1. Physiology of visual analyzer

2. The eyes mediate sight Function Sensory organ for sight
Detects light and converts it into neural responses that the brain interprets

3. EYE
External Eye Structures

4. The eyes are complex sense organs that have evolved from primitive light-sensitive spots on the surface of invertebrates.
Within its protective casing, each eye has a layer of receptors, a lens system that focuses light on these receptors, and a system of nerves that conducts impulses from the receptors to the brain.

5. Lacrimal Apparatus

9. Visual Pathways & Fields
Objects reflect light
Rays refracted by cornea, aqueous humor, lens, vitreous body and onto retina.
Light stimulus is changed to nerve impulses, travel thru optic nerve to visual cortex in occipital lobe
Image on retina is upside down & reversed. At the optic chiasm retinal fibers cross over. Right side of brain looks at left side of world.

12. Parts of the Eye
Sclera: a tough white layer of connective tissue that covers all of the eyeball except the cornea.
Conjunctiva: external cover of the sclera — keeps the eye moist.
Cornea: transparent covering of the front of the eye.
Allows for the passage of light into the eye and functions as a fixed lens.

13. Prevents light rays from scattering and distorting the image.
Choroid: thin, pigmented layer lining the interior surface of the sclera.
Prevents light rays from scattering and distorting the image.
Anteriorly it forms the iris.
The iris regulates the size of the pupil.
Retina: lines the interior surface of the choroid.
Contains photoreceptors.
Except at the optic disk (where the optic nerve attaches).

14. Focusing Light
The lens and ciliary body divide the eye into two cavities.
The anterior cavity is filled with aqueous humor produced by the ciliary body.
The posterior cavity is filled with vitreous humor.
The lens, the aqueous humor, and the vitreous humor all play a role in focusing light onto the retina.

15. ** Internal Anatomy:
Outer layer: sclera it’s a protective white covering, cornea bending light rays to focused on inner retina- cornea sensitive to touch(corneal reflex)-trigeminal nerve(CN V) carries afferent sensation into brain, facial nerve(CN VII) carries efferent messages that stimulates the blink.

16. The Pupil is an Aperture
Opening in the center of the eyeball
Bounded by the Iris
The iris controls the size of the pupil
Opening through which light enters the eye
Pupil
Iris

17. Iris and Pupil Iris = flat, round, regular, even color bilaterally.
Pupils = PERRLA
Resting size norm = 3-5mm
5% population have pupils of 2 diff. Sizes called Anisocoria

18. ** Visual Reflexes:
# papillary light reflex: is a normal constriction of pupil when light shines on retina( a direct reflex & a consensual reflex).
Mechanism: light →retina → optic Nerve(II)__ efferent or sensory → midbrain → CN III (oculomotor) _ afferent(motor) → constriction of iris muscles for both eyes.
Direct reflex → same eye _Consensual reflex → opposite eye.

20. Lenses of the Eye Cornea Crystalline Lens
Primary function = focus the image on the back of the retina
Focus

21. Refraction
Bending of the path of a light wave as it passes across the boundary separating two media
Cause:
Change in the speed of the light wave
No change in speed = no refraction!
Material A (fast)
Material B (slow)

22. Focusing point sources of light
Focusing point sources of light. (a) When diverging light rays enter a dense medium at an angle to its convex surface, refraction bends them inward. (b) Refraction of light by the lens system. For simplicity, refraction is shown only at the corneal surface (site of greatest refraction) although it also occurs in the lens and elsewhere. Incoming light from a (above) and b (below) is bent in opposite directions, resulting in b' being above a' on the retina.

24. Emmetropia
Emmetropia the refractive condition in focus on fovea that parallel lights enter eye through refractive system without accommodation
Punctum remotum of emmetropia: infinite
1．眼球前后径太短，形成轴性远视；
2．眼球前后径太长，形成轴性近视；
3．晶体向前移位，形成近视；
4．晶体向后移位，形成远视。
1．角膜前面或晶体面曲度太平(曲率半径太长)，引起弯曲性远视(或称曲率性远视)；
2．角膜前面或晶体面曲度太峻(曲率半径太短)，致成弯曲性近视(或称曲率性近视)；
3．角膜或晶体面各径向曲度不等，形成散光。
三)眼屈光系各组成因子不同轴
1．晶体倾斜 晶体半脱位或人工晶体位置倾斜，形成散光。
2．视网膜倾斜
眼屈光媒质折射率异常

25. Accomodation Viewing Distant Objects Viewing Nearby Objects
Ciliary muscles relaxed
Lens assumes a flatter (skinnier) shape
Cornea is not pushed out = less curvature
C-L system has a long focal length
Low refractive Power
Viewing Nearby Objects
Ciliary muscles contract
Squeeze the lens into a more convex (fat) shape
Pushes cornea bulge out further = greater curvature
C-L system has a short focal length
High refractive power

26. Accommodation Accommodation
the capability that eyes change refractive condition in order to acquire clear near sight

27. ACCOMMODATION

28. Accommodation Helmhotz accommodation mechanism
Schachar accommodation mechanism
Ciliary muscle contract
Lens zonule relax
accommodation
Elastic deformation of lens
See near
Ciliary muscle contract
Ante-&post-lens zonule relax
accommodation
Peripheral lens flatten
See near
equatorial lens zonule tension
Central lens project

29. Accommodation Accommodation = diopter for far diopter for near
Range of accommodation distance of far point — distance of near point

30. Myopia
Myopia: the refractive condition that parallel lights enter eye through refractive system and focus before fovea on static refraction
Punctum remotum of myopia: a point before eye

31. Hyperopia
Hyperopia the refractive condition that parallel lights enter eye through refractive system and focus after fovea on static refraction
Punctum remotum of myopia: a point after eye

32. Hyperopia
Myopia and correction
Hyperopia and correction

33. RETINA
The retina extends anteriorly almost to the ciliary body. It is organized in 10 layers and contains the rods and cones,
which are the visual receptors, plus four types of neurons: bipolar cells, ganglion cells, horizontal cells, and
amacrine cells
Neural components of the extrafoveal portion of the retina.
C, cone;
R, rod;
MB, RB, and FB, midget, rod, and flat bipolar cells;
DG and MG, diffuse and midget ganglion cells;
H, horizontal cells;
A, amacrine cells.

34. Vision Rhodopsin (retinal + opsin) is the visual pigment of rods.
The absorption of light by rhodopsin initiates a signal-transduction pathway
Receptor potential is hyperpolization .
Fig

35. Vision Rods and Cones synapse with nuerons called bipolar cells
Bipolar cells synapse with galgion cells of optic nerve

36. Near the posterior pole of the eye is a yellowish pigmented spot, the macula lutea. This marks the location of the
fovea centralis, a thinned-out, rod-free portion of the retina that is present in humans and other primates. In it, the
cones are densely packed, and each synapses to a single bipolar cell, which, in turn, synapses on a single ganglion
cell, providing a direct pathway to the brain. There are very few overlying cells and no blood vessels. Consequently,
the fovea is the point where visual acuity is greatest

37. RECEPTORS

39. Visual Acuity
Visual acuity is the degree to which the details and contours of objects are perceived, and it is usually defined in
terms of the shortest distance by which two lines can be separated and still be perceived as two lines. Clinically,
visual acuity is often determined by the use of the familiar Snellen letter charts viewed at a distance of 20 ft (6m).