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The Human Eye - Student Presentation

The Human Eye - Teaching Presentation

The Human Eye - Student Lesson Outline

Educational Video demonstrating how light enters the eye

"How Light Enters The Eye" Educational Video

Jonathan Strickland explains the process and risks of LASIK surgery, from preoperative exams, to lasers in your eyes.

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For centuries we’ve relied on external lenses (like glasses or contacts) for correction. But with modern technology surgeons can actually alter the shape of the eye itself using lasers to change its focal point. The most popular technique is called LASIK, which stands for Laser-Assisted In-Situ Keratomileusis. It’s very effective at treating several visual problems, especially near-sightedness.
Before any reputable eye doctor performs LASIK, they’re going to give you a thorough preoperative eye exam. They’ll measure your current prescription and manually check the surface of your cornea with a dye called Fluoracaine. Other tests map your cornea’s topography and measure the exact diameter of your pupil. To qualify for LASIK, you’ll need to meet a certain range of vision, corneal thickness and pupil size. It’s also risky if you’re pregnant, have severe heart problems, certain diseases, or take some types of drugs.
Once you’ve passed pre-op assessment, you come back for the actual LASIK process, conducted by both the surgeon and a technician operating the laser machine. They’ll put a topical anesthetic in your eyes to numb any discomfort. That’s good, because the next step is to pry open your eyes with special tape and that good old Eyelid speculum. Then they’ll calibrate the laser and mark your cornea for alignment. Using a suction ring and an extremely precise surgical blade called a microkeratome, the surgeon cuts a flap in your cornea and folds it back. You’ll be asked to focus on a red light which isn’t the laser, but helps center your eye.
Now it’s laser time! An Excimer laser mixing reactive gases like chlorine and fluorine with inert gases like argon, krypton and xenon, produces a tightly focused beam of ultraviolet light that vaporizes a microscopic portion of the cornea. This is a “cool laser” that doesn’t heat the surrounding air or surface. Instead it breaks down the molecular bonds of organic materials. The beam itself is microscopic, less than a nanometer wide. The surgeon reshapes the cornea by controlling the size, position and number of laser pulses applied. Surprisingly, this only takes a few seconds. When it’s finished, your corneal flap is replaced with a small antibiotic added. The cornea heals and rebonds immediately, naturally sealing itself again. Taking into account the time for both eyes, the entire procedure is usually done in only 15-30 minutes.
After the operation they’ll give you these cool eye shields that prevent you from touching your eyes but let you see enough to get around. You’ll wear them the rest of the day and sleep in them that night. Of course, someone has to drive you home and once you get there you’ll need to apply rewetting drops, antibiotic drops and possibly a moisturizing gel inside your bottom eyelid. The opthamologist will follow up the next day and on a recurring basis for about a year.
Now you’re probably asking, “But Jonathan, couldn’t there be side effects when a doctor shoots a laser into my eye?” Of course there could. Most commonly, eyes can be undercorrected, overcorrected or get a small wrinkle when the corneal flap is replaced that causes a blur. For the most part these are easily fixed with a second procedure. Sometimes a surgeon won’t even recommend further refining since many recipients of LASIK never achieve “normal vision,” but do reduce their corrective prescriptions significantly. Other, rarer side effects can include halos around lights, light sensitivity and double vision. I’d be lying if I said there wasn’t a chance of partial or complete blindness, but it is miniscule compared to the success rate. This is especially true if you’re seeing a reputable doctor. Keep in mind that there are so many unscrupulous practitioners out there that the FDA had to issue a stern warning about dodgy sales pitches underplaying the risks of LASIK. But twenty-five years after it was invented by Gholam Peyman, LASIK is safer than ever before.

http://health.howstuffworks.com/medicine/surgeries-procedures/lasik.htm
http://podcasts.howstuffworks.com/hsw/podcasts/techstuff/2011-10-24-techstuff-laser-eye-surgery.mp3
YOUR EYES. By: Sklar, Hallie Levine, Health (Time Inc.), 1059938X, Apr2013, Vol. 27, Issue 3
LASIK: Illustration. CRS - Adult Health Advisor, Jun2012

How Does LASIK Work?

The Human Eye is a lesson by Teach Science with Fergy, containing engaging videos, presentations and activities to help develop students' science knowledge.

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