Common Investigations Your Eye Doctor May Ask You to Pay For!
Fluorescein Fundus Angiography (FFA):
In this test a dye, fluorescein Sodium is injected into the vein of your forearm. It takes around 10 seconds for the dye to spread into your retinal vasculature. This can be viewed by the observer using an ophthalmoscope, though more commonly, a digital camera called a fundus camera is used to take multiple photos of the retina shortly after dye injection.
Depending on the areas of perfusion (dye seen) or non-perfusion (dye not seen) or leakage of dye from the vessels into the retina, decisions are made in cases of diabetic retinopathy, age-related macular degeneration etc. about whether to do laser or give some injections or treat with medications .
HRT/GDX :
These are fancy names for computer software in which images of the optic disc and retina are analysed. Accurate measurements are made of optic nerve size, cup/disc ratio, retinal nerve fibre thickness. This is a useful adjunct to diagnose glaucoma and monitor its progression.
Electro-retinography (ERG):
This test is used to find out the function of the retina. This comes in useful when the retina appears normal on ophthalmoscopy but patient has poor vision and also when the retina is not clearly seen due to media opacities. If the ERG is poor or absent, the eye surgeon may decide that the visual prognosis is poor and further surgery to clear the media opacities like a corneal transplant for corneal opacities or a cataract extraction for a mature cataract is not warranted.
M-ERG or Multifocal ERG:
This is the newest version of the ERG. In this a colour map is generated with the area of maximum cone function (macula) showing a steep elevation while the area with no cones (optic nerve ) showing up as flat and blue in colour. In diseases like macular degeneration, the central hill is considerably flattened, making diagnosis a ‘no-brainer’.
Visual Evoked Potential (VEP):
In this test, either a very bright light (Flash VEP) or a checker board pattern is shone into the patient’s eye. The time taken for this to be perceived by the visual area of the brain (situated at the back of the head) and the intensity of the signal is recorded by sensitive electrodes placed at the back of the scalp. This measures the integrity of the visual pathway from the eye right up to the brain. In conditions like optic neuritis, where the optic nerve which carries signals from the eye to the brain is inflamed, the VEP will be reduced. On the other hand, a patient who is feigning blindness will have a normal VEP.
Can a person who has undergone one or more of these tests donate their eyes?
None of these tests is life threatening. However, it is proved that every patient who undergoes any of these tests will die some day, maybe months, years or decades later! If a patient were to die due to natural or accidental causes years after any of these tests were performed, the author does recommend donation of the eyes!
Common Investigations of Your Eye – Part 1
