Question

2. Correcting vision: quantitative. Corrective lenses work because the lens bends light such that it, combined with the eye itself, light forms a clear image on the retina. Another way to think about this is that the corrective lens (glasses) form an image of the object at a location where the eye can see clearly without corrective lenses. For a nearsighted person viewing an object very far away (object at infinity), the lens corrective lens creates an image at the person’s far point. For a farsighted person viewing an object at the normal near point of 25 cm, the lens creates an image at the person’s near point.

a. A nearsighted patient has a far point of 400 cm, as in problem 1c/e. What kind of lens (converging or diverging) is needed to allow this person to clearly see a very far away object (object at infinity)? In other words, what kind of lens would form an image on the retina of this patient's eye? If this lens is placed 2 cm from the eye, what focal length should this corrective lens have? What is the prescription in diopters?

b. A farsighted patient has a near point of 40 cm, as in problem 1d/f. What kind of lens (converging or diverging) is needed to allow this person to clearly see an object 25 cm from the eye? If this lens is placed 2 cm from the eye, what focal length should this corrective lens have? What is the prescription in diopters?

Answer 1