A lot of people ask me if things were different when I returned to optometric practice after an eight-year career break. My reply is that testing sight is the same as it’s always been, but the automated optical equipment we have at our disposal has advanced in leaps and bounds. There has always been so much more to an eye examination than prescribing spectacles. Optometrists can tell a lot from the eyes. We can detect not just ocular problems, but systemic ones too, things that might affect one’s general health. By carrying out various tests, we might see signs of relatively common conditions such as diabetes or high blood pressure. Less common are findings that suggest a neurological condition, such as multiple sclerosis or a brain tumour.
Optical equipment and procedures vary from practice to practice. In some, the patient will have a series of tests on pre-test optical instruments before they see the optometrist. In others, the optometrist will carry out everything themselves during the test. There’s no right or wrong way.
This is a brief guide to some of the automated equipment you might encounter during an eye examination.
An auto refractor measures the correction required to see clearly. The patient sits at the machine, which has a head and chin rest, and looks at an image which goes in and out of focus. The machine shines a light into the eye and measures how the light changes as it bounces off the back of the eye. These readings are combined and converted into a spectacle prescription. Some autorefractors can measure the curvature of the cornea too which is useful for fitting contact lenses.
An autorefractor will never replace an optometrist, but it does provide an accurate starting point which might in turn, make the eye examination a little quicker. The objective nature of this test means it’s excellent for those patients who, for example, cannot communicate or for whom the subjective part of the eye test, (telling the optometrist which is better or worse), might be a challenge. An optical assistant or a dispensing optician, (DO) is likely to perform autorefraction.
A focimeter is a small desktop instrument that looks like a microscope. It might be automated or it might be manual. It measures the power of the lenses in a pair of spectacles. I have a manual one in my consulting room. I use it to see what strength a patient’s glasses are if they are new to our practice and they don’t have a copy of their prescription. Sometimes, focimetry is part of pre-screening. An optical assistant or DO might measure the patient’s glasses before they go through to the optometrist.
A tonometer is a piece of optical equipment that measures the pressure in the eye, (the intraocular pressure or IOP). A non-contact version blows a tiny puff of air onto the front of the eye. It measures the pressure indirectly by the eye’s resistance to the puff. It can make the patient jump a little but it is completely painless. Tonometry is one of the screening tests for glaucoma, an eye disease most commonly characterised by raised IOP. Like autorefraction and focimetry, non-contact tonometry might be part of pre-screening. The non-contact tonometers at the practice I work in are in the consulting rooms, so the optometrists take the readings.
There is another type of tonometry, called applanation tonometry. For this, the optometrist numbs the eye with anaesthetic drops and touches the front surface of the eye gently with a probe. It is highly unlikely that anyone other than the optometrist would perform applanation tonometry.
Perimeter (Visual Field Screener)
A perimeter tests the visual field. When we look at something we see the object we are looking at and also what surrounds it. The area we see, (without moving the head or eye), is called the visual field. The visual field test gives a good indication of the health of the eyes and the whole visual system.
Most visual field screeners require the patient to sit down to look into the machine. The test is performed on each eye separately, while the other eye is covered with an eyepatch. During the test, the patient has to look at a spot in the centre of a screen and respond when the target is seen. The target is usually one or more lights that flash on and off, elsewhere on the screen. The patient might have to click a button once for every target seen, or may asked to respond verbally.
The visual field test can be carried out before, during or after the eye examination. It is particularly useful to help diagnose and monitor glaucoma.
A fundus camera takes photographs of the back of the eye. Again, it might be part of a pre-test, or it might be something the optometrist does during the eye examination. The patient sits with their forehead and chin against a rest while the photograph is taken. Fundus photographs are very useful for for monitoring the progression of certain eye condition or diseases. They are also used to document changes in a known eye conditions, for example, diabetic retinopathy, glaucoma and age-related macular degeneration (AMD). The patient can see the resultant photographs of their own fundi, which is useful if the optometrist needs to explain anything.
An optomap uses scanning laser technology to produce is an ultra-widefield digital image of the retina. The images help to both diagnose eye-conditions (glaucoma, macular degeneration) and those general health conditions that affect the eye, (e.g.diabetes, hypertension). Getting an optomap image is fast, painless and comfortable. Nothing touches the eye at any time. The patient looks into the device one eye at a time and will see a flash of light when the image is taken.
Optical Coherence Tomographer (OCT)
Of all the optical equipment available, the optical coherence tomographer, is, in my opinion at least, THE most exciting. I’m fortunate that the practice I work in has one. Like most of the screening tests I have mentioned here, the patient sits with their chin and forehead against a rest during the scan. OCT uses light waves to take cross-section pictures of the retina. This allows the optometrist to see each of the retina’s distinctive layers. The OCT software produces an array of metrics and images which the optometrist studies and saves in the patient record to compare to previous and subsequent scans. It is fast, painless and non-invasive for the patient. We use the information to diagnose and to monitor eye-conditions. It is particularly useful for seeing retinal detachments or tears and wet macular-degeneration because these can’t always be seen during other methods of examination.
In most cases, the optometrist will share and discuss with the patient the images taken with a fundus camera, an optomap and/or OCT during the eye examination. Optomap and OCT imaging optical equipment might not be available at all optometric practices but there’s no doubt that it’s the way forward. It’s an exciting time for the world of optometry
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