If it is your first time going for a comprehensive eye check or it has been too long since your last one, a read of the following sections will help you understand the different types of tests that are typically done during an eye check to help reduce your doubts and questions.
The following article will cover the series of tests that are typically done for a new eye check visit to check your vision and the health of the front and back of your eyes. Your eye care professional (ECP) will determine the course of your consultation depending on the reason and nature of your visit. The sequence of tests done, examination tools, and the equipment used may vary between clinical practices and countries, and thus this article does not hold precedent over what you experience at your eye check appointment.
To start off
Medical and past eye history taking
If you are seeing a new ECP or having your first eye check, the ECP will ask questions about your general health, history of eye diseases, eye trauma or eye surgery, family history of eye diseases, the reason for your visit, your visual needs, and if any, symptoms that you are currently experiencing. Collecting this information helps your ECP to decide on what tests should be conducted during your eye check. If you are returning to the ECP for a review, they will ask you about any new symptoms, changes in your general health, and progress on a treatment plan implemented since your last visit.
Next is a vision assessment
Visual acuity (VA)
Visual acuity checks how well you can see and allows your ECP to decide on what tests should be conducted during your eye check. There are a variety of VA charts, of which the two main VA charts used are the Snellen (VA measured in feet or metres, such as 20/40 pr 6/12) and LogMAR (VA measured in decimal points, such as 0.30) charts.
VA is conducted one eye at a time and when reading with the right eye, the ECP will give you an occluder or paddle to cover the left eye and vice versa. The ECP will have you read letters or numbers from a chart at a distance that will get smaller as you read down each line. Your VA is then recorded as the smallest line that you can read.
VA is also checked at near with a hand-held chart. According to your ECP’s judgement, if you have reduced vision or cannot see the 6/6 or 20/20 line, a pinhole occluder is used to determine if the reduced vision is caused by a refractive error (VA will improve with pinhole) or by an eye disease (VA that typically does notimprove with a pinhole).
For infants, ECPs will check their vision by assessing their response to light and their ability to follow a target. For children at the preschool age or those still learning to identify alphabets, ECPs will use charts with symbols, pictures, or matching alphabets on the screen by pointing to the corresponding letters on a chart held at a near distance.
Figure 1. A visual acuity test chart.
If you wear glasses, the degree or power of your glasses is measured using an equipment called a focimeter and the readings serve as a reference point for comparison with results from a subjective refraction.
To determine the estimated degree or prescription of lenses that your eyes require to see clearly, a quick and painless test called an auto-refraction is done. Auto-refraction measures how light is affected as it reflects through the eyeball. The readings from an auto-refraction serve as a baseline before a more detailed subjective refraction is performed.
Figure 2. An eye doctor conducting an eye check on a child.
Refraction is the way light bends when entering the eye to form an image on the retina. A refraction test determines the type of refractive error (short-sightedness or myopia, long-sightedness or hypermetropia, astigmatism, or presbyopia) and the prescription of the lenses required to correct the refractive error, allowing you to see clearly. During a refraction, the ECP will ask you to compare various lenses and determine which lens makes your vision clear.
Your response during a refraction test is crucial. In some instances, among both children and adults who are unable to give accurate responses during the refraction test, an additional test called retinoscopy is done. A retinoscope is used to shine light into the eye to check how light bends in the eye and this test is done in dim lighting.
Figure 3. An eye doctor conducting a retinoscopy test.
Accommodation, which is the focusing ability of our eyes to maintain clear vision at different distances, is active in children and young adults. The amount of accommodation can influence the refraction findings, making it appear lower or higher than it is. As such, cycloplegic eye drops that dilate the pupils and temporarily relax the muscles responsible for accommodation are used, allowing the optometrist or ophthalmologist to do a cycloplegic refraction to determine the full extent of your refractive error.
The combination and strength of cycloplegic drops vary according to specific country regulations, but since the accommodation temporarily relaxes, it causes blurring of vision that recovers within a few hours after instillation of the drops.
Assessing the vision function
Checking the pupil
The pupil is the dark spot in the center of the eye. Pupils are an indicator of the communication pathway between the brain and the eye. When checking the pupils, the ECP shines a pen torch to check that both pupils are equal in size, perfectly round, and are reacting to light. Pupils are checked in both dim and bright lighting conditions. The pupils are usually checked during the first visit, and if there are any symptoms related to the pupil or if the ECP suspects any pupil reaction abnormalities.
Colour vision test
Colour vision tests are used to detect colour vision deficiency or colour blindness. There are a few types of colour vision tests that are used to screen for colour vision abnormalities, with the common one being an Ishihara test.
The Ishihara test displays numbers or symbols (dots) that are of a different colour than the dots surrounding them (see Figure 4 below), and you would have to recognize the number or pattern on the test plates. If the colour vision tests indicate a potential colour vision abnormality, a more detailed test called a Farnsworth Munsell 100 hue test is done. This test evaluates the extent to which a person with colour vision deficiency can differentiate between specific colours and hue variations within a specific colour spectrum.
Colour vision tests are usually done during the initial visit to an ECP and is only repeated at subsequent visits if symptoms are reported or if there is an eye disease that can affect the perception of colour.
Figure 4. An Ishihara test chart.
A cover test measures how well both eyes are working with each other and checks for the presence of eye deviation by testing if one eye is working harder than the other. A cover test is done at distance and near. The ECP will ask you to focus on a target and then cover and uncover each of your eyes to check for an eye deviation called a tropia and then cover either eye alternately to check for an eye deviation called a phoria.
A cover test is usually done during their initial visit to an ECP. Subsequently, a cover test is done if there is a presence of an eye disease that may be causing an eye deviation or if there are symptoms that necessitate the test.
Ocular motility test
There are six extraocular muscles in each eye (twelve in total for both eyes). The ocular motility test assesses the health of the extraocular muscles. During an ocular motility test, the ECP will ask you to keep your head still and ask you to follow the movement of a pen torch or target in nine different gazes with just your eyes.
Ocular motility is usually done in children during their first visit to an ECP. It can also be conducted in adults at the discretion of the ECP, particularly in cases of strabismus in adults, the presence of trauma and neuro-ophthalmic disorders, or just as a routine check.
Stereopsis is the ability of both eyes to work together for depth perception and to appreciate the 3D nature of objects. Depending on the type of test being used, you may or may not be required to wear 3D glasses during the stereopsis test. Stereopsis is usually checked in children during their initial visit. The test can also be conducted in adults at the discretion of the ECP, particularly in cases of amblyopia, strabismus, cataract, and age-related macular degeneration.
Amsler grid test
The Amsler grid is a square-shaped grid used to detect or monitor areas of distorted vision or missing areas in your central field of vision caused by disorders of the macula (the area of the retina that allows us to enjoy clear central vision and colour), a common one being age-related macular degeneration.
The Amsler grid test is typically done by an ECP and when necessary, also given as a printout for people to take home and monitor their central vision. The Amsler grid test is done one eye at a time and people with hypermetropia, presbyopia, and/or astigmatism would need to wear their glasses during the test. The Amsler grid test is typically not done routinely. This test is conducted if there is an eye disease that is causing changes in central vision or if there are symptoms that necessitate it.
Figure 5. An Amsler grid test chart.
Examining the health of the front part of your eyes
Measuring eye pressure
Tonometry is a test used to measure the pressure inside the eyes, also known as the intra-ocular pressure (IOP). There are four types of tonometry that are used to measure IOP, where your ECP will decide on the type of test to the best of their expertise or availability in their practice.
- A non-contact tonometer will blow a light puff of air into your eye, while you’re looking at a tiny light inside the machine. Eye pressure readings are done three times and an average of the three values is recorded. The tonometer does not directly touch your eyes and it is a quick and painless process.
- An i-care is a portable handheld device used to measure IOP in which a small probe gently taps on your cornea to get a measurement. An anaesthetic eyedrop (used to numb the eye by temporarily blocking pain signals at the nerve endings in the eye where sensation usually returns about 20 minutes after instillation) is not required as you will barely feel the probe touching your cornea.
- A tonopen is a handheld device that resembles a large marker and IOP is measured by gently tapping the cornea. An anaesthetic eye drop is not required as you will barely feel the probe touching your cornea.
- Goldman applanation tonometry measures the force required to flatten an area of the cornea. This test involves a slit lamp (will be mentioned in the following section) and a blue light shone from a tiny flat-tipped cone that gently meets your cornea, for which an anaesthetic eye drop is instilled to ensure comfort during the test. A yellow dye called sodium fluorescein is instilled before the test and is washed out by your tears within minutes after instillation. Instillation of sodium fluorescein may leave dark yellow or orange tears on your face which are easily removed with water.
The ECP uses a slit lamp, or microscope to examine the structures of your eye under high magnification coupled with a light. A slit lamp resembles a larger version of a microscope that is used in laboratories.
During the slit lamp exam, the ECP will ask you to rest your chin and forehead forward or position your head with a forehead strap and begin examining the structures at the front of your eye: eyelids, cornea, conjunctiva, iris, and lens.
Examining the health of the back part of your eyes
For a better view and thorough evaluation of the retina (light-sensitive tissue at the back of the eye), the ECP may use dilating eye drops to temporarily make your pupils larger. These dilating eye drops usually take about 20 to 30 minutes to start working. It is important to note that dilating eye drops are different from the cycloplegia eye drops that were mentioned earlier in this article.
When your pupils are dilated, more light enters your eye, and you will become more sensitive to light and may have difficulty focusing on near objects. These effects are temporary and typically last for four to six hours. To minimize glare and sensitivity to light, you should bring sunglasses with you. For safety reasons, since your vision will be blurred temporarily, you should avoid driving after your pupils are dilated.
Evaluation of the retina can be conducted by using the following methods:
- Ophthalmoscope: a hand-held instrument held close to your eye
- Volk lens: a thick condensing lens called a volk lens is held near your eye during the slit lamp exam
- Binocular Indirect Ophthalmoscopy (BIO): by shining a bright light from a headband instrument worn by the ECP and holding a thick condensing lens close to your eye.
- Retinal imaging device: captures images of the retina and depending on the type of technological system being used, images of the retina can be captured with or without dilation. A high-resolution image of the retina allows your ECP to see early signs of eye diseases, monitor any eye diseases, or present the image when seeking a second opinion with a fellow ECP to decide on a referral or the best course of treatment, if needed. Across all models of retinal imaging devices, the method of capturing is similar, in which you would need to look at a target inside the machine and hold your blink while the machine releases a camera-like flash of light to capture the image.
Among many additional diagnostic imaging tests available, the following section covers the three main additional diagnostic tests. The three tests mentioned below are conducted one eye at a time and are similar to the slit lamp exam, which requires you to rest your chin and forehead forward during the test. Based on the results of the tests conducted during your eye check explained above, your ECP will decide if these additional tests are required to aid in the diagnosis and/or management of the eye disease.
Humphrey’s visual field (HVF)
HVF is a test to measure the sensitivity of your peripheral vision (vision at the sides). There are a few types of test selections on a HVF machine and the ECP will decide on the required type. The most common type of HVF test is a 24-2. Your peripheral vision is checked by fixating at a tiny light in the center and lights of different intensity are randomly projected within the machine to which, you would need to press a handheld clicker.
During the HVF test, you can blink as per normal. However, it is important to fixate on the tiny light in the center and not on the peripheral lights that are appearing randomly. A HVF test is conducted one eye at a time and your prescription lenses are inserted in a lens holder near the chin rest of the machine. The 24-2 takes about 3 to 5 minutes per eye and the duration is longer for other HVF test types. Among the many eye diseases, HVF is commonly used for the detection and monitoring of glaucoma.
Figure 6. A Humphrey’s visual field (HVF) test machine.
Optical coherence tomography (OCT)
An OCT generates a 3D or cross-sectional image of the retina by providing a detailed analysis of your eye’s internal structures using light waves. An OCT can detect the early onset of eye diseases, monitor their progression, and the efficacy of the treatment being used.
Similar to a retinal imaging device, you would need to look at a target in the machine and hold your blink. Depending on the model, the machine may release a camera-like flash of light to capture the image. OCT scans are used to screen for eye diseases such as diabetic retinopathy, hypertensive retinopathy, age-related macular degeneration, and glaucoma.
Corneal topography creates a 3D map of the surface curvature of the cornea and is used to diagnose, monitor, and treat eye diseases. Corneal topography is also used to fit orthokeratology lenses, to plan surgeries such as laser vision correction, or to diagnose and manage eye diseases such as keratoconus.
For people going for a review or repeat visits to an ECP, please note that the type and sequence of the tests conducted are dependent on the results of your first or most recent eye check and will be determined by your ECP. It is best to communicate with your ECP about any concerns that you might have.
At the end of the eye check
Your ECP will assess all results and suggest the corrective vision solutions, initiate any treatment if necessary, or may refer you to an Ophthalmologist or other health professionals if required.
We hope that this article has been useful for you to better understand what happens during an eye check but please note that your ECP is best placed to determine the necessary tests catered for your individual needs.