This document summarizes the anatomy and function of the human eye. It describes how light passes through the cornea, pupil, and lens, and is focused onto the retina. It explains that the lens is attached to ciliary muscles that can change the lens's curvature to allow for focusing on near and far objects. This accommodation reflex involves both changes to the lens and constriction/dilation of the pupil. The document also discusses pupillary reflexes, lens disorders like myopia and hyperopia, and the roles of the cornea, iris, ciliary body, lens, retina, and associated muscles in vision and focusing.

1. VISUAL REFLEXES

2. ANATOMY OF
EYE

3. How the eyes work?
• The light passes through cornea which is shaped dome shaped,
helping light to bend for eye focus.
• The light enters the eye through an opening called the pupil (PYOO-
pul).
• The iris controls how much light the pupil lets in.
• The light passes through the lens which works together with the
cornea to focus light correctly on the retina.
• When light hits retina, photoreceptors turn the light into electrical
signals which travels through optic nerve to the brain ; forming an
image.

4. OPTICAL MEDIUM OF EYE
• Cornea
• Crystalline lens
• Aqueous fluid filling the eye: which determines the final shape of
wavefront reaching the retinal photoreceptors.

5. What mechanical changes occur when light
passes through eye?
• Light first passes through the cornea at the front of the eye and then
pupil opening, will enter the crystalline lens.
• The lens is attached to the ciliary muscles.
• These muscles relax and contract in order to change the shape of the
lens.

6. How does the curvature of the eye lens
change?
• The eye lens is made up of a fibrous jelly like material.
• Its curvature can be changed by modifying its focal length to some
extent by the ciliary muscles.
• The increased curvature of the lens allows the eye to focus on a close
object.
• When the person then has to look at a faraway object, the muscles
relax and the focus of the lens changes to an object further away.

7. Which muscles participate in this process?
• Superior and inferior rectus
• Medial and lateral rectus
• Superior and inferior obliques

8. What is the order of structures that light
passes through in the eye?
• Light passes through the cornea, then the pupil, the iris and the lens
before it falls on the retina.
• There are two fluid filled chambers called the Anterior chamber
behind the cornea, and the Vitreous chamber, which is the main part
of the eye ball, but these aren’t really structures, these are fluid filled
spaces.

9. There are 2 types of reflexes:
1)PUPILLARY REFLEX
2)ACCOMMODATIVE REFLEX

10. PUPILLARY
REFLEX
When light is shone into the
eyes, the pupils constrict, a
reaction called the pupillary
light reflex.

11. How does pupillary sphincter muscle work?
• The sphincter muscle fibers are located near the pupillary margin and
are slightly anterior to the pigmented epithelium of the iris.
• It encircles the pupil of the iris and functions to constrict the pupil in
bright light via the pupillary light reflex or during accommodation.
• Stimulation of the parasympathetic nerves also excites the pupillary
sphincter muscle, thereby decreasing the pupillary aperture; this is
called MIOSIS

12. How does pupillary dilator muscle work?
• The dilator muscle of the iris contains fibers that extend radically
through the iris of the eye and involuntarily contract as available light
decreases, thus dilating the pupil.
• Pupillary dilation is controlled primarily by the sympathetic nervous
system.
• Stimulation of the sympathetic nerves excites the radial fibers of the
iris and causes pupillary dilation, called MYDRIASIS.

13. ACCOMMODATION
REFLEX
The reflex action of the eye, in
response to focusing on a
near object, then looking at a
distant object, comprising
coordinated changes in lens
shape and pupil size

14. How does a person adjust accommodation to
keep eyes in focus all the time?
• Accommodation of the lens is regulated by a negative feedback
mechanism that automatically adjusts the refractive power of the lens
to achieve the highest degree of visual acuity.
• When the eyes have been focused on some far object and must then
suddenly focus on a near object , the lens usually accommodates for
best acuity of vision within less than 1 second.

15. How does ciliary body work?
• The ciliary body is a circular structure that is an extension of the iris,
the colored part of the eye.
• The ciliary body produces the fluid in the eye called aqueous humor.
• It also consists of ciliary muscles, which changes the shape of the lens
when your eyes focus on a near object.

16. SIGNIFICANCE OF ACCOMMODATION
• The ocular structures involved in accommodation include the ciliary muscle, lens,
and pupil. Below is a short description of these structures.
• Ciliary muscle - The ciliary muscle is a smooth muscle that is shaped like a ring
and it’s located in the middle of the eyes. It holds the lens with the suspensory
ligaments and also adjusts the optical power or shape of the lens during
accommodation.
• Lens - This is a transparent structure in the eye, it is biconvex in shape (both
surfaces are shaped like the exterior of a circle). It is bordered anteriorly (in front)
by a ring it forms with the posterior side of the iris. The lens is held by the
suspensory ligament and has a diameter of 10 mm and a height of 4 mm in an
adult. These measurements vary due to change in the lens structure during
accommodation and aging.
• Pupil - The pupil is located in the middle of the eyes, it is black in color and
constricts to prevent light rays that have diverged from touching the retina and
causing blurred vision.

17. LENS
DISORDERS
Myopia
Hyperopia
Astigmatism

18. Explain
• Nearsightedness (myopia): You see close objects clearly, but objects
farther away look blurry.
• Farsightedness (hyperopia): Objects in the distance look clear, while
things close by look blurry.
• Astigmatism: A problem with the shape of your cornea (or lens)
causes blurry or distorted vision

19. Presented by Pranavi Shewale 203