The Eye VISION Alyssa Jimenez & Cristina Santiago

Components Of the eye ❖ Eyelid (palebra) ❖ Lacrimal apparatus ❖ Extrinsic Muscles ❖ Cranial Nerves

Components cont.

Eyelid ● Also known as the palebra ● Protective shield for the eyeball ● Conjunctiva

Lacrimal Apparatus ● Tear secretion and distribution ● Lacrimal gland ● Nasolacrimal gland

Extrinsic Muscles ● Hold eyeball in orbital cavity and allow for eye movement ● Superior Rectus Muscle ● Inferior Rectus Muscle ● Lateral Rectus Muscle ● Medial Rectus Muscle ● Superior Oblique Muscle ● Inferior Oblique Muscle

Structure of the eye ●three tunics ■ fibrous ■ vascular ■ interna

The outermost tunica function: protection ● Consists of:  Cornea: helps focus incoming light rays  Sclera: protection, attachment of eye muscles  aqueous humor

The middle tunica ● tunica vascular o supplies eye tissue with oxygen and nutrients ● Consists of:  choroid coat: contains many blood vessels  Pupil  lens  iris: colored ring around pupil

 ciliary body: o ciliary muscles: control shape of lens o ciliary processes: hold lens in place. o accommodation: lens changes shape to focus on close objects o Aqueous Humor: thin, watery fluid that fills the space between the cornea and the iris

the innermost tunica ● Tunica Interna  the retina ● inner lining of eyeball ● site of photoreceptors ● vitreous humor

Cranial Nerves ● Occipital Lobe ● Oculomotor Nerve *ex: maintaining the opening of an eyelid/pupil constriction ● Optic Nerve *ex: brightness,perception,contrast

Structure cont. ● Blind spot: no photoreceptors present ● posterior cavity: filled with vitreous humor ● jelly-like fluid,which maintains the spherical shape of the eyeball

Visual Receptors ● Two types of visual receptors  Cones: o color vision o produce sharp images o absorb light o less sensitive in low light levels  Rods: o night vision o produce silhouettes of images o do not differentiate color o sensitive to low light levels o peripheral areas of retina

Rhodopsin & Iodopsin light ● Rhodopsin light: o absorbing pigment o embedded in membranous discs ● Iodopsin light: o a photosensitive violet pigment that occurs in the cones of the retina and is transformed by light into retinal and an opsin protein.

Dark Currents in photoreceptors *Sodium channels stay open in photoreceptor when no light is being absorbed *Constant current of sodium into cell keeps photoreceptor the most active in darkness

Refraction ● The refraction process is similar to the way a camera’s lenses tale in light ● The bending of a wave when a light passes a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media, this is how the eye interprets refraction ● 80% of refraction occurs in the cornea is the most drastic change in the index of refraction which the light experiences ● 20% of refraction occurs in the inner crystalline lens ● Light is refracted, or bent, when it passes from one medium to a medium with different density ● Ex: air to glass to air

Convergent vs. Divergent ● Convergent waves are rays of light that converge light that is traveling parallel to their principal axis - Convex lenses refract light in a towards each other ● Divergent waves are rays of light that diverges light that is traveling parallel to their principal axis; travels through the center of either lens,straight through and is not refracted -Concave lenses refract parallel light rays away from each other

Dark vs. Light Vision ● Dark light is dim vision, when an individual’s eye adapts to a loss of illumination -The pigmentation of the eye in dark vision,is very minimal, consists of rod cells, but since neither rods or cone can survive in the dark for long, blindness is a definite possibility The photoreceptors found in dark light are rods A.Factors that affect Dark Light -Intensity and duration of the pre- adapting light -Size and position of the retinal -Wavelength distribution -Rhodopsin regeneration (deficiency of vitamin A)

Dark vs. Light Vision Cont ● During Light vision, the eye quickly adapts to background illumination and is then able to distinguish and identify objects The photoreceptors found in light vision are cones 1. S- cones, short- wavelength sensitive cones 2. M- cones, middle- wavelength sensitive cones 3. L- cones, long wavelength sensitive cones

Stereoscopic Vision ● The single perception of a slightly different image from each eye ● Gives us the ability to see objects with height, width, and depth ( a sort of 3-D experience)