PBL+Sharing

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=The Eye=

Group 1

media type="youtube" key="YtpRpttPnHw" height="385" width="480" Light entering the eye is focused by two lenses: the __cornea__ and the __eye lens__. The lenses hold their shape due to pressure from the vitreous humor and aqueous humor, as well as a muscle group called the ciliary muscles. __Light is bent by the lenses to focus at the back of the eye.__ As objects get __further away__ from the eye the ciliary muscles relax, allowing the __eye lens to become flatter__ and __bend the light more__. As an object moves closer to or further from the eye, the ciliary muscles adjust the shape of the eye lens so that the light is always focused to the same point on the back of the eye. It is possible to see not only in very low light levels (such as a darkroom) but also in very high light levels (such as a sunny day). In fact, The brightest conditions under which an eye can operate are around 1013times as bright as the dimmest conditions.The __iris changes in size__ to allow different amounts of light to enter your eye.When there is __more light__, the iris __shrinks__. This __blocks out much of the light__,and as is demonstrated by the first activity, thisincreases the sharpness of your vision. If there is less light, the iris increases in size, allowing more light to enter the eye to be processed.

__Group 2 __


 * The retina contains numerous rods and cones which allow for black/white and colour vision respectively//.//
 * These images sent to the optical centre at the back of the brain to be processed.

media type="youtube" key="15P8q35vNHw" height="385" width="480" media type="youtube" key="JunCyiGfreo" height="385" width="480" =Hyperopia=

Gwoop 3


 * Hyperopia, also commonly known as "far-sightedness", is the deformed condition of the eye such that light rays converge behind the retina.

If a person has hyperopia, the light rays focus behind the position of the retina.**

1) Aging During aging, there is "shrinking" of all parts of the body, which includes the eye (just like how our eye grows and expand too fast when we grow causing myopia!). This results in a flattened eyeball (like above) or a shorter and flattened cornea which renders the cornea less refractive. thus only light rays reflected off from objects far away converge on the retina. During aging, the ciliary muscles of the eyes (see figure below) might also be weakened. Ciliary muscles (or ciliary body) play a major role in accommodation of the eye, where they control how thin or thick the lens should become when seeing near or far objects. Hence when the ciliary muscles do not function as well, when seeing near objects they do not contract, hence the lens is unable to become thicker to be more refractive, which results in hyperopia.
 * Causes**


 * Vision of a person with hyperopia:**

So far, hyperopia can be treated by the usage of corrective convex lenses, such that when looking at near objects, light rays can converge on the retina.
 * Treatment**:

Group 4

Hyperopia (Farsighted Vision) Hyperopia is a term used to describe the condition of being farsighted. The causes of hyperopia are typically genetic and involve an eye that is too short or a cornea that is too flat, so that images focus at a point behind the retina. People with hyperopia can usually see distant objects well, but have trouble focusing on nearby objects.

Hyperopia Symptoms People who have hyperopia may have trouble seeing objects that are close up. In some cases, they may not recognize that they have a vision problem, but will notice that their eyes become tired or sore during such activities as reading or writing. This is because, for mildly farsighted people, the lens of the eye has a tendency to accommodate for the refractive error. Over time, however, the lens’ ability to adjust diminishes, and people with hyperopia will need treatment to correct their vision.

Causes of Hyperopia Like myopia, hyperopia is a genetic trait; however, instead of the eye being too long (as in myopia), it is too short, causing images to focus at a point beyond the retina. Though it is not uncommon for hyperopia to be associated with aging, getting older does not cause people to become farsighted. Rather, the aging process hinders the eye’s focusing ability, which can sometimes make pre-existing hyperopia more evident.

VIDEO media type="youtube" key="iVI5Pj-kmvI" height="385" width="480" =Myopia=

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if a person has myopia, the retina is behind the focal point of the light

media type="youtube" key="YiuC7a1lkrk" height="385" width="480"

 Myopia (Greek: μυωπία, //muōpia//, "nearsightedness"), is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed. Those with myopia see near objects clearly but far away objects appear blurred. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye. The opposite defect of myopia is hyperopia or "farsightedness" or "long-sightedness"—this is where the cornea is too flat or the eye is too small.
 * What is myopia?**

Myopia cannot be cured. Myopia can only be corrected through the use of concave lens. Concave lens will cause the light rays to diverge, so that they will be focused on the retina, and not at a point before the retina. Spectacles or contact lens with concave lens are commonly used. The type of lens used in these are convexo-concave lens.
 * How can myopia be cured?**



Group 6

=Fundamentals of Lasik=

Group 7

Group 8 Actual Footage of LASIK Surgery media type="youtube" key="O4kDC4sZ5Jg" width="425" height="350" Explanation of LASIK Surgery media type="youtube" key="f-YkzgfgN2k" width="425" height="350"

LASIK eye surgery is a type of refractive surgery that corrects myopia, hyperopia, and astigmatism.

The procedure begins by the ophthalmologist using either a metal blade or a special laser to make an incision around the iris of the eye. This creates the flap that the ophthalmologist will use to fold over. This allows access to the stroma and middle section of the cornea. The corneal stroma can now be remodeled. With a ultraviolet light laser, the ophthalmologist is able to remove tiny bits of corneal tissue which reshapes it. When the cornea is reshaped the right way the patient will be able to see clearer. The light coming in through the pupil and onto the retina is able to be focused better.

LASIK can be performed to correct both myopia and hyperopia. For patients with myopia, the goal of the surgery is to flatten the cornea because it is too steep. On the other hand, for those with hyperopia, the goal is to form a steeper cornea. Correcting astigmatism is not quite as popular but it can be done by the smoothing the irregularly shaped cornea to a normal shape.

Group 9

LASIK, which stands for Laser-Assisted In Situ Keratomileusis, is a type of surgery which corrects eyesight problems such as myopia (short-sightedness), hyperopia (long-sightedness) and astigmatism by using focused lasers to cut away and shape the cornea such that it will refract light rays entering the eye at a different angle in order to focus light rays coming from an object on a spot on the retina instead of in front or behind the retina, thus removing the need for the person to wear corrective lenses such as spectacles or contact lenses.

Basically, a LASIK procedure starts with the a flap being cut out of the cornea and left attached to the cornea by a hinge. A laser is then used to vaporize part of the stroma (which is the middle layer of the cornea, right under the flap). Finally, the flap is replaced.

An animation of how LASIK works: media type="custom" key="5817559"

=Potential Complications=


 * Group 10

1.** LASIK causes dry eye media type="youtube" key="B7iU__sGs0U" height="343" width="440"
 * Dry eye is the most common complication of LASIK. Corneal nerves that are responsible for tear production are severed when the flap is cut. Medical studies have shown that these nerves never return to normal densities and patterns. Symptoms of dry eye include pain, burning, foreign body sensation, scratchiness, soreness and eyelid sticking to the eyeball. The FDA website warns that LASIK-induced dry eye may be permanent. Approximately 20% of patients in FDA clinical trials experienced "worse" or "significantly worse" dry eyes at six months after LASIK.(1)

2.** LASIK results in loss of visual quality
 * LASIK patients have more difficulty seeing detail in dim light (loss of contrast sensitivity) and experience an increase in visual distortion at night (multiple images, halos, and starbursts). A published review of data for FDA-approved lasers found that six months after LASIK, 17.5 percent of patients report halos, 19.7 percent report glare (starbursts), 19.3 percent report night-driving problems and 21 percent complain of eye dryness.(1) The FDA website warns that patients with large pupils may suffer from debilitating visual symptoms at night.

3.** The cornea is incapable of complete healing after LASIK
 * The flap never heals. Researchers found that the tensile strength of the LASIK flap is only 2.4% of normal cornea.(2) LASIK flaps can be surgically lifted or accidentally dislodged for the remainder of a patient’s life. The FDA website warns that patients who participate in contact sports are not good candidates for LASIK.

LASIK permanently weakens the cornea. Collagen bands of the cornea provide its form and strength. LASIK severs these collagen bands and thins the cornea.(3) The thinner, weaker post-LASIK cornea is more susceptible to forward bulging due to normal intraocular pressure, which may progress to a condition known as keratectasia and corneal failure, requiring corneal transplant. media type="youtube" key="GzjLTdt9rGQ" height="368" width="458"

4.** There are long-term consequences of LASIK
 * • LASIK affects the accuracy of intraocular pressure measurements,(4) exposing patients to risk of vision loss from undiagnosed glaucoma.

• Like the general population, LASIK patients will develop cataracts. Calculation of intraocular lens power for cataract surgery is inaccurate after LASIK.(5) This may result in poor vision following cataract surgery and exposes patients to increased risk of repeat surgeries. Ironically, steroid drops routinely prescribed after LASIK may hasten the onset of cataracts.

• Research demonstrates persistent decrease in corneal keratocyte density after LASIK.(6) These cells are vital to the function of the cornea. Ophthalmologists have speculated that this loss might lead to delayed post-LASIK ectasia.

5.** Bilateral simultaneous LASIK is not in patients’ best interest
 * In a 2003 survey of American Society of Cataract and Refractive Surgery (ASCRS) members,(7) 91% of surgeons who responded did not offer patients the choice of having one eye done at a time. Performing LASIK on both eyes in the same day places patients at risk of vision loss in both eyes, and denies patients informed consent for the second eye. The FDA website warns that having LASIK on both eyes at the same time is riskier than having two separate surgeries.

6.** Serious complications of LASIK may emerge later
 * The medical literature contains numerous reports of late-onset LASIK complications such as loss of the cornea due to biomechanical instability, inflammation resulting in corneal haze, flap dislocation, epithelial ingrowth, and retinal detachment.(8) The LASIK flap creates a permanent portal in the cornea for microorganisms to penetrate, exposing patients to lifelong increased risk of sight-threatening corneal infection.(9) Complications may emerge weeks, months, or years after seemingly successful LASIK.**

=Alternative Eye Care=

Group 11

Exercises for the computer user for quick relief of eye fatigue and strain @http://www.youtube.com/watch?v=W10j2fL0hy0 No risk @http://www.hpb.gov.sg/eyecare/article.aspx?id=194 @http://www.hpb.gov.sg/eyecare/article.aspx?id=426 @http://www.hpb.gov.sg/eyecare/article.aspx?id=188 @http://www.hpb.gov.sg/eyecare/articlemostviewed.aspx