Eye Exam Refraction -- Lesson 271
In this post we would learn about errors of refraction. Astigmatism: - Defective curvature of the cornea or lens of the eye is called Astigmatism. From one or more abnormal curvatures of the cornea or lens this problem leads in. This causes light rays to be unevenly and not sharply focused on the retina, so that the image is distorted. A cylindrical lens placed in the proper position in front of the eye can correct this problem. Hyperopia: - The eye ball in this condition is too short or the refractive power of the lens is too weak. Parallel rays of light tend to focus behind the retina and this result in a blurred image. A convex lens which is thicker in the middle than at tht sides bends the rays inward before they reach the cornea, and thus the rays can be focused properly on the retina. Myopia: - In myopia the eyeball is too long or the refractive power of the lens so strong that light rays does not properly focus on the retina. The image perceived is blurred because th...