N KERALA SSLC BIOLOGY,one of the important chapter 2 is windows of knowledge.We will provide important pdf,notes,videos,questions…..
✅CONJUNCTIVA;secretes mucus which protects the anterior
portion of the eye ball from being dry.
✅Lysozyme; Enzyme present in tears,destroys germs that enter the eyes.
🔘Layers of the eye;
✅1 Sclera 2.Choroid 3.Retina
✔️SCLERA;The white outer layer,gives firmness to
teye. Made up of connective tissues,contain 2parts
- 1.cornea;transparent anterior part of the sclera which refracts light rays to focus on the retina.
- 2conjuntiva; layer which covers and protects the front part of sclera except the cornea.
✔️Choroid;The middle layer,which contains a
large number of blood vessels.
- iris;The part of the choroid seen behind the cornea,pigment
melanin gives the iris a dark colour
- pupil;The aperture seen atthe centre of the iris.
- lens;transparent convex lens,
✔️Retina;The inner layer which has
- yellow spot;plenty of photoreceptors are present in this part,it gives maximum visual clarity.
- blind spot;The part of the retina from where the optic nerve begins.Here is no vision asphotoreceptors are
- Optic nerve;Transmits impulses from photoreceptors
to the visual centre in the brain.
- Aqueous humor – A watery fluid seen in the aqueous chamber [between cornea and lens] , oozes from the blood. This fluid supplies nutrients and oxygen to cornea and lens.
- Vitreous humor – A jelly like fluid filled with in the vitreous chamber between lens and retina.It helps to maintain the shape of eyeball.
✅power of accommodation of the eye.
The capacity of the eye to change the curvature of lens depending up on the distance between the the eye and the object by adjusting the focal length is called the power of accommodation of the eye.
HOW WE CAN SEE NEAR OBJECT AND FAR OBJECTS
When we look at a distant object, the ciliary muscles are in a relaxed position so as to keep the ligaments tight. Therefore the curvature of lens decreases to fix the image on retina
When we look at a near object, the ciliary muscles contract to loosen the ligaments. When ligaments relax, the curvature of lens increases naturally ,to focus the image on retina.
The ability of both the eyes to focus on the same object is known as binocular vision.Binocular vision help us to get a three dimensional image of the object. This help us to calculate the correct distance, depth, height and width of the object.
disorders and diseases that affect on our eyes
✅Hyper metropia(long sight)
Due to shortened eyeball images form behind retina.Cannot see nearby objects clearly
Due to elongated eyeball images form in front of retina.
Cannot see distant objects clearly
Due to the deficiency of vitamin A, no clear vision in
Due to the defect cone cells which detect red and green
colours and fails to detect those colours
Prolonged deficiency of vitamin A results dry
conjunctiva and cornea
Gradual decrease in the power of lens due to
decreasing of transparency of lens
REMEDY;Surgical replacement of lens