The term fundoscopy describes the examination of the eye-fundus, which is the inner lining of the back of the eye. Another name for this examination is ophthalmoscopy.
What is the ocular fundus?
The fundus is made up of the retina (including the macula), the optic nerve and the retinal blood vessels. The retina is the structure which acts like the film in a camera. When light strikes its sensors (rods and cones), the light stimulus is converted into signals, which are transmitted along the nerve fibres of the optic nerve to the brain, where these signals are processed. The retina covers an extensive part of the eye, extending well forwards towards the front, so that examination of these peripheral parts of the retina requires a different technique from the conventional method, which will be described later. The retinal blood vessels form a micro-circulation, making the eye-fundus unique in that is the only part of the human body where such small vessels can be directly observed.
The reason for fundoscopy
Fundoscopy is part of a routine eye examination, which enables the evaluation of retinal symptoms and detects many conditions such as retinal detachment, retinal degenerations (the best-known being macular degeneration), diseases of the optic nerve, like glaucoma, and inflammations. Certain brain disorders may also be detected during a fundoscopy. Abnormalities of the retinal blood vessels are useful in the assessment of conditions like high blood pressure or diabetes. The health of these blood vessels can give a lot of information regarding the health of vessels in other areas of the body, which is the reason why doctors from diverse disciplines often do this examination.
How fundoscopy is performed
There are 4 methods.
You will be seated in a chair in a darkened examination room. The instrument, called an ophthalmoscope, is about the size of a small torch. It has a light source, a mirror, a small disc with rotating lenses for focusing and a small aperture for the examiner to look through. The instrument is held a few centimetres from the eye without touching the eye. This will take only a few minutes and there will not be any discomfort. You might already have experienced this procedure at some point while visiting your GP or optometrist.
Again you will be seated with your chin resting on a support. This time the ophthalmologist will use the slit lamp microscope as a light source while holding the focusing lens in his hand between the light and the eye. The advantage of this method is that it allows 3-Dimensional viewing and presents a much wider view of the fundus. The ophthalmologist often prefers this method.
The next method is known as indirect fundoscopy. You will be in a reclining position, like during a dental examination. The examiner will be wearing a light on a head band like a miner, or on a modified spectacle frame. This time the light will be much brighter, providing a very wide view. Now the doctor will be able to examine the peripheries of the retina to detect things like small holes, which may cause retinal detachment.
Once more you will be seated in a chair and with the help of the slit lamp a contact lens is placed directly on the eye, resting snugly on the cornea. A drop of local anaesthetic is instilled beforehand to make the examination more comfortable. The light-intensity varies and is sometimes quite bright to enable the examiner to look through hazy structures, like cataracts, within the eye. Because of the contact there will be a reflex tendency to try and close the eye, but as you become accustomed to the lens, the light, and the absence of pain, you will be able to relax your eyelids. The examination usually takes about 10 minutes.
How to prepare for the test
For methods 1 and 2 there is no preparation. If, however, there is a cataract or anything else causing a haze, the doctor will need to use a drop to dilate the pupil before proceeding to methods 3 and 4. You should inform your doctor of any medication to which you are allergic or that you are using at the time, or if you have glaucoma or a family history of glaucoma.
Are there any risks?
Fundoscopy is virtually risk free. Obviously the bright lights are sometimes uncomfortable and you may note at the end of the examination that your vision is very dark; this will soon wear off and there will not be any injury to the eye. Very rarely the dilating drop may cause the eye-pressure to rise, precipitating an attack of acute glaucoma. Should this occur, you will experience a pain quite different from the grittiness felt at first, and such development should immediately be reported to your doctor. Reassuringly, your doctor can often predict which eyes are likely to react in this way and will take appropriate steps. Bear in mind that sometimes one has to take small risks in order to diagnose a problem. Dilating drops will also affect the focusing ability of the eye and, especially when having both eyes dilated, you should arrange for someone to drive you home afterwards. And, if possible, choose a day when you are not committed to doing much reading or other fine work. The effect varies from person to person.
Take dark glasses along; it will be much more comfortable while the pupil is dilated.
What are the limitations of Fundoscopy?
There are retinal diseases where, despite the presence of visual defects, the retina may look entirely normal, or show only very subtle abnormalities or variations on the norm. Your doctor will then proceed to evaluate these eyes, using other methods such as specialised photography, or measuring the electrical potentials of the retina, as one does with the heart, (ECG) or brain, (EEG).