Ocular Investigations
There are many Ocular Investigations (Eye Examinations) that are available. Described below are the various examinations and tests that are in common use at our clinic. You may find it useful to refer to the diagram of the eye in the Glossary.
Slit-lamp examination
The slit-lamp allows a highly magnified view of the eye, with well-controlled illumination providing a clear view of the tumour. The source of light can either be diffuse or slit-like (hence the name of the instrument). It is possible to adjust the length of the slit, which can therefore be used to measure the size of a tumour.
A number of hand-held lenses are available to facilitate examination. For example, the Goldmann three-mirror contact lens enables the examiner to see round corners whereas the 'Superfield' lens allows a wide-angle stereoscopic view of a large area of the back of the eye.
Ophthalmoscopy
- Binocular indirect ophthalmoscopy
There are two types of ophthalmoscopy, direct and indirect. With direct ophthalmoscopy the examiner sees the retina directly. With indirect ophthalmoscopy, a hand-held lens is used to project an image in space, a few centimetres in front of the eye, and it is this image that is seen by the examiner. Compared to direct ophthalmoscopy, indirect ophthalmoscopy produces a much wider field of view, which is also three-dimensional and therefore much easier to interpret.
Most tumours can be diagnosed by their appearance on ophthalmoscopy or slit-lamp examination. It may be necessary to monitor a lesion over several months or years to detect growth, thereby confirming the diagnosis.
Difficulties can arise if the tumour is not visible because of haemorrhage or cataract. These can be overcome by treating the cataract, waiting for the haemorrhage to clear spontaneously, or perhaps removing the haemorrhage surgically.
Colour photography
Colour photography is useful for documenting the appearances of the tumour so that any change over time is readily detected. Such photography is possible with tumours extending far back in the eye, near the fovea and optic disc.
Angiography
Angiography is performed by injecting a dye into a vein in the arm and then taking a succession of photographs of the back of the eye.
- Fluorescein angiogram
The dye is fluorescent; that is, it has the property of changing light from one colour to another. The photographs are taken using a flash and a filter of the appropriate colours. The dye can therefore be seen shining brightly as it passes through the arteries and veins and as it leaks through any abnormal areas. There are two kinds of angiography: fluorescein angiography and indocyanine green angiography, which use blue and red light respectively.
The injected fluorescein dye tends to cause yellowing of the skin and urine for a few hours and about one in ten patients experience transient nausea, although vomiting is rare. About one in 2000 patients develops an allergic reaction, which very rarely is fatal (i.e., in about one in two hundred thousand patients).
Optical Coherence Tomography (OCT)
This camera optically produces an image showing a 'slice' of the retina, with the various layers having different colours. It is useful for detecting abnormal fluid at the back of the eye.
- Optical Coherence Tomography Scan of macula
- Optical Coherence Tomography Scan schowing Cystoid Macula Oedema
Ultrasonography
With ultrasonography, high-frequency, inaudible sound waves are emitted into the eye. These waves bounce off any tissue surface back towards the probe, which measures the 'loudness' of the reflected sound and the time taken for the sound to travel into the eye and back again. The intensity of the reflected signal gives an idea of the 'hardness' of the reflecting tissue. The time taken for the reflected signal to be received gives an indication of the distance travelled by the sound.
- Professor Damato performing ultrasonography with the assistance of a nurse
A-scan ultrasonography produces a linear signal, with a series of waves, which reveal the consistency of the tumour. With B-scan ultrasonography, the beam sweeps the eye from side to side, producing a visual slice of the eye and a good idea of the size and shape of any tumour in the eye.
- Ultrasonogram, with tumour at back of eye, next to nerve
Ultrasonography has several applications in assessing an eye with a tumour:
- If the media are opaque, it enables the tumour to be detected.
- Ultrasonography can also reveal tumour extension outside the eye.
- By demonstrating a collar-stud shape, ultrasonography can help establish the diagnosis.
- With calipers, it is possible to measure tumour thickness and basal diameter. These measurements are useful when selecting treatment and measuring how a tumour is growing or regressing over time.
- Ultrasound probe in position
The front of the eye is assessed with a special high-frequency probe, which requires the use of a small eye-bath or a sheath filled a clear jelly-like fluid.
Magnetic Resonance Imaging
Magnetic resonance imaging is performed by emitting pulses of magnetism through the body so that all the atoms spin in the same direction thereby giving rise to electrical fields, which are measured and converted into images. This method produces very clear pictures of the eye, with different tissues showing different degrees of brightness.
Magnetic resonance imaging is expensive and there may be a waiting list. Furthermore, the examination can be quite stressful if the patient suffers from claustrophobia. For these reasons, it is not performed routinely but is only reserved for the rare instances when the diagnosis is not provided by ophthalmoscopy and ultrasonography.
Computerized tomography
CT scans are obtained by passing very fine x-rays through the head from different directions and then reconstructing the results to create an image 'slice' of the eye. This type of scan does not usually provide more information than ultrasonography, which is more convenient and less expensive.
Biopsy
The large majority of intraocular tumours can be diagnosed quite reliably by ophthalmoscopy and ultrasonography. Biopsy is useful for the rare instance when there is considerable doubt about the diagnosis despite full clinical examination.
Trans-vitreal biopsy
- Choroidal tumour biopsy with 25-gauge vitreous cutter
This is performed by passing either a fine 25-gauge needle or a 25-gauge vitreous cutter (like a vacuum cleaner) through the eye into the middle of the tumour and taking small samples for analysis. The vitreous cutter gives a better yield so that it is more reliable.
One might imagine that passing a needle through the retina would inevitably cause a retinal detachment, but this complication is surprisingly rare. There is often a mild haemorrhage, which can cause blurred vision or floaters, but this usually resolves spontaneously in a short time.
Incisional biopsy
Incisional biopsy is performed by creating a small trapdoor directly over the tumour and removing a small sample with scissors. This is a more difficult procedure than trans-ocular biopsy and is usually performed under general anaesthesia, with mild or moderate lowering of the blood pressure.
There is a small risk of seeding tumour cells into the normal tissues around the eye and if the tumour is not treated quickly it may spread through the opening created by the surgery. For these reasons, a ruthenium plaque is usually placed over the area of the biopsy during the same procedure, selecting the time for which the plaque is left in place according to the diagnosis of the tumour.
Excisional biopsy
Excisional biopsy involves total removal of the tumour, thereby providing both a diagnosis and a cure. It is mostly performed if local resection would be the treatment of choice in any case. In exceptional situations, if the eye is blind and painful the most practical solution is to remove the eye and to establish the diagnosis by pathological examination.
