SOURCE

BARCELONA - Regardless of how thick or thin LASIK flaps are made, the flaps cause a considerable reduction in corneal biomechanical stability compared with surface ablation procedures, according to a study presented here.

"Taking into account biomechanical properties but also visual recovery time and quality of vision, the best option is epi-LASIK, according to our results," Jorge Cazal, MD, said at the winter meeting of the European Society of Cataract and Refractive Surgeons.

In a study conducted at CIMA Eye Clinic, two groups of 25 patients were randomly assigned to undergo epi-LASIK with the Moria Epi-K epikeratome in one eye and PRK or thin-flap LASIK in the other eye.

"At 6 months postoperatively, the LASIK eyes experienced a 48% reduction in corneal biomechanics, while the eyes that underwent surface ablation had only a decrease between 10% and 14%," Dr. Cazal said.

"At 6 months, the LASIK group had the highest induction of high-order aberrations, with [root mean square] of 0.73, compared with 0.25 for the epi-LASIK group," he said.

However, visual recovery was fastest with LASIK, followed by epi-LASIK and PRK. Pain scores were also lowest with LASIK, followed by epi-LASIK and PRK, he noted.

Journal of Refractive Surgery Vol. 23 No. 6 June 2007

Richard M. Davis, MD; Jason A. Evangelista, MD

PURPOSE: To evaluate whether the vacuum of a microkeratome suction ring induces ocular structure changes.

METHODS: A prospective case series using A-scan ultrasonography to measure anterior chamber depth, lens thickness, vitreous body, and axial length was performed. Measurements before and during application of a Hansatome microkeratome suction ring were performed on 69 eyes of 39 consecutive patients scheduled to undergo a first-time LASIK procedure with mechanical creation of a corneal flap.

RESULTS: Mean patient age was 43±12.1 years. Of the 69 eyes, 63 (91.3%) had refractive myopia with a mean spherical equivalent refraction of –2.93±1.56 diopters (D) and 6 (8.7%) had refractive hyperopia with a mean spherical equivalent refraction of 1.37±0.31 D. Overall, the mean spherical equivalent refraction of all eyes was –2.56±1.94 D. Ultrasound measurements during suction revealed a decrease in the anterior chamber depth of –0.06±0.36 mm (P<.05) and lens thickness by –0.14±0.45 mm (P<.05) whereas the vitreous body increased 0.25±0.36 mm (P<.05). Although insignificant, a trend toward increasing axial length was noted. No measurements changed over time during the application of vacuum.

CONCLUSIONS: Vacuum by a microkeratome suction ring induced a compression of the anterior chamber and lens with commensurate expansion of the vitreous body. The assessment of vacuum effects during LASIK suggests that measurements of intraocular compartments are more informative than axial length. [J Refract Surg. 2007;23:563-566.]

From the full text:

Quote: Before the application of the excimer laser in LASIK, vacuum is applied to the external surface of the eye by a suction ring in the form of a microkeratome or a femtosecond laser to assist with the creation of a lamellar corneal fl ap. The vacuum may increase the intraocular pressure (IOP) to >90 mmHg in less than 5 seconds, which could induce vitreoretinal changes.

Quote: Although the limiting factor of using A-scan ultrasonography for lens thickness and using mathematical formulations to calculate vitreous body measurements are acknowledged, our study has conclusively shown compression of the anterior structures with elongation of the vitreous body and a trend of increasing axial length (P=.057). We have illustrated the changes to be more complex than previously reported as the anterior and posterior structures respond differently to high vacuum making the axial length measurement less illuminating. Although the clinical significance has yet to be determined, biomechanical deformation by a rapid sequence of compression and decompression associated with LASIK theoretically may increase the risk of vitreoretinal pathology.

J Cataract Refract Surg. 2003 Apr;29(4):825-31.

Viestenz A, Langenbucher A, Hofmann-Rummelt C, Modis L, Viestenz A, Seitz B.

Department of Ophthalmology, University of Erlangen-Nurnberg, Germany. This email address is being protected from spambots. You need JavaScript enabled to view it.

PURPOSE: To evaluate flap dimensions and cut quality with repeated blade use of the automated Summit Krumeich-Barraquer microkeratome (SKBM [LadarVision]).

SETTING: Department of Ophthalmology, University Erlangen-Nuremberg, Erlangen, Germany.

METHODS: The SKBM (160 microm plate, intended flap diameter 9.0 mm) was used to perform a corneal hinged flap in 35 pig cadaver eyes. Seven blades were reused 5 times each. The flap diameter was measured by planimetry, and the thickness was assessed by ultrasonic pachymetry. Scanning electron microscopy (SEM) of blades and stromal beds was performed.

RESULTS: With single use of the blade, the mean central flap thickness was 145 microm +/- 25 (SD). The vertical/horizontal flap diameter was 9.0 +/- 0.03 mm/8.6 +/- 0.03 mm. No thickness gradient was observed from the incision (138 +/- 31 microm) to the flap hinge (130 +/- 30 microm). If the blade was used more than 2 times, the flap was thinner at the incision (157 +/- 34 microm versus 124 +/- 20 microm; P =.003) and the hinge (143 +/- 24 microm versus 122 +/- 31 microm; P =.04), but the central thickness remained unchanged. With multiple use of the blade, SEM analysis showed increasing cut irregularity, more tissue remnants on the blade surface, and a progression in blade irregularities (up to 9.3 microm).

CONCLUSIONS: Reproducible flap size and thickness can be obtained with single use of stainless steel blades in the SKBM. With multiple use, the quality of the blades and the stromal bed deteriorates and the peripheral thickness of the flaps decreases. Thus, single use of blades is recommended.

After LASIK With Microkeratome and Femtosecond Laser Created Flaps

JOURNAL OF REFRACTIVE SURGERY 2007; 23(3):233

By Bryan C. Hainline, MD; Marianne O. Price, PhD; David M. Choi, MD; Francis W. Price, Jr., MD

PURPOSE: To report nine cases of severe central flap inflammation and necrosis after LASIK.

METHODS: A retrospective chart review was conducted on 17,100 LASIK cases performed at two laser centers in Indiana from January 1995 through May 2005. All patients with central lamellar flap necrosis were identified.

RESULTS: Severe central flap inflammation and necrosis occurred in nine eyes of eight patients. Six patients underwent flap creation with a mechanical microkeratome and two with a femtosecond laser. Of eight eyes with >2- month follow-up, one lost at least two lines of best spectacle- corrected visual acuity and two experienced a hyperopic shift in spherical equivalent refraction. Typically, inflammation was minimal the day after surgery, peaked 5 to 10 days later, and subsided by 60 days. Six of nine cases were treated by lifting the flap and irrigating the stromal bed. In each of these cases, few or no inflammatory cells were observed in the stromal bed, the posterior flap surface was intact, and the central portion of the anterior flap had a jelly-like consistency.

CONCLUSIONS: Central lamellar flap necrosis appears to differ from diffuse lamellar keratitis because the location of stromal inflammation is not in the flap interface but rather in the flap anterior stroma. Treatment with corticosteroids seemed to have little effect on outcomes. This is thought to be the first documentation of central lamellar flap necrosis following the use of a femtosecond laser. [J Refract Surg. 2007;23:233-242.]

M.S. Sridhar, Christopher J. Rapuano, and Elisabeth J. Cohen;  Cornea Service, Wills Eye Hospital, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania, USA; *Inquiries to Christopher J. Rapuano, MD, Cornea Service, Wills Eye Hospital, 900 Walnut St, Philadelphia, PA 19107; fax: (215) 928-3854
Manuscript accepted 24 May 2001;

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.

...repeat laser in situ keratomileusis in myopic patients

J Cataract Refract Surg. 2006 Dec;32(12):2080-4.

Das S, Sullivan LJ.

From the Royal Victorian Eye and Ear Hospital (Das, Sullivan) and the Melbourne Excimer Laser Group (Sullivan), East Melbourne, Australia.

PURPOSE: To compare the change in residual stromal thickness and flap thickness between primary laser in situ keratomileusis (LASIK) and repeat LASIK in myopic patients.

SETTING: Melbourne Excimer Laser Group, East Melbourne, Australia.

METHODS: This retrospective nonrandomized comparative trial comprised 46 eyes of 34 patients who had repeat LASIK. The thickness of the residual stromal bed was calculated by subtracting the calculated stromal ablation from pachymetry of the stromal bed after cutting the flap in primary treatment and directly measuring during retreatment. The thickness of the LASIK flap in primary and repeat LASIK was calculated by subtracting the central pachymetry of the stromal bed after creating the flap from pachymetry before cutting and lifting the flap, respectively. The main outcome measures were comparison of the residual stromal bed and flap thickness between the primary treatment and the retreatment.  

RESULTS: The mean thickness of the calculated residual stromal bed after primary treatment was 329.8 mum +/- 40.8 (SD), and the mean measured residual stromal bed at retreatment was 317.3 +/- 42.8 mum. The mean difference in residual stromal bed thickness was 12.5 +/- 13.0 mum (P<.001). Sixteen eyes (34.7%) had a decrease in bed thickness between 11 mum and 20 mum. The mean flap thickness during primary LASIK and repeat LASIK was 145.2 +/- 17.1 mum and 169 +/- 18.3 mum, respectively. The mean interval between primary treatment and retreatment was 7.4 +/- 4.1 months. The mean change in flap thickness was 23.8 +/- 15.2 mum (P<.001). Fifteen eyes (32%) had an increase in flap thickness between 11 mum and 20 mum. There was a negative correlation between refractive error before primary treatment and the difference in flap thickness. No correlation was found between the difference in flap thickness and the interval between the primary treatment and the repeat treatment.

CONCLUSIONS: Intraoperative pachymetry of the stromal bed during retreatment is strongly recommended as the residual stromal bed and flap thickness changes between primary and retreatment. There is a tendency for the measured stromal bed at retreatment to be thinner than the calculated stromal bed and for the flap to be thicker than previously measured.

J Refract Surg. 2006 Nov;22(9):884-9.

Landau D, Levy J, Solomon A, Lifshitz T, Orucov F, Strassman E, Frucht-Pery J.

Cornea and Refractive Surgery Unit, Dept of Ophthalmology, Hadassah University Hospital, P.O.B. 12000, Jerusalem 91120, Israel. This email address is being protected from spambots. You need JavaScript enabled to view it.

PURPOSE: To report our experience treating eye trauma after LASIK refractive surgery.

METHODS: Nine eyes of eight patients (one woman and seven men) were treated for ocular trauma: blunt trauma (n=5), sharp instrument trauma (n=2,) and trauma from inflation of automobile air bags during a traffic accident (n=2). The time from LASIK varied between 3 months and 6 years. All patients were hospitalized as a result of severe decrease in visual acuity and pain.

RESULTS: Seven of nine LASIK flaps had some degree of dislocation and were lifted, irrigated, and repositioned. Two flaps were edematous without dislocation. Intensive topical steroids and antibiotics were used in all patients up to 3 weeks after trauma. Three months after trauma, five eyes regained their pre-trauma visual acuity (between 20/20 and 20/40), and three eyes lost one line of best spectacle-corrected visual acuity.

CONCLUSIONS: Trauma occurring several months or years after LASIK may cause flap injury. Adequate and prompt treatment usually is successful.

Our report, as well as the related literature, indicates that the healing of the flap is incomplete even 6 years after LASIK surgery. The exact mechanism of long-term adhesion remains unclear. In an animal model, Maurice and Monroe20 demonstrated that after creation of a lamellar corneal stromal dissection, the adhesive force of the healed stroma lamellae approximated one-quarter to one-half that of normal. Perez et al21,22 suggested that drying increases stromal-stromal adhesion due to the increased concentration of surface molecules, which have high ionic charge densities and ionic binding. In rabbit corneas, the wound healing reaction after LASIK takes place only at the periphery of the microkeratome wound, leaving the central optical zone clear; similar findings have been described in human eyes after LASIK.

 J Refract Surg. 2006 Apr;22(4):402-4. 

Cheung LM, Papalkar D, Versace P. 

Department of Ophthalmology, Prince of Wales Hospital, Randwick, Australia. 

PURPOSE: To report a case of traumatic flap dehiscence and Enterobacter keratitis 34 months after LASIK. 

METHODS: A 36-year-old man sustained a flap dehiscence following traumatic right eye gouging by a seagull claw. He presented the following day with uncorrected visual acuity (UCVA) in the affected eye of 3/200 and organic foreign body deposits underneath the flap. Systemic and topical antibiotics were administered and urgent surgical debridement and replacement of the LASIK flap was performed. An Enterobacter species was cultured from an intraoperative swab. 

RESULTS: After a prolonged postoperative course, including administration of topical ofloxacin, tobramycin, chloramphenicol, and dexamethasone, UCVA returned to 20/20. 

CONCLUSIONS: Good visual outcome after early debridement and appropriate antibiotics was achieved. Patients should be injury advised to seek prompt ophthalmic consultation after LASIK.

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.

Cohesive Tensile Strength of Human LASIK Wounds With Histologic, Ultrastructural, and Clinical Correlations

Journal of Refractive Surgery Vol. 21 No. 5 September/October 2005

Ingo Schmack, MD; Daniel G. Dawson, MD; Bernard E. McCarey, PhD; George O. Waring III, MD, FACS, FRCOphth; Hans E. Grossniklaus, MD; Henry F. Edelhauser, PhD

SOURCE

PURPOSE: To measure the cohesive tensile strength of human LASIK corneal wounds.

METHODS: Twenty-five human eye bank corneas from 13 donors that had LASIK were cut into 4-mm corneoscleral strips and dissected to expose the interface wound. Using a motorized pulling device, the force required to separate the wound was recorded. Intact and separated specimens were processed for light and electron microscopy. Five normal human eye bank corneas from 5 donors served as controls. A retrospective clinical study was done on 144 eyes that had LASIK flap-lift retreatments, providing clinical correlation.

RESULTS: The mean tensile strength of the central and paracentral LASIK wounds showed minimal change in strength over time after surgery, averaging 2.4% (0.72 ± 0.33 g/mm) of controls (30.06 ± 2.93 g/mm). In contrast, the mean peak tensile strength of the flap wound margin gradually increased over time after surgery, reaching maximum values by 3.5 years when the average was 28.1% (8.46 ± 4.56 g/mm) of controls. Histologic and ultrastructural correlative studies found that the plane of separation always occurred in the lamellar wound, which consisted of a hypocellular primitive stromal scar centrally and paracentrally and a hypercellular fibrotic stromal scar at the flap wound margin. The pathologic correlations demonstrated that the strongest wound margin scars had no epithelial cell ingrowth—the strongest typically being wider or more peripherally located. In contrast, the weakest wound margin scars had epithelial cell ingrowth. The clinical series demonstrated the ability to lift LASIK flaps without complications during retreatments up to 8.4 years after initial surgery, correlating well with the laboratory results.

CONCLUSIONS: The human corneal stroma typically heals after LASIK in a limited and incomplete fashion; this results in a weak, central and paracentral hypocellular primitive stromal scar that averages 2.4% as strong as normal corneal stroma. Conversely, the LASIK flap wound margin heals by producing a 10-fold stronger, peripheral hypercellular fibrotic stromal scar that averages 28.1% as strong as normal corneal stromal, but displays marked variability. [J Refract Surg. 2005;21:433-445.]

 The LASIK flap never heals

WebMDHealth: http://my.webmd.com/content/article/61/68084.htm

Tosi GM, Tilanus MA, Eggink C, Mittica V.

WebMDHealth on flap never healing  

“The LASIK flap never heals… the LASIK flap can be easily dislodged from simple contact with the eye such as a finger poke.”

J Cataract Refract Surg. 2001 May;27(5):781-3.

Traumatic flap displacement and subsequent diffuse lamellar keratitis after laser in situ keratomileusis.

Schwartz GS, Park DH, Schloff S, Lane SS.

Associated Eye Care, Lake Elmo, Minnesota 55042, USA. This email address is being protected from spambots. You need JavaScript enabled to view it.

Late Traumatic Flap Dislocations After LASIK

J Cataract Refract Surg Vol 22, May 2006

http://www.journalofrefractivesurgery.com/showAbst.asp?thing=12869

Excerpts from the full text:

A number of cases of late onset traumatic LASIK flap dislocations have been reported, raising questions about the  strength of the adhesion between the flap and the stromal bed.

In this series, we report three cases of late onset traumatic  LASIK flap displacement and their management. One patient presented 7 years after the initial surgery, which, to our knowledge, is the longest duration reported.

A 23-year-old man with bilateral uncomplicated LASIK 7 years prior presented 2 days after sustaining a left eye injury by another person’s fingernail in a fight.

A 33-year-old woman underwent LASIK and presented after sustaining a broomstick injury 1 year postoperatively.

A 38-year-old woman with a history of uncomplicated bilateral LASIK 2 years before sustained a right eye injury when a folder fell from a shelf.

The creation of a lamellar flap results in a potential plane of weakness in the cornea in which shearing forces can produce flap displacement. Recent  histological and confocal studies have shown a central hypocellular primitive scar in the interface, allowing easy lifting of the flap in trauma.

The fact that this potential plane can be disrupted many years after LASIK (7 years after the initial surgery in patient 1) indicates that corneal integrity is compromised by the surgical procedure and takes a long time, if ever, to restore.

J Cataract Refract Surg. 2005 Mar;31(3):633-5.

Late-onset repetitive traumatic flap folds and partial dehiscence of flap edge after laser in situ keratomileusis.

Miyai T, Miyata K, Nejima R, Shimizu K, Oshima Y, Amano S.

Miyata Eye Hospital, Miyakonojo, Miyazaki, Japan. This email address is being protected from spambots. You need JavaScript enabled to view it.

Excerpt:

A 25-year-old woman had traumatic flap folds and partial dehiscence of the flap edge in the right eye 5 and 30 months after laser in situ keratomileusis. The period from injury to treatment was 4 hours and 9 days, respectively. With the first injury, the flap was lifted and stretched with moistened sponges to clear the folds. With the second injury, the folds were hard so the flap was lifted and sutured to stretch the folds.

 Late Traumatic Dislocation of LASIK Flaps  (1)

Indian J Ophthalmol. 2004 Dec;52(4):327-8. Related Articles, Links

Late dislocation of LASIK flap following fingernail injury.

Srinivasan M, Prasad S, Prajna NV.

Aravind Eye Hospital & Postgraduate Institute of Ophthalmology, Madurai, India.

A case of traumatic flap displacement with a fingernail injury four years after LASIK is reported.

Late traumatic dislocation of LASIK flaps  (2)

J Cataract Refract Surg. 2004 Jan;30(1):253-6. Related Articles, Links

Late traumatic dislocation of laser in situ keratomileusis flaps.

Heickell AG, Vesaluoma MH, Tervo TM, Vannas A, Krootila K.

Helsinki University Eye Hospital, Helsinki, Finland.

Excerpt:

We present 2 patients with late traumatic laser in situ keratomileusis flap dislocation 8 months and 17 months after surgery. One patient had a sharp trauma that caused a partial laceration and the second patient had a blunt trauma that caused a dislocation of the flap. The corneas were examined with slitlamp microscopy, computed corneal topography, and confocal microscopy. One flap was repositioned surgically; the other was treated conservatively with an eye patch.

J Cataract Refract Surg. 2005 Oct;31(10):2016-8. Related Articles, Links

Maldonado MJ, Juberias JR, Pinero DP, Alvarez-Vidal A, Rutzen AR.

From the Department of Ophthalmology (Maldonado, Juberias, Pinero, Alvarez-Vidal), University Clinic, University of Navarra, Pamplona, Spain, and Department of Ophthalmology (Rutzen), University of Maryland, Baltimore, Maryland, USA.

A flap tear occurred during laser in situ keratomileusis (LASIK) retreatment using a flap-lifting technique in 1 eye of 2 patients 4 to 5 months after the primary procedure. In the first case, the tear occurred in a decentered, standard thickness flap (168 mum) in a location close to the corneal limbus and limbal vessels. In the second case, the tear occurred in a well-centered thin flap (116 mum) that involved a peripheral corneal pannus. The false track was identified early, and central extension of the tear was averted. After the flap was successfully dissected, retreatment was performed without further complications. This report suggests that flaps with margins near the limbus or a corneal pannus may be prone to an earlier and stronger healing process at the edge that may lead to a flap tear during LASIK retreatment. This may be of increasing importance because of the trend toward larger flap diameters.

1: J Refract Surg. 2003 Mar-Apr;19(2):113-23.

Flanagan GW, Binder PS.

Gordon Binder Vision Institute, San Diego, CA, USA.

PURPOSE: To determine the factor(s) that influence the dimensions and predictability of the LASIK corneal flap with the Automated Corneal Shaper (ACS) or the Summit Krumeich Barraquer microkeratome (SKBM).

METHODS: We performed a retrospective, comparative interventional case study of 4,428 eyes. Flap dimensions were measured using subtraction ultrasonic pachymetry during LASIK with one of two microkeratomes.

RESULTS: Mean preoperative corneal thickness for all eyes was 555 +/- 35 microm. Corneal curvature and refractive astigmatism were inversely related to preoperative corneal thickness (P<.001). With an attempted flap thickness of 160 microm, the ACS flap thickness averaged 119.8 +/- 22.9 microm; SKBM flaps averaged 160.9 +/- 24.1 microm (P<.001). The coefficient of variation for central pachymetry compared to flap thickness was 6.4% vs. 22.1%. Flap thickness at enhancement was 10 to 17 microm thicker than at primary surgery. An increase in flap thickness was associated with thicker preoperative pachymetry (P<.001) and younger age for both instruments (P<.001) whereas increasing flap thickness was related to flatter preoperative mean keratometry for the ACS (P<.001) and steeper mean keratometry for the SKBM (P=.005). Less preoperative hyperopia or more myopia was related to an increase in flap thickness only for the SKBM (P<.001).

CONCLUSIONS: Flap thickness varies significantly depending on the microkeratome used. Factors that influence flap thickness are primarily corneal thickness, patient age, preoperative keratometry, preoperative refraction including astigmatism, and corneal diameter. By understanding the factors that affect flap thickness, one can select a microkeratome system to allow maximum refractive correction while minimizing the risk of ectasia.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12046880&query_hl=21

J Refract Surg. 2002 May-Jun;18(3 Suppl):S347-51.

Shemesh G, Dotan G, Lipshitz I.

Ophthalmic Health Center, Tel Aviv, Israel.

PURPOSE: To compare the accuracy and consistency of corneal flap thickness in the right and left eye created by three different widely used microkeratomes during consecutive laser in situ keratomileusis (LASIK).

METHODS: Corneal thickness of 132 eyes of 66 patients was measured preoperatively and intraoperatively. Corneal flap thickness was calculated by subtracting the corneal stromal thickness from the total corneal thickness. Three different microkeratomes were used for creating the corneal flap: Chiron Automated Corneal Shaper (ACS), Baush and Lomb Surgical Hansatome, and Nidek MK 2000 microkeratomes. The same surgeon performed all procedures on the right eye first and then on the left eye using the same blade and the same surgical technique.

RESULTS: Mean corneal flap thickness created by the ACS (160-microm depth setting) microkeratome was 128.30 +/- 12.57 microm in the right eye and 122.96 +/- 13.30 microm in the left eye. The Hansatome (160-microm depth plate) microkeratome created a flap of mean 141.16 +/- 20.11 microm in the right eye and 120.95 +/- 26.95 microm in the left eye, and the Nidek MK 2000 (130-microm depth plate) microkeratome created a flap of 127.25 +/- 4.12 microm in the right eye and 127.54 +/- 3.7 microm in the left eye.

CONCLUSION: Corneal flap thickness tended to be considerably thinner than expected on both eyes using the ACS and Hansatome. With the ACS and Hansatome, the difference in corneal flap thickness between the first and second operated eye was statistically significant. With the Nidek MK 2000 microkeratome, there was no statistically significant difference between the first and second operated eye and measurements were close to desired corneal flap thickness. Intraoperative pachymetry is recommended for every LASIK procedure.

Here is a case report of a woman who developed ectasia following LASIK due to inaccurate flap cut.

The surgery was planned with an estimated flap thickness of 150 um.

From the full-text:

"Subjective optical pachymetry at the slitlamp estimated flap thickness to be approximately 200 um."

J Cataract Refract Surg. 2005 Aug

Reversal of laser in situ keratomileusis-induced ectasia with intraocular pressure reduction.

Hiatt JA, Wachler BS, Grant C.

Boxer Wachler Vision Institute, Beverly Hills, California 90210, USA.

A 40 year-old woman had laser in situ keratomileusis for --7.75 --0.75 x 20 in the right eye. Preoperative examinations, including topography, pachymetry, and intraocular pressures (IOPs), were normal, and best spectacle-corrected visual acuity (BSCVA) was 20/20 in each eye. By 4 months postoperatively, the uncorrected visual acuity and BSCVA in the right eye had decreased to 20/40. Corneal topography of that eye was consistent with ectasia. One drop per day of timolol 0.5% (Timoptic XE) was prescribed. Five months postoperatively, the IOP had decreased and BSCVA and topography had improved. At 11 months, BSCVA returned to 20/20 and corneal topography normalized. Topographic difference maps were used to monitor corneal shape changes. In this case, early reduction in IOP completely reversed the ectasia.

The abstract does not reveal that ectasia returned when the patient was taken off pressure-lowering drugs.

http://www.ncbi.nlm.nih.gov/entrez/...t_uids=12502953

Cornea. 2003 Jan;22(1):66-9. Related Articles, Links

Tumbocon JA, Paul R, Slomovic A, Rootman DS.

Department of Ophthalmology, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada.

PURPOSE: To report the occurrence, management, and outcome of late-onset traumatic dehiscence and dislocation of laser in situ keratomileusis (LASIK) flaps.

METHODS: Two interventional case reports of patients with late-onset LASIK corneal flap dislocation after ocular trauma occurring at 7 and 26 months after surgery, respectively.

RESULTS: The flaps were lifted, stretched, and repositioned after irrigation and scraping of the stromal bed and the underside of the flap. A bandage contact lens was placed, and topical antibiotic and corticosteroids were given postoperatively. The dislocated corneal flaps were successfully repositioned in both cases. The patient whose dislocated flap was repositioned 4 hours after the trauma recovered his uncorrected visual acuity (UCVA) of 20/20 1 week after the procedure and had a well-positioned flap with a clear interface. The patient who was managed 48 hours after the injury required repeat flap repositioning at 10 and 24 days after the initial procedure for treatment of persistent folds and striae in the visual axis. His uncorrected visual acuity 2 weeks after the third flap repositioning was 20/40 + 2. Diffuse lamellar keratitis developed in both patients that resolved with the use of topical corticosteroids.

CONCLUSION: Laser in situ keratomileusis corneal flaps are vulnerable to traumatic dehiscence and dislocation, which can occur more than 2 years after the procedure.

J Cataract Refract Surg. 2005 Aug; 31 8 :1664-5.

Nilforoushan MR, Speaker MG, Latkany R.

Laser and Corneal Surgery Associates and New York Eye and Ear Infirmary, New York, New York 10003, USA. This email address is being protected from spambots. You need JavaScript enabled to view it.

Excerpt:

We present a case of late traumatic flap dislocation 47 months after laser in situ keratomileusis (LASIK). This is the latest reported case of traumatic LASIK flap dislocation to date. The patient was examined 5 days after being struck in the face and found to have a flap dislocation.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12498850&query_hl=1

J Cataract Refract Surg. 2002 Dec;28(12):2146-52.

Charman WN.

Department of Optometry and Neuroscience, UMIST, PO Box 88, Manchester M60 1QD, United Kingdom. This email address is being protected from spambots. You need JavaScript enabled to view it.

PURPOSE: To calculate theoretically the magnitude of the excess area between the lower surface of the flap and the underlying ablated stroma.

METHODS: On the initial assumptions of a nonextensible flap and a spherical cornea, flap and ablated stromal areas were determined as a function of myopic correction in the range of 0 to -12 diopters (D) for typical values of corneal radius (7.8 mm) and flap thickness (160 microm), together with a range of ablation zone diameters (4.0 mm, 6.0 mm, 8.0 mm, and 10.0 mm).

RESULTS: Excess flap area increases with the magnitude of the refractive correction and the diameter of the ablated zone. For a -6.0 D correction and an 8.0 mm ablation zone, the excess area is nominally about 1.0 mm(2), giving a potential overlap of the flap at the edge opposite the hinge of about 100 microm.

CONCLUSIONS; Excess flap area may cause striae because of wrinkling. Although a nonextensible flap is assumed in the model, any stretching or contraction due to cutting the flap will be independent of the refractive correction. Hence, a mismatch in areas must still occur. This geometric effect may have clinical consequences in optical aberration, refractive regression, or impaired wound healing.

Am J Ophthalmol. 2005 Jun;139(6):1137-9.  

McLeod SD, Mather R, Hwang DG, Margolis TP.  Francis I. Proctor Foundation and the Department of Ophthalmology, University of California-San Francisco, 10 Kirkham Street, San Francisco, CA 94143, USA. This email address is being protected from spambots. You need JavaScript enabled to view it.  

PURPOSE: To report two cases of corneal pathology associated with anterior uveitis after laser in situ keratomileusis (LASIK).  

DESIGN: Observational case report.  

METHODS: A 47-year-old man and a 50-year-old woman who experienced vision loss and corneal changes associated with acute anterior uveitis after LASIK were examined.  

RESULTS: The 47-year-old man, who had undergone LASIK for low myopia developed an interlamellar fluid pocket at the level of the flap interface, whereas the 50-year-old woman, who underwent LASIK for hyperopia, developed marked flap edema without interface fluid collection.  

CONCLUSIONS: These two cases demonstrated acute corneal fluid accumulation associated with episodes of acute anterior uveitis in eyes that had undergone LASIK. Uveitis should be considered a risk factor for vision threatening corneal complications after LASIK.

J Cataract Refract Surg. 2005 May;31(5):922-9.  

Loh RS, Hardten DR.  Minnesota Eye Consultants, Minneapolis, Minnesota, USA.  

PURPOSE: To report persistent unilateral flap edema following laser in situ keratomileusis (LASIK) in patients with asymmetrical central corneal thickness.  

SETTING: Minnesota Eye Consultants, Minneapolis, Minnesota.  

METHODS: Retrospective, noncomparative interventional case series.  

RESULTS: We examined 6 eyes of 3 patients with asymmetrical preoperative pachymetry who developed persistent unilateral flap edema after uneventful myopic LASIK in the eye with thicker preoperative pachymetry. All cases had asymmetrical preoperative pachymetry with flap edema developing in the eye with higher preoperative mean central corneal thickness (CCT) values, preoperative mean CCT subject eye 622 microm (range 556-664 microm) versus fellow eye 583 microm (range 510-621 microm). There was no associated ocular inflammation or rise in intraocular pressure. Significant flap edema resolved on a combination treatment of topical steroid and hypertonic saline.  

CONCLUSIONS: Laser in situ keratomileusis can cause temporary endothelial cell dysfunction or stress, which manifests as temporary flap edema and subclinical corneal thickening. The edema appears to be limited to the actual flap and there was no loss of epithelial integrity in these eyes and no clinically noticeable interface fluid. This new clinical entity appears to occur in patients with asymmetrical preoperative corneal pachymetry and is associated with postoperative specular microscopy abnormalities. In cases with unexplained asymmetrical corneal thickness, preoperative evaluation should include specular microscopy to evaluate for risk features that may increase the chances of a slower postoperative recovery.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=14555904&query_hl=1&itool=pubmed_docsum

Eye Contact Lens. 2003 Oct;29(4):252-4.

Biser SA, Bloom AH, Donnenfeld ED, Perry HD, Solomon R, Doshi S.

Ophthalmic Consultants of Long Island, Rockville Centre, NY, USA.

PURPOSE: To report a case of bilateral flap folds after a laser-assisted in situ keratomileusis (LASIK) procedure in which the flap was created by the femtosecond laser.

METHODS: Retrospective chart review.

RESULTS: A 43-year-old white woman underwent bilateral simultaneous LASIK. The corneal flap was created with the femtosecond laser. Postoperatively, the patient noted significantly decreased visual acuity, glare, and haloes. She was diagnosed with corneal flap striae, which were treated unsuccessfully with a lifting and stretching procedure, but responded to subsequent bilateral flap suturing.

CONCLUSIONS: Despite the increased accuracy in flap creation with the femtosecond laser, large flap folds may develop.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15808256&query_hl=19

Ophthalmology. 2005 Apr;112(4):645-9.

Effect of microkeratome suction during LASIK on ocular structures.

Mirshahi A, Kohnen T.

Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany.

PURPOSE: To study the effect of microkeratome suction on ocular structures during LASIK.

DESIGN: Observational, prospective case series.

PARTICIPANTS: Twenty-one eyes of 11 patients with myopia or astigmatic myopia (8 females, 3 males) were included. The mean patient age was 36.3 years (median, 37 years; range, 24-48 years), and the mean spherical equivalent was -5.03 diopters (D) (median, -4.63 D; range, -2.38 to -8.38 D).

METHODS: We performed preoperative and intraoperative A-scan ultrasonography during application of suction using the Hansatome microkeratome (Bausch & Lomb Surgical, Munich, Germany) to create corneal flaps during LASIK. We also performed preoperative and postoperative B-scan ultrasonography of the posterior ocular segment with special attention to the presence and size of posterior vitreous detachment (PVD).

MAIN OUTCOME MEASURES: We measured changes in the axial length, anterior chamber depth, lens thickness, and vitreous distance (distance from the posterior lens capsule to the posterior pole) during application of the microkeratome suction ring and recorded new occurrences of or increases in the size of the PVD after surgery.

RESULTS: The lens thickness decreased (mean change, -0.20 mm; P = 0.001; 95% confidence interval [CI], -0.11 to -0.30) in 18 eyes during application of the suction ring. The vitreous distance increased (mean change, 0.20 mm; P = 0.004; 95% CI, 0.08-0.32) in 16 eyes. No statistically significant changes were found in the anterior chamber depth (P = 0.75) or axial length (P = 0.51). After surgery, 3 of 14 eyes (21.4%) experienced PVD that did not have echographic signs of PVD before surgery. Of 7 eyes with preoperative PVD, the PVD enlarged in 1 eye (14.3%).

CONCLUSIONS: During application of microkeratome suction, the lens thickness decreases, whereas the vitreous distance increases, suggesting anterior traction on the posterior segment. The relationship between the observed PVD and LASIK merits further investigation.