14. Aqueous and Vitreous Humor
Aqueous Humor Vitreous Humor
It’s a watery fluid present in anterior
segment of eye.
A jelly like substance present in
posterior segment of eye and is covered
by hyaloid membrane.
Filtered out of ciliary processes. Formed during embryonic development.
It has glucose, salts, amino acids, lactic
acid, pyruvic acid.
It has pyruvic acid, lactic acid, hyaluronic
acid, hyalocytes.
Provides nutrition to avascular
structures of eye.
It maintains spherical shape of eyeball.
It is continuously replaced. It is never replaced.
15. Retina
➢ These are modified bipolar neurons.
➢ These are embedded in pigment layer of
retina.
➢ Pigment Layer: has cuboidal epithelial
cells.
➢ It engulfs discs of outer segment of rods &
cones.
➢ Recycling of vitamin A occurs in this layer.
Rods & Cones (Photoreceptors)
21. ➢ The outer segment of rod has thousands of flattened discs.
➢ Inner segment has the main metabolic machinery like mitochondria, Golgi etc.
➢ The synaptic terminal forms synapse with dendrites of bipolar neurons.
➢ The plasma membrane of disc has photopigment molecules.
Structure of a photoreceptor [Rod]
Retina
24. Retina
Rods Cones
Their outer segment is rod shaped. Their outer segment is cone shaped.
120 million/retina. 6 million/retina.
More abundant towards periphery of retina. More abundant towards centre of retina.
10-100 rods are connected to one nerve fiber. One cone is connected to 1 nerve fiber.
High sensitivity but low activity. Low sensitivity but high activity.
Not sensitive to colours. Sensitive to colours.
Provide vision in dim light (scotopic vision). Provide vision in bright light (photopic vision).
Have rhodopsin pigment. Have iodopsin pigment.
25. Regional peculiarities of retina
➢ It is that region in retina from where optic nerve leaves the eyeball.
➢ Rods & cones are absent here.
Blind spot or optic disc
26. ➢ It is a depressed area of retina just lateral to blind spot.
➢ It has lutein protein.
➢ In its centre Fovea Centralis is present, which has only cones.
➢ It’s the region of sharpest vision or most acute vision.
Macula Lutea (yellow spot)
Regional peculiarities of retina
27. ➢ In some ways the eye is like a camera.
➢ Its optical elements focus an image of some object on a light-sensitive “film”—
the retina.
Image Formation
Working of Eye
28. ➢ To understand how the eye forms clear images of objects on the retina, we
must examine three processes:
1. Refraction or bending of light by the lens and cornea;
2. Accommodation, the change in shape of the lens
3. Constriction or narrowing of the pupil.
Image Formation
Working of Eye
29. ➢ As light rays enter the eye, they are refracted at the anterior and posterior
surfaces of the cornea.
➢ Both surfaces of the lens of the eye further refract the light rays so they come
into exact focus on the retina.
Refraction
Working of Eye
30. ➢ About 75% of the total refraction of light occurs at the cornea.
➢ Lens provides the remaining 25% of focusing power and also changes the
focus to view near or distant objects.
Working of Eye
Refraction
31. ➢ When an object is 6 m (20 ft) or more away from the viewer, the light rays
reflected from the object are nearly parallel to one another.
➢ The lens must bend these parallel rays just enough so that they fall exactly
focused on the central fovea, where vision is sharpest.
Working of Eye
Refraction
32. ➢ Light rays that are reflected from objects closer than 6 m (20 ft) are divergent
rather than parallel.
➢ These rays must be refracted more if they are to be focused on the retina.
➢ This additional refraction is accomplished through a process called
accommodation.
Working of Eye
Refraction
33. ➢ Lens is convex on both its anterior and posterior surfaces, and its focusing
power increases as its curvature becomes greater.
➢ When the eye is focusing on a close object, the lens becomes more curved,
causing greater refraction of the light rays.
➢ This increase in curvature of the lens for near vision is called accommodation.
Accomodation
Working of Eye
34. ➢ It is the minimum distance from the eye that an object can be clearly focused
with maximum accommodation.
➢ This distance is about 10 cm in a young adult.
Near point of Vision
Working of Eye
35. ➢ When you are viewing distant objects, the ciliary muscle of the ciliary body is
relaxed and the lens is flatter.
➢ It is stretched in all directions by taut zonular fibers.
➢ When you view a close object, the ciliary muscle contracts, which pulls the
ciliary process and choroid forward toward the lens.
How accommodation occurs
Working of Eye
36. ➢ Lens is elastic, so it becomes more convex, which increases its focusing power
and causes greater convergence of the light rays.
➢ Parasympathetic fibers of the oculomotor (III) nerve innervate the ciliary
muscle of the ciliary body and, therefore, mediate the process of
accommodation.
How accommodation occurs
Working of Eye
37. ➢ Circular muscle fibers of iris also have a role in formation of clear images.
➢ This autonomic reflex occurs simultaneously with accommodation and
prevents light rays from entering the eye through the periphery of the lens.
➢ Light rays entering at the periphery would not be brought to focus on the retina
and would result in blurred vision.
Constriction of the Pupil
Working of Eye
