1. Sense Organs I: The Visual System
Lecture 15
Sense Organs I: The Visual System

2. Visual System Eye Accessory structures Optic nerve (II)
Eyebrows, eyelids, eyelashes, lacrimal (tear) glands
Optic nerve (II)
Sensory information travels along optic nerve to thalamus then to occipital lobe

3. Accessory Structures of Eye
Eyebrows
Prevent running perspiration into eyes
Shade
Eyelids or palpebrae
Protect and lubricate
Lacrimal caruncle has sebaceous and sweat glands
Extrinsic eye muscles (6)
Lacrimal apparatus
Lacrimal gland (facial nerve VII)
Conjunctiva
Thin mucous membrane over inner surface of eyelids and anterior side of eyeball
Fig

4. Anatomy of the Eye Three coats or tunics
Fig
Three coats or tunics
Fibrous: Consists of sclera and cornea
Vascular: Consists of choroid, ciliary body, iris
Neural: Consists of retina

5. Anatomy of the Eye Fibrous tunic: Outer
Sclera: White outer layer, maintains shape, protects internal structures, provides muscle attachment point, continuous with cornea
Cornea: No blood vessels, transparent, allows light to enter eye and refracts (bends) light
Fig

6. Anatomy of the Eye Vascular tunic: Middle
Iris: Controls light entering pupil; smooth muscle
Ciliary muscles: Control lens shape; smooth muscle
Choroid: pigmented layer that contains melanin

7. Anatomy of the Eye Retina: Inner Cavities
Contains neurons sensitive to light
Macula lutea & Fovea centralis: Area of greatest visual acuity
Optic disc: Blind spot
Cavities
Anterior: Aqueous humor
Posterior: Vitreous humor

8. Anatomy of the Eye
Lens
Held by suspensory ligaments attached to ciliary muscles
Transparent, biconvex

9. Focus and Accommodation
Fig
Far vision: 20 feet or more from eye
Near vision: Closer than 20 feet
Accommodation

10. Review Question
Damage to the retina due to excessive light entering the eyeball could indicate a problem with the
Iris
Ciliary body
Cornea
Conjunctiva
Choroid

11. Points to Remember
Accessory eye structures protect and lubricate the eye.
There are 3 basic layers to the eye: fibrous tunic, vascular tunic and neural tunic.
Image formation on retina by bending of light rays through cornea and lens.
To view close objects, the lens increases its curvature.

12. Questions?