Ординатура / Офтальмология / Английские материалы / LASIK and Beyond LASIK Wavefront Analysis and Customized Ablation_Boyd_2001
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Chapter 19 
Figure 19-1- Shift in decimal equivalent
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Figure 19-2- Best-corrected visual acuity (BCVA)
in decimal equivalent at the 12th month was 0.55 ± 0.26 SD (range 0.17 to 1) [p = 0.34](Figure 19-1). The mean uncorrected UCVA at the 12th month was 0.33 ± 0.27 SD (range 0.1 to 1). The safety index (Mean postoperative BCVA / Mean preoperative BCVA ) was 1.04 and the efficacy index (Mean postoperative UCVA / Mean preoperative BCVA) was 0.6. The mean preoperative spherical equivalent was -14.57±3.15 SD (range -9D to -23D). The mean postoperative spherical equivalent was - 1.36 ± 1.07 SD (range 0D to -2.5D) [p<0.05] (Figure s 19-2 & 19-3).
The details of the results are shown in Table
2. None of our patients had an induced astigmatism
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of more than 0.5 diopters. 2 patients had an induced astigmatism of 0.5 D evident on corneal topography but did not significantly contribute to the refractive correction. Figure 19-4 shows the preoperative topography of a patient and Figure 19-5 shows the post operative topograph of the same patient.
Two patients had a free flap during the procedure; in 1, the BCVA decreased by one line due to persistent grade 2 haze. Three eyes that had a preoperative spherical equivalent of more than -17 diopt-
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PEDIATRIC LASIK
Figure 19-3- Power residue |
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Figure 19-4- Pre-Operative Topograph |
Figure 19-5- Post-Operative Topograph |
LASIK AND BEYOND LASIK 237
Chapter 19
ers developed grade 2 haze, one of which spontaneously resolved by the visit at the sixth month. The other two, (including one eye which had a free cap), had persistent haze even upto the 12th month fol- low-up and subsequently had a drop in their BCVA by one line. None of the patients developed corneal haze more than grade 2. 19 eyes regained their preoperative BCVA after the procedure and 4 eyes improved by one line. None of the eyes developed rise in IOP or any retinal complication. The reason for the haze is not known. The haze was diffuse and present in the interface. It would seem that children have more tendencies than adults for this phenomenon and it could be due to the cornea being younger in children. It was not a very dense haze to cause extreme loss of vision.
The postoperative spherical equivalent was -1D or less in 11 of the 25 eyes (44%), between -1 and -2 D in 10 eyes(40%), -2.5 D in 2 eyes(8%) , -3 D in I eye(4%) and -4 D in one eye(4%).
No child with a low pachymetry reading was included in the study. The minimum pachymetry reading was 570 microns and the range was from 570 microns to 630 microns.
SUMMARY
Myopia is a common refractive error in children. Spectacle correction and contact lenses are the popular modes of correction. In cases of uniocular high myopia, if the refractive error is more than 3.0 D, a high incidence of intolerance because of dissimilar image size and optical aberrations has been found with spectacles. These cases develop anisometropic amblyopia if left uncorrected. This is because of the minifying effect of concave lenses and vertex distance factor. Conventional amblyopia therapy includes occlusion, to which all children are not compliant. Contact lenses do not minify images, do not have optical aberration, and do not have anisometropia problems. But some children become contact lens intolerant and have problems maintaining them.
Studies show that LASIK in adults is accurate and predictable13. LASIK is not usually done in children because myopia does not stabilize until early adulthood. However, treatment resistant anisometropic amblyopia is a strong medical indication for
LASIK treatment. Our goal in this study was to equalize the refractive power and thereby retard the stimulus and, if possible, reverse amblyopia.
The children were sedated for obvious reasons. But the children could not fixate on the light, and the microkeratome footplate was used to aid in fixation. The eyes were patched so that the flap was not disturbed in the immediate postoperative period. Two patients had a free cap, which was sutured in place. The retrospective keratometry value was 39.0 D. One of the eyes lost 1 line of BCVA because of flap striae and persistent grade 2 haze. In 4 eyes BCVA improved, probably amblyopia reversal or better quality of vision after the refractive correction. We do not recommend including cases with keratometry readings below 40.0 D.
Our one year results show that LASIK is a safe alternative to correct pediatric myopic anisometropia. We think that LASIK can be performed in children if done with care. One should first try contact lenses. If this is not possible or successful, LASIK can be performed. The problem we saw in our pediatric patients that is not generally seen in adults was haze in the interface. We think this could be due to the age of the cornea since it seems to appear more in children than in adults. At present, we think LASIK is a good alternative in the treatment of anisometropic amblyopia. The study of LASIK in pediatric hyperopic patients is yet to be conducted and its results to be scrutinised.
REFERENCES
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1. Barraquer JI: Keratoplastic refractive. Estudies Inform 10: 2-21, 1949.
2. Bores L: Lamellar refractive surgery. In Bores L (Ed): Refractive eye surgery. Blackwell scientific publications: Boston 324-92, 1993.
3. Pallikaris I, Papatzanaki M, Stathi EZ et al: Laser in situ keratomileusis. Laser surg Med 10: 463-68, 1990.
4. Luiz Antonio Pereira Santini : LASIK: How to achieve a better outcome. Refractive surgery, Jaypee brothers publications : New Delhi,2000, 29; 306-310.
5. Collins JW; Carney LG. Visual performance in high myopia. Curr Eye Res 1990; 9:217-23.
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6.Lithander J; Sjostrand J. Anisometropia and strabismic amblyopia in the age group 2 years and above: a prospective study of the results of treatment. Br.J.Ophthal 1991;75:111-6.
7.Beardsell R; Clarke S; Hill M. Outcome of occlusion treatment for amblyopia. J Pediatric ophthalmol strabismus 1999;36: 19-24.
8.Jurkus JM. Contact lenses for children. Optom clin 1996; 5: 91-104.
9.Pak KH; Kim JH. Radial keratotomy for the purpose of reducing glasses power in high myopia. Korean J Ophthal 1992; 6: 83-90.
10.Hugo D Nano, Jr, MD,Sergio Muzzin, MD, L. Fernandez Irigaray, MD. Excimer laser photorefractive keratectomy in pediatric patients. J cataract refractive surg 1997; 23: 736-739.
11.Jorge L. Alio, MD, Ph.D, Alberto Artola, PhD, Pascual Claramonte, MD, Maria J. Ayala, PhD, Enrique Chipont, PhD. Photorefractive keratectomy for pediatric myopic anisometropia. J Cataract Refract Surg 1998; 24: 327-330.
12.Marinho A; Pinto MC; Pinto R; Vaz F; Neves MC. LASIK for high myopia: one year experience. Ophthalmic surg Lasers, 1996; 27: Suppl, S517-20.
13.Condon PI; Mulhem M; Fulcher T; Foley Nolan A; Okeefe M. Laser intrastromal keratomileusis for high myopia and myopic astigmatism. Br J Ophthalmol, 1997; 81: 199-206.
T. Agarwal, M.D.
Dr. Agarwal’s Eye Hospital,
19 Cathedral Road,
Chennai (Madras)- 600 086, India
• Part of the text and some of the figures of this Chapter are presented with permission from Agarwal et al textbook on REFRACTIVE SURGERY published by Jaypee, India , 1999.
PEDIATRIC LASIK
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LASIK AND BEYOND LASIK 239
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LOCAL FREEZING FOR EPITHELIAL INGROWTH AFTER LASIK
Chapter 20
FIRST NON-INVASIVE TREATMENT FOR SUBLAMELLAR EPITHELIAL INGROWTH AFTER LASIK BY LOCAL FREEZING
Juan Murube, MD., PhD.
Sequence of Events
Epithelial ingrowth under the corneal flap of LASIK is a frequent complication, affecting between 2 and 10% of the operated eyes (1,2,3,8). The epithelial invasion is usually initiated from a fistulous tract at the edge of the flap. This complication does not occur as a consequence of a free implantation of epithelial cells in the interface during surgery. It forms a continuous sheet with scattered hyperplasic dots, forming geographical figures like an archipelagus.
When the epithelial ingrowth is limited to the peripheral part of the flap, it can give rise to a foreign body sensation, photophobia, necrosis of the suprajacent stroma, and pain. Occasionally it may act as an entry point for interlamellar infection. When the epithelial ingrowth advances centrally and invades the optical zone it provokes irregular astigmatism, haze, dazzling, low visual acuity and low contrast sensitivity (2,4).
Management Techniques Presently
Available
All the methods previously published for elimination of post-LASIK epithelial ingrowth are invasive, and involve lifting of the corneal flap. Some authors detach only the flap sector occupied by the epithelial pearls, while others prefer to lift the whole
flap in order to avoid folds and striae when reattaching it. After lifting the corneal flap, the invading epithelium is removed with a surgical knife, drill, PTK, Nd:YAG laser, or irrigation associated with scraping with the point of a cannula (2, 5, 6, 8). Some authors introduce alcohol or cocaine in the interface to facilitate the scraping.
But invasive methods may give rise to many problems: laceration of the flap edge –especially when six months have elapsed, or when there is keratolysis-, (accidental ablation of corneal stroma), or creation of folds when replacing the flap. The epithelial pearls are easy to detect under the slit lamp or the surgical microscope when the corneal layers are all in place, but when the flap is lifted or detached to remove the pearls, they are undetectable and any remaining epithelium goes unnoticed. Therefore, new methods must be found to avoid use of the currently existing invasive techniques.
The New Non-Invasive Method
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To the best of our knowledge, this is the first non-invasive method reported in the literature. It consists in the destruction of the sublamellar epithelial ingrowth by brief freezing of the invaded sector. This is achieved by application of a surgical cryoprobe over the affected corneal surface, specifically where the epithelium has invaded the interface. The cryoprobe begins to be applied at the
LASIK AND BEYOND LASIK 243
Chapter 20
Figure 20-1: Murube’s Non-Invasive Cryo Application Method to Destroy Invading Epithelial Cells at the Edge of the LASIK Flap
Following LASIK, the epithelial ingrowth invading the edge of the cornea (E) is a complication affecting between 2 – 10% of operated eyes. In this illustration you may observe Murube’s non-invasive method to eliminate the epithelial cells growth. This is accomplished by application of a surgical cryoprobe
(C) over the affected corneal surface and freezing of the invaded sector. This is effectively accomplished without having to lift the flap. (Courtesy of Highlights of Ophthalmology)
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edge of the flap, which is where the epithelial pearls are first located. It is important to apply the cryo before too extensive epithelial invasion is present.
Technique Step by Step
Topical anesthesia is applied to the patient lying flat on a stretcher. A lid speculum is inserted in, and the cornea observed under surgical microscope. The area of intralamellar invasion is marked on the epithelium with a dermographic
gentian violet pencil. The epithelial pearls are more |
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visible with mydriasis. A cryoprobe for retinopexy |
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(Model Erbokryo AE, Erbe, Germany or equivalent), |
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is applied over the edge of the flap in the sector of |
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epithelial invasion, and applied for 3-4 seconds, |
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reaching a temperature of -70/-80ºC (Fig. 20-1). Each |
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application is performed twice (Fig. 20-1). |
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When the ice ball has disappeared and the |
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cryoprobe can be removed from the cornea, a drop |
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of dexamethasone is instilled and the eye is covered |
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for 24 hours. The drops are applied q.i.d for one week. |
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LOCAL FREEZING FOR EPITHELIAL INGROWTH AFTER LASIK
Results
On the first postoperative day the epithelial ingrowth looks very similar to the one seen in the preoperative stages. It is not possible to determine whether the cells are still alive or not. There is a small edema localized where the cornea was frozen. The epithelium stains diffusely with fluorescein. The patient may feel discomfort, and sometimes moderate pain for several hours which diminishes with sedatives and disappears with anesthetic drops.
One week after cryoapplication, the invasive epithelial sheet and most of the pearls have disappeared, and the remaining ones present diffuse, not round, regular edges. The epithelium does not stain. Pachymetry and endothelial count are as they were preoperatively. We do not know if this is because the cells did not die or because they are replaced by the surrounding cells.
One month after cryoapplication, there is no evidence of epithelial sublamellar ingrowth. Occasionaly a diffuse interface opacity may persist. Corneal pachymetry, endothelial cell count and refractometry do not change.
REFERENCES
1.Lin RT, Maloney RK. Flap complications associated with lamellar refractive surgery. Am J Ophthalmol 1999; 127:202-204.
2.Marotta H. Treatment of epithelial ingrowth. In: Buratto L et al. Lasik surgical techniquess and complications. 2000, Slack Inc. Thorofare, NJ, pp. 547-553.
3.Pérez Santonja JJ, Ayala M, Sakla H, Ruiz Moreno J, Alió JL. Retreatment after LASIK. Ophthalmology 1999; 106:21-28.
4.Castillo A, Díaz VD, Gutiérrez A, Tolendo N, Romero F. Peripheral melt of flap after LASIK. J Refract Surg 1998; 14:61-63.
5.Lim JS, Kim EK, Lee JB, Lee JH. A simple method for the removal of epithelium grown beneath the hinge after LASIK. Yonsei Med J. 1998; 39:236-239.
6.Kapadia MS, Wilson SE. Transepithelial photorefractive keratectomy for treatment of thin flaps or caps after complicated laser in situ keratosmileusis. Am J Ophthalmol 1998;126:827-829.
7.Murube J, Murube E, Gómez Carrasquel R, ChenZhuo L, Duran P. Nuevo tratamiento
mediante crioterapia de la invasión sublamelar epitelial tras lasik. Arch Soc Canar Oftalmol 2000;11:117-120.
8.Boyd, B.F.,: Postoperative flap complications after LASIK. Atlas of Refractive Surgery, Highlights of Ophthalmology, 2000; 4:94-99.
Prof. Juan Murube, M.D. |
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Clinica Murube |
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LASIK AND BEYOND LASIK 245
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
Chapter 21
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
Weldon W. Haw, M.D., Edward E. Manche, M.D.
(Note from the Editor in Chief: the following is one of the very best presentations on this subject available today. It is complete, well written, allencompassing, balanced, clear and well organized.
I encourage all ophthalmic surgeons interested in refractive surgery to read the entire chapter.)
period. Often, there is no identifiable cause for a complication. Although optimizing known variables will not guarantee a complication-free procedure, they will dramatically increase the likelihood of a successful outcome. This chapter will discuss the prevention and management of the primary complications following LASIK.
INCIDENCE – RELATION TO MULTIPLE VARIABLES
New advances in lamellar refractive surgery have resulted in an expansion of indications for laser in situ keratomileusis (LASIK). However, the increased popularity of LASIK has also resulted in the recognition of new complications. These complications occur in less than 1 to 5% of cases and include free caps, button-holes flaps, thin, incomplete, and irregular flaps. (1-10) The most severe complication, corneal perforation has also been reported. (11-12)
The incidence of complications depends on
CLASSIFICATION OF
COMPLICATIONS
LASIK complications can be classified as occurring during the intraoperative period, early postoperative period (days to weeks), or late postoperative period (weeks to months). This classification system is artificial, as there may be considerable overlap among many of these complications.
Intraoperative LASIK Complications
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multiple variables. Surgeon variables, microkeratome variables, laser variables, and patient variables must all be evaluated when attempting to assess the cause of a complication. Surgeon variables include appropriate training, experience, and meticulous attention to details. In view of the steep surgical learning curve, it is not suprising that the complication rate is much higher in surgeons with limited experience. Microkeratome variables include the type of microkeratome, proper maintenance, blade quality, and proper assembly. The excimer laser should be routinely calibrated and evaluated with regards to its energy fluence and beam homogenicity. Patient variables include cooperation with intraoperative/postoperative instructions and the individual’s wound healing response during the postoperative
The most severe intraoperative LASIK complications typically occur during the creation of the lamellar keratectomy. These complications should be recognized immediately. In many cases, a me-
ticulous preoperative examination by an experienced
surgeon will identify eyes at risk for these complica- Help ? tions. Although many preoperative and intraopera-
tive maneuvers by experienced surgeons can minimize these risks, they cannot be completely eliminated.
Subconjunctival Hemorrhages
Incidental trauma to subconjunctival vessels during vacuum application of the microkeratome can result in a subconjunctival hemorrhage. An inflamed
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or injected conjunctiva increases the risk of hemorrhaging and can occur immediately following the administration of any topical medication. This is most commonly seen following the administration of a topical anesthetic immediately preoperatively. We routinely use a topical vasoconstrictor to blanch these vessels immediately prior to surgery. Chilled balanced salt solution can also be used for this purpose. Recently, the use of Alphagan for this purpose has resulted in empirical reports of increased flap displacement during the immediate postoperative period. In any case, the significance of subconjunctival hemorrhages is only cosmetic and does not affect the visual outcome. Thus, “treatment” is limited to educating the patient on the natural course of the “bruised eye” and reassurance that it will not affect the visual outcome.
Chemosis
Chemosis during surgery may result from rapid fluid shifts that may occur from a reaction to the instillation of topical medication immediately preoperatively or by repeated attempts/manipulation of the conjunctiva during pneumatic suction ring placement. Chemosis may interfere with obtaining appropriate suction. With severe chemosis, a dry firm methylcellulose sponge should be used to massage the subconjunctival fluid posteriorly. In advanced cases of chemosis, a 30-gauge needle may be used to drain the excess subconjunctival fluid. After these maneuvers, it is best to check that the pneumatic suction ring achieves “true” suction by applanation tonometry (>65mm Hg) or by slightly lifting the globe with the suction ring. If the intraocular pressure is artificially low or the globe does not lift with the pneumatic suction ring, “pseudo” suction (only conjunctiva occluded in the suction ring) has been achieved and the case should be aborted. When in doubt, delaying the surgery is also a viable alternative to risking a poor quality lamellar keratectomy resulting from“pseudo” suction or no suction.
Deep Set Orbits/Small Palpebral Fissure
Adequate exposure during LASIK is an important step that facilitates the entire procedure including placement of the microkeratome. Deep set
eyes with small palpebral fissures limit exposure and should be avoided by inexperienced surgeons. Exposure can be improved by placing downward pressure on the speculum to prolapse the globe anteriorly or by using an adjustable speculum. Occasionally it may be necessary to remove the speculum altogether in order to appropriately position the pneumatic suction ring. A retrobulbar injection or lateral canthotomy are alternative measures that may be required. However, these methods are associated with independent risks and should be carefully considered before implementing.
Limbal Neovascularization/Pannus
Since many refractive surgery patients have a long history of soft contact lens wear, it is not uncommon to be faced with significant superior limbal vascularization. This should be identified preoperatively and appropriate measures should be planned to avoid hemorrhaging during the microkeratome pass. Topical vasoconstrictors may be applied locally by using a methylcellulose sponge soaked in the vasoconstricting agent. Also, purposefully positioning the flap to avoid the vascularization (i.e. superior hinge) or using a smaller keratectomy flap are also useful in limiting intraoperative limbal hemorrhage. Slight inferior decentration of a superiorhinged flap to avoid superior neovasculariztion will also not effect the outcome of the LASIK procedure. Fortunately, limbal hemorrhage can be controlled with application of a methylcellulose sponge to adsorb and place pressure on the origin of hemorrhage during photoablation. Additionally, maintaining the pneumatic suction ring on low vacuum will also limit hemorrhaging during the photoablation. After photoablation careful irrigation with balance salt solution will remove most of the hemorrhage from the interface prior to repositioning of the flap. It is important not to overhydrate the flap or bed as this may result in poor interface adhesion, flap displacement, and microstriae. Following repositioning of the flap, limbal hemorrhage may continue to bleed at the limbus gutter but not within the interface. Residual hemorrhage within the interface can be left alone. Some surgeons may elect to administer stronger topical steroids (prednisolone acetate 1%) postoperatively to patients with residual interface hemorrhage to prevent diffuse lamellar keratitis.
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248 SECTION IV