Orthokeratology

from Wikipedia, the free encyclopedia

The orthokeratology (also:. Ortho-K, English Corneal Reshaping, Orthokeratology) is the targeted change in corneal shape by specially shaped rigid contact lenses , to a time-limited correction of vision defects (in particular, myopia and astigmatism to reach) without corrective lenses. Modern orthokeratological contact lenses are usually only worn during sleep. They are suitable as an alternative to refractive surgery , glasses and contact lenses worn during the waking phase.

history

The fact that flat, rigid contact lenses worn throughout the day lead to a temporary reduction in myopia was discovered as early as the 1960s. The flattening of the central corneal radii was achieved with dimensionally stable contact lenses made of PMMA that were consciously flat . The contact lenses were worn throughout the day and allowed improved vision without correction in the afternoon and evening. This method often took a few weeks to months before a satisfactory result was achieved. Several different contact lenses were also required. In addition, the results were unpredictable and unstable. The maximum possible correction was around -2.50 diopters. Due to the problem presented, this type of contact lens wear did not play a significant role until the 1990s.

Two milestones brought new opportunities for orthokeratology. On the one hand, new, highly gas-permeable materials for dimensionally stable contact lenses were developed at the end of the 1980s. This made it possible to wear large (so-called border limb) dimensionally stable contact lenses without causing an oxygen deficiency ( hypoxia ) of the cornea, even if they are worn for long periods of time and are worn overnight. On the other hand, technological development has made new measuring devices affordable for the optical practice. The corneal topograph made it possible to precisely measure a much larger area of ​​the corneal surface and display it in three dimensions. It was thus possible to observe and control more closely what effects orthokeratology has on the shape of the cornea

The technological advancement in the field of contact lens production also gave orthokeratology a new boost. Innovative so-called "reverse" geometries could be produced, which meant that the contact lenses were more stable on the eye and the process of flattening was significantly accelerated. This is why this type of orthokeratology was called "accelerated" (accelerated) orthokeratology.

FDA approval

The American Food and Drug Administration ( FDA ) approved an orthokeratological contact lens in 1994. However, this was only worn during the day (Contex OK-Lens). In June 2002, the so-called "Corneal Refractive Therapy" (CRT) was approved. With this type of correction, the contact lenses are only worn while sleeping. Modern Ortho-K contact lenses follow this principle to this day.

Typical position of an orthokeratological contact lens, tear film colored with fluorescein
Topographic image of a corneal surface altered by Ortho-K contact lenses

Orthokeratology today

In modern orthokeratology, only dimensionally stable contact lenses made of highly gas-permeable material are used. These contact lenses are worn during sleep and have a special reverse geometry that basically consists of 4 zones. This geometry enables the correction of all ametropia with just one pair of contact lenses, without the need for intermediate steps.

Mode of action

The flattening of the corneal radii is achieved through various changes at the level of the corneal epithelium ( cornea ). On the one hand, the density of the basal cells of the epithelium decreases, and on the other hand, the cells change in size and shape. Further studies also showed a redistribution of epithelial cells. In relation to the total thickness, the central thickness of the cornea is thinned by 2%. In the periphery (around the optic zone) the cornea becomes thicker and irregular.

Limits

The FDA ( Food and Drug Administration ) limits approval to a correction value of –6.00 D and astigmatism down to –1.75 D. However, there are manufacturers who orthokeratologische contact lenses for the correction of higher astigmatism ( astigmatism ), hyperopia ( farsightedness ) and presbyopia offer (presbyopia).

advantages

A clear advantage of orthokeratology over glasses or conventional contact lenses is the fact that you do not have to wear any visual aids during the entire waking phase. Several studies have shown that the quality of life with regard to vision (Vision related Quality of Life, VR-QOL for short) of orthokeratology contact lens wearers is rated higher than that of wearers of glasses or soft contact lenses. The orthokeratological contact lenses are always worn in the same spatial environment, so the risk of loss is very low.

During the day, no aids relevant to contact lenses or glasses (e.g. glasses cleaning cloth, contact lens case, rewetting) have to be carried along. Since the visual acuity is very good even with orthokeratological contact lenses on, there is no longer a moment of blurring after the entry phase (see adjustment below ).

Orthokeratology also offers several advantages over refractive surgery . The procedure is completely reversible. If the wearer cannot cope with the visual side effects (see below), they can use their previous visual aids after a few days without Ortho-K contact lenses. If the strength changes, new contact lenses can simply be fitted, which then lead to the corresponding correction. Orthokeratology does not intervene in the corneal tissue, no structures are damaged, so the risks of an operation do not apply to this procedure.

disadvantage

The structure of the flatter optical zone on the cornea causes a steepening around this zone, which has a higher positive effect and thus causes a stronger refraction of the marginal rays. If these marginal rays reach the eye with the pupil wide open (in poor lighting conditions), so-called halos (circles of light around light sources) are created. It also reduces contrast vision in twilight and night and increases sensitivity to glare. For the best possible effect, contact lenses should be worn for 6 to 8 hours every night. This fact can mean that orthokeratology cannot be integrated into every daily routine. If a contact lens is lost or broken, a replacement must be found quickly. The old ametropia returns every night without Ortho-K contact lenses.

Contraindications

  • extremely dry eyes
  • any chronic diseases of the cornea (e.g. keratoconus , PMD, endothelial dystrophies etc.)
  • corneal hyposensitivity
  • irregular sleep rhythms, extremely long waking phases (24-hour services)
  • poor compliance (hygiene, control rhythms)

safety

Several studies have now shown that wearing Ortho-K contact lenses does not pose any higher risks than wearing conventional contact lenses. The largest study on this topic was published in 2013. Here 1,300 patients, who could prove a total of 2,593 years of wear, were examined. Only two cases of microbial keratitis have been documented. Extrapolated, this means only 7.7 cases per 10,000 years of wear. For comparison: with silicone hydrogel contact lenses worn overnight, 25.4 cases were determined per 10,000 years of wear.

Who offers Ortho-K?

Ortho-K contact lenses are generally only fitted by opticians and ophthalmologists. The prerequisite is the presence of a topographer and a slit lamp microscope. Furthermore, most manufacturers require that the fitter has been trained in a special seminar on the topic and can show a certificate as an orthokeratology fitter.

Adaptation

Before the contact lenses are calculated and manufactured, it must be ensured that the initial values ​​are unloaded and reproducible. This means that contact lens wearers have to take a break from wearing before fitting until the cornea no longer shows any signs of contact lens-induced change in radius. The length of the break depends on the type and position of the contact lenses worn. On the submission date, the contact lenses are only placed very briefly on the eyes to check the visual acuity and fit. Furthermore, inexperienced wearers of dimensionally stable contact lenses have to practice putting them on and taking them off.

The first check-up takes place the morning after the first night with Ortho-K contact lenses. If the effect is not yet sufficient to enable good vision throughout the day, the residual ametropia is corrected with daily replacement contact lenses. In the first few days, there may be a noticeable regression in strength during the day. When a stable correction is achieved over the entire waking phase depends on the level of the initial strength. The higher the refraction to be corrected, the longer the entry phase on average. Studies have shown that in most cases this is completed after 7 to 10 days.

Individual evidence

  1. ↑ N. Jessen: Orthofocus techniques. In: Contacto. 6 (7), 1962, pp. 200-204.
  2. ↑ GN Jessen: Contact lenses as a therapeutic device. In: Am J Optom Arch Am Acad Optom. 41, 1964, pp. 429-435.
  3. ^ RL Kerns: Research in orthokeratology. Part III: results and observations. In: J Am Optom Assoc. 47, 1976, pp. 1505-1515.
  4. ^ PS Binder, CH May, SC Grant: An evaluation of orthokeratology. In: Ophthalmology. 87, 1980, pp. 729-744.
  5. ↑ DL MacKeen, M. Sachdev, V. Ballou, HD Cavanagh: A prospective multicenter clinical trial to assess safety and efficacy of Menicon SF-P RGP lenses for extended wear. In: CLAO J. 18, 1992, pp. 183-186.
  6. ↑ J. Mountford: Orthokeratology Principles and Practice. Butterworth-Heinemann, London 2004.
  7. ↑ D. Ruston, T. Dave: Accelerated orthokeratology - an introduction. In: Optom Today. 37 (20), 1997, pp. 28-34.
  8. ^ PJ Caroline: Contemporary orthokeratology. In: Cont Lens Anterior Eye. 24, 2001, pp. 41-46.
  9. ↑ RJ Wlodyga, C. Bryla: Corneal molding: the easy way. In: Contact Lens Spectrum. 4 (8), 1989, pp. 58-65.
  10. ^ DH Harris, N. Stoyan: A new approach to orthokeratology. In: Contact Lens Spectrum. 7 (4), 1992, pp. 37-39.
  11. ↑ X. Zhong, X. Chen, RZ Xie, J. Yang, S. Li, X. Yang, X. Gong: Differences between overnight and long-term wear of orthokeratology contact lenses in corneal contour, thickness, and cell density. In: Cornea. 28 (3), Apr 2009, pp. 271-279.
  12. ^ A. Nieto-Bona, A. González-Mesa, MP Nieto-Bona, C. Villa-Collar, A. Lorente-Velázquez: Long-term changes in corneal morphology induced by overnight orthokeratology. In: Curr Eye Res. 36 (10), Oct 2011, pp. 895-904.
  13. ^ S. Haque et al: Corneal and epithelial thickness changes after 4 weeks of overnight corneal refractive therapy lens wear measured with Optical Coherence Tomography. In: Eye Cont Lens. Oct. 30, 2004, pp. 189-193, discussion pp. 205-206.
  14. ↑ a b A. Alharbi, HA Swarbrick: The Effects of Overnight Orthokeratology Lens Wear on Corneal Thickness. In: Invest OphthVis Sci. 44, Jun 2003, pp. 2518-2523.
  15. ↑ J. Tsukiyama et al .: Changes in the Anterior and Posterior Radii of the Corneal Curvature and Anterior Chamber Depth by Orthokeratology. In: Eye & Contact Lens. 34, Jan 2008, pp. 17-20.
  16. ↑ Kang, Gifford, Swarbrick: Can Manipulation of Orthokeratology Lens Parameters Modify Peripheral Refraction? In: Optometry and vision science. 2013.
  17. ↑ Kobayashi, Yangi, Chikamoto, Chikama, Ueda, Nishida: Reversibility of effects of orthokeratolgy on visual acuity, refractive error, corneal topography and contrast sensitivity. In: Eye & contact lens. 34, 4, 2008, pp. 224-248.
  18. ↑ Kojima, Hasegawa, Hara, Horai, Yoshida, Nakamura, Dogru, Ichikawa: Quantitative evaluation of night vision and correlation of refractive and topographical parameters with glare after orthokeratology. In: Graefes archive for clinical and experimental ophthalmology. 249, 10, 2011, pp. 1519-1526.
  19. ↑ Maseedupally, Gifford, Lum, Swarbrick: Central and Para Central Corneal Curvature Changes During Orthokeratology. In: Optometry and Vision Science. 2013 / Oleszezynska-Prost: Orthokeratology in myopic children. In: Klinika oczna. 115, 2013, pp. 40-43.
  20. ↑ E. Santolaria et al .: Subjective satisfaction in long-term orthokeratology patients. In: Eye & Contact Lens. 39, Nov 2013, pp. 388-393.
  21. ↑ MJ Rah et al .: Comparison of NEI RQL – 42 scores in LASIK vs. CRT patients. In: Invest Ophthalmol Vis Sci. 45, 2004, e-abstract 1578.
  22. ^ DA Berntsen, GL Mitchell, JT Barr: The effect of overnight contact lens corneal reshaping on refractive error-specific quality of life. In: Optom Vis Sci. 83, Jun 2006, pp. 354-359.
  23. ↑ JJ Walline include: Benefits of contact lens wear for children and teens. In: Eye & Contact Lens. 33 (Pt 1), Nov 2007, pp. 317-321.
  24. ↑ a b Kobayashi, Yangi, Chikamoto, Chikama, Ueda, Nishida: Reversibility of effects of orthokeratolgy on visual acuity, refractive error, corneal topography and contrast sensitivity. In: Eye & contact lens. 34 (4), 2008, pp. 224-248.
  25. ↑ JT Barr, MJ Rah, W. Meyers, J. Legerton: Recovery of Refractive Error After Corneal Refractive Therapy. In: Eye & Contact Lens. 30, Oct 2004, pp. 247-251.
  26. ^ PS Soni, TT Nguyen, JA Bonanno: Overnight Orthokeratology: Refractive and Corneal Recovery After Discontinuation of Reverse-Geometry Lenses. In: Eye & Contact Lens. Oct. 30, 2004, pp. 254-262.
  27. ↑ Kojima, Hasegawa, Hara, Horai, Yoshida, Nakamura, Dogru, Ichikawa: Quantitative evaluation of night vision and correlation of refractive and topographical parameters with glare after orthokeratology. In: Graefes archive for clinical and experimental ophthalmology. 249 (10), 2011, pp. 1519-1526.
  28. ↑ Hebestedt, Jungnickel, Duncker, Sickenberger: Multicenter study on the fitness to drive of orthokeratology contact lens wearers. In: the contact lens. 10/2007.
  29. ↑ MA Bullimore, LT Sinott, LA Jones-Jordan: The risk of microbial keratitis with corneal reshaping lenses overnight. In: Optom Vis Sci. 90, Sep 2013, pp. 937-944.
  30. ↑ F. Stapleton, L. Keay, K. Edwards, T. Naduvilath, JK Dart, G. Brian, BA Holden: The incidence of contact lens-related microbial keratitis In Australia. In: Ophthalmology. 115, Oct 2008, pp. 1655-1662.
  31. ^ JK Dart, CF Radford, D. Minassian, S. Verma, F. Stapleton: Risk factors for microbial keratitis with contemporary contact lenses: A case-control study. In: Ophthalmology. 115, Oct 2008, pp. 1647-1654.
  32. ↑ L. Fan, J. Jun, Q. Jia, J. Wangqing, M. Xinjie, S. Yi: Clinical study of orthokeratology in young myopic adolescents. In: Int Contact Lens Clin. 26, 1999, pp. 113-116.
  33. ↑ H. Owens, LF Garner, JP Craig, G. Gamble: Posterior corneal changes with orthokeratology. In: Optom Vis Sci. 81, 2004, pp. 421-426.

Web links

Wiktionary: Orthokeratology  - explanations of meanings, word origins, synonyms, translations