Retinal laser treatment is completely different from the laser (excimer) used for treating short-sightedness or other refractive problems. It is a very high-energy bright light that, when directed and focussed on to a retina, is absorbed by the retinal pigment epithelium (RPE). The laser heats up the RPE and can, depending on various factors such as the power, size of the laser spot and duration of the laser pulse, either burn the full thickness of the retina or simply stimulate the RPE.
Most retinal laser treatment is done with both the ophthalmologist and the patient sitting at a machine that is similar to a slit-lamp, the instrument used to examine eyes.
In order to focus the laser onto the retina a special contact lens is placed onto the eye after it is completely anaesthetised with several drops over 10-15 minutes beforehand. This contact lens helps keep the eye still and prevents blinking in the eye being treated.
There are two basic patterns of laser treatment, depending on the reason for treatment: focal and scatter.
Focal Laser treatment is applied when treating macular oedema and is quick and painless. Low energies are used with small spot sizes and usually less than 100 very gentle spots of treatment. The treatment is thought to work by either stimulating the RPE to pump out more fluid, by making the retinal blood vessels less leaky or both.
It takes up to 3-4 months for this type of laser to work and it is not uncommon to have to top up treatment after that period of time.
Scatter Laser Or Panretinal Photocoagulation (prp)
This treatment is used when treating ischaemia and uses larger spots with higher energies. The number of spots is generally over 1500 and the treatment is usually broken up into separate sessions. Dr Chauhan uses a technique when lasering that is quite comfortable, reassuring many patients who have had painful scatter laser (or PRP as it is sometimes known) in the past.
The laser works, it is thought, by the laser effectively killing peripheral (less visually important) retina and so reducing the amount of VEGF produced. As a result, new vessels do not develop and any already present may go away. The results of scatter laser are usually apparent after a few weeks.
The main risk of laser treatment is a burn to the fovea, which could permanently damage central vision. This is avoided by following a number of safety procedures and is extremely rare.