How the Eye Works - Light enters the eye through the clear front surface layer called the cornea. The cornea starts to focus the light, which then travels through the fluid filled anterior chamber to the lens. The lens is the major refractive (focusing) structure of the eye. The lens can change thickness in order to focus the light more or less, depending on viewing distance and age. The image becomes inverted at this point, and the light rays then pass through the inner cavity of the eyeball, a jelly-like substance called the vitreous humour. Finally, the light strikes the retina, the inner lining of the eye, and stimulates the light receptors, which send a signal to the brain via the optic nerve. TOP

Myopia - This is often referred to as ‘Near-sightedness’, because individuals with Myopia may be able to see objects near their eyes quite easily, but have difficulty seeing objects far away without the help of glasses or contact lenses. Myopia occurs when the eyeball is too long and/or when the cornea, the clear front portion of the eye, is too curved and therefore optically too powerful. Myopia often begins to develop in childhood and usually increases as the body grows rapidly during adolescence. The level of myopia then usually becomes stable in the adult years. Myopia is often noted when an individual reports difficulty seeing distant objects such as road signs, the TV or the blackboard at school. Myopic patients, particularly children, may be seen squinting as an attempt to clear their vision. Optometrists prescribe concave (minus) glasses or contact lenses to help the eyes form a clear image. Depending on the degree of myopia, these lenses may need to be worn all of the time, or only for specific tasks.TOP

Hyperopia - Hyperopia may also be referred to as ‘Far-sightedness’, because people with this condition may be able to focus on objects far away, but have more difficulty focusing on closer objects. This occurs as a result of the eyeball being too short and/or the clear front portion of the eye, the cornea, being too flat and therefore not optically powerful enough. Because hyperopia in children may go undetected in some school eye-screening tests that may only test distance visual acuity, a full eye health examination with an Optometrist that tests both far and near vision is often necessary to diagnose farsightedness. When hyperopia is detected, convex (plus) eyeglasses or contact lenses may be prescribed to help the eyes bring objects into focus. TOP

Astigmatism - Astigmatism is a condition in which the cornea, the clear front surface of the eye has an irregular curvature, which causes blurred distorted images at all distances. This can cause headaches and/or a feeling of strain on the eyes. If someone were to construct a model of a normal eye with half a basketball serving as the cornea, a model eye with astigmatism would require half of a football as the cornea. Although this example is somewhat exaggerated, it demonstrates that astigmatic corneas are more curved in one direction that the other. Astigmatism is very common and often occurs in addition to nearsightedness or farsightedness. Most of the population has some amount of astigmatism and if it is enough to cause distortions or visual discomfort, corrective lenses will be prescribed. Such lenses are referred to as toric lenses and have an additional power element called a cylinder that must be placed at the correct position. In many cases, astigmatism can now also be corrected with toric contact lenses. TOP

Presbyopia - Throughout life, the lens inside our eye gradually loses its elasticity. As the lens becomes stiffer, it begins to lose some of its ability to change focus for different distances. Although these structural changes begin early in life, it is typically not until our early 40’s that it begins to cause difficulties with near vision. When we are young, the flexible lens changes shape, or accommodates, for both near and distant objects by bending or flattening with the help of tiny ciliary muscles in the eye. However, as we age, and the lens becomes stiffer, changing its shape becomes increasingly difficult and as a result, focusing on near objects becomes challenging.TOP

Unfortunately, presbyopia eventually affects everyone and there is currently no known prevention. However, there is now a range of options available to correct presbyopia. Patients may choose from a variety of bifocal styles, progressive addition spectacle lenses (often referred to as invisible or no-line bifocals), bifocal contact lenses or monovision contact lenses, in which one eye is corrected with a contact lens for distance vision and the other eye is corrected with a contact lens for near vision. Because presbyopia is a gradual change over several years, your prescription will also progressively change and may need to be updated regularly as these changes occur. TOP

Cataracts - A cataract is a clouding that develops in the eye’s normally clear lens as a result of chemical changes within the eye. This causes a variety of visual symptoms, such as blurry or hazy vision, sensitivity to glare, yellowed appearance to colours or a false sensation of having a film over the eyes. Although cataracts usually develop later in life, they can also occur in younger people, including children and even newborns. Cataracts can be a natural change that occurs with time, or they may also occur as a result of injury or disease. Cigarette smoking, certain medications and excessive exposure to ultraviolet radiation are also known risk factors. Although there is no proven method to prevent the development of cataracts, the use of UV-blocking sunglasses can help reduce your risk. When a cataract progresses to the point that it has a significant adverse effect on your lifestyle, your optometrist may refer you to an ophthalmologist for surgical removal of the cataract. The surgery is relatively straightforward and has a very high success rate. Most often, a clear plastic lens (an Intra-ocular lens, or IOL) is inserted into the eye upon removal of the eye’s natural lens. Until surgery is necessary, your optometrist can prescribe any necessary changes to your spectacles that will help you see more clearly. However, surgery is currently the only proven method of ultimately treating cataracts.TOP

Strabismus - Strabismus is a condition in which both eyes do not point simultaneously at an object being viewed. One eye may be turned in, out, up or down, usually as result of an imbalance in the muscles of the eyeball. The eye turn may be present all the time or only at certain times, such as when the person is fatigued, and the deviating (turned) eye may alternate between the left and the right eyes. Because a turned eye causes the brain to receive two different images, the person may see double, or the brain may learn to ignore the image from the deviated eye. Recognising strabismus is of particular concern in children because the eye turn may prevent vision in that eye from developing properly. In some cases, simple visual training exercises prescribed by your optometrist can provide adequate treatment to strabismus TOP

Glaucoma - Despite the vast amount of research in the field of glaucoma, much about this disease still remains a mystery. What is known about glaucoma is that it is often associated with increased pressure inside the eye (intra-ocular pressure). This causes damage to the optic nerve, the nerve located at the back of the eye through which visual information is transmitted to the brain. Damage here results in a variety of visual field defects, or ‘blind spots’. However, there are also cases in which glaucomatous damage occurs, but the intra-ocular pressure falls within the ‘normal’ range. This is known as Low Tension Glaucoma. Conversely, some people have naturally high intra-ocular pressure but never suffer the effects of glaucoma. The visual field defects associated with glaucoma progress so gradually that they may not even be noticed, until the damage is profound. If left untreated, glaucoma can even cause permanent blindness. Therefore, regular eye examinations are very important. Your optometrist can perform tonometry, a painless procedure that measures the intra-ocular pressure, and ophthalmoscopy, which examines the back of the eye to monitor the health of the optic nerve. If glaucoma is suspected, a visual field test may be performed. This is a very sensitive test, which measures the sensitivity of the peripheral vision and can detect the development of abnormal blind spots. It is recommended that patients with a family history of glaucoma should have a full eye examination at least once a year. TOP