Fundamentals, Surgical Techniques, and Complications - part 7 pptx

performed no sooner than 3 months postoperatively to allow for adequate healing and sta- bility. Retreatments are usually indicated for errors of more than 0.75 D away from the tar- get refraction (4,6,13) and UCVA of 20/40 or worse (2). Retreatment may be done for one of the following: I. Dissatisfied patient due to a residual error or an induced error. However, some patients (up to 24%) may be satisfied by a refractive outcome less than ideal and do not ask for retreatment or may not even come for follow-up (2,6,13). The re- treatment rate and number of retreatments may be influenced by such subjective factors as patient expectations and demands (10). Presbyopic patients may well tolerate a small residual myopia. A. The residual error may either be initial undercorrection or regression of the achieved effect over time. 1. Undercorrection may be defined as a residual spherical equivalent error of more than 0.75 D away from the target at the first postoper- ative week (5). Most factories used to configure excimer lasers to provide correction for PRK on the surface of the cornea, and a stan- dard 10% reduction in programmed value was used for LASIK treat- ment. This standard reduction resulted in undercorrection, especially for high errors and when simultaneous astigmatic corrections are un- dertaken (16). LASIK nomograms with linear variability according to the attempted correction (Fig. 1) have decreased the incidence of undercorrection (13). Undercorrection may be induced intentionally in high myopia describing the golfing analogy to the patients. The first procedure will get them onto the green and the second proce- dure will putt them into the hole (8). 2. Regression is a less common problem in LASIK than in PRK (17). Although current laser algorithms aim at emmetropia, they do not al- low for possible external and internal influences that may modulate the corneal healing process. So, following the excimer laser treat- 298 El-Shiaty and Boxer Wachler Figure 21.1 Percentage of reduction with the linearly changing LASIK nomogram. The reduction goes up to 10% for myopia ranging from Ϫ3.1 to Ϫ7.0 D and up to 15% for myopia ranging from Ϫ7.1 to Ϫ15.0 D. (From Ref. 13.) ment, some regression of effect is typically seen. It is more signifi- cant in the first 6 weeks with smaller changes in the first several months (8,13,16). Regression may be defined as residual spherical equivalent error of more than 0.5 D away from the target with 0.25 D or more shift toward the original error between follow-up visits (5). Regression is the cause of retreatment in about 70% of cases (5). B. The induced error may also be initial spherical overcorrection or induced astigmatism. Overcorrection is defined as spherical equivalent error of re- fraction 1 month postoperatively shifting away from the target refraction in the opposite direction of the original error. II. Complications from the primary procedure as central islands (18–20), corneal haze (12,21), epithelial ingrowth (8,22,23), and corneal flap striae (8,24). A. RETREATMENT PROCEDURES AFTER PRIMARY LASIK Although the predictability of LASIK is higher than other refractive procedures, the nature of surgery upon living tissue is such that accurate prediction or refractive outcome is not entirely possible (25). As the field of refractive surgery continues to evolve, an increasing number of surgical options are available for LASIK retreatment. These allow refractive sur- geons to treat a wider range of myopia, hyperopia, and astigmatism effectively with a his- tory of LASIK even if multiple retreatments are required (4,5,7,11). The need for retreat- ment after primary LASIK surgery ranges from 0.7 to 36% (5–7,13,14,26,27). A higher retreatment rate was observed after astigmatic corrections than after spherical corrections (2). Retreatments after LASIK should not be performed earlier than 3 months after the pri- mary procedure for myopia and 3 to 6 months for hyperopia and astigmatism, at which time the refraction has usually stabilized. Generally, retreatment for undercorrection, especially for lower degrees of original myopia, can be done earlier than that for regression or induced errors (8,21). However, some authors recommend waiting at least 3 months for any other ablation (6,7,9,18). 1. LASIK Improvements in instruments and techniques allow for previous made LASIK flaps to be safely lifted for additional ablations even after several years (5,6,9,13). However, sufficient stromal bed thickness of 200 to 250 microns (4–6,8,14) or at least 30% of the total original thickness (18) left after retreatment is necessary to avoid subsequent ectasia. Laser retreat- ment is better avoided in eyes with less than 360 to 460 microns of total remaining corneal tissue after retreatment (4,9,12,14,20). When retreatment is for hyperopic correction, pachymetry should involve the 3 mm away from the corneal center (12). However, periph- eral pachymetry after hyperopic LASIK may be misleading. Epithelial hyperplasia oppo- site the peripheral ablation gutter will overestimate the amount of remaining stromal tissue. Hence it is possible to induce peripheral ectasia after multiple hyperopic ablations. LASIK retreatment can be performed either by lifting the original flap or by creating a new kera- tectomy cut. 2. Lift Flap Retreatments The procedure is done under topical anesthesia. The flap can be lifted rather than cut if the retreatment is performed before 6 to 18 months (8,12,13,17). The edge of the previous flap LASIK Retreatments 299 is best identified on the slit lamp. Gentian violet may be used to mark the edge and the cylindrical axis (4,6,7). An 18-gauge needle (13) or a probe (23) may be used at the slit lamp at a point 180 degrees from the hinge to disengage the flap, with a lateral movement, from its bed along a short section of the flap. Alternatively, a Sinsky or Hunkeler hook can be used under the laser microscope to free the flap edge for 3 or 4 clock hours (Fig. 21.2). The Hunkeler hook has a round ball on the end and is less likely to cause corneal damage (28). The flap is then carefully dissected, under the laser microscope, with a tying forceps or a cyclodialysis spatula without allowing the spatula to exit the flap. The flap is gently lifted with the forceps and bent back (Fig. 21.3), creating a sharp demarcation along the ep- ithelial edge in a technique similar to that used for capsulorhexis in cataract surgery (13) or with a slow and steady traction toward the hinge (8,23). 3. New Keratectomy Flap recut may be resorted to when the initial flap is thin or irregular, or if there is difficulty in dissecting the original flap edge. Larger flaps (13), old flaps (6,13,14), and flaps with a 300 El-Shiaty and Boxer Wachler Figure 21.2 A Hunkeler hook is used to find the edge of the flap and free it for 3 to 4 hours. (From Ref. 28.) Figure 21.3 The flap is carefully lifted and reflected with nontoothed forceps. (From Ref. 28.) history of interface keratitis after the first LASIK (5) are more difficult to lift over time. Thin flaps need more care in handling (6). Intraoperative flap complications during a pri- mary LASIK are best managed by realigning the flap edges as closely as possible and then recutting a new flap after at least 3 months (8). Also patients who have had previous inci- sional keratotomy or corneal transplantation may get torn flaps if blunt dissection is tried 2 months after LASIK (13). Hyperopia resulting from overcorrected myopic LASIK may need a larger flap (17), but since the degree of hyperopia is usually small, the original flap is sufficient in most cases. The technique for recutting involves decentering the suction ring 2 mm so that the new flap edge will be outside the edge of the first flap (Fig. 21.4). This decreases the chance of dislodging the original flap. The recut is usually done 20 microns deeper than the initial procedure (5). Ozdamar et al. (14) use the same microkeratome set- tings when more than 1 year has passed since the initial procedure and have not encoun- tered any flap disconfiguration. Only two peripheral gray circular lines have been seen with small decentration of the suction ring. Peripheral epithelial ingrowth has also been noticed. 4. Laser Ablation Laser ablation may be performed according to the standard LASIK nomogram (4,13,26), reduced by a fixed percentage (7,8), or customized to each eye based on the response to the initial procedure (5). When working with a new laser, reducing the attempted correction is prudent, since most lasers incorporate a healing response that occurs only after primary ex- cimer procedures and does not occur after retreatments. This protects against overcorrec- tion from laser retreatment. As the UCVA is often better than the myopia measured after LASIK would suggest, 60 to 70% of the residual error may only be aimed at (8). In re- treating astigmatism, some nomograms may take into consideration a 33% hyperopic shift as a result of toric ablation in the steep meridian (29). In retreating previous decentered ab- lation, the residual correction is made centered on the undilated pupil as the flap will smooth the edges of the two ablated areas (8). Central islands can be treated by using a dou- ble pretreatment in the 3 mm ablation zone and then performing half the refractive correc- LASIK Retreatments 301 Figure 21.4 To perform a secondary keratectomy beneath the primary one, the suction ring is placed just temporal to the edge of the first keratectomy. (From Ref. 28.) tion according to the Munnerlyn formula (depth of ablation ϭ diameter 2 ϫ height of the is- land/3) (30). This has been applied with both PRK and PTK modalities but with poor pre- dictability (19). A dry technique, in which the cul-de-sac is dried, the flap is lifted, the additional treatment is performed, and the flap is lowered before irrigation, may avoid introduction of any unwanted material underneath the flap (28). Any epithelial tissue detected at the flap edge should be pushed peripheral to the bed by a sponge (Fig. 21.5) (17,23,28). After the flap is reposited, a moistened sponge is used to roll back the epithelium into its original po- sition (28). A soft contact lens can be put if epithelial defects are bothersome and to reduce the risk of epithelial ingrowth (23). 5. Results The results of LASIK retreatment after primary LASIK in the literature are summarized in the table. The efficacy of the procedure can be demonstrated by the achieved UCVA. Thirty-one to 69 percent of eyes can achieve 20/20 or better (4–6,8,12,13,26), and 88 to 100% of eyes can achieve 20/40 or better UCVA (6,8,12,13,26). The predictability can be estimated by the spherical equivalent refractive error achieved. Sixty to 92 percent of eyes may be within 0.5 D (5,6,8,13,26), and 64 to 100% may be within 1.0 D of target correction (4,5,7–9,13,26). However, 12% undercorrection of more than 2.0 D of myopia (9) and about 4% overcorrection of more than 1.0 D (4) have been reported. Retreatment for myopia is more predictable than that for hyperopia (12). The safety of the procedure can be evaluated by the BCVA lost. Only 3 to 14% have been reported to lose one line of BCVA (8,13,26). On the other hand, 14 to 32% (6,8,12,13) have been reported to gain more than one line. LASIK retreatment has been found to im- prove decentration and night vision problems (4,7). In terms of stability, significant refractive changes may occur in the first 3 months but is most unlikely after 6 months (6,8), although regression can develop up to 2 years af- ter LASIK (5). It occurs in 10 to 18% of cases and is correlated to attempted correction, ab- lation depth, flat keratometry, and humidity (4,5). It may be caused by the molecular mem- 302 El-Shiaty and Boxer Wachler Figure 21.5 A sponge is used to reflect epithelial flaps out of host bed to decrease epithelial in- growth. (From Ref. 28.) ory in the corneal collagen fibers, stromal remodeling, the effect of IOP on the thinned cornea, and epithelial hyperplasia in response to an excessively flattened corneal curvature (8). 6. Complications Patients usually have worse UCVA in the first postoperative day than they had after the pri- mary procedure (13). Discomfort, foreign body sensation, and excessive lacrimation also last longer than experienced after the primary LASIK. This is explained by the epithelial irregularity at the flap edge caused by surgical manipulations during lifting the flap, com- pared to the clear cut edge of the primary flap (6,8). Some complications have been en- countered such as transient tear film disturbances (17%), interface deposits (8%), dimin- ished night vision (5%), scarring at flap edge (5%), filamentary keratititis (3%) (6), diffuse lamellar keratitis (22), and keratectasia (31). The risk of epithelial ingrowth (3–30%) is higher than primary treatment due to the irregular flap edge (4,5,26,27). This risk increases with a history of interface inflammation and with the use of a spatula to break the interface by sweeping (17,23). The risk of flap melting (11%) and folds (2–5%) is also high due to poor flap adherence after repeated manipulations (4,5). Flap melting develops commonly on an epithelial ingrowth area on the peripheral flap edge not affecting visual acuity (4). Moderate haze has been recorded at the flap interface after retreatment (8). Other rare flap complications such as flap slippage and dislocation have been recorded (27). Recutting the corneal flap has the added risk of getting a centrally thin or perforated flap and the poten- tial to generate a free corneal wedge of tissue where the two flaps intersect (8). A more meticulous surgical technique with a linear epithelial dissection, a copious irrigation of the interface for removing all implanted epithelial cells, and a strong adhesion with a minimal gap between the flap edge and the stromal bed may decrease the incidence of these com- plications (4,13,23). Although flap relifting is repeatable and has none of the added risks associated with recutting an already centrally flattened cornea, recutting the flap offers the advantage of a rapid visual rehabilitation without epithelial defects (8) but there is a risk of irregular cuts with free stroma1 pieces. The overall intraoperative complication rate is lower for enhancement than for primary procedures, while the postoperative complication rate is slightly higher (27). LASIK Retreatments 303 Table 1 Results of Secondery LASIK Retreatment after Primary LASIK BCVA Ref Rate Time STL Ն20/20 Ն20/40 Յ0.5D Յ1.0D Loss Gain 5 0.7 3 250 68.8 98.1 81.5 97.5 1.3 6 11 3 200 31.4 91.4 91.5 14.3 8 200 37.3 88.2 58.8 86.3 14 15 12 200 48.72 100 43.68 64.1 7.7 30.8 13 7.3 1.5 100 82 100 3 32 26 5.5 250 39.6 96.2 90.6 100 9.4 28.3 Ref ϭ reference number, Rate ϭ rate of retreatment in %, Time ϭ duration between the primary and secondary procedures in months, STL ϭ minimal stromal bed thickness left after retreatment in microns, Ն20/20 and Ն20/40 ϭ % of eyes UCVA, Յ0.5 D and Յ1.0 D ϭ % of eyes spherical equivalent away from the target, and BCVA loss and gain = % of eyes losing and gaining one line, respectively. 7. Photorefractive Keratectomy (PRK) Primary LASIK followed by second-stage PRK has been used to treat extremely high my- opia either simultaneously (32) or with transepithelial PRK after LASIK (33). Transep- ithelial PRK can also be applied to correct small degrees of myopia due to regression after LASIK (17). Bond and Abell (34) described a technique of PRK over incomplete LASIK flaps. After the flap is replaced they use 180–220 phototherapeutic keratectomy (PTK) shots to go through the epithelium. A PRK is then performed as if the flap had never been created. Assuming that epithelial hyperplasia is the main cause of regression after LASIK, Guell et al. have described an intraepithelial photorefractive keratectomy for regression af- ter LASIK. They use a PlanoScan mode, with the largest diameter zone possible, with an ablation depth not exceeding 50 microns for direct epithelial photoablation to avoid Bow- man’s membrane damage (35). Hyperopic PRK has also been used on the epithelial surface of the flap to treat myopic overcorrections (21). Although this is a simple, quick, and safe procedure, its efficacy (52%) is lower than a second LASIK and there is one-day discom- fort and foreign body sensation due to punctate keratitis and tear film unstability. In addi- tion, haze formation is significantly greater than that seen in primary PRK (8,21). This higher risk of haze is expected due to laser impact on the Bowman’s membrane of a previ- ously ablated cornea, which may not make PRK following LASIK a safe option. 8. Incisional Keratotomies Eyes with iatrogenic or secondary ectasia may not be suitable for lamellar or further abla- tive surgery (12). Radial keratotomy (RK) was used for residual myopia after PRK (36) and can be used for residual undercorrected myopia of less than 3 D after primary LASIK when maximal stromal ablation has already been performed (8). However, the predictability is poor due to the previous flattening (21). As most lasers ablate tissue along the steep meridian, they induce some hyperme- tropia. So, astigmatic keratotomy (AK) continues to play an important role in enhancement procedures for induced astigmatism, especially in cases of mixed and high astigmatism and when the spherical equivalent is near the target refraction. AK may be done underneath LASIK flap (11,21,22,27), or later over the flap (17), or outside the corneal flap (27). AK underneath the flap carries the risk of microperforation and the difficulty in obtaining flap adherence, increasing the risk of epithelial ingrowth (17,27). Limbal AK has an advantage over corneal AK of inducing less irregular astigmatism. 9. Laser Thermokeratoplasty (LTK) Thermokeratoplasty by holmium laser has been proposed to correct low hyperopia by steepening the corneal center due to shrinkage of collagen in the midperipheral cornea. This effect is based on the ability of corneal collagen to shrink by 30 to 45% of its original length at temperatures ranging from 58 to 60°C (37). It has been found that corneal lamellar cut- ting 6 to 8 weeks before LTK with spots placed outside the previous lamellar cuts dramat- ically increases the efficacy of LTK with improvement in regression. This may be ex- plained by the discontinuity and alteration of the integrity of Bowman’s layer (38). This improved effect has also been noticed after PRK, suggesting that greater corneal thickness favors regression (39). Since, in LASIK, the Bowman’s layer is interrupted and the corneal thickness is decreased, LTK can be used on the peripheral cornea with holmium laser 6 to 9 months after LASIK to treat under-corrected (40) or induced (21,41) hyperopia. LTK spots are applied first at 7.0 mm diameter regardless of the previous lamellar cut, but it is 304 El-Shiaty and Boxer Wachler better to keep them outside the previous ablation zone if stromal haze is present, to avoid confluent haze. There is usually immediate postoperative myopic shift followed by stable emmetropic refraction in the following weeks with no later regression. The result of the op- eration is good with stable corneal flaps and no loss of BCVA (40,41). It is recommended to perform 50% of intended correction and use only a 6.0 mm ring to guard against over- correction. A 7.0 mm ring may be used later if additional correction is needed. 10. Intrastromal Corneal Segments (INTACS) Intrastromal corneal ring segments (INTACS) have demonstrated safety and efficacy for correction of myopia between Ϫ1.0 and Ϫ3.0 D with the advantage of removability. They have been recently used to correct residual myopia 10 months after LASIK (11,42). This option can be resorted to when the cornea has become too thin for further ablation. It can also be used as a method of monovision by undercorrecting the nondominant eye by two diopters using LASIK. Then INTACS are used to correct these two diopters until presby- opia develops when INTACS can be removed. The procedure is done using the standard nomogram for unoperated corneas, but intraoperative pachymetry in four quadrants at the 7.0 mm optical zone should be done to confirm thickness of at least 600 microns, to allow for 400 microns of corneal stroma overlying the segments after implantation. If the pre- ceding LASIK was decentered to meet the pupillary center, INTACS may likewise be de- centered as long as the segments do not impinge upon the limbus. The vertical incision at 12 o’clock may cross the LASIK flap edge (42). We recommend waiting at least 6 months after LASIK to avoid flap slippage. If done earlier than 6 months, the lamellar dissection of the channel may cause the flap to torque with subsequent high astigmatism. If this occurs, the INTACS need to be removed followed by floating and reposition of the flap one week later. 11. Intraocular Lens Implantation Since the number of LASIK procedures is expected to increase, an increasing volume of cataract surgeries after LASIK is anticipated. Therefore accurate IOL power prediction af- ter LASIK is necessary. However, the change in corneal asphericity and in the ratio between the anterior and posterior corneal curvatures after LASIK leads to inaccurate determination of keratometric diopters. In addition, it is important to measure the stabilized refraction af- ter LASIK before any myopic shift from nuclear sclerosis (43). If the refraction and kerato- metric diopters before LASIK are available to the cataract surgeon, the clinical history method should be applied (44). This involves subtracting the change in spherical equivalent refraction induced by LASIK from the keratometric diopters measured before LASIK. If these data are not available, the hard contact lens method is used, in which the difference be- tween the manifest post-LASIK refraction with and without a plano RGP contact lens is de- termined and subtracted from the known contact lens base curve (power) (44). Keratometry ϭ Basecurve of plano RGP(D) – (S.E. (spherical equivalent) MRx s¯ CTL Ϫ S.E. MRx CTL). Alternatively, the keratometric diopters of the anterior and posterior corneal curvature may be measured separately by a scanning slit topography and entered into an empirical quadratic regression formula (43). 12. Others Homoplastic refractive keratomileusis and lamellar refractive keratoplasty may be used in cases of flap opacity in addition to the residual refractive error, as in cases of postoperative LASIK Retreatments 305 keratitis or stromal melting (12,21). Corneal flap striae can be treated by lifting the corneal flap and refloating it back into place during the first few postoperative days (8,24). B. SECONDARY LASIK RETREATMENT AFTER OTHER PROCEDURES 1. Penetrating Keratoplasty (PKP) The purpose of corneal and intraocular surgeries such as penetrating keratoplasty (PKP), cataract, and even traumatic corneal repair is to obtain an improved BCVA allowing the most possible visual function. In spite of the great advancement of these surgeries, the fi- nal refractive result may need to be refined after stable refraction for 6 months. Refractive unpredictability is common after PKP (45). Various refractive surgeries have been tried for patients with unsatisfactory spectacle or contact lens correction after PKP. PRK has been successful in the treatment of myopia and astigmatism but has a high incidence of compli- cations including haze and scar formation leading to loss of BCVA (46). Since LASIK has the advantage of less loss of corneal sensation than PRK, it has been used to correct all re- fractive errors after PKP with more effective results in treating myopia than astigmatism (12,45,47). Secondary LASIK can be done 8 to 18 months (12,20,45,47,48) after PKP and 6 months after all sutures have been removed (12,20,45,47) or after topographic stability for at least 3 months following all suture removal (48). The flap diameter should equal to or larger than the PKP scar, unless the graft was decentered (12), with an attempt to avoid the temporal scar to allow the flap to drape over the wound, creating better wound apposi- tion (45). The suction time should be minimized to avoid the risk of wound dehiscence (45,47) and retinal vascular or optic nerve compromise (49). More time is allowed for flap adherence before removing the speculum (45), and more postoperative corticosteroids are used than regular LASIK to avoid the risk of graft rejection (45,47). Predictability of 45% within 0.5 D (48), 63–73% within 1.0 D (45,48), and 88% within 2.0 D of target refraction (45) and efficacy of 36–55% within 20/40 UCVA (45,48) have been reported. Observations of 55–60% gain (45,47) and 9–12% loss (47,48) of more than one line of BCVA have been recorded. No graft rejection or loss of graft clarity has been documented (45,48,50). Flap complications such as paracentral perforation and dislocated flap (27,48) can occur. Results of LASIK treatment of postkeratoplasty high astigmatism may be improved by performing arcuate cuts in the stromal bed after laser ablation with the risk of perforation (47). Alter- natively, LASIK can be repeated after elevating the original flap (50). It has also been ad- vocated that making the flap first without ablation, rechecking refraction after some time and then elevating the flap for laser ablation may improve the predictability. LASIK with topographically guided customized ablation has been recently used successfully in the treatment of corneal irregularities following PKP and ocular trauma with significant im- provement in corneal topography, astigmatism, and UCVA (20). 2. Intraocular Lenses (IOL) Improvements in biometry or IOL power calculation have diminished, in most cases, the final refractive defect in cataract surgery as well as in phakic IOL implantation. The latter is becoming a popular technique having the possibility of changing the IOL if there is any postoperative gross refractive error. LASIK has been performed 3 months after pha- coemulsification and after phakic IOLs instead of enlarging the wound to replace the IOL 306 El-Shiaty and Boxer Wachler and to refine the residual astigmatism (12,51). LASIK treatment of high myopia results in thin corneas and small functional optical zones with compromised predictability and sta- bility. Combined surgery to correct high myopia (Ͼ15.0 D) by performing phakic IOL im- plantation followed, 1 to 3 months later, by LASIK has been used effectively and called bioptics. This improves the predictability, as LASIK is more reliable to treat small residual errors and coexisting astigmatism (52,53). Adjustable refractive surgery (ARS) is a modi- fication of this technique in which the lamellar microkeratome cut is done just before the lens implant surgery. The main advantage of this approach is to avoid the risk of endothe- lial-IOL touch during the microkeratome cut (54). Bioptics has given good results with 63–67% of eyes within 0.5 D and 85–100% of eyes within 1.0 D of emmetropia (52,53) and UCVA of 20/40 or better in 69% of eyes with no reported complications (52). 3. Radial Keratotomy (RK) The need for retreatment after RK ranges from 30 to 33% of cases (55). Surface photoab- lation by PRK following RK is associated with a 5- to 10-fold increase in haze formation and at least a 20% reduction in refractive predictability (10). LASIK can be used to treat residual myopia and astigmatism as well as hyperopic shift one year following RK (10,12,56,57). A 0.5 D overcorrection may be aimed at preventing regression from occur- ring during the first week due to the healing process of the previous corneal incisions (10,57). A thorough preoperative slit-lamp microscopy must be performed to verify good incision healing. The presence of an epithelial cyst within an incision may indicate a pre- disposition to interface epithelial ingrowth. In such cases, debridement of the cyst associ- ated with suturing of the incision may be important prior to LASIK (57). A secondary LASIK after RK is better done by a new cut and not by flap dissection. It has been found to be safe to apply suction to these corneas (51). Alternatively, flap hy- drodissection using a 27-gauge cannula placed under the flap near the hinge may be used (58). However, there is a slight risk of the old radial incisions coming apart either on the stromal bed (10) or on the flap during flap manipulation, increasing the risk of epithelial in- growth adjacent to the incisions (12,35,57). So the flap and the pie-like pieces should be perfectly aligned (10). Postoperative recurrent corneal erosions and slight daytime visual fluctuation may occur. UCVA of 20/20 is achievable in 29–56% (10,57) and 20/40 or better in 71% (57) of cases. Refraction within 0.5 D of emmetropia can be achieved in 57% of cases (57) with a 31% chance of gaining one line of BCVA (10). One line of BCVA may be lost in 7% of cases (57). 4. Astigmatic Keratotomy (AK) The combined technique of keratomileusis in situ and AK has been described either simul- taneously (59) outside or beneath the corneal flap (27) or sequentially (60) as a more ef- fective method in the treatment of high astigmatism than each procedure alone (12,60,61). LASIK after AK has been used successfully to treat up to 6 D of astigmatism using the ARC-T nomogram (62) and Limbal AK nomogram (63). Four weeks after topographic and refractive stability of the cylinder, LASIK can be performed using a 6.0 mm optical zone with a peripheral treatment zone of 8.0 mm. Results of 54% within 0.5 D and 85% within 1.0 D of intended cylindrical correction have been encountered with 7% loss and 27% gain of one line of BCVA (60). LASIK Retreatments 307 [...]... (mo) Forseto 22 ACS 6 18 63 4.55 0. 67 4.24 1 .79 NA NA Webber 26 VISX 20/20 Summit Apex Chiron Keracor Chiron Technolas Chiron Technolas VISX VISX 20/20 ACS 6 23 1 07 5.2 1.31 8. 67 2.92 5.91 3.88 ACS 11 24 24 7. 67 1.25 0 .75 NA NA ACS 6 24 71 6 .79 0. 67 (Hyper) 0.64 6 .79 1.93 6 .79 5.5 ACS 6 19 NA 10 .75 2. 37 2. 87 3.5 NA NA ACS ACS 1 12 8 20 44 25 7. 58 9.31 1.09 1.13 3.64 4. 87 1.98 1.5 NA NA NA NA Parisi 1 Koay... 1996;122:801–8 07 SE Wilson LASIK: management of common complications Cornea 1998; 17: 459–4 67 PI Condon, M Mulhern, T Fulcher, A Foley-Nolan, M O’Keefe Laser intrastromal keratomileusis for high myopia and myopic astigmatism Br J Ophthalmol 19 97; 81:199–206 EE Manche, RK Maloney, RJ Smith Treatment of topographic central islands following refractive surgery J Cataract Refract Surg 1998;24:464– 470 MC Knorz,... 3.06 to Ϫ0. 67 Ϯ 0 .77 D 6 months postoperatively (23) Kontos reported 35 eyes that underwent LASIK using the VISX Star S-2 after PRK with a spherical reduction from 1. 87 to 0.3 and average cylindrical reduction from 1.10 to 0.23 (24) 3 Complications a LASIK After Radial Keratotomy Complications were rare in the reported series A major concern in LASIK after RK is incisional dehiscence Other complications. .. plano-2.00 ϫ 95 and OS Ϫ4.50–8.00 ϫ 1 67 Patient underwent a LASIK flap cut with Hansatome microkeratome initially without any laser treatment On postoperative day 7, his manifest refraction OS had stabilized to the preoperative measurement of Ϫ4.50–8 .75 ϫ 155 Subsequently, the flap was lifted and the patient underwent partial treatment of the refractive error The laser was programmed with Ϫ1.8–3 .75 ϫ 170 ... Surg 2000;16:1 87 190 310 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 El-Shiaty and Boxer Wachler DS Durrie, TL Vande Garde LASIK enhancements Int Ophthalmol Clin 2000;40:103–110 AM Gutierrez Reoperations with the excimer laser In: L Burrato, SF Brint LASIK Principles and Techniques Thorofare NJ: SLACK, 1998, pp 339–350 JL Febbraro, KA Buzard, MH Friedlander Reoperations... same authors reported on a group of 67 myopic eyes subjected to bioptics; the mean postoperative spherical equivalent and cylinder after LASIK were Ϫ0.20 Ϯ 0.90 and 0.50 Ϯ 0.50 D, respectively (2) Eighty-five percent ( 57 eyes) were within Ϯ 1.00 D, and 67% (45 eyes) were within Ϯ 0.50 D of emmetropia The most serious complications were cataract formation (one eye) and macular hemorrhage (one eye) Cataract... correct high myopia: iris claw phakic intraocular lens and laser in situ keratomileusis J Refract Surg 1999;15:529–5 37 JL Guell The adjustable refractive surgery concept (ARS) J Refract Surg 1998;14: 271 JL Gayton, M VanDerKarr, V Sanders Radial keratotomy enhancements for residual myopia J Refract Surg 19 97; 13: 374 –381 HD Gimbel Photorefractive keratectomy and laser in situ keratomileusis hyperopic correction... a Technolas Keracor 116 excimer laser to correct myopia and astigmatism Mean spherical equivalent decreased from Ϫ10 .75 to Ϫ2. 37 D after surgery with a mean follow-up of 7 months However, mean astigmatism increased after surgery from 2. 87 to 3.50 D (21) Parisi and associates described LASIK in a case 2 years after PK A Chiron Vision Keracor 1 17 LASIK After Penetrating Keratoplasty 325 Table 2 Results... Average keratometric reduction of cylinder of 7. 95 D has been reported (7) Arffa reported a 77 % reduction in mean astigmatism in six patients treated with relaxing incisions and compression sutures, with a minimum time of 8 months after penetrating keratoplasty (8) Complications of relaxing incisions include corneal perforation, infection, graft rejection, and over- or undercorrection (Figure 23.1) 3 Excimer... decreased from Ϫ4.55 to Ϫ0. 67 D after LASIK with at least 6 months follow-up There was no statistically significant difference between 1-month and 6-month values Mean preoperative cylinder decreased from 4.24 to 1 .79 D after surgery (23) In a series by Donnenfeld and associates, 23 eyes underwent LASIK with a VISX Star excimer laser with a mean time of 44 months after PK and 35.3 months after suture . quick, and safe procedure, its efficacy (52%) is lower than a second LASIK and there is one-day discom- fort and foreign body sensation due to punctate keratitis and tear film unstability. In addi- tion,. because it is both a patient-friendly and a doctor-friendly tech- nique. The LASIK procedure allows for easy and accurate additional treatment to be done 308 El-Shiaty and Boxer Wachler without. of 20/20 is achievable in 29–56% (10, 57) and 20/40 or better in 71 % ( 57) of cases. Refraction within 0.5 D of emmetropia can be achieved in 57% of cases ( 57) with a 31% chance of gaining one line