short brief about trifocals

1. TRIFOCALS
BY ,
SANJANA CHOUHAN.S

2. OUTLINE
 INTRODUCTION
 HISTORY OF TRIFOCALS
 TRIFOCALS VS BIFOCALS
 PURPOSE OF TRIFOCALS
 TYPES OF TRIFOCALS
 DISPENSING TRIFOCALS
 ADVANTAGES AND DISADVANTAGES

3. INTRODUCTION
 Based on the number of focal points, ophthalmic lenses are divided
into four types
 Single vision lenses
 Bifocals
 Trifocals
 Progressive addition lens

4.  SINGLE VISION LENSES - Corrects only one vision at a time .
(Single focal point)
 BIFOCALS – Corrects two vision, Distance and near.(Two focal
points)
 TRIFOCALS – Corrects three vision, distance, near and
intermediate.(Three focal points)
 PROGESSIVE – Corrects different distances.(Many focal points)

5.  MULTIFOCALS
 TRIFOCALS - are eyeglass lenses that enable you to see clearly at
three different distances ( Distance zone -far, intermediate zone –
arm’s lenght , near zone – reading )
 PROGRESSIVE – are eyeglass lenses that enable you to see all the
distances clearly.

7. HISTORY OF TRIFOCALS
 Trifocals, patented in 1827 by John Isaac Hawkins, are eyeglasses
with lenses that have three regions which correct for distance,
intermediate, and near vision.
 Trifocal lenses are designed for performing a particular job or hobby
and are not meant for general-purpose wear.

8. Corrects two
zones of
vision.
It has two
focal points.
BIFOCALS
Corrects
three zones
of vision.
It has three
focal points.
TRIFOCALS

9. PURPOSE OF TRIFOCALS
 A multifocal lens that has a specific purpose, or is created to perform
a specific job, is called an occupational lens.
 If the eye has sufficient accommodation , it may view these objects
which lie at an intermediate. But at the certain stage in presbyopia
accommodation become insufficient that a third pair of spectacles Is
required exclusively for intermediate use.
 What makes these lenses different from other lenses is that the
near, intermediate and far zones for vision are placed on specific
areas of the lens, which makes vision for these particular tasks
easier.

11. Guess the profession ???

15. PROFESSIONS DISTANCE INTERMEDIATE NEAR
ELECTRICIAN To see the switches
whether it ON or
OFF
To take the tools
like srewdrive ,
pliers etc
To join the wires,
fit fan, light.
LIBRARIAN To see the upper
shelf and books
For arranging the
books
For reading the
books and writing
AIR HOSTESS To see the
passengers seated
at the last row
To place the
passengers Luggage
To serve the
passengers
MUSICIAN To see the audience To see the musical
notes
To play the
instruments
SHOPKEEPER To see the products
in upper shelf
To see the computer
for billing
To see the product
details

16. POSTION OF THE INTERMEDIATE
PORTION
 Usually in between distance and near , it can be positions according to
the requirements of the patients
 For example : Electrician , pilots, dentists , artists , musicians

17.  The power which must be added to the distance prescription to
produce the intermediate prescription is called the intermediate
addition. ( + 0.75 DS to + 2.00 DS )
 INTERMEDIATE ADDITIONS may range from about 50 % - 70 %
that of the reading addition.

18.  The IP addition can be given as a ratio of the RP addition expressed
as %
 This is called IP/RP ratio :
 IP/RP ratio = Intermediate addition
Reading addition
100

19.  Scenario 1
 The patient is a carpenter who works mostly at arm's length or closer.
Distance is less important and he has another pair of spectacles for
general wear. He cannot be dispensed a progressive lens as true
straight lines are important.
 Distance power +2.00DS
 Inter power (50%IP/RP) +1.50 (+3.50DS)
 Reading add +3.00 (+5.00DS)

20. COMPUTER USER ??
 If I moved my computer monitor close enough to see the screen
clearly, it was nearly in my lap. If I left the monitor where it should
be, I had to lean forward awkwardly. During my annual eye exam , I
told my optometrist about my workstation discomfort and the strain
that was causing my eyes. I optimize my work environment for
comfort and still have problems.
 the solution may be another pair of glasses

21.  Scenario 2
 The patient needs the shorter IP/RP ratio, for computer use for
example.
 Distance power +2.00DS
 Inter power (66%IP/RP) +2.00 (+4.00DS)
 Reading add +3.00 (+5.00DS)

22. MATERIALS FOR TRIFOCALS
 Crown glass
 Flint glass
 CR-39

23. TYPES OF TRIFOCAL LENSES
1. Split trifocals
2. Cemented trifocals
3. Fused trifocals
4. Solid trifocals

24. SPLIT TRIFOCALS
 Same as franklin type bifocals
 Different power lenses were cut and fitted into the single frame.
Advantages:
- Different powers and high additions are possible.
- Intermediate portion can be positioned anywhere in the frame.
Dis-Advantages:
-Cosmetically poor because of lens attachment and the attachment
space will attract dirt
-Difficult to fit into the frame

25. DP
NP
IP

26. CEMENTED TRIFOCALS
 Small segments of different powers will be cemented to the main lens
Advantages:
-Any powers are possible
-looks better than split trifocals
-Any designs are possible i.e the trifocal segments can be positioned anywhere
in the lens
Dis-Advantages:
-Cemented segments might fall or looks faded.

27. DP
IP
RP

28. FUSED TRIFOCALS
 Common type nowadays
 Same like fused bifocals, composite buttons with different materials
will be fused on to the main Distance Portion Lens
 Here the Intermediate portion is positioned in between Distance and
Reading portion
 And IP is 7 to 8 mm deep
Advantage:
Invisible Segments so – cosmetically looks good.

29. Fused types
1)Univis ‘Trivis’ Trifocal
2) Tillyer ‘S724’ Trifoca
3) Tillyer ‘Sovereign Curve Top’ Trifocal
4) Panoptik Trifocal
5) Shuron ‘Round Top’ trifocal
6) Cromwell ‘Round top’ Trifocal
7) Wiseman ‘Trivue’ trifocal
8) Univis ‘Ultra CV’ Trifocal
9) Double Semgment Trifocal

33. Solid trifocals
 The name SOLID – because all the distance, Intermediate and
Reading portions made from the same material and Single Blank with
different radius of curvature.
 TYPES ARE : Up and downcurve , concentric and band trifocals

35. COMBINATION OF TRIFOCALS
 Occasionally combination of Trifocals can be manufactured
 For eg: Fused Intermediate Segment on the Solid Bifocal

36. Dispensing trifocals
 Trifocals are normally fitted so that the lower limbus of the cornea is
at the centre of the intermediate portion with eyes in the primary
position
 FITTING – Generally fitted 2mm below the bottom of the pupil
 It can be set at a non-standard height, depending upon the patients
requirements
 Size , position and height of the segment depends upon – Occupation
and intermediate demand

38. IDENTIFY ???

42.  https://www.opticianonline.net/features/intermediate-prescriptions
 http://www.nytimes.com/2012/03/15/technology/personaltech/easing-eye-strain-with-the-right-
lenses.html
 http://hellereye.com/your-eye-health/vision-over-40/occupational-bifocal-and-trifocals/
 The principles of ophthalmic lenses by M.O jalie.

43. THANK YOU