In the clinic, bestrophinopathies are diagnosed in a number of ways.
Visual acuityÌý
Vision, i.e. how well you can see, is a baseline test which is measured routinely in clinic. It is a goodÌýguideÌýtoÌýindicateÌýhowÌýan eyeÌýcondition 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 asÌýLogMAR. 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.ÌýLogMARÌýon the other hand has an equal number of letters on each line with logarithmic letter size progression.ÌýÌý
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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 6/6Ìýis described as beingÌýable 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).Ìý
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Slit lamp and Optical coherence tomography (OCT)Ìý
An ophthalmologistÌýis able toÌýlook at theÌýback of theÌýeyeÌý(Fundus)Ìýin magnification through aÌýslit lamp. The doctor can also use aÌývolk lens (directÌýophthalmoscopy)ÌýtoÌýexamine the fundusÌýÌý
An OCTÌýdeviceÌýis now a mainstay in clinics.ÌýOCT can be used toÌýlocalize regions and photograph them for historic keeping, as well as being able to measure thicknessÌýof the retina. A Spectral-domain OCT (SD-OCT)ÌýusesÌýlong-wavelength light to light up theÌýlayers of theÌýretina,ÌýcreatingÌýa virtual image that a practitioner can navigate and ‘scroll’ through.ÌýThis image can be processedÌýto give a view through a slice of the retina, giving detail of the individual layers.Ìý
Volk Lens | Slit Lamp |
OCT ImageÌý
Fluorescein angiography (FA) andÌýfundus autofluorescence (FAF)Ìý
FA involves the injection of a fluorescent dye into the blood stream (usually into the arm of a patient). The dye canÌýthen be imaged asÌýit reaches theÌýblood vessels of the eye. FA gives information about the health ofÌýretinaÌýblood vessels,ÌýhighlightingÌýregionsÌýwhere thereÌýmayÌýbeÌýblockageÌýor infiltration of new vesselsÌýandÌýdeterioration of the retina.ÌýÌý
FAF is a non-invasiveÌýmethod thatÌýdetectsÌýtheÌýautofluorescentÌý(lipofuscin)ÌýmaterialÌýthatÌýbuilds upÌýin the retinaÌýwhen the RPE is no longer able to process retinal waste.
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Electroretinogram (ERG) and Electrooculogram (EOG)Ìý
ERGs and EOGs are very important, particularly in diagnosingÌýbestrophinopathies. Both are examples of electrophysiology tests thatÌýexamine how the visual systemÌýprocessesÌýinformationÌýi.e.ÌýwhetherÌýthe cells in our retina are workingÌýcorrectly. ERGs measure the electrical potential which is generated fromÌýcone and rod photoreceptors.ÌýÌýThe ERG test involves dilating the eye and placing an electrodeÌýcontact lensÌýonto the front of the eye,ÌýwhichÌýrecordsÌýthe responses of the photoreceptors in response toÌýlight stimulation. DifferentÌýlightÌýstimuliÌýcan be used,ÌýgivingÌýrise to different and specific recordings.ÌýERGs can also be obtainedÌýusing a hand-held device with an electrode placed under the eye.Ìý
TheÌýEOGÌýtestÌýassessesÌýthe function of the Retinal Pigment Epithelium (RPE) by measuring the standing potential, an electrical difference between the front and the back of the eye.ÌýFor 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 aÌýmovingÌýred light, movingÌýtheirÌýeyes side to side.ÌýEOGs areÌýinitiallyÌýrecorded inÌýaÌýdarkÌýroom, the light is then switched on to continue the recording of the EOG in the light.ÌýTheÌýEOGÌýcanÌýbeÌýan important test forÌýdiagnosingÌýbestrophinopathies.Ìý
Visual field testingÌý
Visual field testingÌýcan be used to seeÌýwhether a patient has any missing regions of vision.ÌýThe test, also known as perimetry, isÌýautomated, and worksÌýbyÌýgetting 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.ÌýVisual 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.ÌýÌý
Genetic testingÌý
Diagnosis of aÌýbestrophinopathyÌýisÌýgenerally confirmed usingÌýgenetic testing. TheseÌýtestsÌýare used to identify any changes in theÌýDNAÌýsequence of theÌýBEST1Ìýgene.ÌýTo date,ÌýoverÌý250 distinctÌýdisease-causingÌýmutationsÌýhave been recordedÌýin theÌýBEST1.ÌýÌý
Once a patient is seen in clinic with a suspectedÌýbestrophinopathy, they may be asked to provide a blood sample.ÌýDNAÌýis thenÌýextracted from the blood sampleÌýfor use in sequencing. A single geneÌýlike BEST1Ìýcan be sequenced using aÌýtargetedÌýtechnique called Sanger Sequencing,Ìýwhich looks at theÌýorderÌýof A, T, C and Gs in theÌýgene.ÌýAlternatively, the DNA can be submitted for gene panel testing, whereÌýa number ofÌýgenes associated with eye disease are sequenced. For example, theÌýOculomeÌýPanel uses high-throughput sequencing of 429 genes associated with eye disorders.
A family history may also be taken to understand theÌýinheritance patternÌýof the disease.Ìý AÌýDNAÌýchange which is present throughout the family history, often leads to more confidenceÌýwhen diagnosing the disease.ÌýThis is whyÌýthe patient’s family may also be asked to provide blood samples so BEST1ÌýandÌýit’sÌýinheritanceÌýpatternÌýcan be examined in detail.Ìý