Vision Flashcards
Palpebrae
Eyelids
Separated by the palpebral fissure
Meet at the middle and lateral angles
Annular ring in the orbit
Origin of the 4 rectus muscles
6 extrinsic eye muscles
Lateral and medial rectus
Superior and inferior rectus
Superior and inferior oblique
Inferior oblique
Elevates eye and turns it laterally
Superior oblique
Depresses eye and turns it laterally
Fibrous layer
Most external layer of eyeball
Composed of 2 regions of CT
Limbus
Junction between sclera and cornea
Responsible for regeneration of the cornea
Scleral venous sinus
Allows aqueous humor to drain
Vascular layer
Middle coat of eyeball
Composed of choroid, ciliary body and iris
Choroid
Vascular, darkly pigmented membrane
Forms posterios 5/6 of vascular tunic
Brown colour from melanocytes
Prevents scattering of light rays in eye
Ciliary body
Thickened ring of tissue which encircles the lens
Composed of ciliary muscle
Ciliary processes (posterior surface) and ciliary zonule (suspensory ligament)
Iris
Visible coloured part of the eye
Attached to the ciliary body
Composed of smooth muscle
Iris pigmentation
The only pigments are brown pigments
Blue eyed people have brown on the inside of the iris, but none on the outside
NO BLUE PIGMENT
We see blue because of refraction
Pupil
Round central opening in iris
Sphincter pupillae muscle
Dilator pupillae muscle
Pupillary light reflex
Protective response of pupil constriction when a bright light is flashed in the eye
Parasympathetic vs Sympathetic effects on the pupil
PS: sphincter pupillae muscle contracts (inner), pupil size decreases
S: Dilator pupillae muscle contracts (outer), pupil size increases
Retina
2 layers
Deepest tunic
Pigmented layer: single layer of melanocytes
Neural layer: sheet of nervous tissue
3 tunics of the external walls of the eye
Fibrous layer
Vascular layer
Retina
3 main types of neurons in the neural layer of the retina
Photoreceptor cells - signal bipolar cells
Bipolar cells - signal ganglion cells
Ganglion cells - axons from here run along surface of the retina - converge to form optic nerve
Photoreceptors
2 main types: rods and cones
Considered neurons
Light particles modify the visual pigment and generate a nerve impulse
Vulnerable to damage by light or heat
Cannot regenerate if destroyed
Continuously renew and replace their outer segments
Rods vs Cones
Rods: more sensitive to light (vision in dim settings)
Cones: operate best in bright light (enable high-acuity, color vision
They have both inner and outer segments (outer segments are receptor regions where light absorbing pigments are present)
Regions of the Retina:
- Ora serrata
- Macula lutea
- Fovea centralis
- Optic disk
- Neural layer ends at the posterior margin of the ciliary body, pigmented layer covers ciliary body and posterior surface of iris
- Contains mostly cones
- Contains only cones (highest visual acuity)
- Blind spot
2 sources the retina gets its blood from
- Outer third of the retina (supplied by capillaries in the choroid)
- Inner two thirds of the retina (supplied by central artery and vein of the retina)
Vitreous humor
Found in the posterior segment of the eye
Clear, jellylike substance
Transmits light, supports posterior surface of the lens, helps maintain intraocular pressure
Aqueous humor
Found in anterior segment of the eye Renewed continuously Formed as a blood filtrate Supplies nutrients to the lens and cornea Produced by the ciliary body
Lens
Thick, transparent, biconvex disc
Held in place by its ciliary zonule
Lens epithelium covers anterior surface of the lens
Lens fibers form the bulk of the lens (new fibers are continously added, so lens enlarged throughout life)
Myopic eye
Nearsighted (cannot see distance)
The eyeball is too long and the focal point is in front of the retina
Hyperopic eye
Farsighted (cannot see close)
Eyeball is too short and the focal point is behind the retina
Tarsal plates
Connective tissue within the eyelids
Lacrimal caruncle
Reddish elevation and medial canthi
2 eye muscles that aren’t controlled by oculomotor nerve 3
Lateral rectus: abducens nerve (6)
Superior oblique: trochelar nerve (4)
