1. Short-sightedness (myopia) - This condition is when you are able to see clearly up-close, but distance vision is blurry without glasses. If you are in the younger age range, then it can be normal for your lens prescription to change every year as the length of the eyeball changes. It is best to see your optometrist to rule out any other condition, especially if you notice your vision changing. They will refer you to an eye specialist or ophthalmologist, if you require further advice and treatment.
2. Keratoconus - This condition is a progressive eye disease, in which the cornea (front of the eye) becomes thin and bulges forwards. It usually begins in your teens and early twenties but can be diagnosed in a young child, if there is a history of eye rubbing or family history of keratoconus. This can lead to short-sightedness and irregular astigmatism, in which glasses or contact lenses are required to maintain clearer vision. As this is progressive, your optometrist will need to refer you to an ophthalmologist for treatment to stabilize the bulging and prevent further loss of vision.
3. Cataract - This is when the natural lens inside our eyes starts to become hazy and opaque, leading to blurry vision. This most commonly occurs in your fifties, but can occur in the younger age group and continues to progress. Cataracts can cause you to become short-sighted and glasses may be helpful, but only temporarily. Your optometrist may refer you to an ophthalmologist for surgical treatment, if there is significant cataract or angle narrowing which can cause acute angle closure in certain patients. It is best to get a clinical examination.