Question

REVIEW ACTIVITIES FOR EXERCISE 3.5 of these, there are this is also cell layer, then the Test Your knowledge 1. The photoreceptors responsible for color vision are the _different types 2. The region of the retina in which there are no photoreceptors is called the known as the 3. Retinene (retinaldehyde) is derived from which vitamin? 4. When light enters the retina, it first passes through the -cell layer, before reaching the photoreceptors. 5. The axons of cells gather to produce the optic nerve. 6. Define: (a) visual acuity (b) accommodation Match these terms with the appropriate description - 7. myopia (a) abnormal curvature of the core or lens & hyperopia (b) eye too long 9. presbyopia (c) abnormally high intraocular pressure 10. astigmatism (d) eye too short _11. glaucoma (e) loss of lens elasticity Test Your Understanding 12. Describe the muscle layers of the iris and the innervation to these muscles. Use this information to explain how pupils constrict in bright light and dilate in dim light 13. Describe how the curvature of the lens is regulated and use this information to explain how images are kept in focus on the retina as a distant object is brought doser to the eyes.

Answer 1

1. photoreceptor resposible for colour vision is CONE cells,and its of three types ie, RED,GREEN,BLUE.

2. region of reina with no photoreceptors is called OPTIC DISC, which is also called BLIND SPOT.

3. RETINENE is derived from VITAMIN A.

4. The pathway of the ligth reacing the retina should travel through the INTERNAL LIMITING MEMBRANE(10th retinal

layer), and through EXTERNAL LIMITING MEMBRANE(3rd retinal layer) before reaching the photo receptors. Photoreceptors are situated in LAYER OF RODES AND CONES (2nd retinal layer).

5. Axons of retinal ganglion cells gather togrether to produce optic nerve.

6. VISUAL ACUITY: is considered a measure of form sense, so it is refers to the spatial limit of visual discrimination. In terms of visual angle visual acuity is defined as the reciprocal of the minimum resolvable visual angle measured in minutes of arc for a standard test pattern.

ACCOMODATION: Our eyes have been provided with unique mechanism by which we can even focus the diverging rays coming from a near object on the retina in a bid to see clearlt. The mechanism is called accomodation.

MATCH THE FOLLOWING

7. MYOPIA : EYE TOO LONG

8. HYPERMETROPIA: EYE TOO SHORT

9. PRESBYOPIA : LOSS OF LENS ELASTICITY

10. ASTIGMATISM : ABNORMAL CURVATURE OF CORNEA OR LENS

11. GLUACOMA: ABNORMALLY HIGH INTRA OCULAR PRESSURE.

12. IRIS a structure of the eye which regulates the size of the pupil. Iris consist of two types of muscles they are

a) SPINCTER PUPILLAE (Helps to constrict the pupil)

b) DIALATOR PUPILLAE (HElps to dialate the pupil)

When a person looks in to a brigth ligth the spincter pupillae contracts and as a result pupil constricts and reduces the amount of ligth entering the eye.

When a person in a dim ligth , the dialator pupillae contracts and as a result pupil gets dialated and the amount of ligth entering the eye increases and thus the person can perceive the image clearly.

13. Lens is an elastic structure of the eye. its elasticity is responsible for focusing an image to the retina clearly.

As per the struture the anterior curvature of lens is more than that of posterior curvature. The curvature of the lens is regulated by the CILLIARY ZONULES which holds the lens on the place, these zonules are attached to the ciliiary body.

when looking in a near object we need more power for the lens as to increase the power the lens should change its curvature, as a result the anteror curvature of the lens should be increased. When accomodation is at rest the cillairy zonules strectes the lens tigthly so it will not cause any changr in its curvature. When looking to a near object the cilliary zonules relaxes and the anterior curvature of the lens gets more curved and thus the piwer of the lens increase. This mechanism is termed as ACCOMODATION.

14. Myopia is a type of refractive error in which parellel rays of ligth coming from infinity are focussed infront of the retina when accomodation is at rest.

As the image is focused in front of the retina the image is blurred ,and to make this image clear we have to bring the focussed image to the retina. So that we use concave lenses infront of the eye which will refocus the image to the retina.As a result the patient can see claerly.

15. The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina. As it is composed of more cones the image focussed here is more clearer.

when a person is in a dimligth uses the photoreceptor rod cells which helps for the nigth vison as result we can achieve a clear image. and also in dim ligth as the dialator puplillae acts the amount of ligth reaching the retina is increases as we can see more clearly.

16. Carrot contains vitamine A but eating carrot regularly may not help to prevent refracrtive errors. Refractive errors may be due to curvatural changes occuring in the cornea,lens,and also due to the chage in the axial length of the eye ball.So these changes cannot be altered if we eat carrots regularly but we can keep our eye healthy by these supplimentation.

Also vit A is helpful for getting rid from nigth blindness by means of activating rod cells. rod cell are helpfull for the dimligth vision.And the vit A helps to form rod cells from the ligth sensitive pigment called rodopsin by the help of retinal isomerase.

17. Young helmontz theort of colour vison states that we have three colour pigments ie,red,green and blue. Our brain has the ability to combine these images as per our needs. If our eyes has no any defects but the signals which is travelled from the optic nerve to the brain is blocked we will not ble to perceive the image.

As the fact its clear that our brain is resposible for our sigth.

18. Colour blindness may be due to genetical problems in the pathway of the eye.

A person which has colour vision after birth can loss his colour vidion as a part of his life style, having gung foods can cause defects in the photoceptor cells and can lead to colou blindness.

20/300 indicates the vision less that 6/60

LASIK surgery is the reshaping of the cornea, and to alter its curvature to focus the ligth rays to the retina. For this corneal flap is taken and we make the curved cornea flatter thus the ligth rays focuses the reina very well.

19. LASIK surgery is used more to clear distant vision. if a person gets age more than 40yrs he cannot focus to near object as his ability of lens to accomodate is lost so that he should wear his near vision glasses.

Cloudy patches may be due to cataract , that is the opasification of the crystalinelens. as the lens is transparent any opasities formed in it can cause a cloudy vision.

central vision deteroriation may be due to optic nerve defects,gluacoma or scotoma in the centre.