When I examine an eye I never fail to be amazed by its complexity and beauty.
The whole visual mechanism is astoundingly sensitive – in the right conditions able to detect candlelight at a distance of 2 kilometres and capable of distinguishing thousands of different colours. But of course, disease or injury to any of its structures can have a serious effect on vision and function.
We recently had a series of patients with sudden visual loss and I thought it would be helpful to put the message out that this always needs urgent medical assessment. It is common not to realise the seriousness of the situation and therefore delay treatment, contributing to a bad outcome.
So, some anatomy. Working back from the front of the eye, the surface is called the cornea, transparent and highly sensitive, as anybody who has a corneal scratch will attest. Then comes the aqueous humour, in front of and around the lens. High pressure in this area is the cause of glaucoma. The lens itself can become hardened and cloudy (cataract) – surgery for this was done in ancient times though I can’t say I would have volunteered for it.
Then comes the vitreous humour, a jelly-like substance which maintains the shape of the eye and shock-absorbs impact. It is common to see “floaters” in the vitreous, clumps of collagen which dart away if you try to look at them and are more obvious against a plain background. At the back of the eye is the retina, with its millions of rods and cones that transform light into electrical impulses and transmit them to the back of the brain. The most detailed vision occurs in the central part of the retina, the macule.
Gradual visual loss can be caused by cataract, changes in shape in the eyeball, macular degeneration and retinal disease due to diabetes. All of these are treatable and can be dealt with on a non-urgent basis. However, when vision changes abruptly (over hours, days or weeks) you should high-tail it to a doctor or optometrist as soon as possible.
In our series of cases, three had vitreous detachment. This occurs when the vitreous shrinks and pulls away from the retina. The others were due to acute glaucoma; a clot in the retinal veins; polymyalgia rheumatica; and leakage of fluid under the retina. Interestingly, none of them were due to retinal detachment which can be catastrophic unless surgically ‘spot-welded’ back as soon as possible.
Everybody should be aware of the alarm signals for retinal detachment: • The sudden appearance of many ‘floaters’ • Flashes of light • Tunnel vision • Blurred or disturbed vision • A curtain-like shadow over the visual field
Patients with sudden visual loss are usually referred to Greenlane Hospital. People often have to wait there in the Emergency Department for many hours, but access to timely vision-saving treatment is one of the great bonuses of living in a developed country in the 21st Century and I personally am grateful for it.