Anatomy of the Eye PDF

 ✓ Eyes are the most valuable organ of the human body, which process the images of objects in the vicinity. 1. Understand the...

 ✓ Eyes are the most valuable organ of the human body, which process the images of objects in the vicinity. 1. Understand the basic anatomical ✓ The eyes interpret size, shape, color and distance of the objects structures of the EYE and give a 3D picture of the 2. Anatomical position and objects visible Terminology 3. How do eye functions 4. Defects and consequences of vision 1. Eyelids are the outermost protective parts of the eye. 2. They act as shutters and primary barriers against the external environment. 3. Boundaries of eyelids are covered by tiny hairlines termed eyelashes. 1. Terms a. Lacrimal gland b. duct Surface of eye c. Lacrimal puncta d. Lacrimal sac e. Nasolacrimal duct f. Nasal cavity 2. A watery physiologic saline with a plasma- like consistency. 3. Contains the bactericidal enzyme lysozyme 4. it moistens the conjunctiva and cornea 5. lt provides nutrients and dissolved O2 to the cornea. 1. Each one of the two eyeballs is located in the orbit, where it takes up about one-fifth of the orbital volume 2. The remaining space is taken up by the extraocular muscles, fascia, fat, blood vessels, nerves and the lacrimal gland Nervous tunic  The three coats of the eye are as follows: 1. Outer fibrous layer: i. cornea ii. sclera 2. Middle vascular layer (“uveal tract”): i. iris ii. ciliary body – Connecting Suspensory ligaments iii. choroids. 3. Inner nervous layer: i. pigment epithelium of the retina ii. retinal photoreceptors iii. Fovea-Highest visual Acuity.  1. Fibrous Layer 1. Sclera: A white, opaque part of the eye that maintains the shape of the eye and protects the internal components. The sclera is composed of dense connective tissue, which makes it tough and resilient. 1. Cornea: The transparent, dome-shaped front layer allows light to enter the eye and is crucial for focusing vision. The cornea is straightforward and does not have blood vessels, relying on the surrounding aqueous humor for nourishment. 1. Fibrous Layer a. Sclera i. White connective tissue layer ii. Seen anteriorly as the “white of the eye b. Cornea i. Transparent, central anterior portion, it allows for light to pass through ii. Repairs itself easily iii. The only human tissue that can be transplanted without fear of rejection  2. Vascular Layer ✓ Choroid is a blood-rich nutritive layer in the posterior of the eye i. Pigment prevents light from scattering ii. Modified anteriorly into two structures ✓ Ciliary body—smooth muscle attached to the lens ✓ Iris—Pigmented layer that gives eye color it regulates the amount of light entering the eye. i. Pupil—rounded opening in the iris  3. Sensory Layer 1. Retina contains: i. Inner neural layer ii. Contains receptor cells (photoreceptors) a. Rods b. Cones Retina: Sensory Layer 1. Retina forms the inner nervous coat of the eyeball ✓ Inner neural layer contains receptor cells (photoreceptors) 1. Rods 2. Cones 2. It extends from the optic disc posteriorly to the ora serrata anteriorly a. An optic disc b. Macula lutea c. Ora serrata 1. Light Entry: Light enters through the cornea. 2. Pupil and Iris: Light passes through the pupil, controlled by the iris. 3. Lens: The light is focused by the lens, which changes shape to focus on objects at varying distances. 4. Retina: Light reaches the retina, where photoreceptors (rods and cones) convert light into electrical signals. 5. Optic Nerve (Cranial Nerve II): The electrical signals travel along the optic nerve to the brain. 6. Visual Cortex: Signals reach the visual cortex in the occipital lobe, where the brain processes and interprets the visual information. 1. Anterior (aqueous) segment i. Anterior to the lens ii. Contains aqueous humor 2. Posterior (vitreous) segment i. Posterior to the lens ii. Contains vitreous humor Aqueous humor 1. Watery fluid found between lens and cornea, formed by the capillaries of the ciliary body. 2. Similar to blood plasma 3. Helps maintain intraocular pressure 4. Provides nutrients for the lens and cornea 5. Reabsorbed into venous blood through the scleral venous sinus or canal of Schlemm (drainage duct) Vitreous humor Gel-like substance posterior to the lens Prevents the eye from collapsing Helps maintain intraocular pressure Anterior Chamber Angle: 1. The anterior segment comprises the cornea, anterior chamber, iris, lens, ciliary body, and the anterior part of the sclera. 2. Aqueous humor fills both the anterior and posterior chambers. Function of Aqueous Humour 1. Maintenance of intraocular pressure and structural form of the globe 2. Provide nutrition to surrounding tissues Vitreous 1. The vitreous is a clear media which acts as a shock absorbent for the eye. There are firm adhesions between the vitreous and the retina. 2. Viscous- gel like fluid that is composed of 99 % water and mainly type II and some type IX collagen fibres, mucopolysaccharides and hyaluronic acid 3. Volume 4 mL Functions 1. Mechanical stabilization of volume of globe 2. Shock absorption 3. Nutrition supply to lens and retina 1. Held in place by the suspensory ligament attached to the ciliary body. 2. Biconvex contains proteins called crystallin's 3. Cataracts result when the lens becomes hard and opaque with age 4. Vision becomes hazy and distorted, Eventually causing blindness in the affected eye 5. Risk factors include: 1. Diabetes mellitus 2. Frequent exposure to 3. intense sunlight 4. Heavy smoking The iris Sphincter and dilator muscles control pupil size. ✓ Sphincter-Parasympathetic (Alerts) ✓ Dilator-Sympathetic (Controls)  Light Refractory Pathway 1. Bulbar Conjunctiva 2. Cornea 3. Aqueous Humor 4. Lens 5. Vitreous Humor 6. Ganglion Cell Layer 7. Inner Synaptic Layer 8. Bipolar Layer 9. Outer Synaptic Layer 10. Photoreceptor Layer  1. Refractive Errors, Age-Related Muscular Degeneration, Cataract, It causes the light reaching the eye to diverge Diabetic Retinopathy, Glaucoma. 2. Myopic - nearsighted 3. Hypermetropic - Farsighted 4. Presbyopia - age-related failure of lens to accommodate It causes the light reaching the eye to converge 5. Astigmatism - Distorted vision due to irregular-shaped lens or cornea 6. Color Blindness – a genetic defect that causes dysfunction of cones Astigmatism is an optical defect. In other words, it is irregularities in the curvatures of the lens/cornea that lead to blurred vision. i. http://www.allaboutvision.com/cond itions/astigmatism.htm ii. https://www.prokerala.com/health/ eye-care/eye-test/astigmatism- test.php 1. Color blindness-A genetic conditions that result in the inability to see certain colors.Due to the lack of one type of cone (partial color blindness). 2. Test color blinding with → Ishihara Test 3. https://www.youtube.com/watch?v=CWyrp3hu4KE 1. Look at the image above with the plus sign and the circle. 2. Look straight at the image with your nose positioned between the plus and the circle. 3. Close your left eye and focus your eyes on the plus sign with your right eye. Do not look deliberately at the circle. 4. Now move closer to the image slowly. Don’t take your focus off the plus sign while doing this. 5. At some point between 10”-14”, the circle will disappear from your peripheral vision. And the brain will read the surrounding white color to fill up the empty space. 6. This exact spot is your blind spot. Homeostatic Imbalances of the Eyes 1. Glaucoma: The increased intraocular pressure, can damage the optic nerve, which transmits images to your brain. If the damage continues, glaucoma can lead to permanent vision loss. Without treatment, glaucoma can cause total permanent blindness within a few years Test 1. http://www.webmd.com/eye-health/rm- quiz-eyesight-worsening-html