AN ASSINGMENT ON UNDER THE DEPARTMENT OFPHARMACOLOGY, BIOCHEMISTRY & PHYSIOLOGYSUBMITTED BY:Sudipta Nag Himel(11/26) An undergraduate student ofChittagong Veterinary and Animal Sciences University Khulshi, Chittagong-4225.
EYE : The organ of VISION Eyes are the paired organsthat detect light and convert itinto electro-chemical impulsesin neurons.
Types of eye: Simple eye is presence in all chordates Compound eye is presence in case of arthopods
Parts of EYE EYEcomponent mainly divided into parts
Parts of EYE1.Eyeball • Three layers: – Fibrous outer layer • Sclera • Cornea – Vascular middle layer • Choroid, • Ciliary body and • Iris – The inner nervous layer • Retina • Pupil • Structures inside the eyeball are the lens, aqueous fluid and vitreous body.
Parts of EYE2.Accessory structures •Conjunctiva •Eyelid •Eyelashes •Lacrimal gland •Extraocular muscles
Fibrous outer layer Cornea Thin, transparent epithelium Allow the free entry of light. Act as refractive media. Sclera “White part of the eye” Maintaining the shape and form of the eye ball. Contains BVs and insertion site for extrinsic eye muscles.
Vascular middle layer Choroid – Pigmented to absorb excess light – Supplies the retina with nutrients and oxygen via blood supply Iris “Colored part” of the eye which contains BVs, pigment cells, loose connective tissue and pupillary muscle. Adjusts the pupil Regulates amount of light
Vascular middle layer Ciliary Body Ring of smooth muscle around lens Regulates the shape of the lens for accommodation Suspensatory Ligaments – Attach the ciliary body to the lens
The inner nervous layer Retina is a light-sensitive layer of tissue, lining the inner surface of the eye. Functions It helps in Photopic vision Scoptic vision Mesopic vision Steroscopic vision Acuity of vision Color vision Perception of movement
The inner nervous layer Cells of retina- I. Photoreceptor cells II. Bipolar cells III.Horizental cells IV.Amacrine cells V. Ganglion cells • The photo receptor cells are 2 types - (1)The cone cells (2)The rod cells
Difference betweem CONE cell and ROD cellProperty Cones RodsLocation In the fovea Outside the foveaResolution and visual Large SmallacuityTotal number of 5 million 120 millionelementsColor sensitivity Yes NoBrightness sensitivity Small, for daylight Large, for night vision vision Figure
The inner nervous layer Special Areas of the Retina The macula lutea and foveaOptic disc Macula lutea centralis The blind spot Artery Vein Retinal blood vessels. The macula or macula lutea is an oval-shaped highly pigmented yellow spot near the center of the retina Fovea centralis (fovea) is a depresion, located in the center of the macula region of the retina.
The inner nervous layerPupilIs a hole located inthe center of the iris. It helps to pass the light into the eye.
Structures inside the eyeball Closely-packed concentric columnar cells Focuses image on the retina. The lens and ciliary body divide the eye into two cavities. The anterior cavity The posterior cavity
Anterior Chamber of EyeContains aqueous humor which is secreted by ciliary body Maintains shape of anterior eye. Anterior Chamber Constantly produced - leaves eye thru canal that carries it to bloodstream.
Posterior Chamber of EyeContains vitreous humor Maintains shape of posterior eye. Refracts light rays. Is not constantly being produced. Loss of vitreous Vitreous Chamber humor may mean loss of eye.
Accessory structuresLacrimal glandThe lacrimal glands are the sites of tearproduction. Tears function to keep the conjunctiva and corneal epithelium moist and wash away foreign material from the eye.Lacrimal apparatus Secretes and drains tears from the eye
Accessory structuresEyelashesEyelashes are short hairs of eye thatmay occur in double or triple rows. They function to protect the eye from debris. Lashes may also have different lengths and diameters to one another.
Accessory structuresConjunctivaThe conjunctiva refers to the lining of theeye.It has 2 partsPalpebral conjunctivaBulbar conjunctiva It helps lubricate the eye by secreting mucous, and serves as a protective barrier again microbes. It contains many goblet cells which secrete a component of the tears that bath the eye.
Accessory structuresEyelidThe main function of the eyelidis to provide the eye withprotection. There are severaltypes of glands in theeyelids, including tarsal glandsthat produce a sebaceoussecretion that results in an oilysurface of the tear film toprevent the evaporation of thenormal tear layer.
Functions of Extraocular Muscles IO SR IO/SR SR/IO SR IOThese six muscles responsible for eye movement. Four rectus muscles control the movement of the eyein the four cardinal directions: LR MR MR LR Up, Down, SO IR Left and SO/IR IR/SO IR SO Right. The remaining two muscles control the adjustments MR MRinvolved in counter acting head movement. CONVERGENCE
VisionSteps of vision Light Refraction •Cornea and lens Accommodation Photo-pigments Photo-transduction Photoreceptor activity •In the dark •When exposed to light
Refraction Refraction is the phenomenon which makes image formation possible by the eye as well as by cameras and other systems of lenses. The eye, is optically equivalent to the usual photographic camera. The lens system of the eye is composed of four refractive interfaces. Formation of an Image on the Retina. The lens system of the eye can focus an image on the retina. The image is inverted and reversed with respect to the object. However, the mind perceives objects in the upright position because the brain is trained to consider an inverted image as the normal.
Accommodation The process of changing the shape of the lens while focusing on an object is termed as accommodation. At rest focused on distant objects, needs to increase focal power than focus on close objects. The ciliary muscles contract and release tension in the ligaments and the lens becomes rounder in case of close objects.
Photopigments There are four types of photopigments, one in the rods and one ineach of three types of cones. The pigment in the rods is called rhodopsin. Rhodopsin absorbs all visible wavelengths, so that rods provide vision only in shades of grey by detecting different intensities rather than colours. The three types of cones - red, green and blue photopsin, can respond selectively to various wavelengths of light, giving rise to colour vision.
Rhodopsin The photon is absorbed by rhodopsin. The light receptor molecule tightly-packed in the disk membranes One rod contains 10 billion rhodopsin molecules, which ensures an optimum photon capture rateRhodopsin has 2 components Retinal- Vitamin A aldehyde Opsin- single polypeptide containing 7 transmembrane domains
Vitamin A is present both in the cytoplasm of the rods and in the pigment layer of the retina. Therefore, vitamin A is normally always available to form new retinal when needed. Conversely, when there is excess retinal in the retina, it is converted back into vitamin A, thus reducing the amount of light-sensitive pigment in the retina. Night blindness.
Phototransduction The retina therefore signals the brainLight stimulation through an inhibitory response involving a series of physiological reactions Action potentials, Only originate in the ganglion cells,The first neurons in the chain that carry the visual stimuli to the brain. Vision occurs This process is called phototransduction.
ERRORS OF REFRACTION• Astigmatism– defective curvature of the cornea or lens of the eye.• Presbyopia– impaired vision of the cornea or lens of the eye, associated with aging.• Hyperopia– can’t see close objects, rays of light focus behind retina• Myopia- can’t see far away objects, rays of light focus in front of the
COMMON DISORDERS OF THE EYE(A) Acute bacterial conjunctivitis.(B) Anisocoria.(C) Color Blindness Monochromacy lack of 2 of the 3 types of cones Dichromacy: lack of 1 type of normally-function cones Anomalous trichromacy shift in the normal spectrum
Some other Symptoms found in a serious Ocular conditionVisual lossDouble visionSevere eye painForeign body sensation
BooksTextbook of medical physiology / C. Guyton, John E. Hall.—11th edReview of Medical Physiology / William F . Ganong .—22nd edAnimal Physiology / Eckert & Randall -2nd ed Internet