Accommodation is the mechanism by which the eye changes refractive power to focus on objects at different distances. It involves changes in the shape of the elastic lens, controlled by the ciliary muscle. The amplitude of accommodation declines with age as the lens loses elasticity, causing presbyopia. Accommodation is measured using methods like push-up and minus lens, which determine the near and far points of clear vision. The range between these points indicates how much accommodation is available. Accommodation abilities normally decline with age according to established formulas.

1. Accommodation: Mechanism,
theories, ocular changes,
ranges and amplitudes.
Moderator: Presenters
Dr Sanjeev Bhattarai Aaratee Jha
Garima Paudyal

2. ACCOMMODATION
• Accommodation is the mechanism by which the eye
changes refractive power by altering the shape of the lens
in order to focus objects at variable distances.

3. • In an emmetropic eye
-Parallel rays of light coming from infinity are brought to
focus on retina being accommodation at rest.
-Eyes can also focus diverging rays coming from near
object on retina to see clearly due to accommodation.

5. Mechanism of Accommodation
Ciliary muscle contracts Ciliary ring shortens
Equator of lens move forward
As a result
Zonules are relaxed Tension in capsule is relieved
Lens becomes spherical i.e.
convexity increases
Increase in
Dioptric power
Allowing near object to be
focused clearly on retina

7. Anatomy of Accommodation
• The lens fibres of the young crystalline lens forms an elastic
substance.
• Fibres are surrounded by elastic capsule with its maximum
thickness at the equator.
• Age changes in lens on accommodation is explained by
changes in the relative sizes of the lens cortex and nucleus
and their relative softness.
• Eg: In child’s eye, the whole lens is soft and adopts a more
convex spherical shape on accommodation.

8. • In an adult upto 30 years, the cortex has significance
thickness, and hence the softer nucleus forces the central
zone to become more spheric on accommodation.

9. After 30-40 years of age both nucleus and cortex soften
Asphericity of the lens and amplitude of accommodation
decreases with age
Effort required to accommodate decreases
Giving rise to presbyopia

10. With Age: (In summary)
Lens fibers & lens
capsule lose elasticity
The size & shape of the lens
increase
Reduction of
accommodative amplitude
Onset of presbyopia

11. Theories of Accommodation
• The exact mechanism of accommodation is not known
but the principal fact is that Accommodation is a feature
of increase in curvature of the lens which affects anterior
surface mainly.

12. Relaxation theory of HELMHOLTZ
“Capsular theory”
• He considered that the lens was elastic and in normal
state it is stretched and flattened by tension of
suspensory ligaments.
• During accommodation, contraction of the ciliary muscle
shortens ciliary ring and moves towards the equator of
the lens.
• It relaxes the suspensory ligaments, relieving strain.
• Lens assumes more spherical form, increasing thickness
and decreasing diameter.

15. Points in favour of the relaxation theory
• Imaging technique showed that ciliary muscle move
anteriorly and the equatorial edge of lens move away
from sclera during accommodation.
• Gonio-videography show zonular fibers extending from
ciliary processes to lens equator, are relaxed during
accommodation.

16. GULLSTRAND mechanical model of
accommodation
• It is based on HELMHOLTZ hypothesis.
• GULLSTRAND devised a mechanical model to explain
accommodation.
• It shows in unaccommodated state elasticity of choroid is
stronger than lens. When accommodation comes into
play i.e. ciliary muscles contract to overcome elasticity of
choroid.
• It helps lens to take accommodated shape.

18. Points against the theory
• It is not clear how lens alter its shape when tension in
suspensory ligaments is relaxed.
• It is unable to explain what is responsible for decline in
power of accommodation with age.

19. TSCHERNING’STHEORY OF
ACCOMMODATION
Increased curvature of capsule to
increasing tension of the zonules.
Contraction of ciliary muscles pulls
zonules directly
Increases tension of capsule at
equator of lens.
Bulging of poles.

20. Schachar’s Theory of
Accommodation
Ciliary muscles contracts.
Equatorial zonular tension is increased.
Anterior and posterior zonules are
simultaneously relaxed.
Central surface of the lens steepen.
Peripheral surfaces of the lens
flatten.

22. COTENARYTHEORY
As ciliary muscle contracts
It forms a pressure gradient, causing anterior
movement of lens zonules diaphragm
Increasing anterior central curvature
Presbyopia is due to increase in lens volume,
results in reduced response to pressure gradient
created by ciliary body contraction.

23. Accommodation reflex
• When eyes are focused from a distant to near object,
three reactions takes place.
Constriction of pupil
Thickening of the lens due to contraction of ciliary
muscles.
Convergence of both eyes.
These three reactions together constitute near reflex triad.

24. Pupillary light reflex

25. Convergence reflex

27. Ocular changes in Accommodation
Changes in zonules
• Zonules are normally under tension and keep the lens flat
• During accommodation, ciliary muscle contracts
• As a result, tension in zonules is released

28. Contd…
Changes in lens
• Mainly curvature of the lens changes
• Principal change occurs in the anterior surface of the lens
• In unaccommodated state, radius of curvature of anterior
surface of the lens is 11mm and that of posterior surface
is 6mm

29. Contd…
• In accommodated state, the radius of curvature of the
anterior surface of the lens decreases i.e becomes 6mm
from 11mm
• Almost no changes occur in posterior radius of curvature
of the lens
• Anterior pole of the lens moves forward as the radius of
curvature of anterior surface of the lens is decreased
• As a result, Axial thickness of the lens increases

30. Contd…
• Lens sinks down within the globe due to gravity as in
accommodated state lens is held less firmly by zonular
attachment
• In addition to the changes in lens, the pupil constricts and
there occurs simultaneous convergence of the visual axis
of both the eyes
• Choroid is stretched forward due to ciliary muscle
contraction and ora serrata moves forward

31. Contraction of ciliary muscles
Decrease in zonular tension
More spherical shape of the lens
Increased axial thickness
Steepening of the lens anterior curvature
Increased lens dioptric power

32. Far and Near Point of accommodation
Punctum Remotum (Far Point ofAccommodation)/ FPA
The object point that is conjugate with the retina when
accommodation is fully relaxed
In this case, an object placed at the far point will be imaged
on the Retina

34. Far point of accommodation in
different refractive state of eye
Emmetropia
The Far point of accommodation for an emmetropic eye is
at infinity

35. Contd…
Myopia
Far point of accommodation for an uncorrected myopic eye
is a real object point lying in front of the eye

36. Contd…
Hyperopia
Far point of accommodation for an uncorrected hyperopic
eye is a virtual object point located behind the retina

37. Near point of accommodation (Punctum proximum) / NPA
The object point that is conjugate to the retina with
accommodation fully at play
The nearest point at which the object can be seen clearly

38. Near point of accommodation in different
refractive state of the eye
Emmetropia
NPA is a real object point located in front of the eye

39. Contd…
Myopia
NPA is a real object point located in front of the eye similar
to that of emmetropia

40. Contd…
Hyperopia
May be either a real object point located in front of the eye
or a virtual object point located behind the eye depending
upon the amount of hyperopia and amplitude of
accommodation

41. Range of Accommodation
Defined as the linear distance traversed by the point of
conjugacy in moving from the far point to the NPA
It is the distance over which accommodation is available for
a subject and accommodation is effective
An object can be seen clearly only if located at the far point
or near point or at any point between the FPA and NPA
The range of accommodation in either state (Corrected or
uncorrected )is equal to the distance from the FPA to the
NPA

42. Range of accommodation in different
refractive state of the eye
Emmetropia
An emmetropic eye that has a finite (real) NPA and FPA at
infinity has an infinite range of accommodation extending
from infinity to NPA

43. Contd…
Myopia
For a myopic eye , the FPA and NPA are always real object
points located at finite distances in front of the eye
Hence the range of accommodation of a myopic eye is
always less than infinity

45. Contd…
Hyperopia
For a hyperopic eye , having the FPA behind the eye , has
the NPA located at a finite distance in front of the eye, the
range of accommodation is infinite

46. Amplitude of accommodation
Difference in the focus power of the eye while fixating for
near distance and fixating for far distance
Or
The difference between the dioptric power needed to focus
ta near point (P) and to focus at far point (F)
i.e. AA = P – R

47. Q.Why measure Amplitude of
Accommodation ?
• Recommended component of the routine clinical eye
examination
• The detection and management of common refractive
conditions including Presbyopia and Latent hyperopia are
frequently assisted by measuringAA

48. Assessment of Amplitude of
Accommodation
Accommodation can be stimulated either by moving a test
object closer to the eyes or by placing minus lenses
Following procedures are used to determine the AA
-AA using RAF rule
-Push up method / Donders method
-Minus lens method / Sheard’s method

49. Push up method / Donders method
• Ubiquitous
• The commonest and simplest clinical technique to
measure AA
• Determines maximum amount of accommodation that
eyes are capable of producing individually or together
• Well established in clinical practice and research and is
often assessed using RAF (Royal Airforce Rule) or Prince
rule

51. RAF Rule
• Specially designed for
measuring NPC,NPA and
hence AA
• Consists of bar or rule made
from plastic, metal or wood
on which a rider with the test
chart can be moved back and
forth(fixation target)
• At one end of the bar is the
winglike support that fits
over the nose and rests
against the lower orbital
margins during the
measurement

52. Procedure
• Near visual acuity chart placed on near point card
• Direct patient’s attention to 20/20 line of letters on near
point card
• Patient left eye is occluded first

53. Contd…
• Near point card is brought closer to the patient (2-3
inches per sec)
• Patient is instructed to keep the letters as clear as
possible and report when it blurs
• Prompt the patient to clear the target

54. Contd…
• Stop when the patient can no longer clear the target
within 2-3 secs of viewing
• Record the dioptric point on the near point rod that
corresponds with the first sustained blur
• Procedure is repeated for left eye with right eye occluded

55. Minus lens method / Sheard’s method
• Amplitude of accommodation is determined interposing
minus lenses
• Each eye is tested monocularly first
• Then tested binocularly
• Full refractive correction is worn by the patient

56. Procedure
• Near point card is placed at distance of 40cm
• Patient is instructed to watch the 20/20 line of letters first
with right eye and then with left eye ,the opposite being
occluded
• Patient is then asked to report when the letters begin to
blur as minus power is gradually added to his/her
subjective correction

57. Interpretation
• Amplitude of accommodation is then calculated by
adding dioptric power of the minus lens to produce first
sustained blur with the dioptric power of the working
distance
• For e.g.
If working distance (WD)= 40cm
then, dioptric power ofWD = 2.50D
Power of minus lens to make first sustained blur = - 4.00D
Then, AA = (4.00 + 2.50)D = 6.00 D

58. Contd…
• In some cases , it is necessary to add plus lenses to the
subjective lenses to clear up the letters at 40cm
• The amount of plus power necessary to clear up the letter
is subtracted from the considered working distance to
determine the Amplitude of Accommodation

59. Comparison between push up method
and minus lens method
• The angular size of the retinal image of 20/20 letters
increases in direct proportion to the decrease in distance
between the near point card and the eyes
• In minus lens method the angular size of the retinal
image almost remains the same
• For this reason, AA measured by Push-up method is
overestimated compared to that of Minus lens method

60. Amplitude of Accommodation and age
The amplitude of accommodation declines throughout the
life until at about 50 or 60 years of age when it becomes
zero

61. Formula to determine the Amplitude of
Accommodation
Hofstetter formulae for expected amplitude as a function of
age (using the data of Donders, Duane and Kaufman)
• Maximum amplitude = 25 – 0.4 (age)
• Probable amplitude = 18.5 – 0.3 (age)
• Minimum amplitude = 15 – 0.25 (age)

62. Example
• For 20 years old patient,
Maximum AA = 25 – 0.4*20 = 17D
Average AA = 18.5 – 0.3*20 = 12.5
Minimum AA = 15 – 0.25*20 = 10D
NPA = 1/10 = 0.1m = 10cm

63. Rule of 4’s to determine AA with Age
Given by,
Amplitude = 4x4 – (Age/4)
Example
Age of 20
AA = 16 – 20/4
= 11 D

64. Anomalies related to Amplitude of
Accommodation
• Deficient or decreased Amplitude of Accommodation
results in:
- Accommodation Insufficiency
- Fatigue of accommodation
-Presbyopia

65. Accommodation Insufficiency
• The accommodative power is significantly less than the
normal physiological limits for the patient’s age
• Caused due to premature sclerosis of lens and weakness
of ciliary muscles
• Blurring of near vision along with prominent asthenopic
symptoms are present
• Near vision spectacles along with the accommodative
exercise can be used for the treatment

66. Fatigue of Accommodation
• Also called as ill-sustained accommodation
• Measures ability of the eyes to adequately sustain
sufficient accommodation over an extended period of
time
• Can be tested using RAF rule
• With RAF rule, AA is measured repeatedly

67. Contd…
• AA initially sustained with considerable effort, overtime ,
it cannot be maintained
• Hence , decrease ofAA on repeated testing suggests
Fatigue ofAccommodation
• Patient complains of letters becoming blurred after
reading for sometime
• Patient is treated with Push-up therapy or flipper lens
therapy

68. Presbyopia (eyesight of old age)
• Not an error of refraction but a condition of physiological
insufficiency of accommodation due to reduced AA , leading to
progressive fall in near vision or increase in NPA
• Causes are age related changes in lens and age related decline
in ciliary muscle power
• Symptoms are blurring of near vision and sometimes
asthenopic symptoms on prolonged near work
• Optical correction for near can be given for presbyopia

70. Relative Accommodation
• The amount of accommodation to be exerted under fixed
convergence is called relative accommodation
• Two types
Negative relative accommodation
Positive relative accommodation
Negative relative accommodation
• To test patient’s ability to decrease accommodation while
maintaining convergence at 40 cm

71. Contd…
• A reduced snellen chart with 20/20 letters at 40cm
• Place patient’s distance correction in trial frame
• Add plus power in 0.25 steps every 2 secs until patient
reports first blur
Value of negative relative accommodation (NRA)
• Normal values = +1.75 to +2.00DS

72.  Positive Relative Accommodation
• To test the patient’s ability to increase the
accommodation while maintaining convergence at 40 cm
• Add minus power in 0.25 steps every 2 secs until patient
reports first blur
Value of Positive relative accommodation (PRA)
• Normal values : -2.25 to -2.50 DS

73. Interpretation
• NRA and PRA is calculated
• Range of accommodation = NRA + PRA
• Similarly, ADD for presbyopia can also be calculated using
NRA and PRA as
ADD = ½(NRA + PRA)

74. Example
• Working distance = 2.00D
• NRA = +3.00D and PRA = -1.5 D
• Hence ,Range of Accommodation = NRA + PRA = +1.50D
• ADD = ½(+1.50D) = 0.75D

75. References
• Anatomy and Physiology of eye by A.K Khurana
• Optics and Refraction by A.K Khurana
• Clinical optics
• Primary care Optometry