Trifocals

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.

6. 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.

7. 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.

8. Guess the profession ???

9. 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

10. 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

11. 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.

12. 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

13. 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)

14. 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

15. 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)

16. MATERIALS FOR TRIFOCALS Crown glass Flint glass CR-39

17. TYPES OF TRIFOCAL LENSES Split trifocals Cemented trifocals Fused trifocals Solid trifocals

18. 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

19. DP NP IP

20. 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.

21. DP IP RP

22. 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.

23. 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

24. 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

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

26. 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

27. IDENTIFY ???

28. 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 .

29. THANK YOU