Describe the various accommodation problems associated with the cornea, lens, and the shape of the eye.

Expert Solution

Accommodation Reflex is the adjustment of the visual apparatus to focus image of near object on the retina

Changes during accommodation are

Convergence of eyeball
Constrictions of pupil
Changes in anterior curvature of the lens

When viewing fat objects, suspensory ligament of the lens is tensed and traction on the capsule of the lens causes flattening of anterior surface of the lens. When the eye gets accommodated to a near object, ciliary muscle contract causing relaxation of suspensory ligament and elasticity of the lens make it more convex. The more spherical shape of the lens provides additional bending of the light and focus nearby object on retina

Problems of accommodation

Myopia: Also known as nearsightedness. In this condition, the patient is unable to see distant objects clearly but can see the close objects clearly. In this condition image of the distant object is not focusing on the retina but focused in front of the retina due to elongation of the eyeball or increased curvature of the cornea or due to thicker lens ( means eyeball is elongated than focusing power of the cornea and lens)

Myopia can be corrected by concave lens (diverging lens)

Hyperopia (Hypermetropia). Also known as farsightedness. In this condition, the patient is unable to see near objects clearly but can see the distant objects clearly. In this condition image of the distant object is not focusing on the retina but focused behind the retina due to a decrease in the anteroposterior diameter of the eyeball or due to the thinner lens (the eyeball is short than focusing power of the cornea and lens).

This condition can be corrected by a convex lens (converging lens)

Presbyopia: It is adult hypermetropia because it occurs after the age of 40. The lens becomes rigid and the ability to accommodation is lost. Such individuals can not see near objects and letters from usual distance of reading

This can be corrected by convex lens

Astigmatism: In this condition, the curvature of cornea or lens becomes irregular (vary from one plane to another). So, image from all parts of the abject not focused on the retina

This condition can be corrected by cylindrical lens

Sydney Mullin answered 1 year ago

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