Long-sight is when the light entering the eye would be brought to a point of focus beyond the retina, causing a blurred image. This can be caused by the eyeball being too small or the lens not having enough focusing power. It is simply corrected with lenses that cause the image to focus on the retina. You will know you have this if the number in the ‘Sphere’ or ‘SPH’ box on your distance prescription has a +(plus sign) in front of it. It means that things that are close to your eyes might be blurry.
Short-sight occurs when light entering the eye is brought to a point of focus in front of the retina, causing a blurred image. This can be due to the eyeball being too long or the lens having too much focusing power. It is simply corrected with lenses that cause the image to focus on the retina. You will know you have this if the number in the ‘Sphere’ or ‘SPH’ box on your distance prescription has a – (minus sign) in front of it. It means that things in the distance might be blurry.
This is a very common condition where the light rays from objects are not brought to a single sharp focus within the eye. This is often caused by the front surface of the cornea having an irregular shape, i.e. being similar in curvature to he side of a rugby ball, instead of being spherical like a football. It is very straightforward to correct, using lenses with more power in one direction than another. These are called ‘cylinder’ lenses or ‘Cyl’, and must be prescribed with an ‘axis’ to ensure the power is working in the correct direction for your vision.
Presbyopia is a condition where the eye has difficulty focusing on near objects, when reading for example. The process of focusing on near objects is called accommodation. With age the lens, which enables accommodation, becomes less flexible and after we reach our early to mid forties, focusing on close objects becomes increasingly difficult. Although it often seems to occur suddenly, the loss of flexibility takes place over a number of years.
Presbyopia is part of the eye’s natural ageing process. It happens to everyone regardless of whether they need glasses for short-sight, long-sight or astigmatism. It cannot be prevented. One of the first signs of presbyopia is the need to hold reading material further away to see it clearly – a common complaint is “my arms aren’t long enough!”. Other symptoms include blurred vision for reading, or eyestrain and headaches when doing close-up work.
Early on, simply holding close material further away helps, but eventually a near vision correction is the spectacles or contact lenses is required. This is described on prescriptions as a ‘reading addition’ or ‘Add’.
Some short-sighted people can delay the need for a near vision correction by removing their spectacles for reading and close work. The most appropriate type of near vision correction is dependent on your lifestyle, occupation and hobbies. If you have good distance vision and only have difficulty seeing close up, a separate pair of near spectacles is often the easiest solution.
For others, needing separate prescriptions for distance and near means two sets of glasses and this can prove frustrating. In these cases, glasses with varifocal lenses may be more appropriate. Varifocal lens technology has advanced considerably over recent years to provide lenses that provide good vision at all distances, including the intermediate range, which is ideal if you use a computer There are also a wide range of contact lenses options for presbyopia.
This is a visual defect where the eyes are misaligned and point in different directions. There are two different forms of strabismus being referred to:
In each case, the brain will not be able to use the vision from both eyes because each eye will be receiving light from a different direction The brain will suppress the image from the weaker eye, called amblyopia, and three dimensional vision and depth perception will be lost.
This can be corrected in children if detected early enough. However, in adults, it is corrected with glasses containing a ‘prism’ designed to bring light from the same object to both eyes.
A cataract forms when the clear lens of the eye, behind the iris, which focuses light to provide sharp images, becomes cloudy and hardens, causing a loss of sight. Cataracts are painless and gradually develop over a long period of time. Over 50% of people aged over 65 have some form of cataract development and most cases can be treated successfully with surgery, where the lens is replaced by a clear plastic one. It can be caused by age, trauma, diabetes, long term steroid therapy, excessive exposure to UV light or hereditary.
Age Related Macular Degeneration is the most common cause of poor sight in people over the age of 60. The macula is the small central part of the retina, which is responsible for what we see when we look straight ahead, allowing us to see fine detail when reading or recognising faces, as well as allowing us to see colour. The cells of the macula are very delicate and can become damaged over time. When this occurs later in life, it is known as age related macular degeneration (AMD). There are 2 main types of AMD:
This accounts for about 90% of cases. It develops slowly over a number of years causing gradual loss of central vision. People often complain of difficulty with detailed tasks such as reading, writing and recognising small objects. Stronger reading glasses can help in the early stages. Low vision aids such as magnifiers can help make the most of the remaining vision. In the advanced stages of the disease, people may notice a blank patch or dark spot in the centre of their vision, making detailed tasks very difficult. Unfortunately, there is no treatment for dry AMD.
This generally develops more quickly, resulting from new blood vessels growing behind the retina leading to bleeding and scarring. It causes a loss of vision which is often more severe than dry AMD. Wet AMD often causes symptoms of blur or distortion, causing straight lines to appear wavy. Objects may appear an unusual size or shapes. If you develop any of these symptoms suddenly, you should seek advice as soon as you can. Wet AMD is sometimes treated using lasers to seal leaking vessels. This is an area in which research is ongoing and new treatments are constantly being developed.
AMD usually involves both eyes, although one eye can be affected before the other. Using the ‘good’ eye will not wear it out, so don’t be afraid to use it as normal. AMD is not painful, and never leads to total blindness as it only affects the central vision.
The exact cause is not known, but a number of risk factors have been identified: