2. Learning Objectives
• Definition of accommodation
• Mechanism of accommodation
• Components of accommodation
• Terminologies of accommodation
• Assessment of accommodation
3. Definition
• Accommodation is the mechanism by which the
eye changes refractive power by altering the
shape of lens in order to focus objects at variable
distances.
4. • Accommodation is caused by the increased
curvature of anterior area of the eye lens.
• Accommodation is usually the same in both
eyes.
9. 1. Physical Accommodation
The actual physical deformation of the lens.
It is measured in diopter.
Converging power of the eye is increased by
1D.
10. 2. Physiological Accommodation
The contractile power of the ciliary muscle
required to arise the refractive power of lens
by 1D.
It measured in myodiopter.
11. Terminologies of accommodation
Far point:
Position of an object when its image
clearly falls on retina with no accommodation.
• Emmetropic eye : at INFINITY
• Myopic eye : REAL and lies in FRONT OF the
eye
• Hypermetropic eye : VIRTUAL and lies BEHIND the
eye
12. Near point :
Nearest point at which small objects can
be seen clearly.
• Also called punctum proximum.
• It varies with age ; about 7 cm at 10 years of age
25 cm at 40 years of age
33 cm at 45 years of age
13. Range of accommodation:
Distance between far point and near
point.
Range of accommodation= Far point – Near point
(in cm) (in cm)
14. Amplitude of Accommodation :
Difference between the dioptric power,
needed to focus at near point and to focus at far
point.
• Amplitude = Near point – Far point
(in Dioptre) (in Dioptre)
15. Example: Given an emmetropic eye with near
point of accommodation located at 10cm in
front of the eye calculate the range and
amplitude accommodation.
Far point(R) = infinity
Near point(P) = 10cm
Range of accommodation : (R-P)=infinity
Amplitude of accommodation – (P-R)=10D
16. Example: Given uncorrected myopic eye with far
point of accommodation located 50cm in front
of the eye and near point at 10cm in front of eye
calculate range and amplitude of
accommodation.
Far point – 50cm
Near point – 10cm
Range of accommodation – (R-P)=40cm
Amplitude of accommodation – (P-R)=8D
17.
18. A) Assessment of NPA and amplitude of
accommodation
1. RAF rule
2. Measurement of Amplitude of
accommodation using minus lenses
3. Pushup Test
B) Assessment of Accommodative Response
Techniques of Dynamic Retinoscopy
C) Assessment of Dynamic Accommodation
Assessment of accommodation
20. • Using RAF rule we can determine the NPA
• A sliding target with 6/9 letters, numbers or fine
lines is moved from or towards the eye until the
closest is found at which it still can be seen
clearly.
• During the examination, the patient has to wear
his or her full optical refractive correction.
• The NPA is determined first for each eye
separately and then for both eyes together.
• It is marked in centimetres marked on one side
of the instrument bar.
21. • The side of bar marked in dioptres will indicate
the amplitude of accommodation in dioptres.
• The third side of the bar shows the age
corresponding to the accommodation.
• If while measuring the NPA, the patient’s
amplitude of accommodation is found so low
that his or her near point is beyond the length of
the instrument, PLUS lenses are added to his or
her correction until the near point is brought
within limit.
• The dioptric power of these additional lenses is
then deducted from the measured values.
22. • Conversely, in young patients with very high
accommodative power, minus lenses may be
added to the distance correction to move the
near point away from the eyes.
• The dioptric power of those minus lenses is then
added to the measured value of amplitude of
accommodation.
23. 2. Measurement of Amplitude of Accommodation
using minus lenses
• Performed monocularly and the patient has to
wear his or her full refractive correction.
• The patient is asked to fixate the best corrected
near vision target at 40 cm distance and minus
lenses of progressively increasing power are
added before the eye till the patient reports the
first sustained blur.
• The power of this minus lens + 2.5 D (for 40 cm
distance of testing) is equivalent to amplitude of
accommodation in dioptres.
24. • For example,
At 40 cm distance of testing , if the patient
reports blur with -3 D spherical lens, the
amplitude of accommodation would be,
3 + 2.5 = 5.5 D
25. 3. Pushup Test
• A very simple test done which can be done
monocularly as well as binocularly with patient
wearing full refractive correction.
• The patient is asked to fixed it at the best
corrected near vision target at a distance where
the target is seen clearly.
• The near vision chart is moved closer till the
patient reports first sustained blur.
• The linear distance measured between the chart
and patient’s spectacle plane gives NPA.
26. Techniques of Dynamic Retinoscopy
• Monocular Estimation Method :
Patient is asked to fixate the near target at a
distance of 40 cm and the retinoscopy is
performed using streak retinoscope.
The lens power required to attain neutrality is
noted.
27. • Nott Retinoscopy
Same as MEM method , except that the
retinoscopic reflex is neutralised by moving the
retinoscope rather than adding the lenses.
For the ‘with’ movement, the retinoscope is
moved away from the patient and for the
‘against’ movement towards the patient till the
retinoscopic reflex is neutralised.
28. Interpretation of Accommodative
Response
• Lead of Accommodation: The amount by
which the accommodative response of the eye is
greater than the accommodative demand.
It indicates accommodative excess.
• Lag of Accommodation: The amount by
which the accommodative response of the eye is
less than the accommodative demand.
It indicates accommodative insufficiency.
29. Assessment of Dynamic
Accommodation
• Dynamic of accommodation can be assessed by
testing accommodative facility.
• An accommodative Flipper of +2.00 DS with
-2.00 DS is used to test accommodative facility
by rapidly flipping the lenses
30. • Difficulty with plus lenses is seen in patients
with accommodative excess.
• Difficulty with minus lenses is seen in
presbyopes.
