1) Fresnel prisms are thin plastic prisms that can be applied to eyeglasses to correct double vision. They work by refracting light and altering the direction images enter the eye. 2) Prisms can eliminate the need for surgery to correct some types of double vision by optically shifting the image in one eye to align with the other eye. 3) Using prisms in vision therapy has benefits like enhancing depth perception and enabling clearer binocular vision by "tricking" the eyes into a more aligned position. Prisms create changes in the eyes and brain during vision therapy.

1. ENHANCE YOUR BRAIN BY
PRISMS
School of ophthalmic technology
18th batch

2. Who?

3. Sir Isaac Newton was the first to use a glass prism to obtain
the spectrum of sunlight.

4. Case scenario 1

5. Name : Mrs Saparamadu
Age: 45 years
Occupation : school teacher
P.M.H. : Nill F.H. : Nill P.O.H. : using spectacle since 4 years
co : she has changed her spectacle several times within short period of times as
she has eyestrain, indistinct near vision and diplopia while reading.
1st visit : R) plano-1.00×180
L) Plano-0.75×180
2nd visit : R) plano-1.00×180
L) Plano-0.75×180
ADD 1.25 DS
ADD 1.50 DS

6. Today investigations………
1)Visual acuity
2)Cover test
3)Retinoscopy
4)NPC
5)Subjective refraction

7. NPC – 26 cm

9. IPD – 62 mm

10. ADD POWER : R) +1.25-1.00×180
L) +1.25-0.75×180
Optical cross : R)
WD 66cm
+ 1.25
+0.25
+ 1.25
+ 0.50
L)
180
90
180
90
WD 66cm

11. R) L)
62mm

12. R) L)
62mm
X mm

13. Prentices rule
prism power = D × d

15. Case scenario 2

16. Name : Master Raween
Age: 14 years
Occupation : school child
P.M.H. : ocular cutaneous albinism with abnormal head posture
F.H. : mother & farther first cousins marriage
P.O.H. : using spectacle since 4 years
co : double vision in right side
Subjective refraction : R) plano-3.50×180
L) plano-3.00×180

18. What is yoke prism ?
Yoked prisms is a term used to describe a pair of prisms (one in front of the right eye
and the other in front of the left eye) either used therapeutically in glasses or as a tool
in neuro-optometric rehabilitation therapy, where the bases of the prisms are in the
same direction: left, right, up or down.
Before After

20. Theory behind …………

21. Case scenario 3

22. Name : Mrs Shyamali
Age: 34 years
Occupation : Housewife
P.M.H. :Pitiutary gland tumor
F.H. : Nill
P.O.H. : Nill
co : Peripheral loss of vision

23. Bitemporal hemianopia
describes the ocular defect
that leads to impaired
peripheral vision in the
outer temporal halves of the
visual field of each eye.

24. Treatment of
hemianopia with
prism

25. Theory behind …………

26. Case scenario 4

27. Name : Master Minidu
Age: 9 Years
Occupation : school child
P.M.H. : R/ Eye trauma by road traffic accident
F.H. : Nill
P.O.H. : R/ Eye surgery done
co : Double vision
Mild blurred vision
headache
Subjective refraction : R) Plano-3.50×180 -> 6/60
L) Plano -> 6/6

28. Double vision is when
we look at 1 object but
can see 2 images. It
may affect 1 eye or both
eyes.

29. Treatment
❖ Patching ( occlusive ) therapy
❖ Identify and treat the underlying cause of the problem.
❖ Other options include eye exercises,
❖ wearing an eye patch on alternative eyes,
❖ prism correction (Fresnel prism)
❖ In more extreme situations, surgery or botulinum toxin

30. A Fresnel prism is a thin, transparent plastic sheet which induces a
prismatic effect (it alters the direction of the image entering the eye).
One side consists of a series of angular grooves (prisms) and the other
smooth side attaches to the lens of glasses.
Fresnel prism

31. ➢ There are two main types of prisms: Fresnel (press-on) and ground-in.
➢ Fresnel prisms are a thin film that can be stuck onto the inside of the
glasses lens in the office, while ground-in prisms must be made by an
optical shop.
TYPES OF FRESNEL PRISM

32. What happen in prism ?

33. THE FRESNEL PRISM PRINCIPLE
A Fresnel prism, much thinner than a conventional ophthalmic prism
of the same power, can be imagined to be a series of small plastic
prisms lying adjacent to each other on a thin platform of plastic.

34. Optics of Fresnel prism

35. Why prescribe Fresnel prisms ?

37. what you need in preparation for this task.
•Little screwdriver if you have a metal frame.
•Scissor
•A non-permanent marker
•A large bowl filled with water
•Already cleaned glasses
•Your prescription

38. Wearing prism lenses
can eliminate the need
for a surgical solution
to double vision,
but they can only
correct some types of
double vision.

39. ➢ Using prisms during vision therapy has
many benefits: Prisms create changes in
the eyes and brain, and enhance depth
perception.
➢ Prisms enable objects to appear in a
different location, “tricking” the eye into
an aligned position.
➢ Prisms enable clearer, more
comfortable binocular vision