NOTE: Free essay sample provided on this page should be used for references or sample purposes only. The sample essay is available to anyone, so any direct quoting without mentioning the source will be considered plagiarism by schools, colleges and universities that use plagiarism detection software. To get a completely brand-new, plagiarism-free essay, please use our essay writing service.
One click instant price quote
... pascal pulse of 250 is very long compared to other lasers. The discharge is build up in three phases: 1) X-ray pre-ionisation provides a homogeneous distribution of electrons in the discharge area. 2) A high voltage pre-pulse with a very fast rise time multiplies these electrons in an avalanche process, providing a homogeneous ignition of the discharge. Finally the main pulse gives the high current at moderate voltage to create the laser output. The energy per pulse is 1 Joule.
With a repetition rate of 1 kHz this makes an average power of 1 kW. The efficiency of the laser is about 2 %, so 50 kW of electrical input power is required. To reach 1 kHz repetition rate a large flow loop, as in the drawing below, is required. 3) Between every shot the gas needs to be refreshed to start with homogeneous conditions. The used gas is turbulent and contains all kinds of charged particles. A centrifugal blower circulates the gas.
The heat exchanger removes the heat from the blower and the discharge. The settling chamber reduces turbulence and the contractor speeds up the gas flow to refresh the gas between the electrodes within 1 ms (micro-second). The diffuser converts the gas speed back into pressure and then the gas enters the blower again. Types of Laser Eye Surgery Photo refractive Keratectomy (PRK) - treats lower degrees of myopia and astigmatism problems. The procedure is done under what is known as topical anesthesia. Anesthetic eye drops are administered to numb the eye before the surgery begins.
The protective layer of the cornea, known as epithelium, is removed. Then, using the excimer laser, a precise amount of tissue is removed to correct the specific refractive error. The laser removes less than 1 / 1000 of a millimeter of tissue, less than the thickness of a human hair. For nearsighted people, tissue is removed from the central cornea, thus have the effect of flattening the cornea. For farsighted individuals, tissue is removed from the peripheral cornea a steepening effect on the cornea. For astigmatism, the curvature of the cornea is evened out by sculpting tissue along a specific area or axis.
A contact lens, known as a bandage contact is then put in place and will be removed three to four days later, after the epithelium has regenerated. Vision is generally blurry for several days after the surgery but improves after the contact is removed and gradually improves further over the next several weeks. The entire procedure usually takes about 20 to 25 minutes per eye, with a short recovery period after the surgery. Laser Assisted in Situ Keratomileusis (LASIK) - is a procedure used to correct nearsightedness, farsightedness, and astigmatism. The operation is done under what is known as topical anesthesia. Anesthetic eye drops are administered to numb the eye before the surgery begins.
With LASIK, the cornea is reshaped under a flap, thus changing the way the light entering your eye is focused. LASIK is able to correct to correct almost all degrees of refractive errors from low to high. LASIK offers the advantage of quicker visual recovery, because it is done under a flap. A specially designed instrument called a microkeratome is used to create a thin flap of corneal tissue. The flap is then deflected back to expose the underlying corneal tissue. Then, using the excimer laser, a precise amount of tissue is removed to correct specific refractive error.
The laser removes less than 1 / 1000 of a millimeter of tissue, less than the thickness of a human hair. For nearsighted individuals, tissue is removed from the central cornea, thus have the effect of flattening the cornea. For farsighted individuals, tissue is removed from the peripheral cornea, thus having the effect of steepening the cornea. For astigmatism, the curvature of the cornea is evened out by sculpting tissue along a specific area or axis. The corneal flap is then replaced and precisely aligned to its' original position. Because of the natural bonding process that occurs in the cornea, sutures are not required.
Vision is usually much better immediately after surgery and gradually clears over the next 36 to 48 hours. The entire procedure usually takes about 10 to 15 minutes per eye, with a short recovery period after the surgery. Radial Keratectomy (RK) - is an incision al procedure used to correct mild to moderate amounts of myopia. A series of incisions are made with a diamond scalpel, preset to a precise measurement, starting near the center of the cornea and radiating out toward the periphery. No incisions are made in the central cornea, thus allowing light to pass through a clear central window. Usually four to eight incisions are placed equally spaced around the cornea to a depth of 80 % - 90 % of the thickness of the cornea.
The incisions allow the central cornea to flatten, thus reducing the amount of myopia. The number, depth, and length of the incisions determine the amount of correction that can be achieved with RK. With the advent of laser correction, RK is generally reserved for low levels of myopia or for people who for other reasons may not be candidates for laser surgery. Astigmatic Keratectomy (AK) - is an incision al procedure used to correct mild to high amounts of regular astigmatism. Astigmatism occurs when the cornea is shaped like an oval, rather than a circle. The cornea with astigmatism typically has a steep curve in one quadrant and a flatter curve in the opposite quadrant.
Incisions are made with a diamond scalpel, preset to a precise measurement, in the periphery of the cornea in the quadrant where the steepest curvature occurs. These incisions allow the cornea to relax and thus take on the shape of the flatter quadrant. AK is often used in conjunction with both PRK and LASIK when a person has a high amount of astigmatism. The AK can be performed either prior to or after a laser procedure. Automated Lamellar Keratoplasty (ALK) - For those people with higher degrees of nearsightedness, there is another possible procedure for reshaping the cornea. In cases of moderate to severe nearsightedness, and even some cases of farsightedness, many leading ophthalmologists choose to perform Automated Lamellar Keratoplasty, or ALK.
ALK is done with an instrument called a microkeratome. The microkeratome is placed on the eye and the cap of the cornea is lifted and placed to the side. In nearsighted people, a microscopically thin section of the cornea is removed with the excimer laser. Then the cap of the cornea is placed back in position.
It adheres quickly and seals itself without the use of stitches. In farsighted people the cap of the cornea is lifted, as it seals itself, the pressure within the eye pushed up on the cornea, steepening its curve. In either case, the result is a cornea that has been fine tuned to reduce the refractive error. Candidates for Laser Eye Surgery Laser eye surgery cannot be performed if: - The patients glasses or contacts have been significantly changed in the previous 12 months. - The patient is pregnant or intends to become pregnant within 6 months. - The patient is afflicted with unstable or uncontrollable diabetes. - The patient suffers from an autoimmune disease such as AIDS. - The patient takes drugs or is undergoing treatment to suppress the immune system. - The patient is afflicted with uncontrollable vascular disease. - The patient has medical problems related to the eyes, such as amblyopia (lazy eye) or glaucoma. - The patient is under 18 years of age. - The patient has a history of excessive scaring with injuries or other surgeries. - The patient suffers from chronic herpes infections or connective tissue disorders. - The patient has severe dry eye. - The patient, if myopic, pupils dilate greater than 6. 5 mm in dim light. - The patient, if hyperopic, pupils dilate greater than 9 mm in dim light. Befits and Risks of Laser Eye Surgery (Lasik compared with PRK) Benefits: 1) Bowman's layer is spared. 2) No removal of the corneal surface tissue is necessary and therefore post-operative pain is substantially reduced. 3) Post-operative visual acuity is restored within a few days rather than weeks. 4) Less corneal scarring in the long term, less change due to healing (regression) and thus greater stability of the correction.
When comparing only the benefits of Lasik over PRK the first impression is that Lasik has the potential to be a superior procedure. There is however, a very significant list of potential complications or risks and these include: 1) Failure of automated instrument to leave a hinge on the corneal flap, with the first incision. 2) Loss of the corneal flap during the operation. 3) Loss of the corneal flap after the operation. 4) Slipping of the flap and healing off center. 5) First incision too deep (perforation of the eye) or too shallow, causing a hole in the flap. 6) Invasion of the surface tissue into the central tissue of the cornea. 7) Infection of the cornea. 8) Loss of visual acuity - from scarring or from degeneration of the PRK. 9) Technical problems with complex and finicky automated diamond-cutting devices. 10) The procedure is much more dependent upon surgeon's operating skills, than the computerized precision of the PRK procedure.
Free research essays on topics related to: cornea, tissue, eye drops, post operative, dim light
Research essay sample on The Eye And Laser Surgery
