Details About Accomodation

1. ACCOMMODATION

2. DEFINITION
• Our eyes have been provided with a unique
mechanism by which we can even focus the
diverging rays coming from a near object on
the retina in a bid to see clearly, this
mechanism is called accommodation.
• In this increase in the power of crystalline lens
occurs due to increase in curvature of its
surface.

3. • At rest the radius of curvature of anterior
surface of the lens is 10mm and that of
posterior surface is 6mm.
• During accommodation curvature of the
posterior surface remains almost the same but
that of anterior changes. In strong
accommodation radius or curvature of
anterior surface also becomes 6mm.

4. MECHANISM OF ACCOMMODATION
• WHEN THE EYE IS AT REST; The ciliary ring is
large and keeps the zonules tense. because of
zonules tension the lens is kept
compressed(flat)by the capsule.
• CONTRACTION OF THE CILIARY MUSCLE;
Causes the ciliary ring to shorten and thus
releases zonular tension on the lens capsule.
This allows the elastic capsule to act
unrestrained to deform the lens substance.

5. • The lens then alters its shape to become more
convex, the lens assumes conoidal shape due
to configuration of the anterior lens capsule
which is thinner at the centre and thicker at
the periphery.
• FOR POINT AND NEAR POINT; The nearest
point at which small objects can be seen
clearly is called near point or punctum
proximum and the distant point called for
point or punctum remotum.

6. RANGE AND AMPLITUDE OF
ACCOMMODATION
• RANGE OF ACCOMMODATION; The distance
between the near point and the for point is
called the range of accommodation.
• AMPLITUDE OF ACCOMMODATION; The
difference between the dioptric power
needed to focus at near point(P) and for point
(R) is called amplitude of accommodation (A).
A=P-R.

7. ANOMALIES OF ACCOMMODATION
• PRESBYOPIA.
• INSUFFICIENCY OF ACCOMMODATION.
• PARALYSIS OF ACCOMMODATION.
• SPASM OF ACCOMMODATION.

8. PRESBYOPIA
• Is not an error of refraction but a condition of
physiological insufficiency of accommodation
leading to a progressive fall in near vision.
• PATHOPHYSIOLOGY; As we know, in an
emmetropic eye for point is infinity (∞ and
near point varies with age.
• Being about 7cm at the age of 10years,25cm
at the age of 40years, and 33cm at the age of
45 years.

9. • At the age of 10years, amplitude of
accommodation(A)=100/7 (dioptric power
needed to see clearly at near point)-1/∞
(dioptric power needed to see clearly at for
point clearly).
A (at age 10)= 14 Dioptres.
Similarly at the age of 40;
A=100/25 -1/∞ = 4 Dioptres.

10. • CAUSES;
Decrease in the accommodative power of
crystalline lens with increasing age, leading to
presbyopia occurs due to;
1.Age related changes in the lens;
decrease in elasticity of lens capsule,
progressive increase in size and hardness of
the lens substance.
2.Age related decline in ciliary muscle power.
uncorrected hyperopia.

11. • Premature sclerosis of the crystalline lens.
• Chronic simple glaucoma.
• SYMPTOMS;
• Difficulty in near vision,
• Asthenopic symptoms,
• Intermittent diplopia,
• TREATMENT;
• Spectacle and surgical treatment.

12. INSUFFICIENCY OF ACCOMMODATION
• The accommodative power is significantly less
than the normal physiological limits for the
patients age.
• CAUSES;
• Premature sclerosis of lens,
• Weakness of ciliary muscle,
• TREATMENT;
• Treatment of underlying causes,

13. • Near vision spectacle,
• Accommodation exercises,

14. PARALYSIS OF ACCOMMODATION
• Is also known as cycloplegia refers to complete
absence of accommodation.
• CAUSES;
• Drug induced cycloplegia
• Paralytic internal opthalmoplegia
• Complete third nerve paralysis

15. • CLINICAL FEATURES;
• Blurring of near vision,
• Photophobia,
• TREATMENT;
• Self recovery in drug induced cycloplegia,
• Dark glasses to reduce glare,
• Convex lenses if paralysis is permanent,

16. SPASM OF ACCOMMODATION
Refers to exertion of abnormally excessive
accommodation,
CAUSES;
Drug induced spasm of accommodation,
In children who attempt to compensate for a
refractive anomaly that impairs their vision, it
usually occurs when the eyes are used for
excessive near work.

17. • CLINICAL FEATURES;
• Defective vision,
• Asthenopic symptoms,
• DIAGNOSIS;
• It is made with refraction under atropine
cycloplegia,
• Relaxation of ciliary muscle,
• Necessary psychotherapy,
• Correction of associated causative factors,

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