Eye Information

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Common Sight Defects

Rugby Ball Shaped Eyes A.K.A. Astigmatism is responsible for blurred vision due to a difference in the focal power of the eye in different meridians. This results in some parts of the image on the retina being clearer than others. Blurred vision occurs at all distances, the higher the degree of astigmatism, the worse the blur. It is most noticeable when trying to see fine detail.

What causes Astigmatism?

The eyeball is not completely spherical like a football in astigmatic patients but more like a rugby ball with a steep and a flatter meridian. The greater the difference between the curvatures of the eye, the greater the degree of astigmatism. It can be associated with long or short sight or can occur alone.

What are the symptoms of Astigmatism?

The symptoms of astigmatism vary depending on the severity and the type of task attempted. In mild astigmatism, it may be difficult to concentrate on near print and close tasks, eyestrain and fatigue and also headaches at the end of the day may occur. In medium to high levels of astigmatism, achy and burning eyes may interfere with concentrated tasks and irritability may follow sustained concentration. What can be done to manage Astigmatism? Corrective spectacles (or contact lenses) are needed to focus the retinal image properly and enable clear vision. How much spectacles need to be worn depends not only on the prescription but the individual's work and lifestyle. A person with mild to moderate astigmatism may only need spectacles for concentrated tasks such as computer work, reading and driving. A high degree of astigmatism needs spectacles to be worn more or less all the time. In children with high levels of uncorrected astigmatism the blurred retinal image may interfere with the visual system development leading to the child never attaining full adult visual potential.

Constant wear of the corrective spectacles is essential from as early an age as possible to try to prevent permanently stunted visual development.

Can anything be done to stop Astigmatism getting worse?

Astigmatism is due to a difference in the curvature of the eyeball and tends to remain fairly static throughout life. An exception to this is a disease of the cornea called Keratoconus that causes increasing astigmatism, but this is not a common disease.

Can patients with astigmatism be fitted with contact lenses?

Yes, in fact many patients have low levels of astigmatism which allow normal contact lenses to be fitted. For highly astigmatic patients, special lenses called torics are needed to get good vision and fit.

Longsightedness, A.K.A. hyperopia. In hyperopia, it becomes difficult to see close objects clearly without making a more effort than normal. In mild cases the eyes may be able to compensate in childhood and early adult life without any problems. In moderate levels or as the eyes age and they become less well able to compensate, spectacles may be necessary for concentrated close tasks such as reading or computer work. In high levels of hyperopia it may be impossible to sustain clear focus for close work at all and spectacles may be needed all the time. High levels of uncorrected hyperopia in children can lead to a turn in the eyes (squint) and the development of a lazy eye and need swift diagnosis and aggressive treatment to allow the eyes to reach their full adult potential.

What causes Hyperopia?

In hyperopia, the eyeball is too short or the cornea (the clear window at the front of the eye) too flat so that light entering the eye is not focused correctly on the retina ( the back of the eye). The causes of hyperopia are thought to be mostly hereditary. Those families with one hyperopic child should ensure that others are checked particularly if there is a family history of squint.

What are the symptoms of Hyperopia?

In mild to moderate long sight it is difficult to concentrate on near objects for long without eyestrain, fatigue, irritability and often headaches. There may not be blurred vision because the eyes muscles are constantly refocusing the work, but the symptoms are reflected in the increasing tiredness caused by the prolonged excess effort. After long periods of close work the eyes may become achy and tired and if the muscles cannot sustain the refocusing effort the vision will blur intermittently. This can cause loss of concentration and will interfere with schoolwork in the case of a child.

How can Hyperopia be managed?

If the hyperopia is mild to moderate spectacles are prescribed for close and concentrated tasks only, if it is severe or the patient is a child at risk of developing a squint or a lazy eye, spectacles will be prescribed for constant use. Contact lenses may also be used.

Can I do anything to stop Hyperopia getting worse?

Unfortunately, as we age the lens in the eye becomes harder and the focusing muscles find it more difficult to keep close things clear. This means that longsighted people find they will use their spectacles more as they get older. As this is an inevitable consequence of the aging process we need to manage this deterioration be ensuring that the spectacles (or contact lenses) are kept up to date to ensure the best vision. I have heard that hyperopic can cause a squint - is this true? Yes, uncorrected hyperopic in young children can cause what is termed an accommodative squint or turn in the eye. This is because, in order to try to produce a clear image, the eyes over-accommodate and over converge (turn in ). One eye may remain permanently turned in if this is not noticed or corrected at a very early stage.

Shortsightedness, A.K.A. myopia. In myopia, it becomes difficult to see distant objects clearly. In mild and moderate levels of myopia, close objects remain clear but in high levels it may be difficult to see anything clearly unless it is held very close.

What causes myopia?

In myopia, the eyeball is too long or the cornea (the clear window at the front of the eye) too curved so that light entering the eye is not focused correctly on the retina (the back of the eye). The causes of myopia are thought to be partly hereditary and partly environmental with high levels of close work causing stress to the visual system. It is not possible to identify those individuals who are at risk before myopia develops.

What are the symptoms of myopia?

Myopia commonly starts in the teenage years when the most usual presenting symptom is blurred vision affecting the ability of the child to see the board at school. Some young adults start a little later and commonly notice problems when learning to drive or seeing Teletext on the television (or being unable to read the questions on Who wants to be a Millionaire?)

How can myopia be managed?

Initially most myopes (shortsighted people) are prescribed spectacles for distance eg the board at school, television and cinema. Many people need them for driving. It is recommended that regular 6 monthly check-ups are scheduled as myopia can progress rapidly in some individuals, often paralleling the onset of puberty or rapid growth spurts. If the myopia is mild to moderate, it is recommended that spectacles are used only for distance and removed for close work and reading as it is thought that there may be a bio-feedback mechanism which works in some individuals to hasten the worsening of the myopia if spectacles are worn for close work and reading unnecessarily. Recent research has shown that it is necessary to watch the prescription carefully and change even small amounts because the rate of change of myopia may speed up if the vision is not kept clear.

Can anything be done to stop myopia getting worse?

Unfortunately most myopic children will progress to become more myopic over the teenage years and into their 20's. Patients with later onset myopia may find their vision does not stabilize until their 30's. There is some evidence that rapidly progressing myopic patients may benefit from using bifocal or varifocal lenses rather than single vision lenses if the prescription is moderate to high and spectacles have to be worn all the time. Recent research confirms that fitting gas permeable contact lenses tends to slow down the rate of progression, although soft lens wear does not. All under 16's and under 19's in full time education are eligible for free NHS tests and vouchers towards the cost of spectacles when the prescription changes. Please ask any member of staff if you need any more information.

At what age can a shortsighted patient be fitted with contact lenses?

Age is no barrier to contact lens wear. We have several primary school children in the practice who successfully wear contact lenses. Fitting teenagers is a very rewarding part of contact lens practice because it can really help those who are self conscious in spectacles or who simply find them impractical for sport. We have lots of children who wear spectacles part-time and contact lenses for other occasions - and to be honest, are extremely good with cleaning and looking after their lenses, putting some of my adult patients to shame!

Ageing eyes, A.K.A. presbyopia is the term given to age-related changes in the eye, which cause the near focus to deteriorate and start usually between 40 and 50 years of age.

What causes Presbyopia?

The lens within the eye becomes more difficult to focus as we age. In young people, it is very flexible and can be steepened into a different shape to allow easy change of focus from distant objects to close ones. This focus change is called accommodation. As we age, the lens in the eye produces new lens fibres and becomes thicker and stiffer and progressively more difficult to focus. By age 55-60 there is little natural focus remaining.

What are the symptoms of Presbyopia?

Weakening of accommodation is often first noticed as difficulty reading small print particularly in poor light. Some people also find it takes longer for their eyes to refocus from distance to reading and vice versa. As the focus for reading becomes more difficult, spectacles are needed to give extra focusing power ? this is known as a ? reading addition ? . A patient needing a reading addition is termed ? presbyopic ?. The power of the reading addition depends not only on the remaining focusing ability but also on the distance that the close work is done. For example, reading at 30cm needs a different power from working on a computer at 60cm in mid to late presbyopia where little natural focus remains, and special VDU/Computer spectacles may be needed. Your optician will take into account both the working distance and remaining accommodation when prescribing the reading addition to give clear and comfortable vision for the visual task.

How can Presbyopia be managed?

Most patients choose spectacles which can be made in 3 different types to help. * Single vision spectacles (reading only) * Bifocals * Varifocals The choice of type of lens is made considering your occupation, hobbies, convenience and prescription. Our dispensing optician will discuss the different types of lens with you, explaining the advantages and disadvantages of each type relating to your individual needs. Contact lenses and Presbyopia Some patients choose to try special contact lenses if they want to avoid spectacle wear - these need special fitting and can be tricky to adapt to in the early stages, but with the newer modern designs, occasional or regular wear is possible. Back up spectacles will always be needed because lenses cannot always be worn all day every day, especially during illness, or if a lens is lost.

Can I do anything to stop Presbyopia getting worse?

Unfortunately, because the change in vision is age related, it is inevitable that the reading vision will worsen whether you use spectacles or not, but using the correct power of lenses will make it easier to read without straining your eyes.

Squint or turn, A.K.A. strabismus is present where there is an obvious misalignment of the eyes either all the time (constant) or occasionally (intermittent). The deviating eye may turn in (convergent) or out (divergent).

What causes a strabismus?

One of the most common causes of a convergent strabismus is uncorrected long-sightedness. Other causes can be problems with coordinating the eye muscles due to damage e.g. sometimes following a difficult birth or forceps delivery, or, very rarely, by an eye disease or another health problem.

What are the symptoms?

One eye will turn in or out either constantly or intermittently. Mothers are the best at suspecting a problem, and sometimes more than one visit to the optician is necessary before the turn can be detected, especially if it is intermittent.

What can be done to help a strabismus?

Corrective spectacles are needed to focus the retinal image properly and enable clear vision and so the first step is to ensure that they are worn where necessary. All children suspected of having a turn will have their eyes examined using drops which temporarily stop the eye muscles from focusing properly so the full extent of the visual problem (if any) can be diagnosed. If there is an uncorrected visual problem, the first step is constant wear of the corrective spectacles. In many cases this is sufficient to straighten the eyes and stop the turn and in others it will decrease the angle of the turn. It is essential that turns are treated from as early an age as possible and definitely pre-school to try to help prevent a lazy eye, which is caused by stunted visual development in the deviating eye. In children whose strabismus does not respond to spectacle correction, referral to an opthalmologist through the GP is the next step. The child will be assessed by an orthoptist (a specialist in eye co-ordination) for treatment, which may include exercises and patching. In non-responsive cases, the ophthalmologist may decide that surgery is indicated.

Can I do anything to stop a strabismus (turn) getting worse?

The child needs to wear any corrective spectacles all the time to encourage normal visual development. If the orthoptist recommends exercises of patching, they need to be done religiously. There is a short period of time when the visual system will respond and the treatment regime needs to be aggressive at this stage because once the child is 5 or 6 years of age, the visual system starts to become less responsive and less improvement will occur.