In case of myopia, the light focuses in front of, instead of on, the retina when observing far away objects. while for near objects the eye is able to focus the light onto the retina. For most people with myopia, eyeglasses are the primary choice for correction. They prescribe concave lens which shift the focal point backwards such that it lies on the retina.

The eye focuses on an object by bending all of the light rays from a single point on the observed object toward a single point on the retina. In the eyeball, light rays passing through the cornea are bent by its curvature toward the pupil. The lens flexes to change its curvature and finish the focusing process. When an object is located at infinity, the focal length, or the distance from the cornea to the retina, of a normal relaxed eye is about 1.7 cm (17 mm). While if the object is at near point, which is about 25 cm (10 inches) for most people the focal length is around 22.3 mm.

So I want to understand how by shifting the focus point for far objects such that it falls on the retina, how come it does not cause near objects to become blurred?


The eye retains its ability of accomodation. In myopia, the accomodation range is such that only near objects can be focused. With the external lens, the range is shifted. Very near objects can no longer be focused, but distant ones can. Usually only a small range very close to the eye is lost.

  • $\begingroup$ So before the range was not enough for far objects while it could handle near objects. With the lens in place this range shifts enabling the eye to focus. So I would be right to say that the eye will be undergoing ciliary muscle contraction when transitioning from looking at a near object with glasses to without them? $\endgroup$ – Aditya May 17 '18 at 18:00
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    $\begingroup$ Accomodation doesn't change the shape of the eye, but the lens inside. The overall eye shape will be the same. $\endgroup$ – BowlOfRed May 17 '18 at 18:03

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