structure of any organ makes the viewer clear about the structure and probably to relate the function of it to make the viewer understand better

1. SPECIAL SENSES
VISION
- Dr. T. Manopriya,
Dept of Physiology,
AMCRC.

2. SLO's:

3.  Sight/Vision.
§ Auditory/Hearing.
§Smell/Olfaction.
§Taste/Gustation.
§Touch/Tactile.
5 SENSATIONS & ITS TYPES:

5. PRINCIPLES OF OPTICS:
 Refraction & Focusing.
 Light rays travel through air at a velocity of about 300,000 Km/sec.
 But they travel much slower through transparent solids and
transparent liquids. to add text

7. REFRACTIVE POWER:
 Refractive power (RP) of lens = 1 meter / Focal length.
 Measured in "Diopters"(D).
 Focal length : 1 meter is the distance from the lens at which the object is
kept.
§ Diopter (D) is reciprocal of focal length.
§ 1 Diopter = 1 meter / 1 meter.
§ In human eye, average focal length is 17 mm.
§ Therefore,
Refractive power of human eye = 1 m /17 mm (1000mm/17mm) = 59 D.

9. In human eye there are different refractive media with different refractive
indices.
1. Cornea – 1.38.
2. Aqueous humor – 1.33.
3. Lens – 1.40.
4. Vitreous humor – 1.34

10. REDUCED EYE / SCHEMATIC EYE:
 In a schematic eye, all these refractive indices are ignored &
considered as one lens system which is referred to as reduced eye.
It is useful in simple calculations of refractive errors.
 It has an optical center/nodal point which lies in the
posterior part of crystalline lens and it has the refractive power of
59.0 Diopters.
 When the lens is accommodated to distant vision the cornea
provides 43 diopters and Lens provide 16 diopters.

12. TYPES OF LENSES:
• Different types of Lenses are available for
clinical use.
• These refract light rays at all edges of the
lens.
• They are;
1. Spherical Lens.
2. Cylindrical Lens.
3. Contact lens.
4. Intra ocular lens.

13. Lens
Spherical
Biconvex
Cylindrical
Biconcave
Convex cylindrical
Concave cylindrical

14.  Spherical Lenses are either,
Biconvex or Biconcave in shape.
Refract light rays at all edges of the lens.
 Biconvex lens – converge the light rays towards a central ray &focus at
one point.
 Biconcave lenses-Diverge the light rays called as diverging lens.
 Images appear Larger when convex lenses are used.
 Images appear smaller when concave lenses are used. to add text

15. CONTACT LENSES:
 Usually made of soft plastic.
 Have both advantage and disadvantage.
Advantages:
 Prismatic effect of spectacles are eliminated.
 Clear vision greatly improved.
 These give better correction in severe Myopia, Irregular
Astigmatism, Aphakia etc..,
Disadvantages:
 Causes blurring-due to edema of cornea.
 Infection may develop.
 Corneal ulcers on prolonged use.
 Keratoconus-outward conical bulging of cornea.

16. PHYSIOLOGICAL ANATOMY OF EYE:
 Eye – Special sense organ – Sense of Light.
 Adult human Eye ball, hollow, spherical structure.
Diameter -24 mm.
Situated in the orbital cavity.
Only 1/6th of eye ball is visible outside.

20. 3. Inner layer of eye - retina:
a) Outer pigmented layer of epithelial cells – firmly attached to
the whole of the inner surface of Choroid.
b) An inner layer of Nerve cells and Nerve fibers which contain
the Photoreceptors/Light sensitive receptors – Rods &
cones.

21. CILIARY BODY:
 It is attached to the suspensory ligaments
At the end of ligament to join forming the capsule enclosing
the Crystalline lens.
 Ciliary body further continues forward to form the IRIS.
 It contain two types of smooth muscles fibers i.e. Circular muscle &
longitudinal muscle, attached near the cornea scleral junction.
 Ciliary muscles play an important role during accommodation for
near vision.

22. IRIS:
 Pigmented & Opaque muscular structure – gives color to the eye
(Black, brown or blue).
 In its center - has an aperture known as Pupil.
 Through pupil light enters the interior of the eye.
 Pupil is guarded by muscles which determines the size of the pupil.
1. Sphincter pupillae - (circular muscle fibers).
2. Dilator pupillae - (radial muscle fibers).

23. Iris divides the space between posterior surface of cornea &
anterior surface of lens.
• Space behind cornea and in front of Iris - Anterior Chamber.
• Space in front of lens & behind Iris - Posterior Chamber.
• Both the Anterior and posterior chambers are filled with
Aqueous Humor.

24. FUNCTIONS OF IRIS:
 Controls the intensity of light entering the eye.
 Regulated via constriction (or) dilatation of Pupil.
 In addition – Pigmented layer also absorbs extra light entering the
eye.
 Note: Diameter of the pupil can produce up to 5 fold changes in the
amount of light reaching the retina.
 Prevents entry of light through the periphery of the lens, thus
preventing Spherical and chromatic aberration.
 It also increases the depth of focus by constriction of the pupil.

25. LENS:
 Devoid of blood supply but satisfies its low metabolic
requirements by taking up nutrients from – Aqueous humor.
 Glucose is taken up by the lens substance and is metabolized to
lactic acid (anaerobic glycolysis).
 The lactic acid produced diffuses into Aqueous humor.

26. CRYSTALLINE LENS:
 A biconvex circular, transparent body enclosed within a capsule.
 Lies immediately behind the pupil.
 It is held in position by Suspensory ligaments or Zonules.
 The other end of it is attached to ciliary body.
FUNCTIONS:
 It helps in the formation of image on the retina by altering the
curvature of its anterior surface.
 The central core of the lens possess a higher refractive index than the
other areas of lens.

27. RETINA:
All the nerve fibers from the retina converge to form the Optic Nerve – to
finally reach the brain.
• The small area where optic nerve leaves the eye is called optic disc.
• Optic disc lies 3 mm medial to the posterior line of the eye ball.
• It lacks the receptors ( rods and cones), so visual perception is absent
in this area. Therefore, this spot is called “Blind Spot”. t
• At the posterior of the pole of the eye, there is a yellowish pigmented
region called macula lutea (yellow spot) which marks the location of
fovea centralis (1mm in diameter).

29. AQUEOUS HUMOR:
 A thin watery fluid with a pH of 7.1 - 7.3.
 Specific gravity : 1002 – 1004.
 Present in the anterior & posterior chamber of eye.
 Composition :
i. Low in protein.
ii. Formed by diffusion from capillaries.
iii. High content of vitamin-C.
iv. High concentration of sodium chloride (NaCl).

30.  Circulation:
• AH – formed from ciliary process (posterior chamber).
• Via pupil AH enters the anterior chamber.
• Passes across the corneal epithelium lining the canal of Schelm at
the limbus, I.e., junction between cornea & sclera.

32. • Normally AH is completely replaced every 90 minutes.
• Normal pressure in,
 Anterior chamber: 13 – 18 mmHg.
 Venous plexus: 12 – 15 mmHg.
• Thus it helps in continuous drainage of AH into venous plexus.
• Blockage of canal Schelm leads to increase in intra-ocular pressure
(IOP) above 80 mmHg. Eyeball on palpation feels like a stone –
condition is called as "glaucoma".

34.  Functions of Aqueous humor:
1. Provides nutrition to all avascular structures of the eye – cornea &
lens.
2. Maintains intra-ocular pressure at a constant level. Thereby helps
in normal image forming mechanism.

35. Thank you!