision and your ability to discern objects.

Written by Doctify Team 27/04/2020

What is an Eye Test?

An eye test is performed by an ophthalmologist (a medical specialist who deals with eyes) or an optometrist. It consists of a series of tests to assess your vision and your ability to discern objects. Periodical eye examinations are recommended as many eye diseases are asymptomatic. Eye tests can detect blinding eye diseases, ocular manifestations of systemic diseases, sign of tumours or other minor issues like the need to wear a pair of glasses.

How is an Eye Test performed?

Applanation tonometry is used to diagnose glaucoma by measuring pressure needed to flatten a cornea portion, as the tonometer touches the eye. The tonometer can be hand-held or attached to a slit lamp. Local anaesthetic drops will be given prior to the test. Alternatively, puffs of air are blown at each of your eyes, the resistance to the air reflects the pressure in the eyes. The measurement of pressure is obtained using a non-contact tonometer. Corneal and retinal topography can be used to detect scarring and swelling of the cornea or retinal detachment. Fluorescein angiogram involves injection of fluorescein, a dye, into a vein in the arm where it travels through the blood circulation to the eyes and highlights any abnormal blood vessels. Your doctor may also administer eye drops to dilate your eyes for the dilated pupillary examination to examine your retina.

An ultrasound eye test can be carried out to look at the eye’s internal structure. This is helpful to determine the length of the eye before cataract surgery.

An autorefractor is used to determine your ability to focus and produce a readout of your approximate prescription for your glasses. Alternatively, your optometrist may use a retinoscope that bounces a light beam off the back of your eye and back into the instrument to provide an accurate guide to the required prescription. An eye test also consists of a test chart where the optometrist flips different lenses in front of your eyes until you have the clearest vision. Each eye is tested individually as the results can vary between one side to another.

How to prepare for an Eye Test?

You should check whether you qualify for a free NHS-funded sight test before attending one. People aged under 16 and over 60, or people diagnosed with diabetes and glaucoma are eligible for a free eye test. You also qualify if you receive income support or have slightly impaired sight.

You will be asked to remove your contact lenses before the eye examination. If you are wearing glasses, you should also bring your glasses when you go for an examination as you may be required to wear them.

What happens after an Eye Test?

After your eye test, your doctor will discuss the results with you whether you need any prescription or further investigations. If you need a new pair of glasses, you will be given an NHS optical voucher.

If you are diagnosed with serious eye conditions that may potentially impair your sight, your ophthalmologist will discuss the next steps with you whether you need medications or surgical procedures.

How can I keep my eyes healthy?

Eye tests are vital to monitor the health of your eyes, however, there are two other simple ways you can help to ensure your eyes are healthy.

Your diet is essential to maintain optimum eye health. Research has shown certain fruits such as melon and blueberries, vegetables, such as carrots and high protein foods including fish, chicken, and eggs can all help to provide you and your eyes, with the necessary nutrients to stay in peak health.

Protecting your eyes from the sun is another simple way to protect the health of your eyes. Check your sunglasses have a CE; UV 400 standard mark, to ensure they provide adequate levels of protection.

Where can I get an eye test?

Eye tests are normally carried out at an optician’s, by an Optometrists. Your GP or Optometrists will refer you if you have a complex eye condition, that needs to be checked by an Ophthalmologist.

When should you first have your child’s eye tested?

When should you first have your child’s eye tested?

It is advisable to have your children’s eyes tested before they start school.
You can, of course, choose to take them for an eye test earlier.
Symptoms to check to include:

  • Redness of the white of the eye
  • Crossed or misaligned eyes
  • Erratic eye movements  
  • White spots on the pupil
  • Consistently watery eyes
  • Crusts or pus in the corners of the eyes  

Are there special glasses for toddlers?

There are special glasses designed to be worn, my toddlers. One type is called ‘cable temple’ glasses and they are less likely to fall off because they wrap around the back of the ears. The other option are glasses with a strap that goes all the way around the back of the head, often referred to as ‘strap’ glasses.

How often should you have an eye test?

You can have your eyes tested as often as you choose, however Optometrists recommend having your eyes tested a minimum of every 2 years. When you are over 70 or under 16, it is advisable to have an annual eye test.

Why should I have regular eye tests?

Regular eye tests are essential to detect eye conditions that may be present without any symptoms, including, glaucoma and macular degeneration.

A comprehensive eye test can also detect other serious medical conditions including:

  • High cholesterol
  • Diabetes
  • High blood pressure (hypertension)
  • Arthritis
  • Neurological (brain and nerve) conditions
  • Stroke
  • Cardiovascular disease
  • Tumours including brain tumours
  • Thyroid disease (graves disease)
  • Autoimmune disorders such as Lupus

What are the different types of eye tests?

Screening test – checks for colour blindness, usually performed using cards or a book with images made from dots that contain numbers, the numbers you see determine if you are colour blind.

Visual acuity test – measures your standard (20/20) vision, usually performed using a handheld acuity chart and a projected eye chart.

Stereopsis test – measures your depth perception, normally performed using 3D glasses which you wear to look at patterns on cards or in a book.

Autorefractor test or Ocular Motility Testing – performed using an Autorefractor machine, you will be asked to focus on a point of light or an image, the optometrist will then take a measurement to determine your point of focus.

Retinoscopy or Refraction test – measures your level of hyperopia (long-sightedness), myopia (short-sightedness), astigmatism and presbyopia. Performed using a machine called a phoropter with a series of lens pairs to determine your glasses or contact lens prescription.

Keratometry test – measures the shape and curve of the cornea to detect astigmatism. Performed using a keratometer, also called an ophthalmometer. A circle of light is directed onto your cornea which your optometrist or ophthalmologist will then use to measure refraction to detect signs of astigmatism.

Peripheral perimeter visual field test – measures your visual field (peripheral vision). Performed using a perimeter, you will be asked to rest your head on a chin rest and focus on a series of flashes, each time you see a flash you press a button, this tests for blind spots (scotomas) which may indicate the presence of eye conditions including signs of glaucoma.

Non-contact tonometry test (NCT) or Intraocular pressure measurement test – measures your level of eye pressure to detect signs of glaucoma. Performed using a non-contact tonometer that projects a quick puff of air into your eye which measures intraocular pressure (IOP) which may indicate the presence of eye conditions including signs of glaucoma.

Applanation tonometer test or Manual intraocular pressure measurement – provides a more precise reading of your level of eye pressure when an Intraocular pressure measurement test has indicated there may be signs of glaucoma. Normally performed using a tonometer mounted on the slit lamp. Anesthetic eye drops will be used and the Optometrist or Ophthalmologist uses special, handheld instruments to briefly touch your eye to measure the internal pressure.

Slit lamp exam – may be done as a stand-alone exam or as part of an Applanation tonometer test – examines the front of your eye, including the cornea, eyelids, iris, and lens. Performed using a microscope and a small beam of light to check for the presence of any damage or abnormalities with your cornea.

Ophthalmoscopy or Funduscopy test – may also be done using a slit lamp to examine the structures of the eye including the blood vessels, optic nerve, retina, macula, and the choroid coat. You may be given eye drops to dilate your pupils and the optician or ophthalmologist will then direct a light into your pupil to examine the back of your eye (fundus) with the ophthalmoscope to detect any abnormalities. Your sight will be blurred for a short period afterwards.

Optical coherence tomography (OCT) –  measures the thickness of the retina’s layers to detect the presence of retinal eye conditions
Performed using light waves to produce high-resolution 3D images of the distinct layers of the retina.

What should I ask before having an eye test?

  • What eye tests will be carried out?
  • What conditions will you be looking to detect?
  • Will you refer me to an ophthalmologist if you detect an eye condition?




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