Visual Acuity Test
Visual acuity (VA) indicates the clarity of vision dependent on the sharpness of retinal focus along with interpretation by the brain. Visual Acuity Test involves a test where a person has to read letters on a standardized Snellen chart held about 20 feet away. This test is done individually for both eyes. Visual acuity test is part of the routine eye tests to check for vision. Visual acuity is expressed as a fraction where the numerator is the distance of the chart, usually 20 feet. The denominator is the distance where a person with normal eyesight can read the same line correctly. 20/20 is normal vision. Abnormal results on the visual acuity test indicate the need for corrective glasses.
Macular Vision
The macula is a vital part of the retina that is responsible for our central vision. It is involved in processing the light rays entering the central vision field. It is rich in cells called cones that convert light rays into impulses that travel through the optic nerve to the brain. Macular vision is about fine details, color and reading. Macular vision is intrinsic to our good vision. Problems in macular vision are usually due to drying out of certain areas of the macula or wet patches. Macular degeneration happens largely due to aging. Dry Macular degeneration or non-exudative macular degeneration is what is mostly noticed. It does not cause as much damage as wet macular degeneration. Symptoms of dry macular degeneration appear gradually and there is no treatment for this. Wet macular degeneration happens rather rapidly due to abnormal blood vessels in the retina. Photo dynamic therapy (laser) and anti-VEGF inhibitors are used to treat wet macular degeneration. Retinal photographs, visual acuity test, Amsler Grid and Fluorescein Angiography are tests that help determine macular vision problems.
Astigmatism
Astigmatism is a refractive error caused by abnormal curvature of the cornea thereby causing blurred vision. It might occur along with myopia or hyperopia. Some persons suffer astigmatism from birth. Astigmatism can be identified with the routine eye tests. Visual acuity test, keratometry and refraction might be undertaken to diagnose the astigmatism or any other vision problem. Mild astigmatism is not usually corrected. Corrective lens is prescribed after noting the extent and axis of the astigmatism. Orthokeratology is undertaken to implant specially designed rigid contact lenses to gradually reshape the curvature of the cornea. Laser surgery can be done to alter the corneal shape.
Bibliography / Reference
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