Refractive error means that the shape of your eye does not bend light correctly resulting in blurred image.
Types of refractive errors are, myopia (nearsightedness), hyperopia (farsightedness), presbyopia (loss of near vision with age), astigmatism (distorted shape of cornea curvature), amblyopia (lazy eye) and strabismus.( squinting of the eyes).
Myopia (Nearsightedness)
Myopia occurs when the eyeball is too long relative to the focusing power of the cornea and lens of the eye, resulting in light rays focusing at a point in front of the retina instead of directly on its surface, resulting in blurred distance objects.
It can be caused by the cornea and / lens being too curved for the length of the eyeball
It typically begins in childhood and progresses throughout teenage years, it may be hereditary.
Minus lenses are used to correct the curvature of the cornea and lens, bending the light rays correctly relative to its power and the length of the eyeball.
It is a condition in which you can see near objects clearly and distant ones blurred.
Hyperopia (Farsightedness)
It is a common vision condition in which you can see distance objects clearly, but objects nearby may be blurry
It occurs when your cornea is curved too little or your eyeball is shorter than normal, instead of light being focused precisely on your retina, light is focused behind your retina resulting in a blurry appearance for close-up objects
Plus lenses are used to redirect the rays of light from back onto the retina precisely.
Astigmatism
It is a common, mild and generally treatable imperfection in the curvature of your eye, this condition causes blurred vision.
It occurs when the front surface of your eye (cornea) or the lens inside your eye, has a slightly different surface curvature in one direction from the other instead of being smooth and even in all directions, surface may be flatter or steeper.
Astigmatism blurs your vision at all distances.
It is often present at birth in combination with myopia or hyperopia, but often requires treatment beyond 2 years of age by using spectacles,
It may develop after an eye injury, disease or surgery and can be made worse by reading in poor light, sitting close to the television or squinting
Signs and symptoms include blurred or distorted vision, eyestrain and headaches.
Amblyopia (Lazy Eye)
It is a decrease in vision that results from abnormal visual development in infancy and early childhood.
It usually affects only one eye, but it can affect both.
Amblyopia is the leading cause of decreased vision among children, if left untreated; vision loss may range from mild to severe.
It develops when nerve pathways between the brain and the eye are not properly stimulated; as a result, the brain favours one eye usually due to poor vision in the other eye.
The weaker eye tends to wander and may eventually turn away due to poor stimulation.
There are 3 common causes of lazy eye: strabismus (imbalance of muscle responsible for turning the eyes which causes eyes to cross), deprivation (if there is a problem in one eye such as cloudy area in the lens/cataract, which deprives of clear vision), refractive (due to uncorrected refractive error)
Occasionally, a wandering eye is a first sign of an eye tumour.
