Stromal Bed Research Articles

Corneal flap thickness in laser in situ keratomileusis using the summit Krumeich-Barraquer microkeratome

Purpose: To evaluate the thickness of corneal flaps created by the Summit Krumeich-Barraquer microkeratome (SKBM) (Alcon Surgical) and identify factors that may influence flap thickness.Setting: SSK Ankara Eye Hospital, Ankara, Turkey.Methods: Seventy-eight eyes of 50 patients who had laser in situ keratomileusis with the Asclepion-Meditec MEL 70 G-Scan excimer laser and the SKBM were prospectively evaluated. Preoperatively, the central corneal thickness, keratometry, visual acuity, and manifest refraction were measured. The microkeratome with the suction ring designed to create 160 μm thick and 9.0 to 9.5 mm diameter flaps was used in all eyes. Stromal bed thickness was measured with the Pachette ultrasonic pachymeter (DGH Technology, Inc.) after the flap was lifted. Flap thickness was calculated by subtracting the central stromal bed thickness from the preoperative central corneal thickness.Results: The mean preoperative central corneal thickness was 546.7 μm ± 31.9 (SD), the mean manifest refraction spherical equivalent was −6.8 ± 3.4 diopters (D), and the mean corneal refractive power was 42.9 ± 1.5 D. The mean corneal flap thickness created by the microkeratome was 154.9 ± 19.3 μm (range 101 to 202 μm). There was no correlation between corneal flap thickness and the degree of myopia (P = .151) or the corneal refractive power (P = .257). There was a linear relationship between flap thickness and the preoperative central corneal thickness (P = .000). A posterior corneal stroma thicker than 250 μm was preserved in 87 eyes (98.9%).Conclusions: The SKBM produced corneal flaps that were consistently close to the intended thickness. Corneal flap thickness did not appear to be influenced by the degree of myopia or the corneal refractive power; however, there was a linear relationship between flap thickness and the preoperative central corneal thickness.

Steroid-induced glaucoma after laser in situ keratomileusis associated with interface fluid

PurposeTo report the ocular manifestations and clinical course of eyes developing interface fluid after laser in situ keratomileusis (LASIK) surgery from a steroid-induced rise in intraocular pressure. DesignRetrospective, noncomparative interventional case series. Participants/interventionWe examined six eyes of four patients who had diffuse lamellar keratitis develop after uneventful myopic LASIK surgery and were treated with topical corticosteroids. Principal outcome measureSlit-lamp findings, intraocular pressure measurements, and visual field loss. ResultsAll eyes had a pocket of fluid develop in the lamellar interface between the flap and the stromal bed associated with a corticosteroid-induced rise in intraocular pressure. However, because of the interface fluid, intraocular pressure was normal or low by central corneal Goldmann applanation tonometry in all eyes. The elevated intraocular pressure was diagnosed by peripheral measurement in several cases after months of elevated pressure. All six eyes had visual field defects develop. Three eyes of two patients had severe glaucomatous optic neuropathy and decreased visual acuity develop as a result of undiagnosed steroid-induced elevated intraocular pressure. ConclusionsA steroid-induced rise in intraocular pressure after LASIK can cause transudation of aqueous fluid across the endothelium that collects in the flap interface. The interface fluid leads to inaccurately low central applanation tonometry measurements that obscure the diagnosis of steroid-induced glaucoma. Serious visual loss may result.

Pneumococcal keratitis at the flap interface after laser in situ keratomileusis

A 28-year-old woman had uneventful laser in situ keratomileusis in the right eye. Six days postoperatively, she reported ocular pain and a large corneal stromal infiltrate was observed at the flap interface. A second surgery including lifting and excising the flap and scraping the stromal bed was performed. Topical antibiotics were prescribed. A bacterial culture revealed Streptococcus pneumoniae. The keratitis responded well to topical vancomycin. Twelve days after the second surgery, the stromal infiltrate had regressed, the hypopyon had resolved, and visual acuity was hand movements at 0.5 m.

Accidental self-removal of a flap—a rare complication of laser in situ keratomileusis surgery

PURPOSE: To report a rare complication in which the patient accidentally removed the laser in situ keratomileusis corneal flap. METHODS: Interventional case report. A 35-year-old woman underwent uncomplicated laser in situ keratomileusis surgery. Ten days after surgery, she inserted a soft contact lens into the right eye to improve her vision. She tried to remove the contact lens, but had pain and bleeding. She was referred 10 days later with a diagnosis of loss of flap. RESULTS: On examination, she had a best-corrected visual acuity of 20/70 in the right eye. The right eye examination revealed no corneal flap, mild corneal edema, and significant haze. A central epithelial defect was found. CONCLUSION: Accidental corneal flap removal can rarely follow laser in situ keratomileusis surgery. This complication provides insight into the weak adhesion of the flap onto the stromal bed after laser in situ keratomileusis surgery and, hence, the inherent risk of traumatic flap dislocation or amputation, which needs to be explained to the patient.

Epithelial Scraping for Corneal Epithelial Ingrowth after Laser in situ Keratomileusis

Laser in situ keratomileusis (LASIK) is an effective method for correcting a wide range of myopia. However, complications sometimes occur. We report here a case treated with epithelial scraping two years and 4 months after surgery for epithelial ingrowth in the central cornea after LASIK. A 32 year-old woman who had undergone LASIK one year and 4 months before visited our hospital because of visual loss. At the first examination in our clinic, her best-corrected visual acuity was 20/60 in the right eye and 20/15 in the left eye. Epithelial ingrowth was observed in both eyes, but in the right eye, the epithelial ingrowth had reached the central cornea leading to the visual loss. The increased corneal stromal opacity decreased the visual acuity to 20/400. The patient decided to undergo epithelial scraping. The corneal flap was dissected again and epithelial scraping was performed on the stromal bed and back of the corneal flap. The visual acuity was improved from 20/400 to 20/40. However, the stromal opacity and the corneal astigmatism still remained. This case suggests that epithelial scraping should be performed immediately when ingrowing epithelium after LASIK begins to invade the central cornea.

Evaluation of photorefractive keratectomy retreatments after regressed myopic laser in situ keratomileusis

Purpose To evaluate the results of photorefractive keratectomy (PRK) enhancements in eyes previously treated by myopic laser in situ keratomileusis (LASIK) showing an undercorrection due to either a refractive regression or a primary undercorrection, when an in-the-bed enhancement was not advisable because of residual stromal thickness limitations. Design Noncomparative, prospective, interventional case series. Participants Seventeen eyes of 17 patients previously treated by LASIK for a spherical equivalent (SE) correction of −8.125 to −12.50 diopters (D; mean, −9.45 ± 1.01 D), that after a follow-up of 6 to 14 months ended up with a refraction of −1.50 to −3.75 D (SE; mean, −2.48 ± 0.74 D). Intended flap thickness was 160 μm for all eyes. In all cases, the residual stromal bed under the flap was considered too thin (255–305 μm) to allow an in-the-bed enhancement without exceeding an assumed safety thickness limit (250 μm). Intervention Eyes were treated by PRK at least 6 months after LASIK. The PRK ablation parameters (diameter, attempted correction) were selected to avoid theoretical flap perforation. The deepest ablation was 60 μm, for a −3.75-D correction. We used a Bausch & Lomb 217 C excimer laser (Bausch & Lomb, Rochester, New York). Main outcome measures Refraction, uncorrected and best-corrected visual acuity (BCVA), slit-lamp evidence of corneal opacity or other visible complications, and corneal topography. Results Although the initial postoperative period was characterized by very satisfactory refractive results (mean SE error at 1 month, −0.04 ± 0.37 D; range, +0.75 to −0.625 D), during follow-up, a dense haze (grade 3 and 4) developed in 14 eyes (82.3%) that induced a further myopic regression (SE, −1.725 to −5.50 D; mean, −3.11 D) and BCVA loss (two to six lines). These 14 eyes underwent a further surgical treatment to remove the severe haze at 3 to 10 months after PRK. Conclusions Based on these results, we strongly advise against PRK as a possible option to correct eyes previously treated by myopic LASIK that resulted in an undercorrection.

Ultrastructure of the lamellar corneal wound after laser in situ keratomileusis in human eye

A 30-year-old patient with keratoconus, a stable refraction, and normal central corneal thickness had laser in situ keratomileusis (LASIK). Six months later, she had uneventful penetrating keratoplasty for keratectasia. The lamellar LASIK interface could not be clearly identified by light microscopy. The corneal wound site did not stain for methyl metalloproteinase 1 or 2. Both the corneal flap undersurface and the stromal bed were devoid of interconnections and cells. Throughout the lamellar incision, including the laser-ablated zone, the surface was smooth on scanning electron microscopy. The collagen fibrils on both sides of the incision remained well aligned with one another, indicating good flap apposition. Under higher magnification transmission electron microscopy, some collagen fragments were found in the interface, especially adjacent to the hinge. The diameter of the collagen fibrils along the lamellar wound were identical to those farther from the incision. The absence of bridging collagen fibrils and cells between the flap undersurface and the stromal bed confirms the clinically known lack of wound repair at the interface and explains the easy separation of the flap from the stromal bed months after LASIK and the possible formation of an interface fluid pocket.

In vivo confocal microscopy of corneal epithelial ingrowth through a laser in situ keratomileusis flap buttonhole

We report a case of epithelial ingrowth through a buttonhole 6 months after laser in situ keratomileusis. Elevation topography showed irregular astigmatism and an unreliable pachymetric map. In vivo confocal microscopy showed an epithelial basal cell mosaic with prominent borders and distinct nuclei. No corneal nerves were identified in any image. Cells in the anterior stroma possessed bright, reflective nuclei and appeared to form clusters. The interface between the stromal bed and the flap had formation of nests of fibrotic tissue and epithelial cells.

Making Sense of Refractive Surgery in 2001: Why, When, for Whom, and by Whom?

Making Sense of Refractive Surgery in 2001: Why, When, for Whom, and by Whom?

Laser in situ keratomileusis for residual myopia after radial keratotomy and photorefractive keratectomy

Purpose To evaluate the visual outcome, stability, and complications of laser in situ keratomileusis (LASIK) for residual myopia after radial keratotomy (RK) and photorefractive keratectomy (PRK). Setting Dr. Agarwal’s Eye Hospital, Chennai, India. Methods Twenty eyes that had LASIK treatment for residual myopia after RK (10 eyes) or PRK (10 eyes) were retrospectively analyzed. Laser in situ keratomileusis was performed after a mean period of 24.3 months ± 0.75 (SD) in the RK group and 22.0 ± 1.07 months in the PRK group. Results At the last follow-up, the mean spherical equivalent was reduced from −6.05 ± 1.98 diopters (D) to –1.26 ± 0.32 D ( P < .05) in the RK group and from –3.38 ± 1.30 D to –0.55 ± 0.40 D ( P < .005) in the PRK group. The mean uncorrected visual acuity improved from 20/300 (range 20/600 to 20/200) to 20/40 (range 20/60 to 20/20) ( P < .05) and from 20/200 (range 20/800 to 20/80) to 20/25 (range 20/40 to 20/20) ( P < .05), respectively. Two eyes in the RK group and 3 in the PRK group gained 1 line of best corrected visual acuity, and 2 eyes in the RK group lost 1 line. No sight-threatening complications such as a free flap, corneal ectasia, or a retinal complication occurred. There was no statistically significant difference in corneal haze before and after LASIK. Two eyes in the RK group required repositioning of the flap because of irregular apposition to the stromal bed. Conclusion Laser in situ keratomileusis was safe, effective, and stable in the treatment of residual myopia after RK and PRK.

Valacyclovir for the prevention of recurrent herpes simplex virus eye disease after excimer laser photokeratectomy

A variety of factors have been reported as inducing the reactivation of latent herpes simplex virus (HSV), among them stress, trauma, and UV radiation. Excimer laser photorefractive keratectomy (PRK) is a surgical procedure utilizing a 193 nm ultraviolet light to alter the curvature of the cornea and hence correct vision. Reactivation of ocular herpes simplex keratitis following such excimer laser PRK has been reported. All published cases of HSV reactivation following excimer laser treatment in humans are reviewed. The present study evaluates whether stress, trauma of the corneal de-epithelialization prior to the laser, or the excimer laser treatment itself to the stromal bed induces this ocular reactivation of the latent HSV, and whether a systemic antiviral agent, valacyclovir, would prevent such laser PRK-induced reactivation of the HSV.Forty-three normal 1.5- to 2.5-kg New Zealand white rabbits were infected on the surface of the cornea with HSV-1, strain RE. The animals were monitored until resolution, and then all animals were divided into 5 treatment groups: (1) de-epithelialization only, intraperitoneal (i.p.) saline for 14 days; (2) de-epithelialization plus laser, i.p. saline for 14 days; (3) de-epithelialization plus laser, valacyclovir 50 mg/kg per day i.p. for 14 days; (4) de-epithelialization plus laser, valacyclovir 100 mg/kg per day i.p. for 14 days; (5) de-epithelialization plus laser, valacyclovir 150 mg/kg per day i.p. for 14 days. Animals were evaluated in a masked fashion by clinical examination biweekly and viral cultures biweekly through day 28.The reactivation rates were as follows: group 1, 0%; group 2, 67%; group 3, 50%; group 4, 17%; and group 5, 0%. Viral titers were negative in animals that had no reactivation but persistently positive in those that had reactivation (day 6 through day 28).Excimer laser (193 nm) treatment can trigger reactivation of ocular herpes disease (67%) and viral shedding in the latently infected rabbit. De-epithelialization alone is not sufficient to cause reactivation or viral shedding. Prophylaxis with intraperitoneal valacyclovir decreases the recurrence rate in a dose-response fashion. At 150 mg/kg per day, there are no recurrences. The presence of persistent viral shedding in reactivated animals may correlate with cases of late HSV recurrence reported in humans undergoing excimer treatment. The data suggest that humans undergoing excimer laser procedures for correction of refractive errors or treatment of corneal scars with a history of herpetic keratitis are at increased risk for reactivation. Such patients, however, may appropriately be considered for prophylactic systemic antiviral medication at the time of the laser procedure in order to decrease the possibility of recurrence.

Safety and predictability of laser in situ keratomileusis enhancement by flap reelevation in high myopia

Purpose To evaluate the safety and predictability of laser in situ keratomileusis (LASIK) retreatment following primary procedures for high myopia and astigmatism. Setting Corneal Diseases and Excimer Laser Research Unit, Department of Ophthalmology, University of Dundee, Dundee, United Kingdom. Methods This prospective observational study of retreatment comprised a cohort of 109 eyes having primary LASIK for high myopia and astigmatism with a spherical equivalent (SE) of −9.70 diopters (D) ± 4.06 (SD). Twenty-four eyes (22%) with an initial myopic SE of –9.83 ± 3.50 D, a comparable subset of the entire group ( P < .05), had retreatment for residual myopia (−3.02 ± 2.17 D) to improve uncorrected visual acuity (UCVA) by reelevating the corneal flap and ablating the stromal bed. Results The mean follow-up after retreatment was 12.8 ± 5.1 months (range 1.5 to 24 months; 19 eyes ≥6 months, 13 eyes ≥12 months). The mean myopic SE was reduced to +0.53 ± 0.62 D at 1 week, +0.05 ± 0.50 D at 1 month, +0.30 ± 0.50 D at 6 months, and +0.18 ± 0.42 D at the latest follow-up, 12.8 months. At the latest review, 62% of eyes were within ±0.50 D of emmetropia and 100% were within ±1.00 D. The mean refraction did not alter statistically between 1 week and subsequent times. The mean UCVA improved from 6/30 prior to retreatment to 6/9 at the latest follow-up. Uncorrected visual acuity of 6/6 or better, 6/9 or better, and 6/12 or better was achieved by 33.0%, 75.0%, and 95.8% of eyes, respectively. No significant complications that led to a loss of best corrected visual acuity were encountered, although retreatment procedures were more uncomfortable than primary procedures and self-limiting; epithelial ingrowth that did not threaten vision was common, and 2 patients complained of nighttime visual symptoms. Conclusions Retreatment of residual myopia by reelevating the flap was relatively safe and predictable, with a low risk of sight-threatening complications. However, longer term studies may be required to detect late complications.

Prevention of corneal ectasia in laser in situ keratomileusis.

Ectasia after laser in situ keratomileusis (LASIK) is a rare but serious complication. Prevention includes proper patient selection with detection of those at particular risk. Causes of ectasia include predisposition, excessive ablation with less than 250 microm of residual stromal bed, thicker than normal flap, irregular corneal thickness, and different ablation rates. We evaluated corneal curvature patterns and their relationship to corneal topography and pachymetry maps. Corneal topography (axial, tangential, and altimetric) and pachymetry map characteristics of normally astigmatic corneas, keratoconus, false-positive and false-negative cases, as well as contact lens-induced warpage are discussed. Preoperative pachymetry maps for LASIK surgery allow accurate case selection through detection of borderline cases, and provide important documentation of preoperative status, as well as useful information for improving surgical strategy. Another important parameter is the asphericity index.

Laser in situ keratomileusis for the correction of hyperopia from +1.25 to +5.00 diopters with the Technolas Keracor 117C laser.

To assess the efficacy, predictability, stability, and safety of laser in situ keratomileusis (LASIK) in patients with hyperopia and to evaluate the visual and refractive results of the procedure. LASIK was performed on 85 eyes of 53 patients for correction of hyperopia, with a preoperative mean manifest spherical equivalent refraction of +3.31 +/- 0.69 D (range, +1.25 to +5.00 D) and mean refractive astigmatism of +0.91 +/- 1.06 D (range, 0 to +3.00 D). The Carriazo-Barraquer (Moria) manual microkeratome was used to create the corneal flap, and laser ablation was performed using the Technolas Keracor 117C excimer laser with an ablation zone diameter of 6.0 mm and a transition zone diameter to 9.0 mm. Follow-up was 12 months for all patients. Refraction was stable by 3 months after surgery. At 1 year after LASIK, the mean manifest spherical equivalent refraction was +0.43 +/- 0.57 D (range, -1.25 to +2.00 D) and refractive astigmatism was reduced to a mean of 0.36 +/- 0.30 D (range, 0 to 1.00 D). Fifty-two eyes (61.2%) had a manifest spherical equivalent refraction within +/- 0.50 D of emmetropia, and 76 eyes (89.4%) were within +/- 1.00 D. Uncorrected visual acuity was 20/20 in 21 eyes (24.7%) and 20/40 or better in 79 eyes (92.9%). Spectacle-corrected visual acuity was reduced by two lines in one eye (1.2%) and improved by two lines in five eyes (5.9%). There were no significant complications. LASIK was an effective, safe, and predictable procedure for the correction of hyperopia up to +5.00 D and hyperopic astigmatism up to +3.00 D with the Technolas Keracor 117C excimer laser. The large size of the corneal flap obtained by the Carriazo-Barraquer (Moria) manual microkeratome facilitated laser ablation entirely in the exposed corneal stromal bed.

Bilateral infectious keratitis after laser in situ keratomileusis : A case report and review of the literature

Objective To report a case of bilateral infectious keratitis after simultaneous bilateral laser in situ keratomileusis (LASIK) and to explore appropriate preventive, diagnostic, and therapeutic measures. Design Interventional case report and literature review. Intervention A 22-year-old woman had bilateral corneal infiltrates after simultaneous bilateral LASIK. The same set of instruments was used for surgery on both eyes. Corneal scrapings from the edge of the infiltrate and underneath the flap were taken for microscopic examination and inoculation on culture media. Treatment consisted of irrigation of stromal bed with amikacin sulphate (2.5%) solution along with half hourly instillation of amikacin (2.5%) and cefazolin (5%) eye drops. Main outcome measures Causative organism and response to medical treatment. Results Culture revealed a significant growth of Mycobacterium chelonae from the corneal scrapings of both eyes. There was progressive thinning of corneal stroma in the right eye requiring cyanoacrylate tissue adhesive application. The left eye showed progressive worsening after initial response and required penetrating keratoplasty. Conclusions The risk of bilateral sight-threatening complications must be kept in mind when contemplating bilateral simultaneous LASIK. Nontuberculous mycobacteria should be considered as an etiologic agent in cases of infectious keratitis occurring after LASIK. Microbiology work-up of a specimen collected directly from the site of lesion can help in early diagnosis and institution of appropriate therapy.

Late traumatic dislocation of laser in situ keratomileusis corneal flaps

Purpose To report the management and outcome of late-onset traumatic dislocation of laser in situ keratomileusis (LASIK) flaps. Design Retrospective, observational case series. Participants Four patients with late-onset LASIK flap dislocation occurring after mechanical trauma at various intervals (10 days–2 months) after the procedure. Intervention In all cases of postoperative traumatic LASIK flap dislocation, the flap was refloated with scraping and irrigation of the underlying stromal bed within 12 hours of the injury. A bandage contact lens was placed, and a regimen including topical antibiotics and corticosteroids was instituted in all cases. Main outcome measures Best spectacle-corrected visual acuity and complications associated with the surgery were monitored. Results Postoperative follow-up ranged from 4 to 21 months. Nonprogressive epithelial ingrowth was noted in one patient and diffuse lamellar keratitis developed in another patient. All patients recovered pretrauma spectacle-corrected visual acuity. Conclusions Corneal LASIK flaps are prone to mechanical dislocation as late as 2 months after the procedure. Appropriate management results in recovery of optimal visual outcomes.

Epithelial Folds Following Slippage of LASIK Flap

We present a case of a slipped corneal flap after laser-assisted in-situ keratomileusis, LASIK. A 22-year-old, female with myopia and a refractive error of -5.50 D sph OU had an uneventful LASIK performed on her left eye with a Chiron Automated Corneal Shaper (ACS) and a VISX-Star Excimer laser using a nasal hinged flap. On the first postoperative day, slit lamp examination revealed 4.0 mm slippage of the corneal flap. The flap was rolled and folded on itself within the inferior cul-de-sac. With the aid of the operating microscope, the flap was repositioned on the stromal bed. Immediately following the repositioning, many folds were still visible despite centering the flap on the stromal bed and performing stretching maneuvers. Detailed examination showed the folds to be of edematous epithelial origin. The underlying stromal bed was flat. Within days following repositioning, the folds had disappeared and the flap assumed the typical postoperative LASIK appearance. The final uncorrected visual acuity returned to 20/20.

The effectiveness of a topical antibiotic irrigating solution in a model of staphylococcal keratitis after lamellar keratectomy

PURPOSE: To create a model of Staphylococcus aureus keratitis after lamellar keratectomy; to assess the toxicity of an antibiotic irrigating solution on the corneal stromal bed; and to test the chemotherapeutic effectiveness of a topical antibiotic, both alone and with an antibiotic-containing irrigating solution in preventing S. aureus keratitis after lamellar keratectomy. METHODS: The right eye of each of 38 rabbits were used in this study. In 18 eyes, a lamellar flap was created with a microkeratome, and an inoculum of S. aureus (either 1,000, 5,000, or 50,000 CFUs) was instilled under each flap; the eyes were examined for signs of infection and inflammation at 24 and 48 hours. In another five eyes, a lamellar flap was created in the same manner and the stromal bed was irrigated with 0.3% ofloxacin; the eyes were assessed for ocular inflammatory changes and evidence of crystalline deposits. Finally, in each of 15 additional eyes, 1,000 CFUs of S. aureus were instilled under a lamellar flap to create experimental infectious keratitis. The keratitis was treated according to three regimens: irrigation of the stromal bed with sterile balanced salt solution; irrigation of the stromal bed with 0.3% ofloxacin, followed by application of topical ofloxacin four times a day; application of topical ofloxacin only, four times a day. Eyes were examined for infection and ocular inflammatory changes at 24 and 48 hours. RESULTS: Staphylococcus aureus keratitis can consistently be produced under the stromal flap by inoculation of relatively few organisms. Irrigation of the stromal bed with commercial-strength topical ofloxacin does not appear to be toxic to the stromal bed, with no evidence of crystalline precipitates of the antibiotic. In our model of infectious keratitis after lamellar keratectomy, both topical ofloxacin alone and the combination of topical ofloxacin and irrigation of the stromal bed with 0.3% ofloxacin were effective at preventing S. aureus keratitis. However, the combined treatment of antibiotic irrigation plus topical antibiotic was more effective at preventing inflammation than topical ofloxacin alone. CONCLUSIONS: In this model of S. aureus keratitis after lamellar keratectomy, irrigation of the stromal bed with antibiotic plus topical antibiotic appears to be both safe and effective for preventing infection.

Lasik para correção de miopia, astigmatismos e hipermetropia

Objetivo: Relata a experiência em nossos primeiros 329 olhos operados com a técnica de Lasik para miopia, astigmatismo e hipermetropia, com um mínimo de 6 meses de seguimento pós-operatório. Métodos: Foram analisados retrospectivamente os resultados de Lasik em 110 olhos com baixa miopia (grupo I), 113 com miopia moderada (grupo II), 47 com alta miopia (grupo III), 139 com astigmatismo baixo (grupo IV), 31 com astigmatismo moderado (grupo V), 27 com baixa hipermetropia (grupo VI) e 25 com hipermetropia moderada (grupo VII). Resultados: A refração pré-operatória média de cada grupo acima foi, respectivamente: -3,56 ± 1,25 D, -8,31 ± 1,68 D, -14,95 ± 2,85 D, -1,57 ± 0,49 D, -3,98 ± 0,85 D, +2,32 ± 0,65 D, +5,05 ± 1,02 D. Aos 12 meses de pós-operatório, a refração média residual em cada grupo acima apresentava-se, respectivamente, com -0,11 ± 0,69 D, -0,42 ± 0,85 D, -0,69 ± 1,48 D, -0,42 ± 0,73 D, -0,73 ± 1,16 D, +0,35 ± 0,50 D, e +1,32 ± 1,03 D. A regressão do efeito da cirurgia neste período foi clinicamente insignificante em todos os grupos, exceto no dos hipermétropes moderados (0,76 D). Foram necessárias re-intervenções em 4,9% dos olhos operados (3,4% para hipocorreção, 0,6% hipercorreção, e 0,9% para limpeza da interface). Perda de uma ou duas linhas na tabela de Snellen ocorreu em 3,7% dos míopes baixos, 12,4% dos míopes moderados, 0% dos míopes altos, 18,5% dos baixos hipermétropes, e 20% dos hipermétropes moderados. Outras complicações, raras, foram as seguintes: corte completo do disco, entretanto sem perda do disco (0,3%), corte incompleto (0,3%), corte irregular por perda de sucção do anel (0,3%), astigmatismo regular induzido (7,4%), descentração da foto-ablação induzindo astigmatismo irregular (0,3%), opacidades e fragmentos na interface (0,6%), estrias importantes do disco (0,3%). Conclusões: A cirurgia de Lasik demonstra ser segura, eficaz, e previsível para uma grande parte das ametropias.

Corneal ectasia detected after laser in situ keratomileusis for correction of less than −12 diopters of myopia

We report 2 cases of corneal ectasia detected after laser in situ keratomileusis (LASIK) for the correction of less than −12.0 diopters (D) of myopia. Patients were evaluated before and after LASIK by corneal topography and pachymetry. After treatment, visual acuity temporarily improved but was followed by visual impairment, with corneal ectasia detected by topography. There may be a risk of corneal ectasia after LASIK in cases of myopia of less than −12.0 D. Despite the low incidence, we recommend that LASIK be restricted to cases in which more than half the original corneal thickness and more than 250 μm of the stromal bed can be preserved. Careful examination, including preoperative serial topographic evaluation and measurement of posterior stromal thickness, should be performed to improve the quality and predictability of corneal refractive surgery.