Close
In the clinic, bestrophinopathies are diagnosed in a number of ways.
Visual acuity听
Vision, i.e. how well you can see, is a baseline test which is measured routinely in clinic. It is a good听guide听to听indicate听how听an eye听condition is progressing. Usually, vision is measured using a letter chart, more recently a computerized letter chart may also be used. The classic letter chart is known as a Snellen chart and newer computerised charts can use a newer measurement known as听LogMAR. Snellen is often the gold-standard and has one big letter at the top and the letters decrease in size and increase in number as one goes down the chart.听LogMAR听on the other hand has an equal number of letters on each line with logarithmic letter size progression.听听
听
Snellen Chart | LogMAR Chart |
Normal vision is usually noted as 6/6 on a Snellen chart, this is the equivalent of 20/20 vision. A visual acuity of 6/6听is described as being听able to see a letter or read a line at the distance of six meters away. Snellen charts are created and displayed in a way to mimic this (which is helpful as they no longer need to be physically 6 meters apart).听
听
Slit lamp and Optical coherence tomography (OCT)听
An ophthalmologist听is able to听look at the听back of the听eye听(Fundus)听in magnification through a听slit lamp. The doctor can also use a听volk lens (direct听ophthalmoscopy)听to听examine the fundus听听
An OCT听device听is now a mainstay in clinics.听OCT can be used to听localize regions and photograph them for historic keeping, as well as being able to measure thickness听of the retina. A Spectral-domain OCT (SD-OCT)听uses听long-wavelength light to light up the听layers of the听retina,听creating听a virtual image that a practitioner can navigate and 鈥榮croll鈥� through.听This image can be processed听to give a view through a slice of the retina, giving detail of the individual layers.听
Volk Lens | Slit Lamp |
OCT Image听
Fluorescein angiography (FA) and听fundus autofluorescence (FAF)听
FA involves the injection of a fluorescent dye into the blood stream (usually into the arm of a patient). The dye can听then be imaged as听it reaches the听blood vessels of the eye. FA gives information about the health of听retina听blood vessels,听highlighting听regions听where there听may听be听blockage听or infiltration of new vessels听and听deterioration of the retina.听听
FAF is a non-invasive听method that听detects听the听autofluorescent听(lipofuscin)听material听that听builds up听in the retina听when the RPE is no longer able to process retinal waste.
 |  |
听
Electroretinogram (ERG) and Electrooculogram (EOG)听
ERGs and EOGs are very important, particularly in diagnosing听bestrophinopathies. Both are examples of electrophysiology tests that听examine how the visual system听processes听information听i.e.听whether听the cells in our retina are working听correctly. ERGs measure the electrical potential which is generated from听cone and rod photoreceptors.听听The ERG test involves dilating the eye and placing an electrode听contact lens听onto the front of the eye,听which听records听the responses of the photoreceptors in response to听light stimulation. Different听light听stimuli听can be used,听giving听rise to different and specific recordings.听ERGs can also be obtained听using a hand-held device with an electrode placed under the eye.听
The听EOG听test听assesses听the function of the Retinal Pigment Epithelium (RPE) by measuring the standing potential, an electrical difference between the front and the back of the eye.听For the test, electrodes are attached to the skin around the eyes. The head is held in a stationary position and the patient is asked to focus on and follow a听moving听red light, moving听their听eyes side to side.听EOGs are听initially听recorded in听a听dark听room, the light is then switched on to continue the recording of the EOG in the light.听The听EOG听can听be听an important test for听diagnosing听bestrophinopathies.听
Visual field testing听
Visual field testing听can be used to see听whether a patient has any missing regions of vision.听The test, also known as perimetry, is听automated, and works听by听getting the patient to focus on an object on a screen and asking them to press a button when they see a flashing light in their peripheral vision.听Visual field testing allows practitioners to get a real gauge into what the patient sees and is often an important diagnostic test for certain eye conditions, such as glaucoma.听听
Genetic testing听
Diagnosis of a听bestrophinopathy听is听generally confirmed using听genetic testing. These听tests听are used to identify any changes in the听DNA听sequence of the听BEST1听gene.听To date,听over听250 distinct听disease-causing听mutations听have been recorded听in the听BEST1.听听
Once a patient is seen in clinic with a suspected听bestrophinopathy, they may be asked to provide a blood sample.听DNA听is then听extracted from the blood sample听for use in sequencing. A single gene听like BEST1听can be sequenced using a听targeted听technique called Sanger Sequencing,听which looks at the听order听of A, T, C and Gs in the听gene.听Alternatively, the DNA can be submitted for gene panel testing, where听a number of听genes associated with eye disease are sequenced. For example, the听Oculome听Panel uses high-throughput sequencing of 429 genes associated with eye disorders.
A family history may also be taken to understand the听inheritance pattern听of the disease.听 A听DNA听change which is present throughout the family history, often leads to more confidence听when diagnosing the disease.听This is why听the patient鈥檚 family may also be asked to provide blood samples so BEST1听and听it鈥檚听inheritance听pattern听can be examined in detail.听