Tag: disorders of nervous system

Myopia occurs when the light is focused in front of the retina. It occurs because either the eyeball is too long, or because the cornea is too curved. People with short sight are not able to see distant objects clearly. Concave prescription lenses (called as minus lenses) are used to bend light rays slightly outwards. The light rays then have a greater angle to bend back to focus when traveling through the cornea and lens. As a result, the light rays focus further back on the retina.

Glaucoma is a group of ocular (eye) disorders resulting in optic nerve damage or loss to the field of vision, caused by a pressure buildup of the fluid of the eye. The increased pressure, called as intraocular pressure, can damage the optic nerve, which transmits images to the brain. If damage to the optic nerve from high eye pressure continues, glaucoma will cause permanent loss of vision. Without treatment, glaucoma can cause total permanent blindness within a few years.

A cataract is a clouding of the lens in the eye, that affects vision. Most cataracts are related to aging. People with diabetes or those taking high doses of steroid medications have a greater risk of developing subcapsular cataract (the one that occurs at the back of the lens).
Thus, the correct answer is the option (C), 'Steroids'.

Hyperopia or hypermetropia, is a refractive error. Ideally, the cornea and lens, the two focusing structures in the eye, focus images directly on the surface of the retina. If the eye is too short, or the focusing power is too weak, the image is focused behind the retina. At the retinal surface, the image is blurred. Thus, the vision, too, is blurred.

Hypermetropia occurs when the light is focused behind the retina. So, the lens changes its thickness, which aims to bring the light into focus on the retina - a process is called as accommodation. But, people with long sight cannot accommodate fully and so the light does not focus sharply and vision is blurred. This occurs because either the eyeball is too short, the cornea is too flat or the lens cannot become round enough. The simplest, cheapest and safest way to correct long-sightedness is with glasses. 

Rhodopsin serves as a visual purple pigment of rod cells and is responsible for night vision. Rhodopsin deficiency causes night blindness. Myopia is caused by elongation of eyeball while shortening of eyeball causes hypermetropia. The cornea is the transparent anterior window of an outer layer of the eyeball and does not have rods. Thus, the correct answer is option D.

Myopia also known as nearsightedness or short-sightedness is a condition of the eye where light focuses in front, instead of on the retina. People having myopia can see close objects clearly, but objects farther away appear blurred. It occurs if the eyeball is too long or the cornea is too curved. So, the correct answer is option B.

Colour blindness and haemophilia are both X-linked recessive disorders. 

cryosurgery is a treatment that involves extreme cold temperatures by the use of liquid nitrogen to freeze the diseases cells like the tumors, warts on the skin and abnormal cells. Hence the correct answer is option C.

Presbyopia is caused by an age related process. It occurs due to a gradual thickening and loss of flexibility of the natural lens inside the eye. These age related changes occur within the proteins in the lens, making the lens harder and less elastic over time. Age related changes also take place in the muscle fibers surrounding the lens. Changes in the lens curvature progressively cause diminished ability to focus on near objects.