Scientific Overview of Orthokeratology Technique and Safety

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Introduction

Orthokeratology is an innovative non-surgical, non-insidious, and adjustable treatment to tenderly reshape the cornea or remove refractive faults. It is also referred to as OK, ortho-k, or vision shaping treatment (CRT). The impressive high-tech improvements in nightwear contact lenses remove myopia, the necessity of reading glasses, as well as astigmatism when sleeping. OK enables patients to accomplish vivid, prolonged, and good vision during the entire day, even with the lack of glasses or open-eye lenses. Despite being in existence for many years and assisting many individuals, the application of high-tech corneal topographers became common recently. This new technology has helped in the production of precision lenses through computerized lathes, which can successfully regulate the accurate removal of optical errors. This paper gives a scientific overview of orthokeratology by discussing its history to recent developments in the modality.

History of Orthokeratology

Arguably, during the seventeenth century, a technique to minimize myopia by distorting the cornea was discovered in China. This method involved inserting smooth stones or sandbags packed with rice in the eye for a specified time before sleeping. The technique was enormously painful and insidious thus making the outcomes rarely fulfilling. This Chinese concept inspired the development of orthokeratology (Chan, Cho, & Sin 2008). Another remarkable development was in the 1950s when optometrists started fitting polymethyl methacrylate (PMMA) contact lenses that had the rear face of the lens larger than the corneas obverse surface radius and thus patients received better tear alternatives. Due to this innovation, practitioners started to observe modifications in the corneal curvature as well as refractive imperfection in the eyes of the subjects. Alterations were more intense when the lenses became flatter than curvature. Research conducted among 1000 shortsighted children showed a decreased refractive error after using the PMMA lenses for two years. Notably, when the participants removed the PMMA lenses and wore their glasses, they developed vague vision because the cornea adjusted. These observations stirred the efforts to alter myopia across the world via regulated corneal flattening with the application of contact lenses (Allison 2011).

However, the development of orthokeratology is highly accredited to George Jessen. He exemplified a modification technique known as autofocus. Once his lenses were placed in the eyes of a patient, they were occasionally refitted, in most cases six times. The treatment lasted for a year before eliminating myopia. After discreet scrutiny, he noticed that the cornea of his clients flattened that facilitating proper vision even in the absence of a contact lens. Jessen went ahead and used the concept on long-sighted clients and the aftermath recorded some positive effects. In the subsequent years, medical experts such as Neilson and Grant conducted a series of examinations to improve the idea of Jessen. The aim of these examinations was to map out a concept that would help in rectifying flexible lenses that resulted in reduced centration because of the plane middle base curve. In a bid to achieve corneal flattening, the lens base curve was occasionally altered in tiny gaps accompanied by the adjusted radius of the optic zone. In addition, it was advisable for patients to have lenses during the day so that their vision could undergo modification in the evening hours. Patients would also undergo a treatment process that would last for several weeks or even months and the effects were normally erratic if not variable. However, one prevailing observation in these studies was that using lenses that were less flat than the corneal curvature was effective in minimizing shortsightedness whilst preserving a good amount of centration (Watt 2007).

The first scientific examination to determine the efficiency of orthokeratology was performed by Kerns. Kerns scrutiny revealed that the cornea developed a spherical shape when using an ortho-k lens and this shape underscored OK treatment completion. Another research conducted to examine the impact of the ortho-k fitting technique revealed that it was marred with striking variability as well as volatility. It also indicated that the visual impacts of orthokeratology were interim coupled with quick resurgence to profiting points after removing lenses.

Resurgence of Orthokeratology

In the following years, very few practitioners showed interest in the technique, which then resulted in minimal studies in the area. Those who proceeded on to perform these examinations did not receive ample backing from the optometric profession. However, certain events occurred during the 1990s that drew clinical attention towards ortho-k. Whilst the ancient OK used complex tools to check on the performance of lens on corneal curvature, improvement in technology in the 1990s led to the introduction of corneal topographers (Shehadeh-Mashaour et al. 2007).

Through the devices, patients received precise lenses with specifications according to their screening results. With their introduction, the instruments played an integral part in determining the impact of the fitted lens on patients as well as correcting cases where a client experienced substandard results. Currently, the instruments are essential for the daily activities of the contemporary OK practice. The evolution of overnight ortho-k lenses also contributed to this resurgence. The previous PMMA lenses were impervious making patients develop hypoxia due to lack of oxygen. The development of rigid-permeable lenses and the consequent achievement in ensuring the transmission of oxygen to the lens inspired the evolution of the overnight OK lenses. These lenses are aimed at helping clients to achieve unassisted vision during the day after wearing the lenses at the night. Though they required preservation to maintain refractive impact, clients had a proper unassisted vision for over three days (White & Cho 2003).

Nonetheless, one of the major developments that had a significant effect on the rebirth of the OK is the reverse-geometry lens technique. The development of this method is highly accredited to Jessen who had exemplified a related idea to remove the decentration in the autofocus method. He stated that it would be wise to make a concave surface with plane fractions at the borders. Richard Wlodyga and Nick Stoyan also reiterated a similar idea. Reverse-geometry lens caused rapid modifications of the cornea where clinically important impacts take months to accomplish.

Currently, ortho-k has wide application in the interim treatment of mild short-sightedness with reverse-geometry lenses. Statistics show that OK is widely used in East Asia on young patients with about 150,000 patients estimated to have accessed it. Overnight orthokeratology stands out for causing positive effects on patients with notable comfort as well as expediency. Patients have preferred overnight OK lenses because they are worn at night and when users wake up, they enjoy good vision throughout the day without assistance (blu 2011).

Clinical Efficiency of Overnight OK

Several clinical types of research have shown that reverse-geometry lenses are effective in treating myopia through open-eye and closed-eye techniques. The research was done to determine the effect of open-eye wear lenses made of cortex recorded a decrease in the level of short-sightedness by approximately 1.50 D as well as progress in vision. Furthermore, another study revealed that the thickness of the cornea decreased after using the OK cortex modality for a period of one month. Another examination was conducted in China to check the efficacy of overnight OK and open eye lenses on young patients. Before performing the examination, the participants refractive imperfection was approximately 10.75 D of short-sightedness accompanied with 3.00 D astigmatism. The participants underwent the examination for six months and after six months, astigmatism had reduced by almost 75 percent whilst myopia declined to 5.00 D (Sun et al. 2006).

The consistent results of the reduction of the refractive imperfection in these clinical researches might have been subject to the participants level of myopia. Very few clinical researchers used subjects who had myopia above 4.00 D. No examinations have been conducted to determine the impact of the overnight lens on the safe upper stage of refractive modifications that the modern lenses can achieve, though there have been reports of unpredictability (Eisenberg & Cooper 2012). There is still no credible evidence that confirms the most effective lens out of the assorted designs of OK lenses. Research conducted on this issue has only yielded vague conclusions. Fortunately, clinical research has given credible evidence that OK treatment is effective in reducing myopia as witnessed through many patients who have had unaided vision soon after wearing an OK lens (Cheung & Cho 2004).

Nonetheless, the recent OK lenses have recorded minimal achievement in rectifying myopia above 4.00 D. This failure has made some have substandard outcomes of unaided vision, which may compel such patients to seek additional help to achieve a standard visual rectification. Irrespective of this demerit, most patients with serious cases of myopia are thankful that their reliance on spectacles has been minimized. The clinical characteristics of overnight OK are amazing. The first result of using an overnight OK in a single night is a three-quarter decrease in the refractive imperfection of the cornea, and probably after a maximum of ten days, one achieves a refractive correction. Clients normally experience mild weakening effects during the day and thus patients should wear their lenses regularly to contain the effect. From the time the technique was adopted, no solemn case has been recorded. Corneal staining has been a frequent occurrence for some patients, which has drawn the attention of practitioners (Chen, Lam, & Cho 2009).

Mechanisms underlying the corneal response to orthokeratology

After the introduction of OK, it was believed that the cornea was shaped towards the rear side of the contact lens because of the force induced by the lens at the corneal apex when a patient blinked. George Jessen developed the autofocus basing his reasoning on this belief. Jessen placed lenses that were flatter than the curvature depending on the level of myopic refractive imperfection. The aim of this fitting technique was to pick a lens base curve that would correspond to the restyled cornea. This idea earned wide application throughout generations and even in the current OK modality to pick the correct lens base curve (Mountford 2012).

Furthermore, the knowledge that steep fitting lenses were helpful inspired optometrists to develop another concept referred to as a hydraulic theory. Under this philosophy, there was a belief that pressures of fluid in the post-lens tear film initiated the alteration of the corneal shape. Mountford later polished this idea to create the ideal tear layer fitting theory that involved creating a specific post-lens film to fit the corneal figure of a particular patient so that the modification of the cornea is successful (Mountford 2012). Arguably, the ancient OK is often associated with the bending accompanied by the straightening of the cornea; however, this belief has no credible research to back it. Practitioners witnessed hardships when attempting to correct refractive faults with the adjusting keratometric figures of corneal strength caused by the ancient OK. These hardships implied that some other adjustments were taking place in other parts of the eye and these fears prompted optometrists to scrutinize the issue (Krader & Koffler 2012). A number of studies conducted revealed conflicting results. One study performed by Polse showed no corneal thickness adjustments whilst another research led by Coon recorded alterations in the thickness of the cornea. Consequently, the reaction of the cornea towards OK became anonymous (Kading & Mayberry 2012).

Subsequent studies on the topic resulted in disparate conclusions. A group of practitioners concluded that OK did not cause corneal bending after conducting a study on open-eye and reverse-geometry lenses that lasted for one year. They related OK refractive effects to topographical adjustments in corneal thickness as well as sagittal height, but not the corneal bending. Since then, the central epithelial reduction has been associated with overnight OK although its nature in OK is uncertain (Sun et al. 2006).

Previously, researchers assumed that the thinning typified cellular shifting from the area where the lens created a central force. This assumption revolved around Collins cat model. In the cat model, Collins observed that elastomer lenses caused epithelial cells to pile outside the periphery of the lens. This observation hinged on the shifting of epithelial cells from the force that was present at the periphery of the lens. However, this concept could not relate to the reverse-geometry OK lens because of the quick onset impact of the lens. Other studies have suggested that OK lenses do not cause cell movement or destruction of the cell layer, but rather it results in cell compression. Despite these postulations, further studies are necessary to determine the lasting effects of using the OK lens on epithelial health as well reliability (Chen et al. 2010).

Safety of orthokeratology

Irrespective of the method used, OK comes out as an effective strategy in terms of assuring patients of temporary treatment of myopia. However, the dominant question is how safe the technique is to its users. Even though the rigid-gas permeable prevented oxygen from reaching the cornea, the mechanism still stood out as a safe method. However, one insidious effect that presumably exists is microbial keratitis (Meszaros 2012). The inception of overnight OK in controlling myopia and improved knowledge in corneal adjustment has caused a rising fear that its users are at the risk of getting blinding infections (Schultz 2009). Several types of research have shown that using conventionally fitted contact lenses similar to the ones used in overnight ortho-k modality exposes one to risks of developing microbial keratitis, unlike daily lens wear. The studies suggest that continued usage of conventionally fitted contact lenses throughout the day and night is a major cause of the infection. However, this aspect is not the case in the overnight OK lens, which patients should wear lenses during the night. With such discrepancy in wearing hours, one can conclude that overnight lens users would be free from this risk. The means under which this disparate lens shape and lens-wearing techniques cause this vulnerability is a paradox (Cho 2005).

According to statistics from 2001, children and patients of Asian descent are at a high risk of being affected (Kwok 2005). Some studies have reported that the epithelial permeability of Asian patients increases more rapidly than in Caucasian patients after using overnight lenses. This epithelial obstacle can be associated with high vulnerability. Another explanation for this huge number of microbial keratitis is that since Asia had the highest number of clients using the OK modality, probably the number of infections would be high in the region (Ruskiewicz 2009). Though it is normal for the blinding ailment to cause tension, certain facts should come into consideration. Most of the microbial keratitis cases especially in East Asia occurred during an era that had very few skilled practitioners. The period was also characterized by unfettered development in overnight OK. However, over the past years, Asian countries have formulated policies to regulate OK practices to ensure that only professional optometrists undertake the practice. These restrictions are likely to minimize the number of microbial cases in this region (Allison 2011).

Future Direction in orthokeratology

Control of Myopia

The impressive progress of overnight OK in Asia since its resurgence in the 1990s is due to the success of the OK lens in temporarily alleviating myopia, especially in adolescents. A huge number of overnight OK users in Asia are youngsters below the age of 18 years who form close to 80 percent of the entire populace that use the OK modality. These statistics are startling when evidence shows that using OK to contain short-sightedness is unpretentious and allows criticism. Nonetheless, studies that have attempted to disapprove the efficacy of the OK technique have led to unsuccessful results (Chen et al. 2010). The probable means that OK utilizes in the treatment of myopic is uncertain. Some practitioners have suggested that the distortion of the visual experience at the edges of the visual area by regulating the distortion may promote the evolution of refractive imperfection in both animals and humankind. This assumption among others is currently under research, as researchers continue to seek cures to short-sightedness (Krader & Koffler 2012).

Application of OK on other Refractive Errors

Even though numerous clinical studies are being conducted throughout the globe on the application of OK on other refractive imperfections, such as hyperopia and astigmatism, very few have recorded success. Spherical reverse-geometry lenses have had some positive impacts on patients with astigmatism cases. However, most clinical examinations have shown that the effects are not efficient in modifying the corneal or refractive astigmatism with the use of overnight lenses. Another issue that has drawn the attention of practitioners is the application of the OK lens that can be useful in the management of hyperopia and perhaps presbyopia. Optometrists have concluded that the idea is feasible though its response to corneal steepening is gradual at the beginning, variable, and unreliable (Jedlicka 2012).

Understanding and Reducing the Dangers of Microbial keratitis

The success of overnight OK faces the challenge of microbial keratitis. Therefore, medical professionals should take urgent measures to contain or eradicate the infection before it destroys the good history that the modality has written since its rebirth in the 1990s. Clinical examination should focus on determining the vulnerability of getting microbial keratitis if one wears overnight OK lenses in place of other lenses. Since it is clear that overnight OK causes microbial keratitis, ways to regulate this infection is still unclear and studies should be conducted to create lucidity on the matter (Cheung & Cho 2004).

Permanency of Corneal on Refractive Changes

The greatest aspiration of both practitioners and patients is the development of an OK lens that can cause permanent correction of the refractive errors. Even though the ancient OK had shown some signs of unpredictable permanent treatment of refractive errors, clinical examinations ignored this capability. Using periodic retainer lenses can help a patient sustain the refractive modifications induced by the OK lenses. In the 1990s, a method referred to as cornea- plasty was developed. The idea involved loosening the stromal collagen attachments before using an OK lens to restructure the stroma, which is postulated to play an essential role in corneal and refractive alterations. Though there has been a lapse in implementing this concept, practicing the idea would probably promote permanent corneal reshaping (Shehadeh-Mashaour et al. 2007).

Conclusion

The polishing of the Chinese concept of sleeping with sandbags fitted in eyes to reduce myopia had a remarkable impact on the management of myopia even in modern society. A look in the history of OK confirms that the modality has grown from a time when it was a painful process, to when it was less effective and evolved to be effectual in the temporary reduction of myopia. The patients appreciation of the technique is a good encouragement even as further research is expected to boost the concept. Despite the success, OK has faced certain challenges. The huge number of patients complaining about microbial keratitis is disturbing and clinical researchers should discreetly scrutinize the issue. Moreover, the possibility of extending OK for other refractive errors and developing permanent treatment of myopia should be taken into serious consideration.

References

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