This document provides an overview of the optics of the human eye. It describes the main components of the eye, including the cornea, lens, iris, retina, and their functions. It explains how light enters the eye and is focused onto the retina through refraction by the cornea and lens. The document also defines and differentiates several common vision conditions, such as myopia, hyperopia, presbyopia, and astigmatism. Accommodation through changing the shape of the lens allows the eye to focus on objects at different distances.

1. Optics of the eye
BY
ANSIYA PRASAD

2. Objectives :
 Eye and its components.
 Axis and visual angles of eye .
 Describe the properties of light .
 Differentiate between convex and concave lenses.
 Describe Accommodation.
 Describe how the eye focuses light.
 Differentiate between presbyopia , Myopia , hyperopia
and astigmatism.

3. Eye as a camera :
 Eyelids – shuttter .
 Cornea – focusing system.
 Lens – focusing system.
 Iris – diaphragm .
 Choroid – dark chamber.
 Retina – light sensitive film.

4. Cornea :
 Cornea is a plus lens of +42D
 Radius of curvature of ant.surface =
7.8mm
 post.surface = 6.8mm
 Diameter about 11.5mm and thickness of
0.5 – 0.6mm in centre and 0.6 – 0.8mm
periphery.
 An average horizontal diameter = 11.7
mm
 vertical diameter = 11mm.

5. Contd...
 Reasons of refraction :
 curvature
 Significant differences in refractive
index .

6. Crystalline lens :
 Lens accounts for about one-third of refraction of
eye.
 accomodation
 provides a mechanism of focusing at different diatances.
 Radius of curvature
 ant.surface = 10mm
 post.surface = 6mm
 Refractive index
 nucleus- 1.41
 pole – 1.385
 cortex – 1.38
 Total power – 15 -18 D.

7. Anterior chamber :
 Is a cavity between cornea and iris .
 Filled with aqueous humour .
 Refractive index of aqueous humour is
1.336.
 depth of aqueous chamber is 2.5 -
4.00mm
 change in anterior chamber depth ,
change the total power.

8. Iris and pupil :
 Regulates the amount of Light entering
the eye.
 at 2.4mm Pupil size, best retinal image
obtained, as abberation and diffraction
are balanced.
 pupil size varies 2-4mm in diameter in
bright light
 4-8mm in diameter in dim light .

9. Vitreous humour :
 Is a transparent ,colorless ,gelatinous
mass that fills the space in between lens
and the retina .
 is 8-9mm in diameter.
 Refractive index of vitreous humour is
1.337.

10. Retina :
 Maximum resolving power is at fovea
 light sensitive film.
 Concave spherical surface with radius of 12mm.
 22mm in diameter .
 contains about 7 million cones and 75- 150 million rods.
 Advantages of curvature of retina is that
 Curved images formed by the optical system Is brought in the right order.
 A much wider field of view Is covered by the steeply curved retina .

11. Axis and visual angles of eye :
 Optical axis – the line passing through
the centre of cornea and centre of lens
and meets the retina on the nasal side of
the fovea.
 Visual axis – is the line joining the
fixation point , nodal point and the fovea.

12. Axis and visual angles of eye :
 Fixation axis – is the straight line that
joins centre of rotation of eyeball with
fixation point .

13. Visual angles :
 Angle alpha – angle formed between
visual axis and optical axis at nodal point.
 Angle gamma – angle between optic
axis and fixation axis .
 Angle kappa – angle formed between
pupillary line and visual axis .

14. Properties of light
 Electromagnetic radiation
 Visible light
 Wavelength of 400- 700nm
 Violet- short wavelength , highest energy .
 Red- long wavelength , lowest energy.

15. Properties of light
Reflection
 Light blocked by non-
transparent object and bounce
off a surface .
Refraction
 Bending of light as it passes from
another with a different density.

16. Focusing light on the retina :
 Light is bent 3 times
 Enters the cornea
 Enters the lens
 Leaving the lens
 Only can adjust the amount of refraction
through lens.

17. Convex And concave lenses :
Convex lenses
 Light converges as it passes through.
 Converge to single point = focal point
 A thick lens causes more refraction and therefore
shorter focal point .
 A thin lenses causes less refraction and therefore
longer focal point..
 Results in image being upside down and
reversed at focal point.

18. Convex and concave lenses
Concave lenses
 Diverge ( spreads out the light rays that
have been refracted through it )Light .

19. Changing the thickness of lens :
Ciliary muscles

20. Emmetropic eye
 Distance
 Light coming to eye as parallel rays
 Dont need to bend light as much
 Ciliary muscles are relaxed

21. Emmetropic eye
 Near vision
 Light coming in as a divergent rays .
 Need to thicken the lens .
 ciliary muscles contracted.

22. Focusing for close vision
 Accommodation Of lenses
 its the ability of eye to change its focus from distant to near objects ,
this process is achieved by the lens changing its shape .
 Ciliary muscles contract so lens can thicken.
 Far point of vision = Farthest point till where we can see.
 That distance in which no accommodation Is needed ( 6m Or 20ft ).
 near point of vision= the nearest point
 Closest point on which we can focus clearly ( lens cant get any fatter )

23. Contd...
 Constriction of pupils
 Prevents the most divergent light rays from entering
the eye .
 convergence of eyeballs
 Keeps object focus on fovea .
 getting cross eyed.

24. Myopia :
 Near sightedness
 parallel rays of light are focused in front
of retina when accommodation is at rest .
 occurs when eyeball is too long or
cornea becomes too steeply curved .
 Can correct through concave lenses.

25. Hyperopia:
 Long sightedness.
 parallel rays of light coming from infinity
are focused behind the retina with
accommodation being at rest.
 Occur if eye is too short
 can correct through convex lens .

26. Presbyopia :

27. Astigmatism :

28. Thank you