Vision disorders are the conditions which cause impairment in the sense of vision. These disorders are often caused by certain eye diseases or structural abnormalities of the eye balls. The common vision disorders include:
Abnormal colour vision: Abnormal colour vision also termed as colour-blindness is the inability to differentiate between certain shades of colour. It is an inherited condition and men are more likely to be affected with this condition. Certain diseases of the eye and medications may also cause abnormal colour vision. Patients with colour-blindness may not be able to recognize the difference between shades of red and green, and shades of blue and yellow.
Amblyopia (lazy eye): Amblyopia is a condition in which there is reduced vision in one of the eyes because of incomplete development of the optic nerve pathway from that eye to the brain and as a result the brain receives blurred images from one eye. With the time brain ignores the impulses from affected eye thereby causing amblyopia. The affected eye appears normal however fails to send proper impulses to brain and the brain favours the other eye. It can also be caused by strabismus or the conditions in which one eye is more near sighted, farsighted, or astigmatic than the other eye.
Double vision: Double vision also called diplopia is a condition in which the patient complains of being able to see two images of a single object. There are two forms of double vision—monocular and binocular diplopia. Monocular diplopia occurs when there is double vision in one of the eyes only and double vision continues even if the other eye is closed. It is caused by conditions such as abnormal curvature in the front surface of the cornea (astigmatism), cone shaped cornea (keratoconus), thickening of the conjunctiva (pterygium), cataract, dislocated lens, a mass or swelling in eyelid, and dry eye. Binocular diplopia is caused by misalignment of the eyes and in this type, double vision resolves if either eye is covered. It is because of problem in one or more muscles that surround the eye and control the direction of gaze. These problems include strabismus, nerve damage, diabetes, myasthenia gravis, Graves’ disease, trauma to eye muscles.
Light sensitivity (photophobia): Light sensitivity or photophobia is a feeling of discomfort in the eye when exposed to very bright light. Severe form of photophobia may occur with eye problems and may cause severe pain in the eye even at low light intensity.
Refractive errors: Refractive errors may occur if the light does not focus properly on retina because of irregular shape of the cornea. The images may appear blurred. Common refractive errors include:
- Astigmatism (blurred vision): Astigmatism is a condition that causes blurred vision because of the irregular shape of the cornea or curvature of the lens. Light does not get focused properly on the retina and as a result vision becomes blurred at any distance causing eye discomfort. If astigmatism in a child is of a large amount, and it can lead to amblyopia when not given glasses since visual images for the brain in untreated astigmatism is always blurry regardless of viewing distance.
- Hyperopia (farsightedness): Hyperopia or farsightedness is a condition in which objects located far can often be seen clearly but nearer objects do not come into proper focus. This occurs if the eyeball is too short or the cornea has too little curvature. As a result, the light that enters the eye and the image forms beyond the retina. Some of the symptoms of this condition include difficulty in concentrating and maintaining a focus on near objects, strain in the eyes, fatigue or headache after work, aching eyes, nervousness and irritability. If hyperopia is of significant amount, even distant objects are poor when the amount of hyperopia is more than accommodative range of the person. High hyperopia can be amblyopic for a child, in particular the more hyperopic eye if in cases of anisometropia.
- Myopia (near-sightedness): Myopia or near-sightedness is a condition in which nearer objects can be visualised clearly but farther objects appears blurred. This occurs if the eyeball is too long and the cornea has more curvature. The light entering the eye does not focus on retina instead focus images before light reaches retina causing the distant objects to appear blurred.
Presbyopia (decreased lens flexibility): Presbyopia is a condition in which the lens in the eye loses its flexible nature causing difficulty in focusing closer objects. It is a part of the natural aging process and usually noticed in the early to mid-40’s and is not preventable. Blurred vision even at the normal reading distance, tendency to hold the book at an arm’s length, eye fatigue, headache are some of the signs of presbyopia.