This document summarizes key concepts in optics and refraction, including: - Geometrical optics describes the behavior of light rays using principles like rectilinear propagation, reflection, and refraction. - Reflection is when the path of light rays changes without changing the medium, and is demonstrated using plane and spherical mirrors. - Refraction occurs when light passes from one medium to another of different density, and is described using terms like incident ray, refracted ray, and critical angle. It has applications in tools like prisms, gonioscopes, and fiber optics. - Lenses use refraction to bend light rays and form images. Key lens properties are discussed, including cardinal points, focal length,

1. Optics and Refraction
Dr GOPI KRISHNA
MBBS,MS OPHTHALMOLOGY
FELLOW IN PHACOEMULSIFICATION AND SICS ( ANTERIOR SEGMENT)

4. Physiological optics

8. Geometrical optics
• Behaviour of light rays is determined by ray optics
• Where ray of light follows path of straight line
*
• Rectilinear propagation
• Reflection
• Refraction

9. Reflection
• Change in path of rays with out change in medium.

10. Mirrors
Plane mirror – looking mirror,one side is silvered and other side is
polished .
Images formed by plane mirrors – size same as object,laterally
inverted,virtual in nature,same distance
Spherical mirrors : concave and convex

11. • A convex mirror is also known as a diverging mirror as this mirror
diverges light rays when they strike its reflecting surface.
• Virtual, erect, and diminished images are always formed with convex
mirrors, irrespective of the distance between the object and the
mirror.
• By changing the position of the object from the concave mirror,
types of images can be formed.
•

12. Lateral inversion in plane
mirror

14. Virtual erect and diminished

16. Refraction

17. • Incident ,refracted are on opposite sides of normal ,but all are in
da,same plane.
• Refractive index

18. Total internal reflection
• When a light enters from denser medium to rare medium is incident
at an angle greater than critical angle ,then the ray gets reflected back
in to the denser medium .
• Critical angle: angle of incidence in the denser medium corresponding
to which angle of refraction is 90 degree in rare medium
Uses: applantion tonometer,gonioscopes,fibre optics.

20. Prisms

21. Uses of prisms
• In gonoiscopes,aplantation tonometer,keratometry
• Relieve diplopia
• To examine angle of deviation (squint)

23. Lens
• Transparent refracting medium.
1 spherical
A) convex B) concave
2. Cylindrical lens

24. Cardinal points of lens
1. centre of curvature( C ): centre of sphere of which refractive lens is
the part.
2. Radius of curvature ®: radius of sphere
3. Principal axis (AB) : line joining the centre of curvatures of its
surfaces.
4. Optical centre (O): nodal point,point on principal axis passing where
rays do not undergo any deviation
5. Principal focus (F):point on principal axis where parallel rays after
passing through the lens either converge or appear to diverge
6. Focal length (f): distance between optical centre (O) & principal
focus( F).
7. Power : ability to converge or diverge the light (p=1/f)

25. • Principal focus (F)
• Optical centre( O)
• Nodal point (N)
• Principal axis AB
• Power
• Focal length (f)
• Centre of curvature (C) Cardinal points of convex lens

29. Spherical lens
1 .Convex :
• thick at centre and thin periphery,
• Object close to lens appears magnified
• When lens is moved object appears movement in opposite direction
• Uses: hypermetropic correction,aphakia,presbyopia
2 .Concave :
• Thin at centre ,thick at periphery
• Object through it appears minified
• Movement with lens is in the same direction
• Uses: myopic correction

30. Cylindrical
• Lens acts only in one axis
• Convex and concave
• Uses : astigmatism correction ,Maddox rods,

33. Schematic and reduced eye

45. Thank you