In order to see objects clearly, the image of the object must form precisely on the back of the eye (retina). Refractive errors occur when the image forms in front or behind the retina.
Myopia (short-sightedness) is the most common refractive error in the younger population. In myopia, one can see near objects clearly but distant objects appear blurry. It is usually due to having an eye that is too long for the refractive power of the eye. As a result, the image forms in front of the retina.
In hyperopia, the eye is too short for the refractive power of the eye. The image forms behind the retina. If the amount of hyperopia is relatively low, young people can compensate for hyperopia using muscles in their eyes (accommodation). Accommodation brings the image to the correct position on the retina so that one can see objects clearly without spectacles. In older people, accommodation may be too weak to compensate for hyperopia, so they require spectacles to see distant objects clearly.
Astigmatism is when the optics of the eye cause 2 images to form on the retina. People with uncorrected astigmatism tend to mistaken the number ‘6’ as ‘8’, for example.
Presbyopia usually begins at age 40. It can co-exist with myopia, hyperopia and/or astigmatism. Optical correction in the form of reading glasses, progressive spectacles, bifocals, or multifocal contact lenses are needed in order for a presbyopic adult to see near objects clearly.
Binocular Vision Problems
Amblyopia, or lazy eye, is when one eye cannot see as fine details as the other eye even with spectacles. Amblyopia develops in young children when vision is poor, which may be due to uncorrected refractive error or eye turns (strabismus). If the images from one eye is better than the other, the brain starts to ignore the blurrier images from the weaker eye to favour the better eye. Over time, the neglected eye becomes ‘lazy’. Detecting and correcting amblyopia at an early age (< 9 years old) is imperative as it may be possible to reverse the condition. At older age, the visual system is less adaptable and prognosis for correcting lazy eye is poorer.
Strabismus is a condition where the eyes do not point in the same direction. There are many reasons why strabismus may develop such as genetics or birth trauma. In children, strabismus can lead to lazy eye. It is therefore vital that strabismus in children is detected and rectified early.
Glaucoma is known as the silent thief of sight. It is associated with high eye pressure, but this is not the only risk factor. The risk of developing glaucoma increases with age, a positive family history, systemic diseases such as diabetes, and even high myopia. Peripheral vision is lost in the early stages of disease. At the advanced stages, patients may only be left with tunnel vision. Once vision is lost, it cannot be recovered.
Age-related macular degeneration (AMD)
AMD occurs in individuals over age 50 and results in central vision loss. In advanced stages of disease, reading and looking at faces will be difficult. Eye supplements have been shown to benefit a subgroup of AMD patients who are at high risk of developing further vision loss.
By far the most well-known of all age-related diseases, cataract refers to the loss of clarity of the crystalline lens in the eye. It is caused by ageing and UV exposure. Diabetes and high myopia are also associated with cataract formation. Cataract formation can be delayed with proper UV protection and should be started at an early age. Anti-UV spectacles, sunglasses, wide-brimmed hats and umbrellas can reduce the amount of UV rays that reach the eyes. Just as sun block is applied when one is young and active, UV protection for the eyes should also start from young.
A retinal detachment occurs when the light-sensitive tissue inside the eye detaches from the walls of the eye. It is an emergency and medical attention should be sought immediately. If the detached retina is not reattached quickly, vision is permanently lost in that part of the eye. Symptoms of a retinal detachment include sudden increase in floaters (grey, translucent particles that seem to swim around in your visual field) and the appearance of flashes of light (similar to a camera flash). People with high myopia, older age, or a positive family history have an increased risk of retinal detachment. This condition can also be brought about by trauma to the head (e.g. from falls, knocks or high-impact activities).