EDUCATION & DEBATE BMJ: first published as 10.1136/bmj.305.6857.813 on 3 October 1992. Downloaded from Regular Review Surgical correction ofnearsightedness Samir J Bechara, Keith P Thompson, George 0 Waring III Nearsightedness (or myopia) has been recognised for more than 2000 years'; during the past several cen- Surgical procedures to treat myopia turies, efforts have been made to determine its cause and to devise adequate treatment. About a quarter of Refractive keratoplasty-surgical techniques that the population in the West is nearsighted,'`3 and this change the comeal refractive power proportion rises to almost 50% in Asia.4 In the United * Lamellar techniques States nearly a quarter of people aged 12-54 are myopic, and the proportion increases considerably Keratomileusis with family income and educational level. Myopia is Epikeratoplasty less prevalent in men and in blacks.2 Intracorneal lens Myopia occurs when parallel rays of light entering Lamellar keratoplasty the eye are brought to focus in front of the retina, * Refractive keratotomy causing distant objects to be blurred while the near Radial keratotomy vision is preserved.5 The amount ofmyopia is measured Transverse keratotomy for astigmatism in negative dioptres. A dioptre is the unit of measure of the power of a spectacle or contact lens, and one * Excimer laser (photorefractive keratectomy) dioptre is equal to the power of a lens with a focal * Penetrating keratoplasty (refractive aspects) length of one metre. Therefore, a subject who has Intraocular implants-surgical techniques that -5 00 dioptres of myopia needs a concave corrective change the power of the lens lens with a power of -5 00 dioptres to neutralise that * Aphakic intraocular lens refractive error and provide normal visual acuity. * Phakic intraocular lens Among myopic people, 80% have up to - 6 00 dioptres Posterior scleral support-surgical techniques that ofmyopia. act on the axial length of the eye http://www.bmj.com/ Treatment for myopia has included herbs and procedures based on superstitions that predate recorded history.6 For centuries prosthetic devices 20 procedures to treat nearsightedness: they can be such as spectacles were the only option to correct classified according to surgical technique (box)." myopia. Other non-surgical treatments such as ortho- We review the major surgical procedures currently keratology,7 cycloplegic agents,8 and bifocal lenses9 performed in clinical practice to treat myopia, high- failed to show effective or consistent results. Spectacles lighting the aspects that are of interest to non- provide an efficient optical solution but they are often ophthalmologists. on 28 September 2021 by guest. Protected copyright. inconvenient, they limit some activities, and they are considered unattractive by some people. Many myopic people would like normal vision without dependence Refractive keratoplasty on extemal devices, and this is what drives most The comea is the most powerful refracting surface of 10 patients to consider ocular surgery. the eye, accounting for more than two thirds of the Department of Refractive surgery includes any operation intended eye's optical power.'5 Refractive keratoplasty refers to Ophthalmology, Emory to alter the refractive state of the eye." The ideal surgical procedures designed to correct refractive error University School of refractive surgical procedure should provide pre- by altering the refractive state of the comea, either by Medicine, Atlanta, Georgia dictable, reversible, adjustable, and stable correction changing its anterior radius of curvature or by changing 30322, USA without any loss of corrected visual acuity. Surgical its index of refraction. All refractive keratoplasty Samir J Bechara, methods to treat refractive errors were first proposed a procedures attempt to change the radius of the anterior internationalfellow century ago, and the main developments in this field surface of the comea, except when intracomeal lenses Keith P Thompson, are shown in the table. There are currently more than assistantprofessor with a high index of refraction are used. George 0 Waring III, professor Main developments in refractive surgeryfor myopia KERATOMILEUSIS Keratomileusis was proposed by Jose Barraquer in Correspondence and Year Author Contribution Colombia in 1949,15 and he first reported clinical requests for reprints to: results in 1964.20 A disc of anterior comea approxi- 1890 Fukala Removal ofthe lens for myopia" Dr G O Waring III, high 1894 Bates" Keratotomy for astigmatism mately 9 mm in diameter and 300 ,um thick is removed Department of 1898 Lans" Keratotomy for astigmatism with a microkeratome (a cutting instrument consisting Ophthalmology, Emory Eye 1949 Barraquer' Keratophakia and keratomileusis of a vibrating plane that slides across the comea), Center, 1327 Clifton Rd NE, 1953 Sato et al11 Anterior and postenror radial keratotomy Atlanta, GA 30322, USA. 1972 Fyodorov and Dumev' Antenror radial keratotomy ground into a new shape, and sutured back into 1979 Werblin and Klyce' Epikeratoplasty (fig 1). The button is reshaped by cryolathing,2' 1983 Trokel et aPl Excimer laser position BM71992;305:8 13-7 cutting on a mould,22 or with the laser. BMJ VOLUME 305 3 OCTOBER 1992 813 Keratomileusis is indicated for high myopia (-5 00 the reported complications are failure of the epithelium to - 15 00 dioptres), especially when other techniques to recover the lenticule, irregular astigmatism, loss of are considered insufficient to achieve a desired result.'3 best corrected visual acuity, secondary microbial infec- After the operation it may take up to six months for the tion, overcorrection, and undercorrection.32 refraction to stabilise, 4 and most published series Clinical studies of epikeratoplasty for myopia showed indicate that the refractive results of keratomileusis are instability and unpredictability of refraction after unpredictable.2927 operation.32 Accordingly, the United States Food and BMJ: first published as 10.1136/bmj.305.6857.813 on 3 October 1992. Downloaded from Major intraoperative complications include inadver- Drug Administration classified epikeratoplasty as an tent corneal perforation (requiring a full thickness investigational device subject to its regulatory laws.3' corneal transplantation), irregular disc removal, and Now, except for a few investigators, epikeratoplasty is irregular stromal carving."3 Postoperative complica- performed rarely for myopia, and from April 1988 the tions include corneal opacities and irregular astig- Food and Drug Administration limited the distribution matism leading to loss ofbest corrected visual acuity, as of lenticules to surgeons who have previous experience well as overcorrection and undercorrection.242728 with the procedure. Notwithstanding its inherent problems and difficul- If epikeratoplasty is to gain widespread acceptance ties, keratomileusis was the first procedure that pro- as a viable method of correcting myopia a suitable vided correction for high myopia. In the hands of a well synthetic material must be developed.33 Synthetic trained surgeon it offers a reasonable chance of collagen has been used successfully,34 and research to permanent correction of high myopia. The major develop this technique is continuing. disadvantages of keratomileusis are its technical com- plexity, the high cost of instrumentation, and unpre- INTRACORNEAI LENSES dictable refractive outcome. For these reasons only a Intracorneal lenses for treating nearsightedness con- handful of surgeons in the world currently perform sist of placing a synthetic lenticule within the corneal keratomileusis. stroma to change either the cornea's radius of curvature or its index of refraction. Two synthetic materials are EPIKERATOPLASTY currently under investigation: hydrogel and poly- Motivated to simplify keratomileusis, Werblin,'8 sulphone. Kaufman,29 and McDonald31 developed a new tech- The surgical technique for hydrogel intracorneal nique in 1979. In epikeratoplasty a lenticule cut from a lens implantation consists of removing an anterior donated comea is placed on a de-epithelialised cornea corneal disc with the microkeratome (identical to the of the recipient (fig 2). The patient's epithelium then keratomileusis technique), placing the lens on the re-covers the button. corneal bed, and suturing the resected disc of cornea Epikeratoplasty is indicated only for high myopia: of back into position (fig 3). Hydrogels, because of their a larger range than is indicated for keratomileusis.3" high water content, are permeable to water and The surgery decreases the refractive error in almost all nutrients, a key requirement for a successful intra- eyes, but the predictability, like that of keratomileusis, corneal lens. Hydrogel intracorneal lenses were is poor. Although uncorrected visual acuity is improved developed in 1981 and showed good biocompatibility in most people after epikeratoplasty, only 59% achieve and reasonable predictability in animals.3" Clinical a refractive error within three dioptres of emmetropia, trials controlled by the Food and Drug Admini- and about 30% of patients lose some best corrected stration are underway in the United States. Like visual acuity3 through irregularities of the corneal epikeratoplasty, intracorneal lenses can correct higher surface and loss oftransparency. refractive errors than can keratomileusis because there Because the lenticule may be removed, epikerato- is no limit to the thickness of the material used. http://www.bmj.com/ plasty has the advantage