A patient’s guide to hospital eye tests and examinations

A-scan ultrasound biometry

A-scan ultrasound biometry uses sound waves to measure the length of the eye. The A-scan device sends sound waves into the eye, and by measuring how long it takes for these waves to bounce back, it calculates the eye's length with high accuracy. This measurement is important for determining the right lens power if you need cataract surgery, as it helps the doctor select the lens replacement option that will give you the best possible vision after the surgery.

Autorefraction

In this test, a computer-controlled instrument determines the lens power required by your eye to focus light on your retina. During the test, you look into a machine called an autorefractor that shines light into your eye while you focus on a small image or a point of light. The machine automatically measures how the light reflects off your retina at the back of your eye, giving a reading of your eye's prescription. This test helps to get an accurate idea of any vision problems, like short-sightedness (myopia) or long-sightedness (hypermetropia), and it is often done before a more detailed eye examination.

Biometry

A biometry eye test measures the shape and size of the eye as well as assesses corneal curvature, and lens thickness while you look into a machine. This is often done in preparation for cataract surgery or refractive lens exchange procedure. The measurements help eye doctors choose the right intraocular lens (IOL), ensuring clear vision post-surgery.

B-scan ultrasonography

B-scan ultrasonography is an eye imaging technique that uses sound waves to create a two-dimensional image of the eye structures, including those at the back of the eye. It is particularly useful when the view of the retina is obscured, such as in cases of vitreous haemorrhage, dense cataract, or in other conditions that cloud the view. The test involves placing a small probe usually on the eyelid which sends sound waves into the eye. These waves bounce back and create a detailed image of the eye's interior, including the retina, optic nerve, and eye muscles. B-scan ultrasonography helps eye doctors detect and diagnose a range of eye problems, including both benign and potentially vision- and life-threatening conditions.

Corneal pachymetry

Corneal pachymetry measures the thickness of your cornea. Before the test, numbing eye drops are applied so you won't feel any discomfort. During the test, a small probe gently touches the surface of your eye, and the measurements are taken. Together with the corneal topography, this imaging test helps your consultant assess the health of your cornea and make decisions about your treatment and care.

Corneal topography

This is a computerised test that generates 3D image of the surface of the cornea which plays a crucial role in focusing light onto the retina, and its shape greatly affects your vision. During the test, you’ll sit in front of a device that takes multiple images of your cornea using light patterns, without touching your eye. The resulting map shows the curvature and shape of your cornea, helping eye doctors diagnose conditions like astigmatism, keratoconus, or other irregularities, and also plan for vision correction surgeries.

Endothelial Cell Count

Endothelial Cell Count is an imaging eye test that measures the number of specialised cells lining the back of the cornea. These cells are vital for keeping the cornea healthy and clear by helping to maintain its proper thickness and removing excess fluid. If the number of endothelial cells decreases too much, it can lead to corneal swelling and vision problems. This test is especially important for people considering eye surgery, such as corneal or cataract surgery, or for those with certain eye conditions, like Fuchs' dystrophy, that can affect the cornea.

Heldelberg retinal tomography (HRT)

HRT is an advanced eye imaging technique sometimes requested by the consultants as an additional tool to detect and monitor eye diseases like glaucoma. It creates detailed pictures of the retina and the optic nerve using a special diagnostic laser that scans the back of the eye and provides precise measurements of the shape and thickness of the retina and optic nerve. The procedure is not invasive, and the diagnostic laser uses a safe low intensity light.

Keratometry

Keratometry measures the curvature of your cornea to understand how well your cornea is focusing light. During this imaging test, you look into an instrument, called a keratometer, which shines a light onto your cornea and measures how the light reflects back. This helps eye doctors determine the shape and curve of your cornea, which is important for diagnosing conditions like astigmatism, fitting contact lenses, and planning eye surgeries such as cataract surgery.

OCT scan

An optical coherence tomography (OCT) is a non-invasive imaging test that uses light waves to take cross-sectional scans of the retina in the back of the eye. During the scan, you look into a machine that uses light waves to capture cross-sectional images of your retina, much like an ultrasound uses sound waves. The test helps eye doctors see each layer of the retina in detail, allowing them to detect and monitor conditions like age-related macular degeneration (AMD), diabetic retinopathy and glaucoma. This scan is especially useful for catching eye problems early, often before symptoms appear.

Refraction

Refraction is an eye test that measures how light bends as it passes through the eye, helping to assess vision and determine the right spectacle prescription if you need one. During the test, you are asked to look through a trial frame or a special device called a phoropter and view letters on a chart while switching between different lenses. The goal is to find the lenses that make the letters appear the clearest.

Schwind Peramis

The Schwind Peramis test uses a high-resolution device that maps the cornea while measuring vision imperfections (aberrations) in the eye. Using a special sensor, it detects these imperfections with exceptional precision. This allows for a detailed comparison of data from both the cornea and the entire eye, pinpointing the exact location of any irregularities. This test is often used in planning laser eye surgeries. It is quick and non-invasive, you simply look into the machine while the device captures the necessary data.

Slit-Lamp Examination

A slit-lamp examination is a consultant-led test that provides a detailed view of the different parts of the eye, such as the eyelids, cornea, iris, lens, and the anterior chamber (the fluid-filled space between the cornea and the iris). The consultant is also able to examine the back of the eye by using some special lenses. During this exam, you sit in front of a special microscope with a bright light, which is called a slit lamp because it shines a thin, focused beam of light into your eye. This helps the consultant check for signs of various eye conditions and assess the overall health of your eyes.

Tonometry – applanation

This is a consultant-led examination during which a special device is used to gently touch the surface of the eye to measure the pressure inside the eye. Before the test, numbing eye drops are applied so you won't feel any discomfort. Applanation tonometry provides a very accurate measurement of eye pressure including in patients with irregular corneas, higher eye pressure, or certain eye conditions.

Tonometry -iCare

This is a contact eye pressure test that requires no drops or air pressure. A small handheld device called the iCare uses a rebound measuring principle when a tiny probe briefly pops out, touches the cornea and rebounds back while taking 6 measurements of the intraocular pressure.

Tonometry (ORA)

Tonometry, also referred to as ORA and known as the "air puff test," measures the pressure inside your eye, which is an important factor in detecting and monitoring glaucoma. During the test, you are positioned on a machine and a small puff of air is directed at your eye. This puff of air measures how the eye responds, allowing the machine to calculate the internal pressure without touching the eye. The test only takes a few seconds.

Ultrasound biomicroscopy

Ultrasound biomicroscopy is a specialised eye imaging technique that uses high-frequency sound waves to create detailed images of the front part of the eye, including structures like the iris, cornea, lens, and the drainage angle where fluid flows out of the eye. This test is particularly useful when a more precise look at the eye tissues is needed; it is a non-invasive procedure that is helpful for diagnosing and managing various eye conditions.

Ultrawide imaging

Ultrawide field imaging captures more than 80% of the retina in a single image allowing eye doctors to see areas that are often difficult to view. It’s a quick, comfortable, and non-invasive procedure where you simply look into a specialised camera for a few seconds. The test can help eye care professionals detect various stages of retinal and choroidal diseases, damage to the retina, and blood vessel abnormalities that may affect vision.

Visual acuity

This test is first and one of the most important parts of an eye exam commonly assessing the clarity and sharpness of your vision and any changes in it over time. During the test, you are asked to read letters or symbols from a chart, usually from a distance, with one eye at a time, while covering the other. The letters get progressively smaller to determine the smallest size you can read accurately. At Moorfields Private it is performed using a computerised Snellen chart.

Visual field

The test is used to assess and monitor central and peripheral vision. It provides important information about the function of the brain, retina and optic nerve and helps to detect certain eye conditions, most commonly glaucoma, at the early stages. During the test which usually takes just a few minutes, you are asked to look straight ahead into a device while small lights or objects appear in different areas of your visual field. You press a button whenever you see them, without moving your eyes.

Written in association with

Moorfields Private ophthalmic and nursing teams, including:

Lea Cabaluna (Matron), Kiruthiga Alagarasan Kamsaladevi (Senior Ophthalmic and Vision Science Practitioner and Training Lead), Aron Medroso (Senior Ophthalmic Technician), and Andrea Church (Sister).