Eye Areas and Problems
General
It is not always obvious to the individual when an eye problem is developing or has happened. Whilst some well noticed conditions can heal quickly with rest others happen without knowledge and if nothing is done damage may be permanent. This is why it is advisable to consult an optometrist.
Optometrists have the instrumentation and knowledge necessary for detecting disease. If there are problems requiring further treatment the optometrist will refer the patient via their GP for further consultation (e.g. it may be recommended that the patient is seen by an ophthalmologist, orthoptist, neurologist, dermatologist as decided by the GP after assessing the optometrist's report. Optometrists deal with more than refractive errors and prescribing lenses. The title 'optician' strictly applies to an individual who arranges to make spectacles to the prescription of an optometrist. Registered dispensing opticians have an extensive knowledge of frame and lens materials. Lens designs are increasingly complex and to gain the best performance we only employ dispensing opticians registered with the general optical council.
Cataract
A cataract is a lens opacity. Opaque or cloudy areas develop within the crystalline lens of the eye and cloud sight. An optometrist can identify developing cataracts at a stage long before any acton is required. Brighter lights and stronger lenses for reading are the first responses to early developing cataracts. Patients with cataracts tend to report the following symptoms. Night driving causes glare. Direct low sunlight is particularly disturbing to the vision - hence many will choose to wear brimmed hats or caps to shade the eyes. The opacities can cause internal reflections leading to ghost images. Vision seems more variable but is probably simply more sensitive to ambient lighting, position of light sources and pupil size. Mostly colours are faded and less vivid and feint text is particularly difficult to discern. Some Cataracts reduce contrast more that they blur the image. As some cataracts progress the lens hardens and this increases the refractive index which in turn drives the eye more short sighted. THe old notion that caaracs have to be left to mature no longer applies. Obviously the operation for cataract will not be appropriate until the benefits outweigh the risks but the likely outcome is not generally improved by waiting with modern techniques. Despite fears, operations are normally successful in improving vision.
Cataracts are removed by surgery. Modern cataract surgery uses the technique of phacoemulsification. An ultrasonic vibrator breaks up (emulsifies) the lens, which is then vacuumed away through a hollow needle. A replacement lens is placed in the eye to correct the focusing. The incisions are so small that healing is very swift. It is usually not necessary to stay in hospital or to have a general aneasthetic. The worst eye is usually operated on first. The initial cataract surgery does not involve use of a laser. However Lasers may be used later if a fibrous membrane develops over the implant. When this occurs, a laser is used to open this membrane, restoring vision in several days.
Other disorders of the cornea (also a loss of transparency and impaired sight) can come from injury or a byproduct of disease like glaucoma.
Retina
Any damage or derangement involving the retina seriously threatens vision. Among the most common causes of blindness are diseases that damage the retina and inherited conditions such as retinitis pigmentosa that compromise its ability to function.
Optic Nerve
Glaucoma is an unusual eye disease that causes damage to the optic nerve. Glaucoma threatens and can destroy sight (if untreated) and yet it is rarely noticed by the sufferer for many years if at all. The incidence and cause is not fully documented and much remains to be understood. Glaucoma rarely occurs under the age of 40 years, it is more prevalent in afro-caribbeans, and the chances of it affecting us increases as we get older or if we have relatives with glaucoma. The end result of the disease is damage to the optic nerve at its point of entry into the eyeball. This damage is often (but not always) associated with raised intra-ocular pressure. Intra-ocular pressure is the tension of the eye. Imagine a ballon partly inflated - here there is low tension; the balloon would have high tension if the inflation was increased and it was taut. If the pressure rises it can cause damage to the optic nerve possibly by mechanical means or by compromising the blood supply at the head of the nerve. The tissue of the optic nerve then dies and insensitive or blind areas start to form in the visual field. Glaucoma detection in optometry relies upon three checks.
1. Intra-ocular Pressure
Optometrists measures intra-ocular pressure with a tonometer. This is frequently done with an instrument which blows a jet of air onto the eye. The air jet force required to compress the eye by a miniscule amount is recorded (rather like prodding a balloon) and this relates to the pressure within the eye. Some optometrists (and hospital consultants) prefer to assess pressure with a tonometer that lightly rests on the eye. There is no discomfort with either technique.
2. Assessment of the Optic Nerve Head
The optic nerve in glaucoma can show signs of damage. In the early stages these signs are subtle but can be the first sign of glaucoma. Suspect optic discs can be viewed in 3 dimensions to refine the diagnosis.
3. The Visual Fields
Most patients are now familiar with the automated field testers that are now present in many optometrist's practices. These allow a sophisticated analysis of the eyes' sensitivity at key points in the visual field. We are checking for blind areas, or areas that may become blind. These machines do much more that just check for glaucoma as the pattern of defects helps to localise the sight of damage. The results help to establish where the damage lies, between the eye and the occipital cortex in the brain. Which is the best test?
It is broadly agreed that intra-ocular pressures alone are not very sensitive in detecting glaucoma. Additionally many individuals have unusually high intra-ocular pressure but do not have glaucoma. Some practitioners argue that the optic nerve assessment is the best way to pick up early glaucoma. Others contest that visual field screeners offer the most sensitive and specific test. Everybody agrees on one matter though - the combined use of all three tests helps to correctly diagnose the presence of glaucoma.
4. The treatment of glaucoma.
Most patients with glaucoma are treated with eye drops. These work either by reducing the fluid secreted within the eye, or by improving the drainage of fluid from the eye. Surgery may be appropriate for certain glaucomas. The goal of the treatments is to reduce intra-ocular pressure and thereby reduce the stress on the optic nerve. Much research is being undertaken to establish the pathogenesis of glaucoma and in developing new pharmaceuticals and modes of treatment.
Regular eye checkups are therefore essential for both young and old. Appropriate eye protection prevents injury, pain, and disability (including blindness).
Remember that eyes do not have to deteriorate significantly and may become useful to someone else after death.