Warning: Please take into account that the thesis shown is from 1995. Any given figures in units of diopters for certain refractive procedures do not necessarily correspond to 2005 standards! However, the basic concept and ideas have not changed.
2.6Laser In Situ Keratomileusis (LASIK)
The LASIK procedure, being today's most promising refractive surgical technique, is discussed and compared with other refractive techniques.2.6.1The Development of LASIK
L. Buratto, Italy and I.G. Pallikaris, Greece, first realised the theoretical advantages in joining the Seiler's PRK with Barraquer's intra stromal keratomileusis: combining the precision of the excimer laser with intra stromal keratomileusis leaving the epithelium and the Bowman's layer untouched.
The procedure was very similar to freeze keratomileusis, but instead of freezing the 300 µm lamellar tissue and turning it on a lathe, they applied Laser treatment from the stromal side. The results of this treatment were very good especially for high myopes of up to -30 D. Pallikaris first applied the LASIK procedure in 1989, he was capping the eye with a microkeratome of about 140µm and applying laser treatment on the stromal bed directly. However, his manual microkeratome was not easy to handle for daily operations. Barraquer's former student L. Ruiz, Colombia and G.O. Waring, US, could overcome this technical problem by using their Automated Corneal Shaper, a microkeratome, originated from the Barraquer microkeratome, constructed for Ruiz's procedure of ectasie and the procedure of in situ keratomileusis. As in ectasie the thickness of the cut is of utmost importance, using this microkeratome for only capping the cornea to allow laser ablation intra stromal, the microkeratome has been rather "abused" for a much easier job than it was originally designed for.
Many western ophthalmologists think that LASIK is a totally new procedure, developed after superficial PRK had been invented. LASIK as intra stromal PRK. However, they forget that intra stromal freeze keratomileusis has been successful for over thirty years. LASIK is keratomileusis with the means of today's laser technology. Conceptually it builds onto a long existing experience. The microkeratome has been improved over this period of time and is nothing but a new invention. Often mentioned difficulties in the application of the microkeratome are rather due to lacking experience of using this device than that LASIK is in the investigational phase. On the contrary superficial PRK has only been done for seven years, and there is no long term experience in respect to the destruction of Bowman's layer. Intrastromal excisions however, have had no side effects for over 30 years.2.6.2Description
The following description of Laser In Situ Keratomileusis will be conceptual and limited to the surgical process, for detailed and overall process see the sixth chapter.
The surgery is ambulant and with topical anaesthesia. Correcting one eye the patient will not spend more than five minutes in the operation room with an experienced surgeon. After usual surgical preparations, the automated microkeratome is applied, producing a circular segment of 160µm thickness and a diameter of about 8 mm. This corneal flap is moved to the nasal side there the flap remains attached to the cornea. The eye is now centered and laser ablation will be started (fig.4). The flap is moved back without stitches. The patient is strongly advised not to touch or rub his eye. After three months the flap can hardly be removed.2.6.3Conceptual Advantages to former techniques
Why should the easy superficial PRK procedure be replaced by a more complex procedure as LASIK? Answering this question is not trivial and in the author's point of view, its benefit is rather for the patient than for ophthalmologists or laser manufactures. The in part higher complexity and the necessity of sterile operation conditions induces centralisation of this medical service. Instead of many local, superficial PRK ophthalmologists like today's contact lens specialists, there will be instead few LASIK centres, less surgeons and less lasers sold. Evaluating the pros' and cons' of LASIK one must take these economic factors into account.
Of the many developed surgical techniques, until LASIK, only two survived a bigger market introduction: RK and superficial PRK. RK was successfully practised during the late seventies until the early 90's and PRK since the early 90's. There have been many discussions, as to whether PRK or RK brought better results. However, both procedures have a similar limited diopter range of application: myopic patients of up to -7 diopters. Above six diopters RK seems too dangerous and PRK too unpredictable. Theoretically speaking, the superficial PRK suffers from the effect of the Bowman's bark function, resulting in haze, pain and slow recuperation of vision. RK suffers from the indirect applied effect of changing of cornea's biostatics, its refractive effect is difficult to control and difficult to calculate without long manual surgical experience.
Somehow, cultural beliefs and the countries' infrastructure decided whether PRK or RK was preferred. For instance, in Germany, -low risk taking, and technocratic- the ophthalmologist community denied Refractive Corneal Surgery, especially the manual RK procedure. However, with PRK, interest is growing. Germany's ophthalmologists' associations in this field assume the word laser rather than the word refractive in its name, limiting themselves to one technology. In America, Refractive Corneal Surgery has been supported, and RK was tolerated, often even accepted, due to the overall good results and quick recuperation of vision. Their association, and representative journals stick to the name Refractive Corneal Surgery.
Replacing one technique by another there must be significant advantages to justify the friction of change. Limitations of RK and PRK are summarised in the following diagram, not for criticism (both have been milestones) but to demonstrate the LASIK progress.
As already mentioned the idea of LASIK is combining the 30 year experience and the advantages of freeze keratomileusis with the precision and ease of laser ablation. Former experience denied any destruction of the Bowman´s membrane without the occurrence of strong side-effects. With the superficial PRK, side-effects of Bowman's membrane destruction were surprisingly low and for low myopia even acceptable. However, it still seems to be of great advantage to avoid the destruction of the Bowman's membrane due to undesired effects of its barkfunction and the difficulty in controlling its refractive influence due to its form shaping corset function [2.2.2]
2.6.4Results of various LASIK studies
Since the beginning, LASIK expected best results, especially for high myopes. However, formal results seemed to be rare and PRK protagonists started being sceptical about the assumed better results. Nevertheless, during the last year a couple of studies were published. What they all have in common: 1. results above 6 D. are much better than in superficial PRK, (even with a 6 mm zone), 2. instant results, 3. no haze, 4. no pain, 5. no significant change in best corrected vision. [BF93, PDS94, FT95, Kno95, RS95, GM96, HSB+96]
Variation in outcome in the superficial PRK procedure strongly depends on the laser, the diameter of the treated zone and the patient selection. Results in LASIK seem most influenced by the surgeon's experience and skills. Conceptual ablation software for LASIK should be different than that for superficial PRK. Ablation is closer to the retina and the tissue is slightly different. In practice however, these effects seem to be insignificant or even compensate one another. It even looks as if the original spherical ablation software works better for LASIK than for superficial PRK procedure. However, newer designed ablation software for superficial PRK, which does not strictly follow the thickness law, will most probably result in overcorrection when using them for LASIK.7
Although all the theoretical effects, have so far not been proven, the results obtained are excellent. The following diagram will summarise LASIK's characteristics.
This chapter will close with a macroeconomic round up to give a feeling of the amount of patients, who are going to be expected for Refractive Corneal Surgery in the near future. In the author's point of view the economics must be considered. In oversized Refractive Corneal Surgery centers, the lack of patients might be negatively influencing the application of surgery due to financial pressures. Overcrowded centres might lower their standards of procedures to fulfil the amount of patients to be treated, hence lowering the quality.
As already mentioned, the interest patients have in surgical treatment is strongly influenced by cultural beliefs and a country's optometrist infrastructure. Members of higher developed countries are commonly low risk taking, and have little need to go without glasses due to indoor work requiring short sight. Moreover, community pressure on wearing glasses is relatively low in developed countries. Although the average income in third world countries is much smaller, people would often give everything not to wear glasses, either due to their necessity to work outside, in conditions which are difficult for glasses or contact lenses, or due to there being no available optometrist's infrastructure. Furthermore, in many of these countries wearing glasses is very unpopular, especially for women.
At first glance it might seem surprisingly, but there might be more potential market in China or Colombia than in financially rich countries like Sweden and Germany. Moreover, the unequal distribution of capital in many third world countries and different cultural values often lead to bigger partial markets for "high end beauty products" than in strongly industrialised countries, which to some extend applies to Refractive Surgery.
Two markets are investigated in brief.2.7.1The US Market
The US Market seems to be one of the most interesting markets: rich and the world's highest soap usage per habitant [BM94] indicate a high cultural importance of aesthetic values. Indeed, radial keratotomy has spread more in the US compared with other highly industrialised countries.
However, forecasts in laser Refractive Surgery give the prognosis that the US market is not as big as was commonly thought and that it is going to take a while to grow. Furthermore , the "conversions" from spectacles and lenses will be low initially, but increasing later as the procedure becomes less expensive and more widely accepted. 28% of the US population is myopic, 70 million. Only half of them fall in the 20 to 54 year old group that will want and could really benefit from laser surgery. Only half of this group will be able to afford the operation, with initial fees of $1500 to $2000 per eye. Only half of this group will qualify for the current superficial PRK procedure (-1dpt. to -6dpt. and other selection requirements) The final patient pool: about 9 million, the LASIK procedure might double this number as it also applies for high myopia. This final pool must still be converted from existing correction systems to laser procedure. Conversion rates to RK have been 0.25% to 0.5% a year compared with a conversion rate from hard to soft lenses of about 2%. American ophthalmologists suggest possible conversion rate of 5% to 10% in the medium future. Eventually, interest will reach a peak and only a smaller group of the most sceptical patients will be left. The surgical volume will rise and fall over time in a bell-shaped curve [Hay85].
J.C. Noreika [Nor95] and K. Taylor director of Arthur D. Little come to a similar conclusion today. An older study from 1989 of Arthur D. Little suggested two million sculpting procedures will be performed annually five years after FDA approval. However, some assumptions may have changed.
There will be five primary competing interests: 1. manufactures, 2. owners of laser, 3. surgeons, 4. referring optometrists and 5. patients. Technological development will be quick, but the after market for old lasers will be low as patients want cutting-edge technology. Further analysis show that interests beneficial to the surgeon seem to always be opposed by either the manufacturer or the laser owner, with one exception: all parties gain if the volume of procedures increases [Nor95].2.7.2Challenges for Refractive Corneal Surgery in Germany
In the author's opinion, the German market will be most difficult to cover. Although the application was never formally prohibited like in the United States, the cultural beliefs of surgeons and patients seem very conservative. Moreover, cosmetic operations are socially not accepted or tolerated. Since lasers are available, the taboo for Refractive Corneal Surgery seems to be changing slowly. The belief in accurate machines is somewhat higher than in artistic surgeons' creativity. This seems fully understandable given the environment. Germans average ophthalmologist is more likely a "scientist" than a surgeon with excellent skills. The medical market is strongly restricted and there exist many market barriers. Until now, the interest groups can be simplified into three groups: 1. manufacturers, 2. ophthalmologists (=laser owners) 3. patients.
Comparing excimer laser companies in the US and in Germany will bring three surprises. Firstly, it seems quite astonishing how many US-Americans it needs to build an excimer even with the help of foreign scientists, compared to German companies, one of which is even a one man company (Inpro) building a good laser. Secondly, German lasers seem to be more reliable whereas American lasers show better customer product research. Thirdly, American excimer manufacturers seem to better organised in management, always ready for taking over foreign technology.
Patients are very conservative and usually take their ophthalmologist's opinion as the first true reference. The relationship towards physicians is traditionally very respectful, and their opinions are hardly questioned.
Germany's medical infrastructure is strongly controlled and structured by the government, securing free and equal medical care for everybody. However, this structure brings some undesired side effects. The climate between ophthalmologists seems one of envy, producing unbenefical decisions and opinions. Local ophthalmologists fear any centralisation of power. Laser centers are watched with jealousy as their existence could degrade them even more to being merely better optometrists, being consulted for unprofitable postopertory controls. Some of them started practising laser Refractive Surgery in do it yourself manner. The high inversion of owning a laser, and the game of money being lost or gained, seems to be easily influencing diagnosis. In a typical German ophthalmology consultation practice, it needs about 160 patients a year to be treated with superficial PRK until the first profit is made [Zei95]. With the LASIK procedure requiring a sterile operation room the number of patients required will be much higher. Although four patients a week does not seem a high number, time spent on individual consultation and "convincing" patients is underestimated. Moreover, the typical four minute consultation period will not be possible with private patients. In the author's point of view decentralised ambulant Refractive Surgery lacks practically skilled surgeons and well organised consulting practices due to missing overall quality management.
The goal of the laser manufacturers to sell many lasers, rivalry between ophthalmologists, the naive and overoptimistic investment calculations of some ophthalmologists and the following financial pressure to amortise the investment and highly emotional opinions about Refractive Surgery can often end in very contradictory recommendations for the patient.