Name the following:
(i) Area of sharp vision in the eye ...............................................................
(ii) The kind of lens used for correcting near-sightedness ...........................
(iii) The condition in which the lens of the eye turns opaque .....................
(iv) The capacity of eye to focus objects at different distances ...................
Answers
Answer:
Macula: The portion of the eye at the center of the retina that processes sharp, clear straight-ahead vision
2 concave lens is used
3.catarct is the disease
4.it is called accommodation
Answer:
i) Fovea centralis .
ii) biconcave
iii) Cataract.
iii) accomodation.
Explanation:
Fovea centralis is a small depression in the macula lutea where the cones are densely packed. This lacks blood vessels and is the point where sharpness of vision is greatest.
Near-sightedness is also called myopia. In this refractive abnormality, the lens are thicker than normal and the image is formed in front of the retina. myopic person cannot see distant object. In such case placing a biconcave lens in front of eyes diverges the light rays before striking the eyes and the image is formed on the retina.
Cataract is a condition when the lenses of eyes become thick less flexible and cloudy. This results from accumulation of broken eye tissues on the lens. Cataract may result as ageing symptom,can be genetic or from injury caused to the eyes. If left untreated it may result in permanent blindness.
The ciliary muscles of the eye expand or contract to adjust the focal length of the eyes depending upon the distance of the object we focus on. This capacity of the eyes to adjust the focal length is called accomodation.