Myopia or short sighted-ness, is a condition where distant objects appear out of focus or blurry. A myopic eye is unable to adjust focus in the distance, so requires glasses to attain clear distant vision. Up close objects are in focus for myopic eyes, hence the common name short/near-sighted; can see well at short distances.
At birth, the eye is initially very short and does lots of growing in the early years of life. Think of the eye like a thin string balloon being inflated, it grows mostly length-ways towards the brain, growing with age like our arms and legs. This process usually slows down and stops around age 7, though can continue to grow in small amounts throughout teenage years. Myopia arises when there are problems with the normal growth and development of a healthy adult sized eye.
There are many parts of the eye that work together to create a crisp, clear image. Light begins its journey passing through the front window of the eye, the cornea, which acts to do most of the focusing. Sitting behind the iris inside the eye, the lens also helps to focus an image, with the added role of making fine adjustments to achieve clarity at many distances. These two structures focus light to a point on the retina, at the back of the eye. The retina is like the sensor of the camera, detecting light to be sent to the brain.
If the light isn’t focused correctly on the retina, distance objects appear blurry. If the cornea or lens have an abnormal shape, they focus the light onto the retina incorrectly. Additionally, if the eye is too long, the sensor will be in the wrong place, away from where the light is being focused. Myopia occurs when the normal process of eye growth doesn’t slow down, allowing the eye to grow too long, putting the retina in the wrong spot. An abnormal shaped cornea or lens can also result in myopia. Often there is a combination of both abnormal focusing structures and abnormal eye length.
Not only does myopia cause blurry vision, myopic eyes often tend to be at higher risk of eye disease and vision impairment later in life. Thinking back to the balloon, a balloon that is too inflated will be more stretched, the plastic will be thinner and the balloon will be more likely to pop. Myopic eyes don’t pop and they don’t grow as long as balloons, though they do become more stretched and fragile. This is why we need to take very good care of these eyes, watching them closely to make sure they remain healthy
When caring for the health of myopic eyes, it is important to know how long the eye is, how abnormal the shape of the eye is, as well as how well the eye focuses light. This helps us understand how all of the relevant structures in the eye are behaving. A combination of this information provides an understanding of the risk of future change and possible damage to the eyes, to compose the best long term management.
Author: Wesley Butler, Optometrist
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