A 60 kHz IntraLase Femtosecond Laser Creates a Smoother LASIK Stromal Bed Surface Compared to a Zyoptix XP Mechanical Microkeratome in Human Donor Eyes

PURPOSE

To compare the stromal surfaces created by the latest mechanical microkeratome and femtosecond, laser technologies.

METHODS

Laser in situ keratomileusis (LASIK) flaps were created in six fresh human globes unsuitable for transplantation. The eyes were placed in one of two groups of three globes each. One group had LASIK flaps created with a Zyoptix XP microkeratome using a 120-microm head and a fresh blade for each eye. Another group had flaps created at an attempted 100-microm thickness using the 60 kHz IntraLase femtosecond laser. Immediately following flap creation, the stromal beds were prepared for scanning electron microscopy (SEM). Qualitative roughness of the SEM images was graded by masked observers. Quantitative roughness of the SEM images was assessed using computerized software designed for roughness analysis. Mann-Whitney non-parametric statistical analysis was performed to compare groups.

RESULTS

A statistically significant difference was noted in bed smoothness as measured by qualitative roughness and quantitative roughness scores. The IntraLase samples showed smoother stromal beds compared to the Zyoptix group (qualitative roughness = 2.0 +/- 0.7 pm vs 3.6 +/- 1.6 pm, P = .03; quantitative roughness = 20238 +/- 1869 pm vs 26368 +/- 8133 pm, P = .03).

CONCLUSIONS

The 60 kHz IntraLase femtosecond laser and the Zyoptix XP 120-microm head using a new blade produced smooth, good quality, compact stromal beds qualitatively and quantitatively. Because the 60 kHz femtosecond laser permits a tight spot/line separation using low energy, it creates a smoother corneal stromal bed compared to previous femtosecond laser engines.

Evaluation of Four Microkeratome Models: Quality and Reproducibility of Cut Edge and Cut Surface as Determined by Scanning Electron Microscopy

PURPOSE

To compare the quality and reproducibility of cuts produced by four automatic microkeratomes: Amadeus, Hansatome, Summit-Krumeich-Barraquer (SKBM), and Supratome. For the adjustable models (Amadeus and SKBM), the effects of oscillation frequency and blade feed rate were determined.

METHODS

Eight cuts (flap thickness 160 to 180 microm) were made with each microkeratome at each parameter setting and examined using a scanning electron microscope. Quality of the cut surface was scored for each flap according to four criteria, and results were averaged to give a maximum possible score of 64. Quality of the cut edges was scored from 1 (blurred indistinct edge) to 3 (sharp and clearly visible edge).

RESULTS

The four microkeratomes performed similarly on overall quality of the cut surface (range: 78% to 88% of theoretical maximum). The Hansatome scored highest (88%), followed by SKBM (86%; 1.0 mm/s blade feed and 7000 rpm oscillation), Amadeus (84%; 2.5 mm/s, 8000 rpm), Supratome (84%; 16.6 mm/s, 12,500 rpm), Amadeus (81%; 3.0 mm/s and 13,000 rpm), and SKBM (78%; 1.5 mm/s, 14,000 rpm). Performance differences were clearer for cut edge quality. The Amadeus produced cuts of the highest quality in 62.5% of cases (at both settings), compared with only 12.5% of cases with the Hansatome, 25% of cases with the Supratome and SKMB (1.0 mm/s, 7000 rpm), and in no cases with the SKBM at 1.5 mm/s and 14,000 rpm.

CONCLUSIONS

Overall, high frequency with low blade feed rate is desirable for reproducible sharp edges and cut area quality. However, at very high frequencies (e.g., 14,000 rpm with the SKBM) tissue is displaced, producing an uneven cut area. Oscillation/feed quotients of 2000 to 4000 (rpm/mm x s) are a good compromise. Sharp edges are believed to reduce the risk of comeal erosion, introduction of epithelial cells into the interfacial region, and scarring during wound healing.

Flap Quality in Single Versus Multiple Use of the Same Blade in the Flapmaker Microkeratome

PURPOSE

We evaluated experimentally the variability of cut thickness, flap diameter, and cut quality produced by the Flapmaker corneal microkeratome (IOLTech), with single and repeated use of the same cutting blade.

METHODS

Keratectomy was performed with twelve cutting heads (8.5-mm diameter, 160-microm cutting depth) on 47 corneas and with six cutting heads (8.0-mm diameter, 180-microm cutting depth) on 18 freshly enucleated swine eyes in a repeated manner. Ultrasonic pachymetry was determined at the initial, central, and final microkeratome pass zones, first before the flap was created and subsequently after the flap was reflected. Flap diameter was measured by planimetry. After the procedure stromal portions were submitted for scanning electron microscopy.

RESULTS

On the first blade use, mean central flap thickness was 145 +/- 32 microm and mean vertical flap diameter was 8.4 +/- 0.26 mm with the 8.5-mm blades. With the 8.0-mm blades, mean central flap thickness was 155 +/- 23 microm and mean vertical flap diameter was 8.0 +/- 0.27 mm. Scanning electron microscopy disclosed smooth cut surfaces when new blades were used, but with repeated blade use, increasingly prominent stromal bed folds were observed.

CONCLUSIONS

The evaluated blades produced reproducible flap size and thickness and good cut quality with single use, but after the first use, cut quality markedly deteriorated. Repeated use of Flapmaker cutting blades is not recommended.

Evaluation of corneal flap dimensions and cut quality using the SKBM automated microkeratome

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.

Changes of posterior corneal astigmatism and tilt after myopic laser in situ keratomileusis

PURPOSE

The purpose of this study was to assess the changes of posterior corneal astigmatism and tilt after laser in situ keratomileusis (LASIK) and to correlate these changes with the amount of correction and the residual stromal bed thickness.

METHODS

This prospective nonrandomized (self-controlled) comparative trial included 57 eyes from 14 females and 15 males, whose mean age (+/- standard deviation [SD]) at the time of surgery was 33 +/- 9 years (range, 19-53), with a spherical equivalent (SEQ) of -1.00 to -15.50 (mean, -5.07 +/- 2.81) diopters (D). All LASIK procedures were accomplished with the Keratom II Coherent-Schwind excimer laser and the Moria Model One microkeratome (150-microm head). Subjective refractometry, Orbscan slit-scanning corneal topography analysis, and pachymetry were performed before and 3 months after LASIK for myopia (n= 35; -1.00 to -15.50 D [mean, -4.75 +/- 3.07]) or myopic astigmatism (n= 22; sphere, 0.00 to -9.75 D [mean, -4.75 +/- 2.36]; cylinder, -0.75 to -3.50 D [-1.68 +/- 0.86]). Intended ablation depth ranged from 12 to 108 (mean, 48 +/- 22) microm. Topographic raw data were decomposed into a set of Zernike polynomials as published in detail previously, and parameters for detection of asymmetric mechanical deformation of the cornea were derived. Posterior corneal astigmatism and tilt before and after LASIK were compared, and changes in these variables were correlated with the SEQ change (DeltaSEQ) and the residual corneal bed thickness (RBT).

RESULTS

The RBT after LASIK ranged from 186 to 373 (mean, 280 +/- 42) microm. Overall, astigmatism (0.19 +/- 0.07 D/0.22 +/- 0.13 D; p= 0.80) and tilt (3.58 +/- 0.35 degrees /3.65 +/- 0.48 degrees; p= 0.61) did not change significantly by 3 months after LASIK. In eyes with RBT < or =250 microm, the average change in astigmatism (0.05 +/- 0.11 versus 0.01 +/- 0.13 D; p= 0.46) and tilt (0.21 +/- 0.45 degrees versus 0.04 +/- 0.55 degrees; p= 0.30) was not greater than in eyes with RBT > 250 microm. Change in astigmatism (p= 0.19) and tilt (p= 0.56) did not correlate with the RBT during LASIK.

CONCLUSIONS

Zernike decomposition of topographic height data discloses that no significant asymmetric mechanical deformation of the posterior corneal curvature occurs after myopic LASIK. Further studies with long-term follow-up are needed to clarify whether this symmetry of the posterior corneal surface can indeed be preserved over time after LASIK if the RBT is < 250 microm.

Scanning electron microscopic evaluation of the surface characteristics of 4 microkeratome systems in human corneas

PURPOSE

To evaluate the surface characteristics of keratectomy specimens created with 4 microkeratomes by scanning electron microscopy (SEM).

SETTING

Two university institutions.

METHODS

Keratectomies were performed in 10 fresh, unfrozen human eyes with 1 of 4 microkeratomes: the Draeger rotary microkeratome (Storz Instruments), the Universalkeratome (Phoenix), the Automated Corneal Shaper (Bausch & Lomb), or the Hansatome (Bausch & Lomb). The beds and edges of the keratectomy specimens were then examined by SEM. Standardized photographs were taken, and the surface and cut-edge characteristics of the keratectomies were compared.

RESULTS

Irregularities were noted in the cut edges of Bowman's membrane and the surface of the keratectomy beds with all instruments. The irregularities were most prominent in corneas cut with the Draeger instrument and least prominent in those cut with the Universalkeratome. The serrations in Bowman's membrane and the irregularities in the keratectomy bed appeared to be related to the blade movement in oscillating blade instruments.

CONCLUSIONS

All 4 microkeratomes caused some degree of surface irregularity. The Draeger microkeratome, which uses a continuously rotating blade, resulted in the greatest number of Bowman's membrane serrations and irregularities in the keratectomy bed. The tissue irregularities may be related to the development of pressure ridges ahead of the blade. In instruments that use an oscillating blade, chatter marks appear to be related to the reciprocating movement of the blade as it travels across the corneal stroma.

Posterior corneal curvature changes after myopic laser in situ keratomileusis

OBJECTIVE

To assess the posterior corneal power and asphericity changes after myopic laser in situ keratomileusis (LASIK) and to correlate these changes with the amount of correction and the residual stromal bed thickness.

DESIGN

Prospective nonrandomized (self-controlled) comparative study.

PARTICIPANTS

Fifty-seven eyes of 14 women and 15 men, mean age at the time of surgery 33 +/- 9 (range, 19-53) years with a spherical equivalent (SEQ) of -1.00 to -15.50 (mean, -5.07 +/- 2.81) diopters (DI).

INTERVENTION

All procedures were performed with the Keratom II Coherent-Schwind excimer laser and and the Moria Model One microkeratome (150-microm head). Subjective refractometry, Orbscan slit scanning corneal topography analysis and pachymetry were performed before and 3 months after LASIK for myopia (n=35, -1.00 to -15.50 D, mean -4.75 +/- -3.07 D) or myopic astigmatism (n=22, sphere 0.00 to -9.75 D, mean -4.75 +/- 2.36 D; cylinder -0.75 to -3.50 D, mean -1.68 +/- 0.86 D). Intended ablation depth ranged from 12 to 108 (mean, 48 +/- 22) microm. Topographic raw data were decomposed into a set of Zernike polynomials as published in detail previously, and parameters potentially indicative for detection of a "mild keratectasia" were derived.

MAIN OUTCOME MEASURES

Posterior central corneal power and asphericity before and after LASIK were compared, and changes of these variables were correlated with the SEQ change (deltaSEQ)and the residual corneal bed thickness RBT).

RESULTS

The mean RBT after LASIK was 280 +/- 42 microm. Overall, change of posterior power (-6.28 +/- 0.22 D/ -6.39 +/- 0.23 D, P=0.02) was statistically significant and change of asphericity (0.98 +/-0.07/1.14 +/- -.20, P<0.0001) was highly significant. In eyes with RBT < or =250 microm, the average change of posterior central power (-0.20 +/- 0.10 D vs. -0.08 +/- 0.18 D) was significantly greater than in eyes with RBT >250 microm (P=0.003). The change of posterior corneal power correlated significantly with deltaSEQ (P=0.004) and the RBT (P=0.002).

CONCLUSIONS

Increased negative keratometric diopters and oblate asphericity of the posterior corneal curvature suggest that mild "keratectesia" of the cornea may be common early after LASIK. Further stuudies with longer follow-up are required to clarify whether this biomechanical deformation is progressive and whether a residual bed thickness of >250 microm can completely prevent it.

Laser in situ Keratomileusis Results of DOS and Windows Software Versions for the Nidek EC-5000 Excimer Laser Using the Same Nomogram

PURPOSE

To compare the results of laser in situ keratomileusis (LASIK) correction for myopia and myopic astigmatism between the previous DOS software version and the Windows software version for the Nidek EC-5000 excimer laser, using the same nomogram.

METHODS

This retrospective review included 2021 eyes (980 patients) after LASIK using the Nidek EC-5000 excimer laser. Of these, 1,632 eyes were corrected with the DOS software version and the other 389 eyes were corrected with the Windows software version of the laser. Both groups were treated with the same surgical nomogram. Minimum follow-up time was 6 months. Patients were classified into range of myopia: low, moderate, and high.

RESULTS

Postoperative uncorrected visual acuity was not statistically significantly different between the two groups in any range of refractive error. There was no loss of best spectacle-corrected visual acuity for any patient. Uncorrected visual acuity equal to or better than 20/40 was achieved in 96.3% of eyes in the Windows version group and 94.9% in the DOS version.

CONCLUSION

Results for the correction of myopia or myopic astigmatism were similar using the Nidek EC-5000 excimer laser with either the DOS software version or Windows software version, with the same surgical nomogram.

Cut Edges and Surface Characteristics Produced by Different Microkeratomes

PURPOSE

To determine the cutting characteristics of seven different microkeratomes and to compare the cut edges and surface characteristics of the corneas with respect to different keratome parameters, ie, blade oscillation frequencies and keratome speed.

METHODS

Lamellar keratectomies were performed using each microkeratome on eight freshly enucleated porcine corneas. The freshly cut corneal bed was then examined using scanning electron microscopy. A scoring system was used to evaluate the serration of the cut edge and the regularity of the corneal wound bed.

RESULTS

Serrated cut edges were produced by the Microtech microkeratome, the Automatic Corneal Shaper, the Draeger rotor keratome, and the Schwind microkeratome. The other tested cutting devices generally yielded a smooth cut edge. Smooth and regular wound surfaces were obtained with the Schwind microkeratome, the Automatic Corneal Shaper, the Microtech microkeratome, and the MKM set. The specimens cut with the Schwind microkeratome showed particularly regular surface characteristics.

CONCLUSION

The relationship between keratome propulsion speed, blade oscillation frequency, and blade material appears crucial for the quality of the microkeratome cut. Our results favor a low advancement/oscillation ratio among automated microkeratomes.

Optical coherence tomography evaluation of the corneal cap and stromal bed features after laser in situ keratomileusis for high myopia and astigmatism

OBJECTIVE

To study the corneal microstructure by optical coherence tomography (OCT) after laser in situ keratomileusis (LASIK) for high myopia with and without astigmatism.

DESIGN

Nonrandomized self-controlled comparative trial.

PARTICIPANTS

Sixty-three consecutive LASIK eyes with spherical equivalent refraction between -6.0 and -17.0 diopters (D) and astigmatism between 0.0 and -5.0 D were prospectively recruited for examination.

INTERVENTION

LASIK was performed with the Chiron Hansatome microkeratome (160-microm fixed plate) and Summit Apex Plus excimer laser using a 5.5/6.0/6.5-mm multizone pattern. Proper preoperative calculations were performed to ensure stromal beds thicker than 250 microm.

MAIN OUTCOME MEASURES

OCT imaging and measurement of corneal thickness was performed preoperatively. In addition, corneal cap and stromal bed thickness measurements were performed 1 day, 1 month, and 3 months postoperatively.

RESULTS

The average central corneal pachymetry was 538.9 +/- 26.2 microm preoperatively. Mean corneal cap thickness measured 124.8 +/- 18.5 microm 1-day postoperatively. Mean stromal bed thickness was 295.2 +/- 37.1 microm on the first postoperative day. Compared with the 1-day postoperative examination, the average stromal bed thickness increased significantly by 5.9 microm (P = 0.001) and 7.2 microm (P = 0.001) at the 1-month and 3-month postoperative examinations, respectively. Mean difference between actual (118.7 +/- 27.8 microm) and predicted (104.1 +/- 20.8 microm) central ablation depths was 14.6 +/- 16.7 microm (P = 0.0001). A weak but statistically significant positive association was found between preoperative refraction and the difference between expected and real ablation depth values (R = 0.26; P = 0.042). Posterior stromal beds were more than 250-microm thick in 58 eyes (89.9%) 1 day postoperatively. This safety requirement improved at the 1-month postoperative examination, when the partial regression accounted for slightly thicker stromal beds and only two cases (3.2%) exhibited posterior stromal tissue thinner than 250 microm. These two cases were seen only for corrections exceeding 12 D (P = 0.04).

CONCLUSIONS

OCT appears to be a useful tool for the evaluation of both the qualitative and quantitative anatomic outcome of LASIK. Corrections of higher degrees of ametropia run a higher risk of producing a thinner than expected central cornea. Particularly, corrections greater than 12 D may lead eventually to stromal beds thinner than 250 microm, despite proper preoperative calculations. Because corneal flaps are usually thinner than expected with the microkeratome used herein, adequate posterior corneal stroma is preserved in most instances.

Experimental evaluation of two current-generation automated microkeratomes: the Hansatome and the Supratome

PURPOSE

To compare flap dimensions, cut quality, and blade deterioration after reuse in an experimental setting using two current-generation microkeratomes for laser-assisted in situ keratomileusis.

METHODS

Two pivoting-head principle microkeratomes, the Hansatome and the Supratome, were used to perform a corneal flap in 50 freshly enucleated pig cadaver eyes, with an intended thickness of 160 microm. Provided stainless steel blades were used from one to five times. Flap diameter was measured by planimetry and thickness calculated using ultrasonic pachymetry at three different locations. Scanning electron microscopy of stromal beds and blades' cutting edges were performed to assess the cut and blade deterioration after repeated use.

RESULTS

Mean flap central thickness (Hansatome/Supratome) was 151 microm (SD 18)/192 microm (SD 32). Progressive thinning/thickening of the flap was observed in the direction toward the hinge (P = .003/P = .021). Mean vertical flap diameters of 8.9 mm (SD 0.3)/8.0 mm (SD 0.4) differed significantly (P = .001). No correlation was found between thickness and diameter (r = 0.03, P = .935/r = 0.12, P = .603). At scanning electron microscopy, smooth cuts were observed with both keratomes using a new blade. Periodical chatter lines at keratectomy edge were present and were more pronounced after blade reuse. Cut quality, blade deterioration, and small tissue remnants on the blade surface were noted with repeated blade use, especially using the Supratome.

CONCLUSIONS

Local flap thickness and flap diameter variations are inherent to the instrument used. Comparable cut-surface quality can be obtained with new blades. Although cut and blade deterioration appears to be minor after two reuses, the presence of tissue remnants on the blade surface still limits its reuse.

Evaluation of Corneal Flap Dimensions and Cut Quality Using the Automated Corneal Shaper Microkeratome

PURPOSE

To evaluate flap dimensions and cut deterioration with repeated blade use in an automated microkeratome.

METHODS

The Automated Corneal Shaper (Chiron-Adatomed, Munich, Germany), 160-microm plate attached, was used to make a corneal flap in 90 pig cadaver eyes, reusing blades up to five times. Flap diameter was measured by planimetry and thickness was calculated by ultrasound pachymetry. Scanning electron microscopy of stromal beds and blade cutting edges was performed to assess cut deterioration after repeated blade use.

RESULTS

Mean flap central thickness was 125 +/- 32 microm. Mean vertical flap diameter was 7.6 +/- 0.4 mm. No correlation was found between thickness and diameter (r = 0.15, P = .45). Progressive thinning of the flap was observed in the direction of the flap hinge. Smooth cuts (using new blades) with periodic chatter lines at the keratectomy edge and in the stromal bed were observed with scanning electron microscopy. Increasing tissue remnants on the stromal bed and decreasing cut quality occurred with repeated blade use. Blades showed larger tissue remnants, nicks, and even folds on the cutting edge proportional to the number of times blades were used.

CONCLUSION

Satisfactory cut quality and reproducibility were obtained after a single use of stainless steel blades in the Automated Corneal Shaper microkeratome. Cut quality was degraded dramatically by repeated use of blades.

Analysis of corneal topography after automated lamellar keratoplasty

PURPOSE

The purpose of the study is to evaluate the effects of myopic automated lamellar keratoplasty (ALK) on corneal topography.

METHODS

The authors performed a retrospective study of computer-assisted topographic maps obtained before surgery and at the last follow-up visit of 9 patients (13 eyes) who underwent ALK without enhancement to correct moderate-to-high myopia during a 12-month period.

RESULTS

Follow-up ranged from 3.5 to 13 months (mean, 5.8; standard deviation, 3.1). The mean manifest spherical equivalent changed from -10.5 +/- 2.2 diopters (D) before surgery to -1.1 +/- 1.8 D at the last follow-up visit. Mean simulated keratometry (Sim K) decreased from 45.6 +/- 1.9 D to 38.9 +/- 2.7 D. Mean corneal astigmatism increased from 1.3 +/- 0.8 D to 2.1 +/- 0.9 D. The mean surgically induced cylinder vector (calculated by vector analysis) was 1.1 +/- 0.6 D. Mean surface regularity index (SRI) and surface asymmetry index (SAI) increased from 0.37 +/- 0.38 and 0.32 +/- 0.43 before surgery to 1.00 +/- 0.32 (P < 0.001) and 0.75 +/- 0.36 (P = 0.01), respectively, at the last visit. A positive correlation was observed between the decrease in mean Sim K and the increase in manifest spherical equivalent (reduction of myopia) (r = 0.77, P = 0.002), increase in SRI (r = 0.73, P = 0.005), and increase in SAI (r = 0.58, P = 0.04). The change in manifest spherical equivalent was significantly less than the change in Slm K (P < 0.001).

CONCLUSIONS

Myopic ALK significantly flattens the cornea and reduces myopia. However, it induces corneal astigmatism and decreases corneal surface regularity and symmetry. The degree of myopic correction, as well as the surgically induced corneal surface irregularity and asymmetry, is positively correlated with the amount of corneal flattering derived from the surgical procedure.

Keratomileusis in situ for high myopia

PURPOSE

To examine the safety and efficacy of myopic keratomileusis in situ (automated lamellar keratoplasty) using an automated microkeratome.

SETTING

Jules Stein Eye Institute and the Department of Ophthalmology, UCLA School of Medicine, Los Angeles, California.

METHODS

A retrospective study was done on 135 consecutive eyes of 91 patients who had keratomileusis in situ for myopia by one surgeon between October 4, 1993, and February 23, 1995. Mean preoperative myopia was 8.30 +/- 2.50 diopters (D) (range 4.50 to 20.50). Follow-up ranged from 1 (108 eyes) to 6 months (52 eyes). No eye had enhancement surgery before 3 months; eyes were dropped from the study at the time of enhancement.

RESULTS

Three months after myopic keratomileusis in situ, the mean difference between attempted and achieved correction was an undercorrection of 0.90 +/- 1.50 D; 32 of 83 eyes were within 1.00 D of attempted correction. Forty eyes were undercorrected by more than 1.00 D, and 11 were overcorrected by more than 1.00 D. Uncorrected visual acuity improved to 20/40 or better in 42 of 83 eyes at 3 months. Best spectacle-corrected visual acuity (BSCVA) declined by two or more lines in 8 of 83 eyes at 3 months and 1 of 52 eyes at 6 months. In eyes with 6 months of follow-up, a mean myopic shift of 0.40 D occurred between 3 and 6 months. Two eyes had clinically significant ingrowth into the interface. The variability in outcome (standard deviation in achieved less attempted correction) at 3 months was 1.70 D in the first 45 cases, 1.20 D in the second 45 cases, and 1.10 D in the last 45 cases.

CONCLUSION

Myopic keratomileusis in situ is relatively effective and safe for the correction of high myopia; however, a mild loss of BSCVA is not uncommon in the early postoperative period. Surgeon experience may be important for refractive accuracy.

Automated keratomileusis in situ: clinical study of 142 eyes

PURPOSE

To compare a modified automated lamellar keratoplasty (ALK) technique that uses two blades with the original technique, which uses one blade.

SETTING

Buzard Eye Institute, Las Vegas, Nevada.

METHODS

This study comprised 142 eyes of 85 patients who had ALK: 107 using the original one-blade technique (Group 1) and 35 eyes using the modified two-blade technique (Group 2). Mean follow-up was 11 months in Group 1 and 3 months in Group 2.

RESULTS

Mean preoperative spherical equivalent was -8.93 diopters (D) +/- 2.80 (SD) in Group 1 and -8.33 +/- 2.80 D in Group 2. No patient had worse than 20/80 best corrected visual acuity preoperatively. Mean spherical equivalent at 1 month was -2.06 +/- 2.00 D in Group 1 and -0.79 +/- 1.20 D in Group 2 (P < .05). Mean postoperative spherical equivalent at last follow-up was -0.43 +/- 0.90 and -0.65 +/- 1.10 D, respectively. At last follow-up, 104 eyes (97%) in Group 1 and 34 (97%) in Group 2 had a spherical equivalent between +1.00 and -3.00 D, and 90 eyes (84%) in Group 1 and 27 (77%) in Group 2 had 20/40 uncorrected visual acuity. Seven eyes (7%) in Group 1 and 1 (3%) in Group 2 lost two or more lines of best corrected visual acuity at last follow-up. Three months after ALK (for equal comparison), 25 eyes (23%) in Group 1 and 3 (8%) in Group 2 required radial keratotomy; 20 (19%) and 2 (6%), respectively, needed ALK revision; and 45 eyes (42%) and 17 (47%) needed astigmatic keratotomy.

CONCLUSIONS

The results suggest that ALK is capable of impressive myopic corrections across a broad range of refractive error. The procedure is not accurate enough with a single microkeratome pass and requires enhancement procedures including recuts of the bed with the microkeratome and astigmatic and radial keratotomies. Using two blades to achieve an even cut gives better spherical equivalent and best corrected visual acuity results and lower enhancement rates.

Picosecond Laser In Situ Keratomileusis with a 1053-nm Nd:YLF Laser

BACKGROUND

Excimer laser in situ keratomileusis requires a microkeratome to generate an anterior corneal flap, plus an excimer laser to ablate the underlying stromal tissue. In this paper we introduce the concepts of laser flap formation and in situ keratomileusis using a picosecond laser.

METHODS

A neodymium-doped yttrium-lithium-fluoride (Nd:YLF) laser with a plano-plano quartz applanation lens was used to generate various patterns of intrastromal photodisruption in human donor eyes to fashion anterior corneal flaps and generate intrastromal lenticules.

RESULTS

Smooth intrastromal dissections, 6 mm in diameter, were generated 160 microns below the corneal surface when the laser delivered pulses at 1 kHz with energies of either 40 microJ/pulse or 60 microJ/pulse, placed 20 microns apart in an expanding spiral. This enabled us to fashion anterior corneal flaps. The ease of the surgery and quality of the dissection corresponded well, and it was evident that both deteriorated noticeably when the laser pulses were separated by 25 microns or 30 microns, regardless of pulse energy. Using 40 microJ laser pulses placed 20 microns apart we also created a 5-mm diameter, 320 microns thick (130 microns-450 microns deep) stromal lenticule below a corneal flap that was easily extracted when the flap was raised.

CONCLUSIONS

Anterior corneal flaps were easily fashioned using a Nd:YLF laser. Picosecond laser in situ keratomileusis with a Nd:YLF laser could offer a favorable alternative to combined microkeratome/excimer laser in situ keratomileusis.

Automated In situ Keratomileusis for Myopia

BACKGROUND

In situ keratomileusis is a rapidly changing refractive corneal surgical procedure for the correction of myopia. We report here the results of a retrospective study of in situ keratomileusis with the refractive cut made with a microkeratome. The technique represents an intermediate stage of development that used a sutured corneal disc, an early automated microkeratome, and no reoperations for residual refractive error.

METHODS

We carried out a retrospective chart review of the first 107 consecutive eyes (73 patients) that received in situ keratomileusis with an automated microkeratome (Ruiz corneal shaper) at the El Maghraby Hospital in Jeddah, Saudi Arabia between November, 1991 and February, 1993. Sixty-three eyes (59%) were followed for a mean of 1 year. Manifest refraction measured by an ophthalmologist or optometrist was the major response variable. Surgery followed the Ruiz nomogram, which specified an anterior corneal disc approximately 7.2 mm in diameter and 160 microns in thickness and a plano in situ refractive cut a mean of 4.2 mm in diameter and 93 microns in thickness.

RESULTS

The mean baseline spherical equivalent of the manifest refraction was -11.97 +/- 5.30 diopters (D) (range, -3.75 to -28.00 D). At a mean of 1 year after surgery, the mean refraction was -1.86 +/- 3.13 D (range, -13.25 to +4.63 D); 13 eyes (21%) had a refraction within +/- 0.50 D and 22 (35%) within +/- 1.00 D. Undercorrection of more than -1.00 D was present in 36 eyes (57%). At baseline, 48 of 63 eyes (75%) could see 20/40 or better with spectacle correction. At 1 year, 13 of 63 eyes (21%) could see 20/40 or better uncorrected. To measure the stability of refraction in 61 eyes, the mean refraction at 1 month of +0.62 +/- 2.43 D was compared to that at 1 year after surgery (mean, -1.41 +/- 3.10 D), indicating a loss of effect in the direction of increasing myopia. Nine eyes (14%) lost two to five lines of spectacle-corrected visual acuity. Two eyes had central epithelial implantation plaques in the lamellar bed that required removal.

CONCLUSION

In situ keratomileusis using an automated corneal shaper and sutured corneal discs at an intermediate stage of development produced less than desirable refractive and visual acuity results.