1. Physiology of Vision
Optics of Eye
Dr. Sumera Gul

2. Learning Objectives
At the end of the lecture the students should be able to:
Explain the basic physiological anatomy of eye
Discuss the refractive index, refractive power and refractive principles to lenses applicable in eye
Explain focal length and focal point
Discuss the effects of various types of lenses on refraction of light rays

5. The Eye

6. Protectors of the Eye Boney Orbit of the eye Exto-ocular muscles
Eye lids
Eye lashes
Conjunctiva
Tears (enzyme lysosyme inhibits bacterial growth)

7. The Structure of the Eyeball
The Sclera, - thick fibrous outer coat which gives resistance and durability to the eye.
The Choriod - delicate vascular coat which supplies nourishment to the inner layer of the retina.
The Retina - photosensitive layer of the eye which translates the light impulses into electronic impulse which travels down the optic pathways to the brain.

8. Cornea Transparent avascular tissue with 5 distinct layers.
Function is to allow light rays to enter the eye.
Surrounded by a vascular layer known as the limbus which nourishes the cornea.
Should be smooth and clear.

9. Tears Normal Tears Reflect Tears Lubricant
Protect from bacterial infections
Contain an enzyme called lysozyme
Reflect Tears
Mostly water
Back-up for irritation, emotions and dryness

10. Lens
The lens capsule is a biconvex, avascular, colorless almost clear structure
About 65% water and 35% protein
Function is to help focus light waves onto the retina by changing the curvature of the lens
No pain fibers, blood vessels or nerves in the lens.

11. Retina
Thin semitransparent multi-layered sheet of neural tissue that lines the inner layer of the posterior section of the globe of the eye.

12. Refractive Index

13. Refractive Index
Light rays travel through air at a velocity of about 300,000 km/sec.
Velocity of light rays is much slower through transparent solids and liquids.
The ratio of the velocity of light in air to the velocity in the substance.
The refractive index of air is 1.00.

14. Refractive Index
If light travels through a particular type of glass at a velocity of 200,000 km/sec. What will be the refractive index of this glass?

15. Refractive Index
If light travels through a particular type of glass at a velocity of 200,000 km/sec. What will be the refractive index of this glass?
Refractive index of a substance = The velocity of light in air
The velocity of light in the substance.

16. Refractive Index
If light travels through a particular type of glass at a velocity of 200,000 km/sec. What will be the refractive index of this glass?
Refractive index of a substance = The velocity of light in air
The velocity of light in the substance.
= 300, = 1.50
200,000

17. What happens when light rays traveling forward in a beam strike an interface that is perpendicular to the beam?

18. The rays enter the second medium without deviating from their course.
The only effect that occurs is decreased velocity of transmission and shorter wavelength

19. What happens when light rays traveling forward in a beam strike an interface that is angulated to the beam?

20. Refraction
This bending of light rays at an angulated interface is known as refraction.
Note particularly that the degree of refraction increases as a function of
(1) the ratio of the two refractive indices of the two transparent media and
(2) the degree of angulation between the interface and the entering
wave front.

21. Convex Lens Focuses Light Rays.
focal point

22. Concave Lens Diverges Light Rays.

23. Focal Point
The distance beyond a convex lens at which parallel rays converge to a common focal point is called the focal length
of the lens.

24. Refractive Power

25. The more a lens bends light rays, the greater is its “refractive power
This refractive power is measured in terms of diopters.

26. The refractive power in diopters of a convex lens is equal to 1 meter divided by its focal length.
Thus,a spherical lens that converges parallel light rays to a focal point 1 meter beyond the lens has a refractive power of +1 diopter.
If the lens is capable of bending parallel light rays twice as much as a lens with a power of +1 diopter, it is said to have a strength of +2 diopters, and the light rays come to a focal point 0.5 meter beyond the lens.

31. The lens system of the eye is composed of four refractive interfaces:
(1) the interface between air and the anterior surface of the cornea,
(2) the interface between the posterior surface of the cornea and the aqueous humor,
(3) the interface between the aqueous humor and the anterior surface of the lens of the eye,
(4) the interface between the posterior surface of the lens and the vitreous humor.