Thisisthebestslideonophthalmicprisms.pptx

Describes about different kinds of opthalmic prisms

1. Ophthalmic Prisms

2. Ophthalmic Prisms A prism is defined as a portion of a refracting medium bordered by two plane surfaces which are inclined at a finite angle. The angle between the two surfaces is called the refracting angle or apical angle of the prism.

3. Ophthalmic Prisms

4. REFRACTION THROUGH PRISM Light passing through a prism obey Snell’s law at each surface. The ray is deviated towards the base of the prism.

5. For a prism in air ,the angle of deviation is determined by three factors 1. The refractive index of the material of which the prism is made. 2. The refracting angle of the prism 3. The angle of incidence of the ray considered.

6. All varieties of spectacle lens has the effect of a prism when viewed through a point away from the optical center. The further the away from the optical center, the greater is the prismatic effect

7. Image formation using prism

8. CHARACTERISTICS OF PRISM A prism does not change the vergence of the rays. A prism does not magnify or minify the image. A prism also disperses incident pencil rays into its component colours.

9. Image Formation The image formed by a prism is Erect Virtual Displaced towards the apex of the prism.

10. Units of prisms The power of a prism can be expressed in various unit. 1. The prism dioptre 2. The centrad

11. DEVIATION PRODUCED BY PRISM(IN LENS) The deviation so produced can be measured by the Prentice’s Rule: Δ = hD is commonly known as Prentice’s rule h= image displacement in cm D=lens power

12. PRISM ORIENTATION Prism can be oriented in front of the eye using notations Base-in Base out Base up Base down All other base directions require 360° notation

13. PRISM ORIENTATION

14. PRISM ORIENTATION

15. Prescription of prisms Generally when prescribing prisms, the correction is split between the two eyes . The apex of the prism must always be placed towards the direction of deviation of the eye.(apex towards deviation )

16. Convergence or eso deviation Base out prism ,e.g. 8 prism diopter base out R and L. Divergence or exo deviation prisms must be base -in , e.g. 6 prism diopter base in R and L.

17. Prisms in optical instruments Slit lamp bio microscope Applanation tonometer keratometer