Question: 100% NCERT covered from Particular Keyword.Explanations are 100% from NCERT | [Difficult level:Hard] NOT From NCERT NEET 2019.
Which of the following statements is correct?
1. Cornea consists of dense matrix of collagen and is the most sensitive portion of the eye.
2. Cornea is an external, transparent and protective proteinacious covering of the eye-ball
3. Cornea consists of dense connective tissue of elastin and can repair itself
4. Cornea is convex, transparent layer which is highly vascularised
Ans:1. Cornea consists of dense matrix of collagen and is the most sensitive portion of the eye.
Cornea
👉Information regarding changes in the environment is received by the CNS
through the sensory organs which are processed and analysed. Signals are then
sent for necessary adjustments. The wall of the human eye ball is composed of
three layers. The external layer is composed of cornea and sclera. Inside sclera is
the middle layer, which is called the choroid. Retina, the innermost layer, contains
two types of photoreceptor cells, namely rods and cones. The daylight (photopic)
vision and colour vision are functions of cones and twilight (scotopic) vision is the
function of the rods. The light enters through cornea, the lens and the images of
objects are formed on the retina.
👉UV radiation of wavelengths shorter than UV-B, are almost completely
absorbed by Earth’s atmosphere, given that the ozone layer is intact. But,
UV-B damages DNA and mutation may occur. It causes aging of skin,
damage to skin cells and various types of skin cancers. In human eye,
cornea absorbs UV-B radiation, and a high dose of UV-B causes
inflammation of cornea, called snow-blindness, cataract, etc. Such
exposure may permanently damage the cornea.
👉Parts of an eye
nearly a spherical structure. The
wall of the eye ball is composed
of three layers (Figure 21.6). The
external layer is composed of a
dense connective tissue and is
called the sclera. The anterior
portion of this layer is called the
cornea. The middle layer,
choroid, contains many blood
vessels and looks bluish in
colour. The choroid layer is thin
over the posterior two-thirds of
the eye ball, but it becomes thick
in the anterior part to form the
ciliary body. The ciliary body
itself continues forward to form a pigmented and opaque structure called
the iris which is the visible coloured portion of the eye. The eye ball contains
a transparent crystalline lens which is held in place by ligaments attached
to the ciliary body. In front of the lens, the aperture surrounded by the
iris is called the pupil. The diameter of the pupil is regulated by the muscle
fibres of iris.
👉The space between the cornea and the lens is called the aqueous
chamber and contains a thin watery fluid called aqueous humor. The
space between the lens and the retina is called the vitreous chamber
and is filled with a transparent gel called vitreous humor.