Taking a look at eye examinations

In this article, consultant optometrist Dr Daniel Hardiman-Mccartney explains what patients can expect at an eye examination.

What is an eye examination? 

An eye examination (sometimes called an eye test, eye exam, or sight test) is a series of tests conducted by an optometrist, doctor, or ophthalmologist. There are different types of eye examinations to assess various aspects of vision, and it is recommended that people of all ages undergo regular eye examinations to check eye health and detect any potential abnormality or disease. 

What happens during an eye examination? 

Typically, an eye exam involves the following:

·        A medical history review and a description of any problems in vision, if applicable

• Visual acuity (sharpness, acuteness) measurements to check if glasses or contact lenses may be needed
• An assessment of the shape of the eye, which is also used to determine if the patient needs to wear glasses or contact lenses for distance or near vision
• Eye pressure measurements
• Assessment of binocular vision, which checks how the eyes work together and muscular functionality
• Retinal imaging using a camera or a scanner called an optical coherence tomographer (OCT)
• Additional analysis for signs of other general health problems which can manifest in the eyes, such as high blood pressure and diabetes.

Ultimately, the goal of an eye exam is to assess the entirety of the eyes’ health. Each session is tailored to the needs and family history of the patient, and there may be additional testing for colour vision, driving standards, and visual fields. The optometrist looks for evidence of conditions such as glaucoma, cataracts, macular degeneration, and many more. 

If the patient needs glasses or lenses to correct their vision, they will be given a copy of their prescription, and they can choose to get glasses made at an optician or designer of their choice.

How can I prepare for an eye examination?

If you wear contact lenses or glasses, make sure to take them with you (including any cleaning fluid and cases) when you go to the appointment, so the doctor can check if your prescription is accurate. Some tests dilate the pupils, so you may want to have sunglasses on hand, as the eyes will be sensitive to bright lights after this type of exam. Please bring a copy of your previous eye prescription and a list of any medications you are on.

Depending on the type of test performed, you may wish to arrange for someone to take you home afterwards, as certain tests can cause a little discomfort or blurred vision. If you optometrist or ophthalmologist uses eye drops to dilate your pupil, you may not be able to drive until the drops have worn off, which can take two to six hours.

Why is an eye examination performed?

Eye examinations should be performed regularly as part of routine health checks. This means the optometrist sees differences in the patient’s eyesight, checks for any abnormalities, and can correct any vision problems. A healthy adult with no known vision problems should expect to have eye tests around every two to four years whilst in their twenties and thirties, every two years when aged forty and upwards. The optometrist will recommend how often they should have an eye examination based on their clinical needs and family history.

Patients who are already using glasses or contact lenses, have a family history of eye diseases in their family, or suffer from chronic illness that puts them at a greater risk of developing an eye issue should have their eyes tested more frequently.

Understanding an eye prescription

If you need glasses, the optometrist will write you a prescription. It may have a lot of unfamiliar terms and abbreviations, which can make it daunting to navigate. Here is a simple guide to what the words and codes you may find on the prescription sheet:

• Sph (sphere) represents how long or short-sighted you are. This can be positive (+) for long sight or negative (-) for short sight. The higher the number, the stronger your lens.
• Cyl (cylinder) represents the amount of astigmatism present. Astigmatism distorts both your near and far vision and is caused by your eye being shaped more like a rugby ball than a football.
• Axis indicates the direction of the part of the lens that corrects your astigmatism.
• Prism is the bend of the light without altering its focus. Prisms are used to help people whose eyes do not work perfectly together (i.e. they turn in too much, or turn out too much), which may cause eyestrain or double vision.
• VA (visual acuity) refers to how clearly you can see shapes and detail from a set distance away (six metres in the UK), with your glasses on if you wear them. It is shown as a fraction, and the higher the number, the better your visual acuity. For example, if you have a VA of 6/6, you can see really clearly, and if your VA is 1/6, it means that you need to be a metre away from an object to see it as clearly as people can normally see from six metres away.
• Add (reading addition) refers to the additional magnifying power needed in the bottom part of a multifocal lens for reading and other close work. This is usually only needed for patients over 45, for whom focusing ability declines as part of ageing (presbyopia).
• Pupil distance (PD) is not a required component of your spectacle prescription, but is essential for ensuring your glasses are made correctly. The dispensing optician or spectacle maker will measure this when fitting your glasses. Your PD is different for distance and near vision