This document discusses accommodation, or the ability of the eye to focus on near objects. It defines accommodation and describes the three adjustments made: convergence of the eyeballs, constriction of the pupil, and an increase in the anterior curvature of the lens. The mechanism of accommodation involves the ciliary muscle contracting to relax the suspensory ligaments and allow the lens to become more spherical for focusing on near objects. The pathway for the accommodation reflex involves visual signals traveling from the retina to the visual cortex and frontal lobe, where efferent signals are sent to the ciliary muscle, sphincter pupillae, and medial rectus to enact the adjustments for accommodation. Presbyopia is described as the age-related loss

1. ACCOMODATION
By
Prof.Dr.Nusrat Tariq
M.Islam Medical &Dental College

3. ACCOMMODATION
or
NEAR RESPONSE

4. „
DEFINITION:
Accommodation is the adjustment
of eye to see near objects clearly. It is
the process by which light rays from
near objects are brought to a focus
on retina

5. Mechanism Of
Accommodation:
It is achieved by various
adjustments made in
the eyeball

6. Adjustments Made In The Eyeballs
When a person looks at a near object after
seeing a far object, three adjustments are
made in the eyeballs:
1. Convergence of the eyeballs
2. Constriction of the pupil
3. Increase in the anterior curvature of
the lens (lens becomes more spherical)

7. 1. Convergence of the eyeballs due
to contraction of the medial recti.
2. Constriction of the pupil due to
the contraction of
constrictor/sphincter pupillae of
iris.
3. Increase in the anterior
curvature of the lens due to
contraction of the ciliary muscle.

11. Mechanism Of Accommodation (Focusing)
.

12. MECHANISM OF ACCOMMODATION
When the eyes are fixed on a distant object:
 lens is flat due to the traction of suspensory
ligaments.
When vision is shifted from the distant object to a
near object :
Ciliary muscle contracts. Stimulation of the
parasympathetic nerves contracts both sets of ciliary
muscle fibers,
The contraction of the ciliary muscle relaxes the
suspensory ligaments, and the lens assumes a more
spherical shape

13. PATHWAY FOR
ACCOMMODATION REFLEX

14. VISUAL PATHWAY

22. Pathway For Accommodation Reflex

23. ACCOMMODATION REFLEX
Receptors: ?

24. Receptors:
Rods and Cones

25. ACCOMMODATION REFLEX
Afferent Pathway:
Visual impulses from retina pass through the
optic nerve, optic chiasma, optic tract, lateral
geniculate body and optic radiation to visual
cortex (area 17) of occipital lobe. From here,
the association fibers carry the impulses to
frontal lobe.

26. ACCOMMODATION REFLEX
Center
The center for accommodation lies in:
frontal eye field (area 8) that is
situated in the frontal lobe of
cerebral cortex.

27. Efferent Pathway
1.Efferent fibers to ciliary muscle and sphincter
pupillae:
From area 8, the corticonuclear fibers pass via internal
capsule to the Edinger-Westphal nucleus of third
cranial nerve.
The preganglionic fibers pass through the third cranial
nerve to ciliary ganglion.
Postganglionic fibers from ciliary ganglion pass via the
short ciliary nerves and supply the ciliary muscle and the
constrictor pupillae.

28. 2. Efferent fibers to medial rectus:
Some of the fibers from frontal eye
field terminate in the somatic motor
nucleus of oculomotor nerve. The
fibers from motor nucleus supply
medial rectus.

29. Effectors:
???

30. Effectors:
The ciliary muscle and the
constrictor pupillae.
Medial rectus

31. Pathway For Accommodation Reflex

33. Presbyopia: Loss of Accommodation by the
Lens.
Presbyopia :
Failure of accommodation to near objects due to gradual
diminution of lens elasticity with advancing age is called
Presbiopia.
 The power of accommodation decreases from 14 diopters in a
child to less than 2diopters at age 70 years.Thereafter, the
lens remains almost totally non accommodating (presbiopic).
 In presbyopia the eyes can no longer accommodate for both
near and far vision. To see clearly both in the distance and
nearby, an older person must wear bifocal glasses, with the
upper segment focused for far-seeing and the lower segment
focused for near-seeing (e.g., for reading).

34. Causes OF Presbyopia
It is due to:
1. loss of elasticity the lens grows larger and
thicker and becomes far less elastic.
(denaturation of the lens proteins).
2. sclerosis of lens capsule or suspensory
ligaments .
3. weakness of the ciliary muscles.

35. Advantages of Pupillary constriction
 Spherical abberation.
(The constriction of pupil allows the light to pass
through the centre of the lens with least bending )
 Chromatic abberation
 No Image distortion
 Depth of focus