As we learn about refractive errors and a few of the common eye conditions that we encounter in our day-to-day life, it is equally important to be aware of the associated medical conditions that may bring about fluctuating eyeglass prescriptions, elevated ocular pressure, eye-fatigue and so on. Let's first look at the normal eye.
Normal eye or emmetropia:
A bundle of light rays from infinity passes through the cornea and the lens which help them to focus onto the retina - the back of the eye. The cells in the retina absorb and convert the light to electrochemical impulses which are transferred along the optic nerve and on to the brain.
The amount of light going through the eye is controlled by the pupil which dilates and constricts accordingly to the surrounding. This control is necessary as too much light may cause retinal damage and too little will result in difficulty in seeing or reading. This causes acute strain on the eyes and results in eye-fatigue and frustrations.
There are basically three types of refractive errors: myopia, jypermetropia and astigmatism. And then there is another condition known as presbyopia or 'Old Sight' or 'The Ageing Eye
Myopia or short-sightedness:
A condition of the eye in which parallel rays are focused in front of the retina. Objects will be seen distinctly only when near to the eye. Myopia is also known as near-sightedness.
In this condition, the eyeball is longer than normal; or the cornea (the clear front cover of the eye) is too curved. As a result, the light entering the eye is not focused correctly, and distant objects look blurred.
Hypermetropia, hyperopia or long-sightedness:
Hypermetropia, also called hyperopia, is the term used to define being long-sightedness. Here; parallel rays of light coming from infinity focus behind the retina when the eye is at rest. This means that light is focused too far back in the eye, causing things which are up close to appear blurred.
The cornea is flatter or the axial length is too short preventing the images to focus by the time they reach the Retina. To focus properly, the eye needs to accommodate; pushing the eyes to work harder in order to see near objects clearly. This results in eye-fatigue and headaches an diminishes work capacity.
A defect in the eye or in the lens - resulting in distorted images, as light rays are prevented from meeting at a common focus. In an astigmatic eye, the eyeball is not completely round, unlike that in a normal eye. Astigmatism may be present from birth, or it may develop after an eye injury, disease or surgery. It is common with both; Myopia and Hyperopia. Symptoms include, blurry vision, Eyestrain, Headaches and trouble seeing at night.
As you age, you notice a gradual loss of your eyes' ability to focus on nearby objects. Almost everyone experiences some degree of presbyopia after age 40.
Diabetes, Multiple Sclerosis or cardiovascular diseases can increase your risk of premature Presbyopia and so do certain drugs including antidepressants, antihistamines and diuretics. pathological
Aside from Refractive errors there are other pathological conditions that may affect the health of your eyes and your eyesight. Cataract, diaabetes and hypertension also play a part in this phenomenon. Eyes become dry and irritative if you are suffering from Thyroid symptoms.
Diabetic eye disease: is a group of eye problems that can affect people with diabetes. These conditions include diabetic retinopathy, macular edema, cataracts, and glaucoma. It is extremely important to have your eyes evaluated every year if you are Diabetic. Over time, this condition can cause damage to your eyes that can lead to poor vision or even blindness.
Cataract: is an opacity of the normally clear lens which may develop as a result of aging, metabolic disorders, trauma or heredity. Subtle changes in vision, a dull color perception and loss of contrast sensitivity may be experienced at the onset of the cataract.
Thyroid eye disease: A condition whereby eye muscles, eyelids and tear glands may become inflamed. This can cause the eyes to become red, swollen and uncomfortable and the eyes can be pushed forward ('bulging' eyes)
High blood pressure: If unmanaged, Hypertension can affect your eyesight and may cause damage to the blood vessels in the retina.
Glaucoma: often called 'The Thief of Sight' is an eye disease that is often associated with elevated intraocular pressure. This may cause damage to the optic nerve and can lead to loss of vision.
Keratoconus: Corneal curvatures must be evaluated during every annual visit. Steep parameters denote the onset of Keratoconus, a visually debilitating progressive disease.
As part of our routine eye examination, it is imperative that comprehensive tests are conducted regularly.
- Dr Murtaza Somji is an ophthalmic optician at Eyestyle Opticians