2. A dioptric change in the power of the eye to see clearly
3. Relaxation Theory of Helmholtz
Proposed by Thomas Young
Elaborated by Hermann von Helmholtz
Most widely accepted
4. Relaxation Theory of Helmholtz
eye is at rest and focused for distance
ciliary muscle is relaxed
eye makes an effort to focus on a near object
ciliary muscle contracts
bulk of the anterior ciliary body moves
forward
release in tension on the zonular fibres
elastic capsule moulds the lens into a
spherical form
5. Relaxation Theory of Helmholtz
Increase in surface curvatures causes an increase in optical
power of the lens and therefore an increase in power of
the eye
6. Helmholtz’s Theory: Disaccommodation
ciliary muscle contraction ceases
posterior zonular fibres pull the ciliary muscle
backward
increases tension on the zonular fibres
increase in lens diameter, decrease in lens thickness
and a flattening of the anterior and posterior lens
surface curvatures
decrease in optical power
7. Shortcomings of Helmholtz’s Theory
Since the equatorial diameter increases with age, zonules
should relax, and power of the crystalline lens should
increase.
Lens should become unstable
8. Schachar’s Theory
Proposed by Ronald Schachar
Alternative theory
Contradicts the classical Helmholtz’s mechanism
9. Schachar’s Theory
ciliary muscle contracts
equatorial zonular tension is increased
anterior and posterior zonules are
simultaneously relaxed
central surfaces of the lens steepen
peripheral surfaces of the lens flatten
11. Shortcomings of Schachar’s Theory
Based on his theory, Schachar introduced a new surgery in
1992 i.e. the use of scleral expansion bands to increase the
distance between the lens equator and ciliary muscle.
Poor results of this surgery challenged the validity of his
theory
12. Catenary (hydraulic suspension) Theory
Proposed by Coleman DJ in 1970
Demonstrated in 2001
Explains the precise anatomical reproducible shape of the
lens in accommodated state
Assumption : the lens, zonule and anterior vitreous
comprise a diaphragm between the anterior and vitreous
chambers of the eye
14. Catenary (hydraulic suspension) Theory
ciliary muscle contracts
initiates a pressure gradient between
the vitreous and aqueous
compartments
anterior capsule and the zonule form
a trampoline shape or hammock
shaped surface
steep radius of curvature in the center
of the lens with slight flattening of
the peripheral anterior lens
15. Clinical Assessment
Reading progressively smaller letters at near
NPA using RAF rule
Relative positive accommodation using minus lenses
Accommodative flipper test using paired +/– lenses
Dynamic Retinoscopy
Dynamic Distant Direct Ophthalmoscopy
16. TERMS TO REMEMBER:
Range of Accommodation
Amplitude of Accommodation
Relative Amplitude of Accommodation
Lead
Lag
Facility of Accommodation
17. Range of Accommodation: The distance between the far
point and near point ie the distance over which
accommodation is effective
Amplitude of Accommodation: The difference between
dioptric power needed to focus at far point (at rest) and at
near point (fully accommodated)
18. Relative amplitude of accommodation: The total amount
of accommodation which the eye can exert while the
convergence of the eyes is fixed
It can be positive (using concave lenses until the image
blurs). This is called positive relative accommodation
(PRA).
It can be negative (using convex lenses until the image
blurs). This is negative relative accommodation (NRA)
19. Lead of Accommodation: The amount by which the
accommodative response of the eye is greater than the
dioptric stimulus to accommodation
Lag of Accommodation: The amount by which the
accommodative response of the eye is less than the
dioptric stimulus to accommodation
20. Clinical Assessment
Measurement of NPA:
It is the closest point at which an object can be seen clearly
Also called “near point” or “punctum proximum”
Measured with the RAF rule
21. DDDO
An emmetropic eye has “with” movement on retinoscopy
and “superior” crescent on DDDO while 1D myopia (due
to accommodation) shows “no movement” on retinoscopy
and disappearance of superior crescent on DDDO
DDDO is an easier test than DR
Location of bright crescent moving from top to the
bottom of the pupil is probably easier to recognize[Fig. 5]
than change in the movement of the retinoscopy reflex
(“with” movement to the “against” movement), more so
when the pupils are dilated
22. Anomalies of Accommodation
General symptoms:
Problems are longstanding
Intermittently blurred vision
Eyestrain and/or headache with visual tasks
Fatigue/sleepiness with visual tasks
Inattentiveness over time
24. Accommodation Insufficiency
The accommodative amplitude is distinctly below the
lower limit of the expected amplitude in relation to the
age of the individual
Similar to presbyopia
Can result from systemic conditions such as diabetes
mellitus, multiple sclerosis, anemia, general physical
fatigue, myasthenia gravis, trauma, malnutrition,
convalescence from debilitating illnesses and chronic
alcoholism
25. Accommodation Insufficiency
Specific symptoms:
Blurred vision/eyestrain with NEAR visual tasks
Intermittent diplopia due to associated disturbances of
convergence
Examination findings
Reduced amplitude of accommodation
Higher than normal lag of accommodation
Difficulty clearing -2.00 D lenses on monocular and
binocular accommodative facility testing
PRA (positive relative accommodation) lower than -1.50
26. Causes of Unilateral Accommodation Failure:
Congenital unilateral third nerve palsy
Transient, post traumatic, accommodation failure associated with
traumatic mydriasis
Causes of Bilateral Accommodation Failure:
Cortical vision impairment
Foveal hypoplasia (albinism, aniridia)
Down syndrome
Iso-ametropic amblyopia
Ectopia lentis
Macular degeneration
Nanophthalmos
Near vision palsy
Rule out…
27. Treatment: Accommodation Insufficiency
Spectacle correction
For near- weakest convex lenses should be prescribed
If there is associated convergence insufficiency base out
prism may be added to patient comfort
In cases with convergence excess full spherical correction
should be prescribed
ACCOMMODATION TEST-CARD EXERCISE
28. Vision Therapy: To stimulate accommodation mono-
ocularly
Small print targets that are slowly moved CLOSER to the eye
Reading print through MINUS lenses (gradually increasing
the power) using “Monocular minus lens rock”
Monocular lens flippers
Monocular minus lens clear/blur/clear (for fine voluntary
control)
Binocular lens flippers
Treatment: Accommodation Insufficiency
29. Ill-sustained Accommodation
Initial stage of true insufficiency
Range is normal
During prolonged near work, accommodative power
weakens, the near point gradually recedes and vision
becomes blurred
30. Inertia of Accommodation
Rare condition
Difficulty in altering the range of accommodation
Requires time and effort to focus a near object after
looking into distance
Treatment:
Correction of refractive error
Accommodative Exercises
31. Paralysis of Accommodation
Causes:
Drug induced cycloplegia –atropine ,homatropine
Internal opthalmoplegia [paralysis of cilliary muscle &
sphincter pupillae]
Neuritis associated with chronic alcoholism, diabetes
CNS infections
Head Injury
Specific Symptoms:
Blurring of near vision
Photophobia [glare]
32. Treatment: Paralysis of Accommodation
Self recovery occurs in drug induced paralysis
Dark glasses are effective in reducing the glare
Convex lenses for near vision may be prescribed
34. Treatment: Accommodative Excess
Prescribing lenses
Distance lens prescription
Added plus lenses are not usually accepted for near work
Vision Therapy: To relax accommodation monocularly
Small print targets slowly moved AWAY from the eye
Reading print through PLUS lenses (gradually increasing the
power)
35. Spasm of Accommodation
Abnormally excessive accommodation which is out of
voluntary control of the individual
Causes:
Drug induced spasm after use of strong miotics
Spasm of near reflex
36. Spasm of Accommodation
Specific symptoms:
Blurred vision at DISTANCE after performing near visual
tasks
Examination findings:
Lead of accommodation
Difficulty clearing +2.00 D. lenses on monocular and
binocular accommodative facility testing
NRA lower than +1.50
37. Treatment: Spasm of Accommodation
Relaxation of ciliary muscle: the most effective method of
treatment is complete ciliary paralysis with atropine
38. Accommodative Infacility
Specific symptoms:
Blurred vision when CHANGING focus far → near and near
→ far
Examination findings:
Difficulty clearing both +2.00 and -2.00 D. lenses on
monocular and binocular accommodative facility testing
PRA lower than -1.50 and NRA lower than +1.50
39. Treatment: Accommodative Infacility
Vision Therapy: to stimulate/relax accommodation
monocularly
Alternately focusing on small print targets at near and far
(with the near target slowly moved closer to the eye).
Reading near print through alternating PLUS and MINUS
lenses (gradually increasing the power)
Editor's Notes
Also called capsular theory
Equator is getting nearer to the ciliary muscle
Because of the increased equatorial zonular tension on the lens during accommodation, the stress on the lens capsule is increased and the lens remains stable.
As the equatorial diameter of the lens continuously increases over life, perilenticular space is reduced and ciliary muscle contraction can no longer tense the zonules and expand the lens coronally. This results in presbyopia.
Hammock shaped surface is reproducible depending on the circular dimensions, i.e. the diameter of the ciliary body.
Presbyopia occurs due to increasing lens volume with age, which results in reduced response of anterior lens to vitreous pressure gradient
When the eye is at rest, we call the refraction as static. When the refraction is alteres by exercise of accommodation, it is called as dynamic.
Collectively called as asthenopia
the accommodation test card consists of a black vertical line draw on a white card . Patient holds it at considerable distance from eyes & then brings it closer until the line appears blurred & indistinct . By repeating this he should be encouraged to attempt to bring his near point as close as possible
Causes and treatment are same as for Accommodation insufficiency
Spasm of near reflex is a clinical syndrome often seen in tense or disturbed individuals who present with excessive accommodation, excessive convergence & miotics
