Structure of the Eye

1. Structure of the Eye • The following are the major areas of the eye and its function • Cornea: covers the iris and pupil • Sclera is the white part of the eye and the conjunctiva is the clear membrane that covers it • Iris and the pupil form the aperture that light passes through to the lens • Lens focuses light by refraction to the back of the globe to the retina • The retina is a collection of neurons that triggers the optic nerve and carries the “image” to the occipital lobe of the brain

2. The eye contains two chambers as well. The aqueous humor which is filled with water and the vitreous humor in the back of the eye • The lens is controlled by the muscles of the ciliary body which adjusts the lens to control refraction of light • The basic function of the eye is to focus and concentrate light waves to a focal point on the retina which converts it to electrical impulses (EI). EI are carried to the brain via the optic nerve

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4. Diseases of the eye • Visual acuity problems: • Myopia: nearsightness, patient can see at a distance. Corrective lens is indicated • Cataracts: dead corneal cells that have clouded over the opacity of the lens. Surgery to remove the cataract • Astigmatism: A refractive error in the cornea; focal point is not on the retina. Corrective lens, contacts or refractive surgery is indicated

5. Infections of the eye • Style: a bacterial infection of the sebaceous glands of the eye lid. Antibiotics like ophthalmic erythromycin can be used but infection is self limited and will resolve in usually seven days • Blepharitis: inflammation of the eyelids cause by usually bacteria. Tx: Blephamide® (prednisolone/sulfacetamide) is a combination Abx/steroid used to treat this disorder • Conjunctivitis is an inflammation of the conjunctival membrane of the eye. • Allergic conjunctivitis (red eye) • Bacterial conjunctivitis • Viral conjunctivitis (Pink eye)

6. Allergic Conjunctivitis • Inflammatory condition of the conjunctiva caused by seasonal allergies and airborne allergens • Called “red eye” • Intensive itching • Eye watering • Tx: Ophthalmic antihistamines products: (Visine A® naphazoline 0.025% and pheniramine 0.03%) or Patanol®, olapadine which is Rx only antihistamine

7. Bacterial Conjunctivitis • Caused by mixture of different bacterial • Symptoms same as for allergic conjunctivitis • In addition pus and mucus causes the lids to “stick together”. This is the hallmark of this infection • Usually resolves on its own but antibiotics can be used • Ciprofloxacin 0.3% (ciloxan®), Erythromycin Ophthalmic Ointment USP, 0.5% and others

8. Neonatal Ophthalmia • Women infected with chlamydia or gonorrhea can pass bacteria to their infants as they pass through birth canal • Erythromycin ophthalmic ointment 0.5% USP has been used to treat the infants • Can cause blindness if not treated

9. Viral Conjunctivitis • Commonly called pink eye • Commonly caused by the same viruses causing the common cold (adenovirus) • Other virus can include varicella and herpes simplex virus • No therapy except supportive. Oral acyclovir is used for cases caused by varicella zoster virus or herpes simplex virus.

10. Glaucoma • Glaucoma is a disease of the eye where the pressure inside the eye ball is elevated above normal • Open angle glaucoma is the most common type (90%) with closed angle glaucoma (10%) following • Treated with drugs that reduce the pressure in the eyeball by relaxing the trabecular network and increase aqueous humor outflow. Beta Blockers and carbonic anhydrase inhibitors are examples of drugs in this category. (Cosopt ® is a combination of timolol and dorzolamide) • Xalatan ® (Latanoprost) and Travatan® (travaprost) are prostaglandin analogues that increase outflow of humor as well. They are both ophthalmic drops give once a day • Can lead to a loss of vision if not treated

11. General structure of the ear • The outer ear consists of the pinna and auricle • Auditory canal leads from the outer ear to the tymphanic membrane (ear drum) • Middle ear: the three ossicles vibrate in response to sound waves and transmit the energy of the sound waves into the inner ear • Inner ear: The cochlea is a conical shape organ filled with fluid and lined with hair cells. The energy of sound waves is transmitted here and the movement of hair cells to electrical action potentials in cochlear nerve (CN VIII)

12. Infections of the ear are the most commonly treated malady of the ear • Medications include otic antibiotics that contain a combination of antibiotics and a steroid. • Example is Cortisporin Otic Solution (neomycin and polymyxin B sulfates and hydrocortisone otic solution, USP) is a sterile antibacterial and anti-inflammatory solution for otic use. Each mL contains: neomycin sulfate equivalent to 3.5 mg neomycin base, polymyxin B sulfate equivalent to 10,000 polymyxin B units, and hydrocortisone 10 mg (1%)

13. Middle Ear Infections • Bacteria that infect the eustachian tube include: Staphylococcus pyogenes, Streptococcus pneumoniae, moraxella species, and haemophilus influenza • Very common in children because of the horizontal nature of the tube position • Caused intense pressure in the middle ear that can rupture the eardrum and ozze pus from the ear • Myringitis is the associated inflammation of the eardrum • Called Bacterial Acute Otitis Media • In children, Amoxicillin is normally prescribed usually as suspension and given three times a day • In refractory cases, Augmentin ® (amoxicillin/clavulunate sodium) is used

14. Miscellaneous Drugs • Parasympathomimetics (Cholinergic drugs) • MOA: agonists at the cholinergic receptor in the eye • Indications: pupillary constriction and glaucoma tx • Drugs • Pilocarpine (Pilocar) • Carbachol (Miostat) • Sympathomimetics (mydriasis agents) • MOA: binds to beta and alpha receptors or blocks cholinergic receptors • Indications: dilate the pupil for ophthalmic exams • Phenylephrine • Cyclopentolate (Cyclogyl) • Atropine