VISION Protects eyeballs from foreign object. o Lacrimal ApparatusANATOMY o Group of structures that produces and drains lacrimal Eyelids fluid or tears. o ―Palpebrae‖ o Lacrimal Glands o Upper eyelid, more movable than the lower eyelid. Produces 1mL lacrimal fluid/ day o Palpebral fissure Shape and size of an almond Space between upper and lower eyelids. Secrete lacrimal fluid. Exposes eyeball. o Excretory lacrimal ducts o Lacrimal Caruncle Empty tears on the surface of the conjunctiva of 1. Reddish elevation at the medial commissure. the upper eyelid. 2. Has sebaceous and sudoriferous glands. o Lacrimal punctum o Commissures Two small openings where tears enter after 1. Medial commissure passing medially over the anterior surface of the Broader. eyeball Near nasal bone. o Lacrimal canals 2. Lateral commissure Two ducts that leads to the lacrimal sac Narrower. o Nasolacrimal duct Closer to temporal bone. Duct that carries lacrimal fluid into the nasal cavity o Conjunctiva o Lacrimation Thin, protective mucous membrane. Lacrimal glands over secrete tears if there is 2 divisions: irritant present Bulbar Conjunctiva Protective mechanism Anterior surface of eyeball. Tears dilute and wash away irritating substance o SORE EYES - Dilation and congestion of Tears contains lysozyme(protective bactericidal blood vessesl on this area. enzyme), salts and some mucus. Palpebral Conjunctiva Lubricates ,protects and moistens the eyeball. Inner aspect of eyelids. *Colds, obstruction of nasolacrimal ductsand bloacks o Tarsal Plate drainage of tears. Fold of connective tissue. *Crying, response to parasympathetic stimulation. Lacrimal Gives form and support to the eyelids. gland produces excessive lacrimal fluid that spill over the Embeded in it: edges of the eyelids and fill nasal cavity with fluid (runny Tarsal or Meibomian Glands nose). Modified sebaceous gland Keeps eyelids from adhering to each EXTERIOR OF THE EYEBALL other Eyeball - CHALAZION - infection of the tarsal o 2.5 cm in diameter, anterior 1/6 is exposed gland o Composed of 3 Layers: o Eyelashes and Eyebrows 1. Fibrous Tunic o Sebaceous ciliary glands (Glands of Zeis) Superficial coat of eyeball. Release fluid at the base of the hair follicles. Avascular. STYE - infection on this gland. Anterior cornea o Eyelashes Transparent coat, covers colored iris. Project from border of the eyelid. Focus light onto the retina. o Eyebrows Outer surface: nonkeratinized startified Arch transversely above upper eyelid. squamous epithlium.
Middle surface: collagen fibers and Parasympympathetic, bright fibroblasts. light, iris contract decrease pupil Inner surface: simple squamous epithelium. size Posterior sclera Pupil ―Scler-‖= hard. Hole at the center of Iris. White of the eye. Autonomic reflexes regulate pupil Layer of dense CT (collagen fibers and diameter in response to light levels. fibroblasts) 3. Retina rd Covers entire eyeball except cornea. Inner and 3 coat of eyeball. Give shapes and rigidity to eyeball. Lines posterior ¾ of eyeball. Protects inner part. Beginning of visual pathway. Scleral Venous Sinus Optic disc- where optic nerve, central retinal Canal of Schlemm artery and vein exits. - Where aqueous humor drains. Blind spot (no rods or cones).2. Vascular Tunic Cosnsists of: ―Uvea‖ - Pigmented layer Middle layer of the eyeball Sheet of melanin-containing Has 3 parts: epithelial cells. Choroid Melanin- absorbs stray Posterior portion of vascular tunic. light. Lines internal surface of sclera. Prevent reflection and Provides nutrients to the surface of scattering of light w/in sclera. eyeball Anterior: ciliary body. Location between choroid and Extends to ora serrata, jagged anterior neural part of retina. margin of retina. Other cell types: horizontal and amacrine cells. Ciliary Body Neural Layer A. Cilliary processes Outgrowth of brain that processes visual data. Protrusions on the internal surface of the 3 layers: separated by outer and inner retina. synaptic layer Contains blood capillaries—secretes Bipolar cell layer aqueous humor. Ganglion cell layer Where zonular fibers extends. Photoreceptor layer B. Ciliary muscle Rods: low light threshold, no Circular band of smooth muscle that color vision alters shape of lens. Cones: higher threshold, For adaptation to near and far vision. produce color vision Iris Macula Lutea Colored portion of eyeball. At the exact center of the posterior portion of Suspended between cornea and lens. retina. Consists of smooth muscles: Central fovea - Radial (dilator pupillae) Small depression at the center of Sympathetic, dim light, iris macula lutea. contract, increase in pupil size Contains only cones. - Circular (sphincter pupillae) Has the highest visual acuity or resolution.
Lens 1-3 new discs are added to the base of outer o Behind pupil and iris. segment every hour. o Crystallins - make up the lens. Cones: o Transparent and lacks blood vessels. Tapered/Cone-shaped. o Focus images of retina for clear vision. Old discs go at the tip and phagocytized byINTERIOR OF THE EYEBALL pigment epithelial cells. Divided in 2 cavities by the lens o Inner segments o Anterior cavity Cell nucleus, golgi complex and many Filled with aqueous humor – watery fluid that mitochondria. nourishes lens and cornea. o Proximal end Produce intraocular pressure (16mmhg)- Expands into bulblike synaptic terminals. maintains shape of eyeball and prevents it CONES RODS from collapsing. Drains at the canal of schlemm and are being Center (Macula) Periphery replaced. Bright Dim Posterior chamber Iodopsin Rhodopsin Behind iris, in front of zonular fibers and lens. Anterior chamber 1 ganglion : 1 2 ganglion : 4 Between cornea and iris. Form and color (Photopic) Intensity/Movement o Vitreous membrane (Scotopic) Lies between lens and retina. Visual acuity and color Visual firlds, light and dark - Has vitreous body. perception adaptatiom Jelly-like substance , contributes to intraocular pressure. Photopigments Vitreal floaters o Integral colored proteins in the plasma membrane. Collection of debris, can cast shadow to o Absorption of light leads to chemical changes. retina. o Two parts of photopigments: Harmless, common to old individuals. Opsin Hyaloid canal Glycoprotein. Narrow channel runs through vitreous Different amino acid sequence, different body from the optic disk to the posterior colors are absorbed. of the lens. Retinal Holds retina flush against choroid Light-absorbing part. For even surface of reception of ear Vitamin A derivative (from carotenoids). images. o Rods: Does not undergo constant replacement. Rhodopsin Absorbs blue to green light.PHOTORECEPTORS AND COLOR BLINDESS Pleates pinch off from plasma membrane forming Photoreceptors discs. o Outer segments o Cones: Transduction of light energy into a receptor 3 different cone photopigments. potential occurs here. Absorbs blue, green, yellow orange They are easily replaced. Blue/Short wavelength (S) Rods: Green/Medium wavelength (M) Cylindrical/Rod-shaped. Red/Long wavelength (L)
Plasma membrane folds back and forth in a Rods: Contribute little to daylight. pleated fashion. Cones: Regenerate rapidly. Cis retinal always presentPhotopigments – Visual Transduction o Isomerization o When light level decreases Retinal is in bent shape (cis-retinal) fitted to Increased sensitivity and then more slowly. opsin. In complete darkness When it absorbs light, retinal straightens (trans- A threshold, light flash is seen as having a retinal). color. Isomerization is the transformation from cis-to- Rhodopsin regenerates more slowly, trans retinal. increasing the visual sensitivity. Chemical stability is affected. Even a single photon can be detected. Leads to receptor potential. At low light levels, only rods are functioning. o Bleaching Occurs for about a minute. Release of Neurotransmitters by Photoreceptors Trans-retinal separates from opsin. o Photoreceptor in the absence of light Final colorless product. Na inflow (“dark current”) into photoreceptor o After bleaching outer segment. Rods: Half of them regenerate in 5 minutes. Ligand-gated Na channels. Cones: Half of them regenerate in 90 seconds. Guanosine monophosphate (cGMP). o Enzyme retinal isomerase o Inflow partially depolarizes the photoreceptor. An enzyme converting the trans retinal to cis Membrane potential: -30 mV retinal again. Triggers release of NT at synaptic terminals o Regeneration NT in rods and cones: Amino Acid Glutamate Cis retinal back to opsin to form a functional (Glutamic Acid) photopigment. o Glutamate In rods, Between rods and bipolar cells at synaptic Pigmented layer adjacent to photoreceptors terminals. has high quantity of Vitamin A. Inhibitory NT Regeneration of rods. Inhibits postsynaptic potentials. If retina detaches from pigmented layer, Hyperpolarizes bipolar cells. regeneration of rhodopsin is low. o Photoreceptor in the presence of light In cones, Cis retinal goes isomerization. Photopigments regenerate more quickly. Enzymes are activated leading to breakdown of Less dependent on pigmented layer. cGMP. Some cGMP ligand-gated Na channelsLight and Dark Adaptation closes. o From darks surroundings, light adaptation Na inflow decreases. Visual system adjusts into bright surroundings. Membrane potential: -70 mV Visual system decreases sensitivity. Hyperpolarize receptor potential o Into a darkened room, dark adaptation Decrease in release of NT Visual system increases sensitivity over minutes. o Dim Lights o When light level increases Cause small and brief receptor potentials. More photopigments are bleached. Partial shutdown of some NT release. In daylight, regeneration of rhodopsin cannot o Brighter lights keep up with the bleaching process. Elicit larger and longer receptor potentials.
Complete shutdown of NT release. Visual Pathway Process RETINA Color Blindness o Receptor potentials arise in rods and cones o Inability to distinguish between certain colors. o Spread through the inner segments to the synaptic o Absence or deficiency of one of three cone terminals. photopigments. o Neurotransmitter molecules (glutamate) are released. o Red-green color blindness o Neurotransmitters induce local graded local potentials Most common. in bipolar cells and horizontal cells. Photopigment sensitive to orange-red/ green 6 and 600 rods synapse with bipolar cells. light is missing. Increases the light sensitivity of rod vision but Person cannot distinguish between red and green. slightly blurs the image perceived. o Vitamin A deficiency and consequent below normal Stimulation of rods by light excites their amount of rhodopsin bipolar cells. o Night blindness/ Nyctalopia. Cone more often synapses with just one bipolar Inability to see well at low light levels. cell. o Deuteranopia Less light sensitivity but has higher acuity due Absence of green cones. to one-to-one synapses between cones and o Protanopia their bipolar cells. Absence of red cones. Stimulation of rods by light may either excite o Tritanopia or inhibit cone bipolar cells. Absence of blue cones. o Horizontal cells transmit inhibitory signals to bipolar cells in the areas lateral to excited rods and cones.VISUAL PATHWAY AND VISUAL FIELDS Enhances contrasts in the visual scene between Neuronal cell types: areas of the retina that are strongly stimulated and o Photoreceptors (rods and cones) – transmit signals to adjacent areas that are more weakly stimulated. the outer plexiform layer, where they synapse with Assist in the differentiation of various colors. bipolar cells and horizontal cells. o Amacrine cells are excited by bipolar cells, synapse o Horizontal cells – transmit signals horizontally in the with ganglion cells and transmit information to them. outer plexiform layer from the rods and cones to Signals a change in the level of illumination of the bipolar cells. retina. o Amacrine cells – transmit signals in two directions, o Ganglion cells become depolarized and initiate nerve either directly from bipolar cells to ganglion cells or impulses. horizontally from axons of bipolar cells to dendrites of OPTIC NERVE the ganglion cells or to other amacrine cells. o Axons within the optic nerve pass through the optic o Ganglion cells – transmit output signals from the retina chiasm. through the optic nerve into the brain. Crossing point of the optic nerves. o Interproximal cell o Medial half of the axons cross the opposite side and Transmits signals in the retrograde direction from the lateral half of the axons remained uncrossed. the inner plexiform layer to the outer plexiform o After passing to the optic chiasm, the axons, now part layer. of the optic tract, enter the brain and terminate in the The signals are inhibitory and control lateral lateral geniculate nucleus in thalamus. spread of visual signlas THALAMUS Help control the degree of contrast in the viual o The axons synapse with neurons whose axons form image. the optic radiations, which project to the primary visual area in the occipital lobes of the cerebral cortex.
CORTEX o Both surfaces of the lens of the eye further refract the o Large number of optic fibers project to the lateral light rays so they come into exact focus on the retina. geniculate nucleus of the thalamus, where information 25% of focusing power (changes the focus to view from the different ganglion cell types is kept distinct. near or distant objects) o Receive input from the brainstem reticular formation o Image is focused on the retina: upside down and and input relayed back from the visual cortex. undergo right to left reversal. Control the transmission of information from the o Focusing power of the lens: retinal to the visual cortex. Object is 6 meters (20 feet) or more: light reflected Involved in our ability to shift attention between from the object are nearly parallel to one another. vision and the other sensory modalities The rays must be bent enough to be focused o Lateral geniculate nucleus sends action potentials to on the retina. the visual cortex. Object is closer than 6 meters (20 feet): light rays Processed simultaneously in a number of reflected from the object are divergent. independent ways in different parts of the cerebral The rays must be refracted more to be cortex. focused on the retina. Reintegrated to produce the conscious sensation 2. Accommodation of sight and the perceptions associated with it. o When the eye is focusing on a close object, the lens Constriction of pupil. becomes more curved and refracts the light more. Suprachiasmatic nucleus: establishes pattern The lens of the eye is convex on both its anterior of sleep and other activities in response to and posterior surfaces. intervals of light and darkness. Increase curvature of lens (for near vision) = Brainstem and cerebellum: coordination of Increase focusing power head and eye movements. o Near point vision: minimum distance from the eye o Cells are organized to handle information about line, that an object can be clearly focused with maximum contrast, movement, and color. accommodation. Form a spatial and temporal pattern of electrical activity. Contraction of ciliary muscle Visual Field Relaxation of zonular fibers o Visual area seen by an eye at a given instant. Relaxation of lens (becoming more o Nasal field of vision - area seen to the nasal side. spherical) Light rays fall on the temporal half of the retina. o Temporal field of vision - the area seen to the lateral Near objects brought into focus side. Light rays fall on the nasal half of the retina. 3. Constriction o Extend farthest on the temporal sides o Narrowing of the diameter of the pupil through which o Limited by: light enters. Superiorly – Brows Contraction of the circular muscles of iris to Inferiorly – Cheeks constrict the pupil. Medially – Nose o Occurs simultaneously with accommodation. o Prevents light rays from entering the eye through theIMAGE FORMATION periphery of the lens. 1. Refraction o As light rays enter the eye, they are refracted at the anterior and posterior surfaces of the cornea. 75% of the total refraction of light
VISUAL ACUITY AND PUPILARY REACTION TO LIGHT Pupillary Light Reflex Visual Acuity o A reflex that controls the diameter of the pupil, in o Measure of the eyes’ ability to distinguish object details response to the intensity of light that falls on the retina and shape at a given distance. of the eye. o Normal Vision o When light is shown into the eyes, the pupils constrict. Occurs when light is focused directly on the retina o ↑ light intensity= ↑ intensity of signals transmitted by rather than in front or behind it. the bipolar, horizontal, amacrine, and ganglion cells o Far Vision (neural adaptation). Typically measured at twenty feet. o Mechanism of Pupillary light reflex: Rays of light from a distant object are Optic nerve/ CN II- responsible for the afferent practically parallel. limb of the reflex. It senses the incoming light. Little accommodation is required. Oculomotor nerve- responsible for efferent limb of o Snellen Chart pupillary reflex. It drives the muscles to constrict. Numerator: the distance the patient is from the Its pathway begins with retinal ganglion cells, chart which convey information from photoreceptors to Denominator: the distance at which an normal eye the optic nerve. could see the optotype on the chart. Visual Acuity OCULAR MOVEMENTS Eg. 20/50 Innervated by CN III, IV, VI A patient sees at twenty feet what the patient o Superior Rectus with no refractive error or ocular pathology Elevation, adduction and medial rotation of the would see at fifty feet. eyeball 20/20 visual acuity- ―normal visual acuity‖ o Inferior Rectus denominator value, the better the acuity; elevation, adduction and lateral rotation of the denominator value, the poorer the acuity. eyeball 20/40 vision in at least one eye is the vision o Lateral Rectus required to pass the driving test Abduction of eyeball 20/200- ―legally blind‖ o Medial Rectus o Hyperopia Adduction of eyeball The eyeball is short relative to the focusing power o Superior Oblique of the lens and cornea. Depression, abduction and medial rotation of Timid or lazy lens. eyeball Corrected by using eye glasses with convex lens. o Inferior Oblique o Myopia ELevation, abduction and lateral rotation of The eyeball is too long relative to the refractive eyeball. power of the lens and cornea. Enthusiastic lens. DISORDERS OF THE EYE Corrected by using eye glasses with concave lens. CATARACT o Presbyopia o Clouding of the eyes natural lens. Lens loses elasticity and thus its ability to The lens is mostly made of water and protein. The accommodate. Therefore, older people cannot protein is arranged in a precise way that keeps the read print at the same close range as can lens clear and lets light pass through it. But as we youngsters. age, some of the protein may clump together and Usually begins in the mid-forties. start to cloud area of the lens. Age 40: 20 cm (8 in) o Most common cause of vision loss in people over age Age 60: 80 cm (31 in) 40.
o Principal cause of blindness in the world. shadowy areas in your central vision or unusually Signs and Symptoms fuzzy or distorted vision. o Vision is blurred a little. o Slow, painless loss of vision st Note on 1 bullet. like looking through a cloudy rare case, however, vision loss can be sudden piece of glass or viewing an impressionist painting Causes o May make light from the sun or a lamp seem too bright o Hereditary disorders or glaring o Infections o The oncoming headlights cause more glare than o Trauma before o Tumor o Colors may not appear as bright as they once did o Advancing age*A cataract starts out small and at first has little effect on your o Smokingvision o High blood pressure Causes o Obesity o Advancing of age o Lighter eye color o Infection Like in the skin (melanin) o Trauma Prevention o Ultraviolet radiation o Diet with high levels of: o Diabetes Antioxidants o Smoking Omega-3 fatty acids o Heavy alcohol consumption Lutein (eggs, spinach, turnips) Prevention o Amsler grid o Regular eye check-up straight lines, with a reference dot in the center o Wearing of sunglasses Treatment o diet high in antioxidants o No satisfactory medical treatment Beta-carotene (vitamin A) o Optical aids (i.e. glasses) Selenium Vitamins C and E GLAUCOMA Treatment o Silent thief of sight o Severe condition Typically cause no pain and produce no symptoms Surgical removal of lens and is replaced with an until noticeable vision loss occurs artificial lens o Excessive pressure build-up in the aqueous humor*Plastic intraocular lens (IOL) – artificial lens Producing too much fluid, or its not draining o For impaired vision properly Visual aids i.e. glasses, bifocals, appropriate o Results from an interference with normal re-entry of lighting aqueous humor into the blood or from an overproduction of aqueous humor MACULA DEGENERATION Pressure within the eye can close off the blood o Common in older people. vessels entering the eye and may destroy the o Central vision loss may occur. retina or optic nerve, resulting to blindness Signs and Symptoms *Normally, IOP should be below 21 mmHg o Yellowish spots (drusen) Signs and Symptoms form in the back of the eye or retina are an early *The word "glaucoma" came from a Greek word which means, sign of "dry" macular degeneration. "opacity of the crystalline lens." (Cataracts and glaucoma were It is believed these spots are deposits or debris not distinguished until c.1705) from deteriorating tissue. o Typically, none o Early signs o In a specific type of glaucoma
Blurry vision, halos around lights, intense eye pain, nausea and vomiting Prevention o Exercise Lowers OPP or ocular perfusion pressure* OPP is a mathematical value that is calculated using apersons intraocular pressure and his or her blood pressure. o Gonioscopy Make sure the aqueous humor (or "aqueous") can drain freely from the eye In gonioscopy, special lenses are used with a biomicroscope to enable your eye doctor to see the structure inside the eye (called the drainage angle) that controls the outflow of aqueous and thereby affects intraocular pressure. o Visual field testing to determine if you are experiencing vision loss from glaucoma o Imaging technology create baseline images and measurements of the eyes optic nerve and internal structures. o Tonometer measure your intraocular pressure, or IOP Treatment o Depending on the severity glaucoma surgery Lasers medications o Glaucoma eye drops Keeps IOP low