F 1 D 0 -- 02 03 21 at 23 00 Structure of the Eye, and Common Surgery performed. Host: Donna Newhouse Speaker: Dr Francis, an eye surgeon in Thunder Bay Dr Francis has a background in treating problems with eyesight in the elderly, and has also worked in a mobile Lasik clinic throughout Ontario. Thanks to Jean Petree, near Boston, for reviewing this document prior to publication and to http://www.biols.susx.ac.uk/home/George_Mather/Linked%20Pages/Physiol/The%20Eye.html for supplemental information and images. Structure of the Eye The skin of the cornea has three layers. An oily layer, a watery layer, and a mucous layer. The Oily layer keeps water from evaporating. The Watery layer, made in the lacrimal ducts, lubricates the eyes. The Mucous layer provides nutrients and fights infection. Dry eyes is a common complaint. The tears produced by the body lessen over time. Q: My mother got surgery recently for a new lacrimal duct. What went wrong (with her eyes)? A: Sometimes we put in a plug to prevent loss of tears. Q: That was Not the Problem. She had excessive tearing. A: "DCR". Dacryo-cysto-rhinostomy. We fashion a new passageway for tears. If you feel in the corner, there is a bump. Lacrimal Sac. We run a tube so the tears pass into the nose. Q: So the tears are just carried away? A: Tears flow constantly into nose, and into the bloodstream. The Canal of Schlemm drains tears from around the eye into the blood and the nose. Q: This gets into the immune system? A: Correct. The immune reaction, especially from viral contact. Look under a microscope, and you see all these bumps. If you get allergic, you see bumps all over the conjunctiva. Blephritis. This is inflammation of the lids, and the glands around the eye lashes. The eyelids produce tear film. So the tears don't happen properly. This is often misdiagnosed or treated incorrectly, and causes a nagging recurring problem for the patient. Rather than just prescribing drops for lubricating the eye or for a surface infection, we found the real treatment is to clean under the lid, and remove any infections we actually find there. It is still a difficult area to treat, and can take 3 or 4 weeks of treatment. The Cornea. This is the first structure that light hits. Contact lenses sit on the cornea. This is also treated during refractive surgery using lasers. By altering the shape we can fix blurred vision. The layers of the Cornea: - epithelium - Bowman's layer - stroma - descemets membrane - endothelium The Epithelium is the outside skin, and is most likely to be injured if something comes in contact with the eye. Pencils, tree branches, fingers; these all tend to affect the epithelium. This heals very well, often in only 48 hours. Bowman's layer is a very thin layer underneath the epithelium. This is *not* replaced by the body. This is often damaged in construction environments, like with staples or other flying bits from power equipment. When this layer heals, a white spot remains in the field of vision forever. The Stroma. That's the "beef" of the cornea! This forms the lens. It is made of fiberglass and collagen. The cornea and aqueous humor make a lens. The cornea has a lens power of 43 diopter. Q: How often do you perform Cornea Transplants? A: They are fairly uncommon. We refer one person per year here in Thunder Bay. In Toronto we did 3 or 4 a week. So I'd say perhaps ten a week in the Province of Ontario. Compare that to Thousands of cataract operations done each week in the province. Q: I've heard that corneas are Irreparable. A: Well, specifically when that happens, it warrants a transplant. When people have donated their eyes, we take a circle, the size of a dime. Q: So what causes irreparable damage? A: This varies, but I've seen it caused by scarring from injury. From stitches. From infection. Caraconis. From cold sores in the eye. Damaged cornea will Swell up. When damaged, they do not let water move in and out, and so you can diagnose the problem. When shaving a cornea, we must be very careful not to remove too much of it. Inflammation. The cornea can become cloudy. Caraconis. The cornea becomes thin and irregular in places, making vision blurry. Anterior Chamber. This is 3mm in depth. Filled with fluid, called Aqueous Humor. Moved from ciliary body into the anterior chamber, fluid drains out of the Trabecular Meshwork, into the Schlemm Canal into the venous system. Iritis. We see white cells in the humor. Like arthritis, it is caused by a problem immune system. It looks like the dust we see in the light of a cinema. Pupil. An aperture, or hole in the iris. This isn't actually a tissue, but is the absence of tissue. The pupil regulates the amount of light getting in. People with light blue eyes and people without pigment are not as good at blocking light, so they become light sensitive. Lens. Provides refractive power of 15-17 diopters. This makes a total of 60 diopters of power in the eye. The lens has no blood supply, so it depends on the other chambers for nutrients. The lens can change its shape. It loses this ability, usually to create nearsightedness. This happens after 40 years of age. So children have incredible focus power, perhaps 20 diopters. At 40 years of age this will drop to 4-5 diopters. And at 80 years perhaps 1 diopter. The lens becomes thicker with age. It is surrounded by a Capsule. When we remove a lens, we are very careful to preserve this capsule all around. We do this by making a very small incision. Vitreous. This weighs about 4g. It is twice as dense as water. As people get into their 50s and 60s the vitreous gets watery. The pressure in the eye changes, and bits of the wall of the eye can get loose. When patients report flashing lights, or floaters, this suggests such a loosening of the retina. With early diagnosis, we use a laser to fasten it back against the wall of the eye. This procedure for retinal detachment reduces vision at the points where the laser strikes tissue, but it spares the important vision, and is usually effective. There are 10 layers of cells in the retina. The rods and cones are light receptors. There are two places in the retina we give special names to. The Fovea is the centre, and is where very fine detail vision takes place. Around that is the Macula, where fine detail, such as reading happens. Macular Degeneration. Sometimes abnormal blood vessels grow underneath, causing bad vision in the elderly. Diabetic Retinopathy. Strokes cause venal or arterial interruption in blood supply. Such events must be cared for within hours as the retina ceases to function if deprived of oxygen for longer than that. Q: Do you ever see rapid degeneration? A: Sometimes it can make a hole, or a tear in the tissue. We check blunt injuries right away. Also with Blood Trauma. Sometimes we see bruising in the periphery. Q: Diabetes. How does this cause retinopathy? A:  Diabetes causes failures in circulation.  Diabetes causes production of an enzyme which encourages arteries to grow in wrong places. Sclera. That is the white part of the eye. The solid part. This is 1mm thick at the back, and only .5mm thick at the equator. Common cause of eruptions. Sometimes we have to lift up and look under the sclera for damage. Limbus. Transition zone. Uvea. Uveitis is the same as Iritis. This is the coloured part of the eye. It is very vascular, and has constrictor muscles. It has ciliary body which functions to produce fluid which goes into another chamber. It alters the tension on the zonials which change the shape of the lens. Choroid Layer. These have blood vessels which nourish the retina. Zonnules of Zinn is the drainage area of the cornea. These are a network of collagen fibers which hold the lens like a hammock. These fibers connect the lens to the ciliary process and are sometimes called suspensory ligaments. They does Not drain the Vitreous Humor, just the Aqueous Humor. Glaucoma is where pressure in the eye is elevated. It is thought to be affected by the Trabecular Meshwork. Glaucoma first affects the peripheral vision and often goes unnoticed, even while it is causing damage. This tends to affect people aged 50 and over. Q: is it treatable? A: There are lots of treatments.  There are drops which act on the ciliary body.  There are drops which work on the Outflow side, the Trabecular Meshwork.  We can use Laser on the Trabecular Meshwork. It is primitive but effective! We make a 50 micron hole, and do fifty of them. This damages the meshwork. This is because the TM is working too hard at pumping, so we just weaken it.  Surgery, to put a drain in the eye. We do this through the Cornea, under the Conjunctiva. That is because if fluid can flow out, then it can also flow back in, and that would be a serious source of infection. Q: So there is no pain in Glaucoma? A: No pain. We usually detect it when the people need glasses, as part of a routine examination. Fortunately, we have public awareness. Also, we have time on our side. If the eye has a pressure of 25 (normal pressure is 20) it takes ten years to cause damage. So most people have eye examinations often enough to catch this. Q: I've heard that Marijuana reduces eye pressure. A: You know, people will do *anything* to get a doctor to prescribe a joint ;-) While what you say is true, it has a lot of sedetive and analgesic properties, and it increases appetite. So marijuana is a better choice for different medical problems, such as terminal illness and extreme pain. Optic disk, also called the Blind Spot has 1,000,000 axons. This is the optic nerve from the retina. This is where we see axons dying off due to high pressure. The rim of the optic nerve is the tissue, not the cup. We use this to help assess nerve damage. We look at the Cup to Disk Ratio. Normal is .3 cup, where .6 or .8 is suggestive of damage. MS, Multiple Sclerosis. This often causes Optic Neuritis. Young people 25-40 years old experience loss of vision in one eye, with pain. That is because the nerve behind the eye has become inflamed, and when they look around, say left or right, they move it, and it hurts. Conjunctiva. This is what gets inflamed in Pink Eye infections. There are four rectus muscles. The Oblique muscles are involved in rotational movement. When someone is cross eyed, or wall eyed (Dr Francis used the correct terms) we can detach the muscles (surgically) and re-attach them, closer or further as needed to correct the rest position of the eye. Video Presentation I - Lasik Procedure This doesn't take very long. We make a flap in the cornea by cutting the epithelium and and flipping it back, carefully leaving it attached. Using the laser, we vaporize just a little of the Corneal Tissue. As needed, we keep it lubricated and moist. When we have finished, we flip the epithelium back over again. It seals almost instantly. So we quickly remove any wrinkles, and remove any debris. To assist the instant healing, we keep the middle of the cornea moist, but let the cut edges dry. Q: The patient, he looks like he is awake! A: Yes, he is. He may be sedated with Ativan, but we need him to look forward and concentrate during the procedure. We used to do laser surgery differently. The PRK, PhotoRefractive Keratectomy involved vapourizing the Stoma right through the Epithelial tissue. This was a simpler procedure for our clinics, and had a good success rate. The problems involved healing and vision. The Lasik procedure heals almost instantly, where the PRK procedure took two weeks, during which the patient had much discomfort. To protect the cornea, we sent the patient home with a contact lens. It wasn't an effective way to handle all vision problems, such as astigmatism and far sightedness. Also, we are getting some reports that some of the early patients are getting some clouding where we vapourized the tissue. Lasik procedures are improving. We can now treat farsightedness by trimming the edges of the cornea. Video Presentation II - Cornea Transplant Surgery We cut a circular opening. We inject the eye with gel to keep the pressure high during the procedure. We spin the nuclear material, and use ultrasound to break it up. We slide a pocket under the capsules so we can just slide the old lens out, and the new lens in. This is a difficult procedure, as we must control the rip we have made in the eye. The cornea is easy to see and remove. We use a clear self sealing film over the eye like Saran Wrap to close the openings we have made. Slide Presentation A series of pictures of disorders and abnormalities we see in the clinic. That's all I know.