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Wave front guided photorefractive keratectomy is a specific type of refractive laser eye surgery designed to make it possible for patients to have good eyesight. This is an add on to the original LASIK laser that was developed in 1991 and provides new technology to correct the eye. This new technique and others like it are the result of research into different methods of the laser correction surgery. It uses a “cold” to shape the cornea for refractive purposes. There are also several other ways that this particular procedure may help people with particular conditions. They can be extremely helpful when paired up with corneal topography systems to aid in the discovery and treatment of eye problems. The photorefractive keratectomy is also a separate type of laser eye surgery, and it has its own flaws and facts. It, by itself, is not as effective as some other types of surgery. Cite error: A<ref>tag is missing the closing</ref>(see the help page).. Vision scientists then got hold of this new technology which allowed them to understand the image quality of the eye. In 1994, a group of scientists utilized a Shack-Hartman wave front laser to describe faults in the human eye[1]. AShack-Hartman wave front sensor is a narrow, infrared beam that acts as a beacon source that is produced by a super-luminescent diode and is projected into the retina. Several years later, the same group of scientists used the wave front laser with an adaptive optics mirror to correct aberrations in the human eye.[2]. This sensor allows measuring the cause of these refractive errors.
Problems that can be corrected with eyeglasses or contacts are lower-order aberrations, such as farsightedness, nearsightedness, or astigmatism. Usually it is only the higher-order aberrations that require this type of surgery. There may be a point where there are some things that cannot be detected in a traditional exam, and only are determinants of the acuteness of vision. These are things such as starbursts, halos, double vision, ghosting, and several other conditions, which can be a result from post-operative complications. There were studies that found that there were connections between pupil size and aberrations . Apparently, the larger the pupil, the more likely it has to have higher order aberrations after undergoing surgery. Just having LASIK surgery, there is a significant risk that patients will have side effects such as haze and regression[3]. The wave front sensing allows the surgeon to measure the irregular astigmatism as a higher order aberration [4]. They can see the refractive status of an optical system through wave front sensing. Using the combination of a wave front sensor and a deformable mirror can produce better than normal vision because the two compensate for the eye’s aberration. This technology also shows us that higher order aberrations are more likely to occur in larger eyes. Wave front sensing also can tell the phase transfer function of the eye, which can be especially important for larger eyes. They can measure the wave aberration for many different points in the eye at the same time, and gives a more precise look and decreases the amount of error[5]. Refractive surgery is becoming more popular and is a solution to one wearing glasses and contact lenses. The technological improvements have also contributed to this, and they show that there are many more people opting to undergo this surgery. Wave front aberrations are gaps which are measured by the wave front coming from a perfect optical system compared to the non perfect eye that requires the corrective surgery. The lower-order aberrations are They measure it in microns and/or fractions of wavelength while it is shown in root-mean-square. Wave front analysis assesses the optical quality of an eye by analyzing the shape of the wave front. They can do this by separating the wave into segments called Zernlike polynomials [6]. It is interesting to note that the numbers of aberrations increase with age, yet the actual aberrations are much larger in younger eyes. This shows that as you age, the aberrations in your eyes detach from each other, which some speculate is the reason that vision and eye quality deteriorate over time. There is also much speculation about whether or not the aberrations in one eye, perhaps the left eye, correspond to aberrations in the right eye. (Liang, 1997) It is a proven fact that astigmatism and defocus are the same in both eyes, which may lead us to correlate some other irregularities as well. A study of the biological and genetic factors of the human eye shows that there must be mirror symmetry between the two eyes. There is also some speculation that aberrations are results of random errors in the genetic makeup, because of there are confirmed reports that aberrations can have slight disparities from one observer to another. But some researchers have found that one person looking at both the left and right eye can see analogous aberrations.[7] The wave front technology allows the measurement of the eye so that the surgeon may take into account all of the elements of the optical system such as tear film, anterior corneal surface, corneal stoma, posterior corneal surface, anterior crystalline lens surface, crystalline lens substance, posterior crystalline lens surface, vitreous, and retina. One study has shown that wave front technology is superior to corneal topography[8]. There are some limits to how one may increase the extent of human vision. This includes pupil diameter, chromatic aberrations, higher-order aberrations, accommodative lag, rapid changes in wave aberration with time or age, depth of field, photoreceptor sampling and neural factors, biomechanical effects in the cornea, and accuracy of centration of correction. There are also some certain surgical limits when it comes to this procedure. The cornea is not fixed and can fluctuate easily and change shape. There are particular biomechanics of the eye that have to be taken into consideration before undergoing surgery[9]. There are several studies being conducted on this particular type of eye surgery.
One of the studies by Dr. Schallhorn, MD, used the CustomVue S4 Laser, and found it “to be safe and effective and to induce fewer higher-order aberrations” [10].The Navy has also contributed greatly to this type of laser surgery ,[11]. They use Photo reflective keratotomy more than other types of laser surgery. The Navy’s personnel must have strict visual standards in order to participate in their various assignments and missions in the Navy so they put significant emphasis on using like this technique since it is very effective and they put significant emphasis on the visual capacities of those who do undergo this procedure. The Navy has been researching this particular issue since 1993 and will continue to do so [12]. Another study was done on 13 patients that had complications after having LASIK surgery. The complication that they had was central buttonhole for five patients, a short or incomplete flap in another five, and a thin or irregular one in three. They used no-touch phototherapeutic keratotomy for some patients and manual debridement in the other patients. The patients all had better eyesight and they didn’t have any stromal haze. One patient had to undergo a second laser treatment because they had severe haze and regression following the PRK treatment, after their flap complication.
This procedure has also been used as a correction after using LASIK surgery when there is some residual myopia and straie left over after the surgery. LASIK, which stands for laser in situ keratomileusis, has quick visual recovery, lesser postoperative discomfort, predictable results, and a low complication rate. [13]. Yet, it is not rare that flap complications may occur during the course of the surgery. The wave front PRK has been found to be effective in treating these effects of LASIK surgery, along with the help of another procedure, PTK, which is short for phototherapeutic keratectomy, which is also another example of a “cold” laser that removes possibly damaged tissue for medical reasons. The combination of these two procedures helps widen the scope available in the eye that doctors can use. They specifically enlarge the optical zone, enabling doctors to remove more of the straie left over from LASIK. There are also examples of patients who went through some previous refractive surgery and have certain effects such as the loss of the corrected eyesight and some visual effects such as having glare, halos, and loss of contrast [14]. There are many studies that find that this procedure is effective in the higher level aberrations. Some surgeries are able to note that healing happens within a week after surgery and the patient can remove the bandages and can regain their sight . One study found that after the surgery, the error had significantly decreased after two weeks, even to the extent that there was no difference between the actual and intended correction [15]. These types of complications are rare, and cause significant problems for both the patient and the surgeon. They then used PRK to correct these problems caused by the LASIK and then they found that the results were favorable, resolving the problem caused by surgery, and restoring the patients vision to normal. This procedure is so important because if they try to correct the problem with LASIK, there is a certain risk that vision loss could occur. These flap complications are usually fixed by positioning the lamerall tissue. Using this method after a flap complication seems to produce little or no haze after the procedure. Flap complications can usually be fixed by repositioning the flap without further laser treatment. [16] All of these options, however, have created some difficulty for ophthalmologists to choose the most appropriate procedure for specific patients. Researchers are continually finding new types of surgery, so that there are many options available thanks to the speed that this research is being conducted and put into practice. [17]. There is even the possibility of better than normal vision. There are technologies that are being developed such as high-resolution opthamoloscopes and surgeries that are designed for the specific needs of a patient.
References Guttman, C. (2006). Study characterizes course of corneal healing after wavefront-guided PRK. Ophthalmology Times, 31(6), 42-43. Kuo, I. C.,. (2008). Photorefractive keratectomy for refractory laser in situ keratomileusis flap striae. Journal of Cataract and Refractive Surgery, 34(2), 330. Maeda, Naoyuki MD Wavefront technology in ophthalmology Current Opinion in Ophthalmology, 2001, 12(4), 294-299 MacRae, S. M., & Williams, D. R. (2001). Wavefront guided ablation. American Journal of Ophthalmology, 132(6), 915-919. Moreno-Barriuso, E., Lloves, J. M., Marcos, S., Navarro, R., Llorente, L., & Barbero, S. (2001). Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced changes measured with laser ray tracing. Investigative Ophthalmology Visual Science, 42(6), 1396-1403. O'Brien, T. P., & Ide, T. (2007). Update on customized wavefront-guided versus wavefront-optimized excimer laser ablation: Next steps in the quest for perfect vision. Expert Review of Ophthalmology, 2(3), 379-384. Schallhorn, S. C. (2004). Wavefront-guided PRK may be superior to standard. Ophthalmology Times, 29(24), 21-21. Talsma, J. (2004). PTK/PRK useful technique to resolve residual corneal striae.(combined approach)(phototherapeutic keratectomy) Ophthalmology Times, , 29,8,44 J. Liang and D. R. Williams, "Aberrations and retinal image quality of the normal human eye," J. Opt. Soc. Am. A 14, 2873-2883 (1997) Stanley, Philip F a; Tanzer, David J b; Schallhorn, Steven C Laser refractive surgery in the United States Navy. Current Opinion in Ophthalmology. 19(4):321-324, July 2008.