1. The document discusses presbyopia, which is the age-related loss of accommodation that begins around the age of 40 and leads to difficulty with near vision. 2. It defines presbyopia and explains the physiological changes that cause it, including lenticular and extra-lenticular changes. 3. Various types of multifocal lenses are described that can help with presbyopia, including bifocal, trifocal, and progressive addition lenses, along with their advantages and disadvantages. Precise fitting of these lenses is important to reduce issues like prismatic effects and distortions.

1. Dr Zaid Azhar
M.B.B.S
Ophthalmology Resident SIH
PRESBYOPIA

2. • Progressive Age-related loss of accommodation
• Starts in adult life
• Early 40s: Functional vision affected
• Complete loss of accommodation by 5th to 6th decade of life
• Most prevalent ocular affliction – affects 100% of population
PRESBYOPIA - DEFINITION

3. Recap: Amplitude of Accommodation
• Amplitude of accommodation: Dioptric power difference between rest and
fully accommodated eye.
A = P-R (near point) or A = V-R (intermediate point)
( A: amplitude of accommodation; P: dioptric value of near point; V: dioptric
value of intermediate point and R: dioptric value of far point.)

4. • The amplitude of accommodation decreases steadily with age. This
occurs due to:
1) Lenticular Changes
• lenticular sclerosis
• changes in capsular elasticity
• changes in zonules
• 2) Extra-lenticular Changes
• Neuromuscular changes
• Ciliary muscle changes
PRESBYOPIA: PATHOPHYSIOLOGY

5. VISION WITH PRESBYOPIA
Distance Intermediate Near

6. AMPLITUDE OF ACCOMMODATION WITH
AGE

7. • In order to focus on an object at a reading distance of 25cm, the emmetropic eye must
accommodate by 4D (1/0.25= 4)
• However for comfortable near vision 1/3rd of accommodation must be kept in reserve.
• This means that patients having 6D of accommodation start experiencing difficulty in near vision
(1/3rd of 6D= 1.5D, hence 4.5 D of accommodation is being used)
• This usually occurs between age of 40 and 45.
• It’s hard to define presbyopia in terms of remaining amplitude of accommodation because every
one has a different preferred working distance, nature of close work and length of time for close
work.
PRESBYOPIA IN EMMETROPIC EYE

8. • In order to help the presbyopic patient achive comfortable near vision, a supplementary convex
lens is used called a presbyopic lens.
• The amount of presbyopic correction can be calculated if the following are known:
1) Desired working distance
2) Near point
PRESBYOPIC CORRECTION

9. • An emmetropic patient has a near point of 33cm. What should be his presbyopic correction if his
working distance is 25cm?
• Step 1: Calculate Ampilitude of accommodation from near point:
A = P – R
A =1/0.33 -1/ infinity
A = 3-0, A=3
• Step 2: Calculate available/usable accomodation:
1/3rd of 3D = 1D so, (3-1) = 2D
• Step 3: Calculate accommodation required at working distance:
1/0.25 = 4D
• Step 4: Calculate Presbyopic Correction
Accomodation Required at working distance – Usable accommodation
4D - 2D
=2D
CALCULATING PRESBYOPIC
CORRECTION

10. CALCULATING PRESBYOPIC
CORRECTION

11. • Onset of presbyopia occurs earlier in uncorrected
hypermetropia.
• Onset of presbyopia is delayed in uncorrected
myopia.
• This is because hypermetropes already use all their
accommodation to focus on a far object meanwhile
myopes have excess accomodation intact.
PRESBYOPIA IN AMETROPIC EYE

12. MULTIFOCAL LENSES

13. • A single pair of spectacles with bifocal lenses.
• Provide separate distance and near prescriptions for each eye.
• Distance prortion is larger – major portion – upper part of lens.
• Near portion is smaller – lower part of lens.
BIFOCAL LENSES

14. • Earlier design, now almost obsolete.
• Flat bottom of upper distance lens abuts flat part of
lower near segment.
• Advantages:
1. Large field of view.
2. As the optical centres are at the dividing line there is no
vertical prismatic jump.
3. Less chromatic aberrations.
• Disadvantages:
1. The lenses are held together by frame and come apart
easily.
2. Dividing line produces annoying reflections.
3. Dust accumulation at dividing line.
4. Lens is heavier.
5. Difficult to align the two pieces in case of cylindrical
prescription.
SPLIT/FRANKLIN BIFOCALS

15. • Constructed by attaching a supplementary lens wafer to
surface of a distance lens with same refractive index.
• Adhesives ike UV-cured epoxy which is transparent are
used.
• Advantages:
1. Cosmetically more appealing.
2. Has less optical aberrations.
• Disadvantages:
1. Dividing line tends to collect dirt.
2. Adherence of wafer is affected by changes in temperature.
3. Wafer had a tendency to fall off.
CEMENTED BIFOCALS

16. • Made by heat-fusing bottom of flint glass to
corresponding depression in a main lens.
• Main lens has a lower refractive index.
• Bottom lens is ground to equalize surface
curvature of both segments.
• Different types of flint glass offer different
variations in refractive index.
• Advantages:
• Different shaped near segments to suit different
demands.
• Disadvatages:
• Different in refractive indices may cause
chromatic abberation near segment edge.
FUSED BIFOCALS

17. • Single piece construction.
• Near portion constructed using different curvature of
either front or back surface of same lens.
• Usually plastic construction.
SOLID BIFOCALS

18. • Distance Visual Point (DVP) and Near Visual
Point (NVP): positions on a lens through which
the visual axis is directed when the lens is being
used.
• NVP is 2mm nasal and 8mm below the DVP.
• Important to know about these points because
alignment of near segment needs to be precise.
DISTANCE AND NEAR VISUAL POINTS

19. OPTICAL
PROBLEMS WITH
BIFOCALS

20. • A prismatic effect occurs at any non-axial point on a lens.
• If optical center of each portion of lens coincides with NVP and DVP then prismatic effect
increases towards junction of distance and near portion of lens.
• When the patient looks from one portion of the lens to another, the prismatic power will
suddenly change.
• This is because prismatic power is proportional to dioptric power of each portion.
PRISMATIC JUMP

21. • Prismatic jump can be reduced if the optical centres of
the two lenses lie at junction of two points.
e.g Executive bifocal lenses – optical centres coincide at
junction
• Prismatic jump can also be reduced by adding using
shaped segments because segment top is only a short
distance from it’s optical centre.
e.g using a base-up prism in near segment for patient
with anisometropia causing excessive vertical imbalance.
AVOIDING PRISMATIC JUMP

22. • This is the sum of prismatic effect at main lens and
due to the downward segment at NVP.
• This causes image displacement.
• Image displacement refers to the total apparent
distance between an image viewed through the
distance lens versus through the add segment
• The magnitude of image displacement is a function of
the total net prism acting on the image through the
bifocal segment
• In fused/cemented bifocals optical center of segment
overlies the NVP hence the prismatic effect is
reduced.
IMAGE DISPLACEMENT - PRISMATIC
EFFECT AT NVP

23. AVOIDING IMAGE DISPLACEMENT

24. • When the Near Visual Axis does not not
correspond with the optical axis of the near portion
of lens, astigmatic aberrations can occur when light
passes obliquely through the lens.
• To counter this, bifocal spectacles are made so
that the top of each lens is tilted 10 to 20 degrees
forward. This is called Pantoscopic tilt.
• This makes visual axis more perpendicular to near
portion of lens.
ASTIGMATIC ABERRATIONS

25. • Bifocal glasses may not be tolerated by people with anisometropia because the prismatic
effect on each eye will be different.
• More than 1.5 prism dioptre of vertical prismatic effect will make binocular vision difficult and
may cause diplopia.
• Patients with high refractive errors may also find bifocals intolerables because the prismatic
effect is large.
• Care must be taken for prescribing bifocals glasses to people with vertical extraocular muscle
imbalance.
PROBLEMS WITH BIFOCALS

26. • It is important to consider individual needs of a patient.
• Patients with a lot of near work e.g a typist need larger near
portion with reduced presbyopic correction.
• Some patients need intermediate or near addition while looking
up e.g plumbers, mechanics – they can be prescribed double D
lens.
• Patients with a lot of outdoor work needs a larger distance
segment.
• Patients working at tall heights e.g scaffoldings – bifocals are
contraindicated because downgaze will be affected by near
portion.
• Patient who is elderly and unsteady on feet or with vertigo –
bifocals should be avoided because of aberrations on downward
gaze.
PRESCRIBING BIFOCALS -
CONSIDERATIONS

27. • In patients where little or no accommodation remains
trifocal lenses can be used.
• These comprise of a distance, intermediate and near
segment.
• Intermediate segment is of lesser (usually half) power
of near segment and focuses on middle/intermediatev
distances.
• May not be tolerated by patients with anisometropia.
TRIFOCAL LENSES

28. • One piece lens.
• Lens power changes gradually between distance and near
visual points.
• 5 segments:
1. Distance: Larger upper segment
2. Near: Smaller lower segment
3. Corridor – segment where lens focuses for intermediate.
Increases progressively in power from distance to near.
4. 2 peripheral segments: Distortion occurs progressively more
at peripheral segments.
PROGRESSIVE ADDITION LENSES (PALS)

29. • The change in power is achived by
constantly changing the radii of curvature
in both horizontal and vertical directions.
PROGRESSIVE ADDITION LENSES (PALS)

30. • Hard design:
 Wide distance and near portions with narrow
corridor.
 Progression window is smaller
 More aberrations close to progression window.
• Soft Design:
 Smaller distance and near portions.
 Progression window is larger.
 Less aberrations close to progression window.
PALS - HARD VS SOFT DESIGN

31. • Advantages:
 No visible segments – cosmetically pleasing
 Continuous field of clear vision
• Disadvantages:
 Diistortion at peripheral regions leading to poor vision while turning to the side.
 Require very precise fitting.
 Costly
PALS – PROS AND CONS