Residual bed thickness and corneal forward shift after laser in situ keratomileusis

Regional analysis of posterior corneal elevation after laser refractive surgeries for correction of myopia of different degrees

PURPOSE

To evaluate regional changes in the posterior corneal elevation after three laser refractive surgeries for correction of myopia of different degrees.

SETTINGS AND DESIGN

Retrospective, comparative, and non-randomized study.

METHODS

Two hundred patients (200 eyes) who underwent laser epithelial keratoplasty (LASEK), femtosecond-assisted laser in-situ keratomileusis (FS-LASIK), and small-incision lenticule extraction (SMILE) were included in this study. According to preoperative spherical equivalent (SE), each surgical group was divided into two refractive subgroups: low-to-moderate myopia (LM group) and high myopia (H group). The posterior corneal elevation from Pentacam Scheimpflug tomography was analyzed preoperatively and at 1 month, 3 months, 6 months, and 12 months postoperatively. Three subregions of the posterior cornea were divided in this study as the central, paracentral, and peripheral regions.

STATISTICAL ANALYSIS USED

Generalized Estimating Equations (GEE).

RESULTS

For all three surgical groups, similar changing trends were seen in the two refractive subgroups. H group presented a larger changing magnitude than the LM group in FS-LASIK over time ( P < 0.05), whereas no significant difference was noted in the two refractive subgroups of LASEK or SMILE ( P > 0.05). At 12 months postoperatively, the central posterior corneal elevation returned to the preoperative level in LASEK ( P > 0.05) but shifted forward significantly in FS-LASIK and SMILE ( P < 0.05).

CONCLUSION

Different posterior corneal regions respond differently to corneal refractive surgeries. LASEK, FS-LASIK, and SMILE demonstrate different trends in the regional changes in posterior corneal elevation. The corneal shape seems more stable in LASEK than in FS-LASIK and SMILE.

Factors associated with changes in posterior corneal surface following laser-assisted in situ keratomileusis

PURPOSE

To identify factors associated with changes in the posterior corneal curvature following laser-assisted in situ keratomileusis (LASIK).

METHODS

This retrospective study included myopic astigmatic eyes that underwent LASIK between January and December 2013 at Care-Vision Laser Center, Tel-Aviv, Israel. The average posterior keratometry was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgically induced change in average posterior keratometry and preoperative parameters such as preoperative sphere, cylinder, spherical equivalent, central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci (BCV) index, ablation depth, percent of tissue altered (PTA), and residual stromal bed (RSB) are reported.

RESULTS

A total of 115 eyes with a mean age of 32.5 ± 8.3 years (range 22-56 years) were included. Central corneal thickness (p < 0.005), preoperative sphere (p < 0.001), spherical equivalent (p < 0.005), and preoperative posterior inferior/superior ratio (p < 0.05) were all significantly correlated with the percentage of change in the mean posterior K. According to ranked stepwise multiple regression analysis, 22% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were the percentage of change in posterior inferior/superior ratio, preoperative subjective sphere, and preoperative mean posterior K (for all, p < 0.001).

CONCLUSIONS

The percentage of change in posterior inferior/superior ratio, subjective sphere, and preoperative mean posterior K are all correlated with change in the mean posterior K after LASIK. Understanding of the variables that can influence posterior corneal changes following refractive surgery may play a role in the prevention of iatrogenic keratectasia.

Factors associated with changes in posterior corneal surface following photorefractive keratectomy

PURPOSE

To identify factors associated with changes in the posterior cornea curvature following laser refractive surgery.

MATERIALS AND METHODS

This retrospective study included myopic astigmatic eyes that underwent PRK between January 2013 and December 2013 at Care-Vision Laser Centers, Tel-Aviv, Israel. The average posterior K was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgical induced change in average posterior k and preoperative parameters such as central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci index (BCV), ablation depth, percent tissue altered (PTA), and residual stroma bed (RSB) were analyzed.

RESULTS

A total of 280 eyes with a mean age of 24.9 ± 6.1 years (range, 18-47 years were included in this study. The mean PTA was 14.8 ± 6.0%. A greater change in posterior K was found in females (p = 0.01), smaller treatment zones of 6.0 mm (p = 0.02) and PTA > 20% (p < 0.001). A lower CCT (r =  - 0.24, p < 0.001), higher myopia (r =  - 0.34, p < 0.001), higher astigmatism (r =  - 0.17, p < 0.001), higher total BCV (r = 0.13, p = 0.03), lower back BCV (r =  - 0.12, p = 0.05), higher front BCV (r = 0.16, p = 0.01), higher posterior I-S ratio (r = 0.16, p = 0.01), and a lower RSB (r =  - 0.42, p < 0.001) were all significantly correlated with percentage of change in mean posterior K. In ranked stepwise multiple regression analysis, 26.2% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were PTA (p < 0.001), CCT (p = 0.001), and posterior I-S ratio (p = 0.001). PTA alone accounted for 15% of the variance in posterior K changes in multivariate analysis.

CONCLUSIONS

Understanding of factors affecting a change in posterior cornea after refractive surgery may have an important practical value for the prevention of iatrogenic keratectasia. Preoperative CCT, posterior I-S ratio, and PTA were significantly associated with changes in posterior K after PRK. PTA was the strongest predictor of posterior corneal changes (p < 0.001).

Is the axial length a risk factor for post-LASIK myopic regression?

PURPOSE

To assess the relationship between the axial length and post-LASIK regression in myopic patients.

METHODS

This is a retrospective case series study conducted at a private eye centre, Ismailia, Egypt. The clinical records of the patients, who experienced LASIK to correct myopia from January 2016 to January 2018, were analysed for myopic regression. The patients were operated on, examined, and followed-up 1 year by one surgeon (AAG).

RESULTS

This study included 1219 patients (2316 eyes) with myopia. Mean ± SD of pre-operative spherical equivalent (SE) was - 4.3 ± 2.1D, range (- 0.50 to - 10.0D). Mean ± SD age of the patients was 26.4 ± 6.8 years, range (21 to 50 years). Male to female ratio was 30.5 to 69.5%. The cumulative incidence rate of myopic regression according to the medical records of the patients was 25.12% (582 eyes out of total 2316 eyes) along the 2 years of this study (12.6% per year). Of the total patients, 14.94% had pre-operative high myopia, 35.84% had pre-operative moderate myopia, and 49.2% had pre-operative low myopia. Of the patients with myopic regression, 52.6% had pre-operative high myopia, 34% had pre-operative moderate myopia, and 13.4% had pre-operative low myopia. The mean ± SD of the axial length of the patients with myopic regression was 26.6 ± 0.44 mm, range (26.0 to 27.86 mm), while the mean ± SD of the axial length of other patients with stable refraction was 24.38 ± 0.73 mm, range (22.9 to 25.9 mm) (t test statistic = 69.3; P value < 0.001).

CONCLUSIONS

Pre-operative high axial length increases the risk of myopic regression after LASIK.

Longitudinal evaluation of posterior corneal power by anterior segment optical coherence tomography 18 months following photorefractive keratectomy

PURPOSE

To investigate the change in anterior, posterior, and net corneal power more than 18 months after photorefractive keratectomy (PRK) by RTVue anterior segment optical coherence tomography (OCT).

SETTING

Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran.

DESIGN

Prospective observational study.

METHODS

PRK was performed using Technolas TENEO 317 laser platform. Anterior, posterior, and net corneal power was measured by the RTVue-XR anterior segment OCT system with the Pachymetry + Cpwr scan pattern at baseline and months 1, 3, 6, 12, 18, and more than 18 (up to 27) after PRK.

RESULTS

Three hundred twenty-six eyes of 163 patients (61 men [37.4%], 102 women [62.6%]; mean age 29.71 years; range 18.5 to 46.5 years) were enrolled in this study. Mean preoperative spherical equivalent was -3.15 ± 1.50 diopter (D) (range -8.37 to -0.62 D). The mean change in net corneal power was 3.052 D, 3.281 D, 3.324 D, 3.114 D, 3.446 D, and 3.972 D at months 1, 3, 6, 12, 18, and more than 18 postoperatively compared with baseline, respectively (P < .001 for all comparisons). The mean change in posterior corneal power at postoperative visits compared with baseline was not statistically significant (P > .1) except for 1 month postoperatively, which increased by 0.13 D (P < .001). Changes in posterior corneal power were not correlated with any of the preoperative clinical and Scheimpflug variables.

CONCLUSIONS

Posterior corneal power did not change for more than 18 months after PRK, except for an early small increase at 1 month postoperatively.

Predictors of Myopic Regression for Laser-assisted Subepithelial Keratomileusis and Laser-assisted in Situ Keratomileusis Flap Creation with Mechanical Microkeratome and Femtosecond Laser in Low and Moderate Myopia

Purpose: To determine the predictive factors of postoperative myopic regression in subjects who have undergone laser-assisted subepithelial keratomileusis (LASEK), laser-assisted in situ keratomileusis (LASIK) with flaps created using a mechanical microkeratome (MM) or LASIK with flaps created using a femtosecond (FS) laser for -0.50 D to -6.0 D myopia.Materials and Methods: This study was designed as a retrospective comparison. We included 236 eyes in the LASEK group, 1,178 eyes in the MM-LASIK group and 1,333 eyes in the FS-LASIK group. Refractive outcomes were recorded at one day; one week; and one, three, six and 12 months postoperatively. Predictors affecting myopic regression and other covariates were estimated using a Cox proportional hazards model for the three methods of surgery.Results: At 12 months, the survival rates (no myopic regression) were 63.36%, 74% and 77% in the MM-LASIK, LASEK, and FS-LASIK groups, respectively. Risk factors for myopic regression were indicated for patients with greater preoperative central corneal thicknesses (CCT) (P = .02), female patients (P < .01), patients with aspherical ablations (P = .01) and those with larger transitional zones (TZ) (P < .01). Among the three surgeries, MM-LASIK had a significantly higher probability of postoperative myopic regression (P < .01). Longer durations of myopia (P = .03), steeper corneal curvatures (K_max) (P < .01) and larger optical zones (OZ) (P < .01) were protective factors.Conclusion: MM-LASIK had the highest risk for myopic regression. OZ, TZ, aspherical ablations, preoperative corneal curvatures and being a female patient had significant influence on myopic regression in -0.50 D to -6.0 D myopia.

Predictors affecting myopic regression in - 6.0D to - 10.0D myopia after laser-assisted subepithelial keratomileusis and laser in situ keratomileusis flap creation with femtosecond laser-assisted or mechanical microkeratome-assisted

PURPOSE

To investigate the predictive factors of postoperative myopic regression among subjects who have undergone laser-assisted subepithelial keratomileusis (LASEK), laser-assisted in situ keratomileusis (LASIK) flap created with a mechanical microkeratome (MM), and LASIK flap created with a femtosecond laser (FS). All recruited patients had a manifest spherical equivalence (SE) from - 6.0D to - 10.0D myopia.

METHODS

This retrospective, observational case series study analyzed outcomes of refraction at 1 day, 1 week, and 1, 3, 6, and 12 months postoperatively. Predictors affecting myopic regression and other covariates were estimated with the Cox proportional hazards model for the three types of surgeries.

RESULTS

The study enrolled 496 eyes in the LASEK group, 1054 eyes in the FS-LASIK group, and 910 eyes in the MM-LASIK group. At 12 months, from - 6.0D to - 10.0D myopia showed that the survival rates (no myopic regression) were 52.19%, 59.12%, and 58.79% in the MM-LASIK, FS-LASIK, and LASEK groups, respectively. Risk factors for myopic regression included thicker postoperative central corneal thickness (P ≦ 0.01), older age (P ≦ 0.01), aspherical ablation (P = 0.02), and larger transitional zone (TZ) (P = 0.03). Steeper corneal curvature (K_max) (P = 0.01), thicker preoperative central corneal thickness (P < 0.01), smaller preoperative myopia (P < 0.01), longer duration of myopia (P = 0.02), with contact lens (P < 0.01), and larger optical zone (OZ) (P = 0.02) were protective factors. Among the three groups, the MM-LASIK had the highest risk of postoperative myopic regression (P < 0.01).

CONCLUSIONS

The MM-LASIK group experienced the highest myopic regression, followed by the FS-LASIK and LASEK groups. Older age, aspheric ablation used, thicker postoperative central corneal thickness, and enlarging TZ contribute to myopic regression; steeper preoperative corneal curvature (K_max), longer duration of myopia, with contact lens, thicker preoperative central corneal thickness, lower manifest refraction SE, and enlarging OZ prevent postoperative myopic regression in myopia from - 6.0D to - 10.0D.

Refractive regression after laser in situ keratomileusis

Uncorrected refractive errors are a leading cause of visual impairment across the world. In today's society, laser in situ keratomileusis (LASIK) has become the most commonly performed surgical procedure to correct refractive errors. However, regression of the initially achieved refractive correction has been a widely observed phenomenon following LASIK since its inception more than two decades ago. Despite technological advances in laser refractive surgery and various proposed management strategies, post-LASIK regression is still frequently observed and has significant implications for the long-term visual performance and quality of life of patients. This review explores the mechanism of refractive regression after both myopic and hyperopic LASIK, predisposing risk factors and its clinical course. In addition, current preventative strategies and therapies are also reviewed.

Twelve-Year Follow-Up of Laser In Situ Keratomileusis for Moderate to High Myopia

Purpose

To assess the long-term clinical outcomes of conventional laser in situ keratomileusis (LASIK) for moderate to high myopia.

Methods

We retrospectively examined sixty-eight eyes of 37 consecutive patients who underwent conventional LASIK for the correction of myopia (−3.00 to −12.75 diopters (D)). At 3 months and 1, 4, 8, and 12 years postoperatively, we assessed the safety, efficacy, predictability, stability, mean keratometry, central corneal thickness, and adverse events.

Results

The safety and efficacy indices were 0.82 ± 0.29 and 0.67 ± 0.37, respectively, 12 years postoperatively. At 12 years, 53% and 75% of the eyes were within 0.5 and 1.0 D, respectively, of the targeted correction. Manifest refraction changes of −0.74 ± 0.99 D occurred from 3 months to 12 years after LASIK (p < 0.001). We found a significant correlation of refractive regression with the changes in keratometric readings from 3 months to 12 years postoperatively (Pearson correlation coefficient, r = −0.28, p = 0.02), but not with the changes in central corneal thickness (r = −0.08, p = 0.63). No vision-threatening complications occurred in any case.

Conclusions

Conventional LASIK offered good safety outcomes during the 12-year observation period. However, the efficacy and the predictability gradually decreased with time owing to myopic regression in relation to corneal steepening.

Comparative evaluation of visual outcomes and corneal asphericity after laser-assisted in situ keratomileusis with the six-dimension Amaris excimer laser system

Purpose

To compare the visual and refractive outcomes after laser-assisted in situ keratomileusis (LASIK) surgery for correction of myopia or myopic astigmatism using a six-dimensional Amaris excimer laser.

Methods

In this retrospective cohort study, we enrolled 47 eyes of 28 patients (age: 19–36 years) with myopia or myopic astigmatism. We used the Custom Ablation Manager protocol and performed ablations with the SCHWIND AMARIS system. LASIK flaps were cut with an iFS Advanced Femtosecond Laser. Mean static (SCC) and dynamic cyclotorsion (DCC) were evaluated. Visual and refractive outcomes were evaluated during 6 months’ follow-up. Corneal asphericity (Q-value) was analyzed at 4 months postoperatively.

Results

The spherical equivalent (SE) reduction was statistically significant reduce 1 day after refractive surgery (P < 0.001), with no additional significant changes during follow-up (P = 0.854). SCC registration rates were 81% in the Aberration-Free mode (AF) and 90% in the Corneal Wavefront mode (CW). SCC measurements were within ± 5 degrees in 57% (AF) and 68% (CW) of eyes. Mean DCC was within ± 1 degree in 96% (AF) or 95% (CW) of cases. At 6 months, the uncorrected distance visual acuity was 20/25 or better in all eyes. At last follow-up, both steep and flat keratometry values had significantly flattened in both groups (P < 0.001). Corneal asphericity also increased significantly during the postoperative period for an 8-mm corneal diameter (P < 0.001).

Conclusions

LASIK for myopia or myopic compound astigmatism correction using the six-dimensional AMARIS 750S excimer laser is safe, effective, and predictable. Postoperative corneal asphericity can be analyzed by linear regression to predict the changes in postoperative corneal asphericity with this approach.

Residual stromal bed thickness correlates with regression of myopia after LASIK

Purpose

The purpose of this study was to evaluate the correlation between residual stromal bed thickness (hereinafter bed thickness) and regression of myopia after LASIK, taking into consideration the long-term outcomes.

Subjects and methods

A total of 177 patients (309 eyes) and 41 patients (70 eyes) were retrospectively reviewed at 5 and 10 years after surgery, respectively. These patients were also continuously examined throughout the study. All patients underwent laser in situ keratomileusis (LASIK) for myopia in our clinic and scored at least 1.0 (0 logMAR) uncorrected distance visual acuity (UCVA) 1 month after surgery. Bonferroni–Dunn method and Student’s t-test were used for statistical analyses.

Results

Cases with a refractive value (spherical equivalent) of less than −6.0 D (Group A) were compared to those with −6.1 D or higher (Group B). There was a statistically significant decrease in Group B UCVA of 0.04 logMAR and 0.12 logMAR at 5 and 10 years after surgery, respectively. With regard to the relationship between regression of myopia and bed thickness in the long-term, there was a significantly higher frequency of regression of myopia in cases with less than 350 μm bed thickness compared to those with 350 μm and more, in a surgical volume of more than −6.1 D (Group B).

Conclusion

The present study indicates that bed thickness correlates with regression of myopia after LASIK and enough bed thickness is important to maintain good UCVA in the long-term.

Corneal Thickness Profile Changes After Femtosecond LASIK for Hyperopia

Purpose:

To compare changes in the corneal thickness profile before and 6 months after femtosecond laser in situ keratomileusis (LASIK) for hyperopia.

Methods:

In a prospective noncomparative case series study, 24 eyes of 20 hyperopic patients undergoing femtosecond LASIK were examined preoperatively and 6 months postoperatively. Corneal profile was measured using Pentacam HR device. Paired t test was used to compare preoperative and postoperative values. Spearman correlation analysis was performed to evaluate the relationship between the central corneal thickness changes and attempted spherical equivalent refraction (SER).

Results:

The mean uncorrected distance visual acuity significantly improved after surgery (P<0.001). Significant differences in central, midperipheral, ablative annular, and peripheral corneal thicknesses were observed from preoperatively to 6 months postoperatively (all P<0.001). There was no significant correlation between the changes in the central corneal thickness and attempted SER (P=0.23).

Conclusions:

The corneal thicknesses across the whole ablation zone including central corneal thickness, significantly decrease postoperatively compared with preoperatively.

No change in anterior chamber dimensions after femtosecond LASIK for hyperopia

Objective:

To compare the changes in anterior chamber volume (ACV), anterior chamber depth (ACD) and anterior chamber angle (ACA) before and 6 months after femtosecond laser in situ keratomileusis (LASIK) for hyperopia using the Pentacam HR device.

Methods:

A total of 24 eyes of 24 consecutive hyperopic patients undergoing femtosecond LASIK were examined preoperatively and 6 months postoperatively. Anterior chamber volume; ACDs in the central, superior, inferior, nasal, and temporal quadrants; and ACA were measured using the Pentacam HR device. Comparisons of preoperative versus postoperative values were performed using paired Student t test. Linear regression analysis was performed to evaluate correlations between ACV change, central ACD change, age, and attempted maximum ablation depth.

Results:

Preoperative and postoperative mean ACVs were 153.6 and 158.2 μL, respectively. Preoperative and postoperative mean ACDs were 2.81, 2.28, 2.53, 2.16, and 2.61 mm, and 2.84, 2.31, 2.54, 2.16, and 2.65 mm, respectively. Preoperative and postoperative mean ACAs were 33.3° and 32.0°, respectively. There were not statistically significant differences in ACV, ACDs, and ACA from preoperatively to 6 months after femtosecond LASIK (all P>0.05). The change of central ACD was correlated significantly with age at 6 months postoperatively (R²=0.18, P=0.039).

Conclusions:

Anterior chamber profiles, including ACV, ACA, and central and peripheral ACDs did not significantly change after femtosecond LASIK for hyperopia.

Refractive, anterior corneal and internal astigmatism in the pseudophakic eye

PURPOSE

To evaluate the correlation between refractive astigmatism (RA) and anterior corneal astigmatism (ACA), and determine the internal astigmatism (IA) in 184 pseudophakic eyes.

METHODS

The study was a prospective non-masked single-centre study. Patients were examined 8 weeks after phacoemulsification with implantation of aspheric one-piece monofocal IOLs. Examination included autokeratometry and subjective refraction. All refractive data were converted to the corneal plane. The corneal refractive index, taken to be 1.376, was used to estimate the ACA. All astigmatisms were converted to net curvital and net torsional powers with the steeper corneal plane as the reference meridian. Curvital power is the force acting along a given meridian, and torsion is the power twisting the astigmatic direction out of that plane. The internal astigmatism (IA) was calculated as the difference between RA and ACA.

RESULTS

For curvital powers, the refractive astigmatism (KP(Φ)RA ) could be described as a function of anterior corneal astigmatic magnitude (KP(Φ)ACA ) and direction α by the multiple linear regression equation: KP(Φ)RA = -0.09 + 0.61*KP(Φ)ACA + 0.33*cos2α, (r(2) = 0.59, p < 0.0001). The average internal astigmatism amounted to 0.47 D inclined 92° relative to the steeper anterior corneal meridian. The magnitude of internal astigmatism depended on the angle α of the steeper anterior corneal meridian, averaging 0.86 D at 91° for with-the-rule, 0.37 D at 95° for oblique and 0.17 D at 97° for against-the-rule corneal astigmatisms.

CONCLUSIONS

The internal astigmatism varies as a function of the direction of the anterior steeper corneal meridian. In patient candidates to surgical correction of astigmatism, measuring only the curvature of the anterior corneal surface and neglecting that of the posterior corneal surface can lead to inaccurate evaluation of total corneal astigmatism.

Longitudinal evaluation of posterior corneal elevation after laser refractive surgery using swept-source optical coherence tomography

PURPOSE

To investigate the change in posterior corneal elevation up to 1 year after myopic femtosecond-assisted LASIK and photorefractive keratectomy (PRK).

DESIGN

Prospective, longitudinal, comparative study.

PARTICIPANTS

Patients undergoing femtosecond-assisted LASIK or PRK.

METHODS

Corneal imaging was performed using swept-source optical coherence tomography at baseline and at each postoperative follow-up. A 2-way analysis of variance model with repeated measures and a linear mixed effect model were used to compare the differences in posterior corneal elevation between LASIK and PRK at different points after adjusting for the preoperative spherical equivalent (SEQ), central corneal thickness (CCT), thinnest corneal thickness (TCT), residual bed thickness (RST), and ablation depth (AD).

MAIN OUTCOME MEASURES

The changes in posterior corneal elevation 1 month, 3 months, 6 months, and 12 months after surgery.

RESULTS

Ninety-eight eyes of 49 patients (mean age 35.2 ± 8.5 years) (62 LASIK, 36 PRK) were included. The mean change in posterior corneal elevation values after LASIK and PRK were 4.88±0.47 μm versus 3.67±0.48 μm (B-1), 2.42±0.56 μm versus 3.00±0.47 μm (B-3), 3.76±0.46 μm versus 2.76±0.46 μm (B-6), and 2.92±0.46 μm versus 2.72±0.46 μm (B-12), respectively. Significant differences in posterior corneal elevation after LASIK were found from month 1, to month 3, to month 6, to month 12 (P ≤ 0.001), whereas posterior corneal elevation did not change significantly from month 3, to month 6, to month 12 (P ≥ 0.373) after PRK. LASIK and PRK eyes showed significant differences at months 3 and 12 (P ≤ 0.023). A similar pattern was observed for the changes in posterior corneal elevation after LASIK and PRK after adjusting for the effect of SEQ, CCT, TCT, RST, and AD. The adjusted forward displacements of the posterior corneal surface were statistically significant throughout the study period after both refractive surgeries (P < 0.05).

CONCLUSIONS

The findings of our study suggested that there was a mild but significant forward protrusion of the posterior cornea after femtosecond laser-assisted LASIK and PRK. The posterior cornea fluctuated during the first postoperative year after LASIK, whereas it stabilized as early as 3 months after PRK.

Scheimpflug imaged corneal changes on anterior and posterior surfaces after collagen cross-linking

AIM

To compare the anterior and posterior corneal parameters before and after collagen cross-linking therapy for keratoconus.

METHODS

Collagen cross-linking was performed in 31 eyes of 31 keratoconus patients (mean age 30.6±8.9y). Prior to treatment and an average 7mo after therapy, Scheimpflug analysis was performed using Pentacam HR. In addition to corneal thickness assessments, corneal radius, elevation, and aberrometric measurements were performed both on anterior and posterior corneal surfaces. Data obtained before and after surgery were statistically analyzed.

RESULTS

In terms of horizontal and vertical corneal radius, and central corneal thickness no deviations were observed an average 7mo after operation. Corneal higher order aberration showed no difference neither on anterior nor on posterior corneal surfaces. During follow-up period, no significant deviation was detected regarding elevation values obtained by measurement in mm units between the 3.0-8.0 mm-zones.

CONCLUSION

Corneal stabilization could be observed in terms of anterior and posterior corneal surfaces, elevation and higher order aberration values 7mo after collagen cross-linking therapy for keratoconus.

Change in keratometry after myopic laser in situ keratomileusis and photorefractive keratectomy

PURPOSE

To compare the change in keratometry (K), spherical equivalent (SE), and visual acuity after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).

SETTING

Academic tertiary care center.

DESIGN

Retrospective review.

METHODS

The postoperative K, SE, and uncorrected and corrected distance visual acuities were measured 6 months, 9 months, 1 year, 2 years, 3 years, 4 to 5 years, 6 to 7 years, and 8+ years postoperatively. A difference (Δ) for each variable was calculated from its 6-month postoperative baseline. The rates of change were grouped based on the magnitude of myopic correction (0.00 to 2.99 diopters [D]; 3.00 to 5.99 D; 6.00 to 8.99 D), type of surgery (LASIK versus PRK), and age (<34 years; 34 to 45 years; >45 years).

RESULTS

Statistically significant differences were found in the rates of change between low and moderate corrections to high corrections for ΔKavg (P=.0472 and P=.0091, respectively) and ΔSE (both P<.0001). Statistically significant differences were found in the rate of change in ΔKavg between all 3 ages groups (P=.0330, P=.0051, and P<.0001) and in ΔSE between ages less than 34 years and 34 to 45 years to ages over 45 years (P=.0158 and P=.0015, respectively). There was no significant difference in the rate of change in ΔKavg and ΔSE between LASIK and PRK (P=.3599 and P=.9403, respectively).

CONCLUSION

There was keratometric and refractive regression for myopic LASIK, with the rate of regression depending on treatment magnitude and age.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Use of Scheimpflug corneal anterior-posterior imaging in ray-tracing intraocular lens power calculation

PURPOSE

To examine improvement with the use of Scheimpflug imaging of the anterior and posterior corneal surfaces in the accuracy of ray-tracing intraocular lens (IOL) power calculation for normal cataractous eyes.

METHODS

Prospective case series comprised 136 eyes of 136 consecutive patients who had undergone cataract surgeries. Scheimpflug imaging of the cornea was included with routine preoperative examinations. Postoperative refractions were predicted using three methodologies; ray-tracing calculation using Scheimpflug imaging and Placido topography, ray-tracing calculations using Placido topography, and the SRK/T formula using autokeratometry. Prediction errors from the manifest refraction at 1 month postoperatively were compared between the methods. Influence of the posterior corneal curvature was also evaluated.

RESULTS

Mean prediction errors were 0.008, -0.103 and -0.042 D, respectively without significant difference between the three methods (p = 0.23). The prediction errors were significantly correlated with the posterior corneal curvature when the Scheimpflug imaging was not used (p < 0.03).

CONCLUSION

Use of Scheimpflug imaging in ray-tracing IOL power calculation was as accurate as the other calculations in normal cases, showing no bias in the posterior corneal curvature, as is the case with the other calculations.

Evaluation of corneal changes after myopic LASIK using the Pentacam®

BACKGROUND

In this study, we used a Pentacam® device to evaluate the corneal changes that occur after laser-assisted in situ keratomileusis (LASIK).

METHODS

Our study included 60 eyes of 32 patients. All patients were treated for myopia and myopic astigmatism using LASIK. The eyes were examined preoperatively and 3 months postoperatively using a Pentacam to assess corneal changes with regard to curvature, elevation, and asphericity of the cornea.

RESULTS

A statistically significant decrease in mean keratometric power of the anterior corneal surface (P = 0.001) compared with its pre-LASIK value was detected after 3 months, but there was no significant change in keratometric power of the posterior surface (P = 0.836). Asphericity (Q-value) of the anterior and posterior surfaces increased significantly after LASIK (P = 0.001). A significant forward bulge of the anterior corneal surface 4 mm and 7 mm from the central zone was detected 3 months post-LASIK (P = 0.001 for both), but there was no significant increase in posterior elevation at 4 mm and 7 mm from the center (P = 0.637 and P = 0.26, respectively). No cases of post-LASIK ectasia were detected. Correlation between different parameters of the corneal surface revealed an indirect relation between changes in pachymetry and anterior corneal elevation at 4 mm and 7 mm from the central zone (r = -0.27, P = 0.13, and r = -0.37, P = 0.04, respectively), and a direct proportion between changes in pachymetry and mean keratometric power of the anterior and posterior corneal surfaces (r = 0.7, P = 0.001 and r = 0.4, P = 0.028, respectively).

CONCLUSION

LASIK causes significant changes at the anterior corneal surface but the effect is subtle and insignificant at the posterior surface.

Effect of timolol on refractive outcomes in eyes with myopic regression after laser in situ keratomileusis: a prospective randomized clinical trial

PURPOSE

To compare the effects of timolol on refractive outcomes in eyes with myopic regression after laser in situ keratomileusis (LASIK) with a control-matched group.

DESIGN

Prospective, randomized, parallel-controlled, double-masked clinical trial. A computer-generated randomization list based on random block permutation (length 4 to 8) was used for treatment allocation.

METHODS

setting: Basir Eye Center, Tehran, Iran.

PATIENT POPULATION

Of 124 eyes with myopic regression after LASIK using Technolas 217-Z, 45 eyes in each group were analyzed.

INTERVENTION

Patients were randomly assigned into either Group 1, who received timolol 0.5% eye drops, or Group 2, who received artificial tears for 6 months.

MAIN OUTCOME MEASURE

Spherical equivalent (SE) at 6 months posttreatment.

RESULTS

In Group 1, SE improved from -1.48 ± 0.99 diopter (D) before treatment to -0.88 ± 0.91 D and -0.86 ± 0.93 D 6 months after treatment and 6 months after timolol discontinuation, respectively (P < .001). In Group 2, it was -1.57 ± 0.67 D, -1.83 ± 0.76 D, and -1.91 ± 0.70 D, respectively (P < .001). SE was significantly better in Group 1 6 months after treatment and 6 months after discontinuation of treatment (P < .001 for both comparisons). There was a 0.26 D decrease in SE improvement every 4 months after the surgery in the Group 1 (P < .001).

CONCLUSIONS

Timolol application is effective for the treatment of myopic regression after LASIK compared with control group. Its effects last for at least 6 months after its discontinuation.

Time course of refractive and corneal astigmatism after laser in situ keratomileusis for moderate to high astigmatism

PURPOSE

To assess the time course of refractive and corneal astigmatism after laser in situ keratomileusis (LASIK) in eyes with moderate to high astigmatism.

SETTING

Department of Ophthalmology, Kitasato University, Kanagawa, Japan.

DESIGN

Retrospective case series.

METHODS

Keratometric readings and corneal astigmatism were determined with an autokeratometer in consecutive patients who had LASIK for moderate to high astigmatism (≥2.00 diopters [D]).

RESULTS

The study enrolled 48 eyes of 35 patients with a mean age of 34.0 years ± 8.1 (SD), a mean spherical error of -5.10 ± 2.11 D, and a mean cylindrical error of -2.74 ± 0.99 D. Postoperatively, the mean spherical refraction changed significantly from 0.38 ± 0.80 D at 1 week to -0.13 ± 0.90 D at 1 year (P<.001, Wilcoxon signed-rank test). The mean cylindrical refraction showed no significant change (-0.67 ± 0.54 D at 1 week to -0.63 ± 0.63 D at 1 year) (P=.54). There were significant increases in the flattest and steepest keratometry readings at 1 week and at 1 year. However, no significant change in corneal astigmatism was found at either time point (P=.10).

CONCLUSIONS

After LASIK, there was significant refractive regression in the spherical component but not in the cylindrical component. This suggests that refractive regression occurs by corneal steepening in the spherical component and that astigmatic regression does not occur, even in moderately to highly astigmatic eyes.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Posterior corneal curvature assessment after Epi-LASIK for myopia: comparison of Orbscan II and Pentacam imaging

PURPOSE

To compare the changes in posterior corneal curvature using scanning slit topography (Orbscan II) and Scheimpflug imaging (Pentacam) before and after Epi-laser in situ keratomileusis (LASIK) for myopia.

METHODS

In a prospective observational case-series study, 20 myopic patients having undergone Epi-LASIK were examined serially with two different devices, Orbscan II and Pentacam, preoperatively and one month postoperatively. Posterior central elevation (PCE) and posterior maximal elevation (PME) were compared between the two devices, and the changes in parameters after Epi-LASIK were analyzed using a difference map.

RESULTS

All parameters (preoperative and postoperative PCE and preoperative and postoperative PME) that were measured using the Orbscan II were significantly greater compared to those of the Pentacam (for all p < 0.001). PCE and PME were significantly increased one month postoperatively in the Orbscan II measurements (p < 0.05) but were not significantly increased in the Pentacam measurements. Also, ΔPCE and ΔPME, in the difference map obtained by each serial scanning, were significantly greater in the Orbscan II measurements than with the Pentacam (p = 0.012, p = 0.016).

CONCLUSIONS

The Pentacam measurements displayed significantly reduced values in all parameters related to posterior corneal elevation compared to those of the Orbscan II. The Pentacam showed no significant change in posterior corneal curvature after Epi-LASIK, based on the difference map.

Posterior corneal elevation after LASIK with three flap techniques as measured by Pentacam

PURPOSE

To evaluate and compare posterior corneal changes using elevation data obtained from Pentacam (Oculus Optikgeräte GmbH) Scheimpflug imaging in eyes undergoing LASIK with three different modes of flap creation: IntraLase femtosecond laser FS60 (Abbott Medical Optics) (femtosecond group), Amadeus (Ziemer Group AG) mechanical microkeratome (keratome group), or flap formation using 20% alcohol laser epithelial keratomileusis (LASEK) (LASEK group).

METHODS

Ninety myopic patients (90 eyes) undergoing refractive surgery were recruited. The change in posterior corneal elevation at 21 predetermined points in the central 5-mm area was measured using exported elevation data from the Pentacam before LASIK and 18 months postoperative and was compared among and within three modes of flap creation.

RESULTS

Mean change in posterior elevation in the central 5-mm area was 5.13±4.16 μm for the femtosecond group, 5.78±4.42 μm for the keratome group, and 6.68±4.72 μm for the LASEK group and was similar among groups (P=.59). Change in posterior elevation before and after LASIK was not significant within any group (P=.342, P=.232, and P=.321 for the femtosecond, keratome, and LASEK groups, respectively). Preoperative spherical equivalent, central corneal thickness, ablation depth, and estimated residual bed thickness did not correlate with change in posterior corneal elevation for the femtosecond, keratome, or LASEK groups (P>.05).

CONCLUSIONS

Using Pentacam elevation data, there were no significant changes in posterior corneal elevation following LASIK among or within the three methods of flap creation. At 18 months after LASIK, the posterior corneal surface is not displaced anteriorly significantly and is equally stable using these three surgical techniques.

Effect of age on changes in anterior chamber depth and volume after laser in situ keratomileusis

PURPOSE

To evaluate the effect of age on anterior chamber depth (ACD) and anterior chamber volume (ACV) after laser in situ keratomileusis (LASIK) for myopia.

SETTING

Department of Ophthalmology, Keio University School of Medicine, and a private clinic, Tokyo, Japan.

METHODS

In this retrospective study, patients who had uneventful LASIK for myopia or myopic astigmatism were divided into 2 groups: younger (younger than 40 years) and older (40 years and older). Central corneal thickness, central corneal true net power, ACV, and central ACD were measured using a rotating Scheimpflug camera preoperatively and 1 month postoperatively. These parameters were compared between the 2 groups.

RESULTS

The study evaluated 161 eyes of 83 patients (mean age 34.5 years +/- 8.3 [SD]). The decreases in central ACD and ACV after LASIK were statistically significant in the younger group (P<.0001 and P = .0050, respectively) but not in the older group.

CONCLUSION

Central ACD and the ACV decreased significantly after LASIK in younger patients (<40 years) but not in older patients, indicating that age influences changes in ACD and ACV after LASIK.

Long-term stability of the posterior cornea after laser in situ keratomileusis

PURPOSE

To study long-term changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) using Scheimpflug topography (Pentacam, Oculus, Inc.) in eyes 1 year after LASIK.

SETTING

Department of Ophthalmology, Albany Medical Center, and a private practice, Albany, New York, USA.

METHODS

One hundred two myopic eyes of 52 consecutive patients presenting for their 1-year follow-up were prospectively evaluated using the Pentacam to determine elevation changes to the posterior corneal surface between preoperative and 1-year postoperative measurements. Changes in posterior elevation were performed by comparing the best-fit sphere preoperatively and postoperatively with a fixed reference sphere determined by the central 9.0 mm preoperative cornea. Statistical and graphical analyses were performed.

RESULTS

One hundred two post-LASIK eyes (mean correction -4.33 diopters; mean ablation depth 68.70 microm; mean estimated residual bed thickness 327 microm) had a mean posterior displacement of -0.47 microm +/- 3.48 (SD) (range -10.0 to +7 microm). The mean follow-up period was 13.6 months (range 8.8 to 19.3 months).

CONCLUSIONS

In this population, no patient had significant forward protrusion of the posterior corneal surface a mean of 14 months after LASIK. The posterior cornea in post-LASIK myopic eyes was very stable. Contrary to results in previous studies, progressive changes to the posterior corneal surface did not routinely occur after LASIK performed within established parameters.

Corneal changes after laser refractive surgery for myopia: comparison of Orbscan II and Pentacam findings

PURPOSE

To determine the agreement between scanning slit topography (Orbscan II, Bausch & Lomb) and Scheimpflug imaging (Pentacam, Oculus) in corneal elevation, corneal curvature, and anterior chamber depth (ACD) measurements before and after laser refractive surgery for myopia and to compare the postoperative changes seen with these devices.

SETTING

Noor Vision Correction Center, Tehran, Iran.

METHODS

In a prospective observational case-series study, 23 consecutive myopic patients having laser refractive surgery were examined with the Orbscan II and Pentacam preoperatively and 6 weeks postoperatively. Readings of ACD, anterior (A-) and posterior (P-) best-fit sphere (BFS) size, central elevation (CE), maximum elevation (ME), axial power in the 3.0 mm zone (AX3) and 5.0 mm zone (AX5), and tangential power in these zones (TG3 and TG5, respectively) were collected and used in the analyses.

RESULTS

Statistically significant interdevice differences were found preoperatively for all parameters except P-TG3 (P = .014) and in operated eyes for ACD, anterior parameters of A-AX3 and A-AX5, and all posterior corneal parameters. In posterior corneal measurements, Orbscan II demonstrated significant postoperative changes in all parameters except P-AX5 (P = .004) and P-TG5 (P = .034), although none of the differences was statistically significant with the Pentacam. The devices measured similar postoperative changes in anterior curvature parameters and in P-AX5 and P-TG5; all other changes were significantly different.

CONCLUSIONS

Compared to the Pentacam, the Orbscan II yielded larger posterior elevation values before and after surgery and significant postoperative changes in P-CE and P-ME. Further studies can determine which device gives more accurate images of the cornea and redefine screening criteria.

Matched Population Comparison of the Visian Implantable Collamer Lens and Standard LASIK for Myopia of -3.00 to -7.88 Diopters

PURPOSE

To compare matched populations of LASIK and Visian Implantable Collamer Lens (ICL) cases in the correction of myopia between -3.00 and -7.88 diopters (D).

METHODS

One hundred sixty-four LASIK eyes with prospective data collected from a single center and 164 ICL eyes from the multicenter US ICL Clinical Trial were compared in this observational non-randomized study. The LASIK and ICL groups were well matched for age, gender, and mean level of preoperative spherical equivalent refraction.

RESULTS

At 6 months, best spectacle-corrected visual acuity (BSCVA) > or = 20/20 was 85% with LASIK and 95% with ICL (P = .003) compared to preoperative values of 93% and 88%, respectively (P = .292). Loss of > or = 2 lines of BSCVA was significantly lower with the ICL at 1 week (0.6% vs 10%, P < .001) and 1 month (7% vs 0%, P = .001) with comparable outcomes at 6 months (0% vs 1%). At 6 months postoperatively, uncorrected visual acuity (UCVA) > or = 20/15 (11% vs 25%, P = .001) and > or = 20/20 (49% vs 63%, P = .001) was better in the ICL cases. Predictability within 0.50 D at 6 months for ICL cases was 85% (67% LASIK, P < .001); 97% of ICL cases were within 1.00 D (88% LASIK, P = .002). Refractive stability (+/- 0.50 D) between 1 and 6 months was 93% with ICL compared to only 82% with LASIK (P = .006).

CONCLUSIONS

The ICL performed better than LASIK in almost all measures of safety, efficacy, predictability, and stability in this matched population comparison, supporting the ICL as an effective alternative to existing refractive laser surgical treatments for the range of myopia studied.

No forward shifting of posterior corneal surface in eyes undergoing LASIK

PURPOSE

To evaluate structural changes in the cornea and anterior chamber (AC) after LASIK for myopia.

DESIGN

Retrospective nonrandomized study.

PARTICIPANTS

One hundred sixty-one eyes of 83 patients (mean age, 34.5+/-8.3 years) who underwent uneventful LASIK for myopia and myopic astigmatism. The preoperative refractive error (spherical equivalent) and corneal thickness were -6.02+/-2.10 diopters (D) and 549.9+/-29.3 mum, respectively.

METHODS

The AC volume (ACV), AC depth (ACD), corneal thickness, central corneal true net power, and posterior corneal tangential curvature were measured using a rotating Scheimpflug camera before and 1 week and 1 month after surgery. In 84 eyes of 42 cases, anterior and posterior corneal elevations and corneal thicknesses also were measured by scanning-slit topography before and 1 month after surgery.

MAIN OUTCOME MEASURES

Time course of the ACV, ACD (central, midperiphery, periphery), corneal thickness, central corneal true net power, posterior corneal tangential curvature using the Scheimpflug camera, and amount of forward shifting of the posterior corneal surface at the center of the difference map using scanning-slit topography.

RESULTS

Preoperative and 1-month postoperative mean ACVs were 198.1 mm3 and 196.4 mm3, respectively, and preoperative and postoperative mean ACDs (center, midperiphery, periphery) were 3.24, 2.65, and 1.89 mm, and 3.21, 2.63, and 1.87 mm, respectively. The corneal thickness within the optical zone, subjective refraction, and central corneal true net power significantly changed by tissue subtraction after LASIK (P<0.0001). There were no significant differences in the ACV, ACDs (center, midperiphery, periphery), peripheral corneal thickness, and posterior corneal tangential curvature from preoperatively to 1 month after LASIK. However, using scanning-slit topography, the posterior corneal surface displayed a mean forward shift of 29.0+/-19.0 microm 1 month after surgery.

CONCLUSION

The posterior corneal curvature, peripheral corneal thickness, ACDs, and ACV were consistent. These observations indicated that neither forward shifting of the central posterior corneal surface (bulging) nor backward shifting of the peripheral posterior corneal surface due to corneal swelling after ablation occurred after LASIK.

Repeatability and Reproducibility of Posterior Corneal Curvature Measurements by Combined Scanning-Slit and Placido-Disc Topography after LASIK

OBJECTIVE

To assess the repeatability and reproducibility of posterior corneal curvature (PCC) measurements made by combined scanning-slit/Placido-disc topography (Orbscan II) after LASIK.

DESIGN

Experimental instrument validation study.

PARTICIPANTS

We recruited 22 consecutive postmyopic LASIK patients for the repeatability study and another 50 consecutive postmyopic LASIK patients for the reproducibility study.

METHODS

To analyze intrasession repeatability, 1 examiner measured 22 postmyopic LASIK eyes 10 times successively in the shortest time possible. To study intersession reproducibility, the same operator obtained measurements from another 50 eyes with stable refraction in 2 consecutive visits at the same time of the day between 6 and 9 months after myopic LASIK. We explored any association between residual stromal bed thickness and measurement variability.

MAIN OUTCOME MEASURES

Orbscan II scanning-slit PCC data, precision, within-subject coefficient of variation (CV(w)), limits of agreement (LoA), and intraclass correlation coefficient (ICC).

RESULTS

For intrasession repeatability, precision was 0.067 mm (best-fit sphere [BFS]), 0.110 diopters (D; power within 5 mm), 0.158 D (power within 3 mm), and 0.46 (eccentricity). Repeatability was high for PCC BFS and power measurements within 3-mm and 5-mm zones (CV(w) ranged from 0.5%-1.2%) but poor for eccentricity data (CV(w), 31.6%). Correspondingly, ICCs ranged from 0.89 to 0.98 for PCC BFS and power, and the ICC was 0.20 for PCC eccentricity values. For intersession reproducibility, on average, no difference in PCC measurements could be found, indicating that when there is variability, it is due to random factors. The width of the 95% LoA between sessions was clinically acceptable for BFS (0.25 mm) and power (0.4 D [within 5 mm] and 0.6 D [within 3 mm]). Similarly, ICCs indicated good intersession reliability for BFS and power (0.98, 0.96, and 0.85 for BFS, power within 5 mm, and power within 3 mm, respectively) but poor reliability for eccentricity (0.59). Repeatability and reproducibility were unrelated to stromal bed thickness.

CONCLUSIONS

Orbscan II provides reliable post-LASIK PCC data for symmetrical parameters (BFS and power), independent of the residual stromal bed thickness, but is unreliable for measurements that are radially asymmetrical (eccentricity). Orbscan II is useful for monitoring the PCC after LASIK once the early postoperative period is over.

Posterior Corneal Curvature Changes after Undersurface Ablation of the Flap and In-the-Bed LASIK Retreatment

OBJECTIVE

To analyze LASIK retreatment-induced changes in the posterior corneal curvature (PCC) with undersurface ablation of the flap (UAF) and in-the-bed techniques.

DESIGN

Nonrandomized, comparative, interventional study.

PARTICIPANTS

Forty-six eyes with a residual spherical equivalent refraction between -0.37 and -2.75 diopters (D) and astigmatism between 0.0 and -1.25 D were included prospectively. In 23 eyes, the calculated postenhancement flap thickness exceeded 150 microm using micropachymetric optical coherence tomography, whereas with further ablation of the bed, the residual bed thickness (RBT) would have been <250 microm, or <55% of the pre-LASIK central pachymetry. In another 23 eyes, RBT allowed the planned ablation for a calculated post-retreatment RBT exceeding 250 microm, >55% of the pre-LASIK central pachymetry.

INTERVENTION

Eyes with insufficient RBT for further ablation underwent UAF retreatment, whereas those with adequate RBT received conventional in-the-bed LASIK retreatment. Examinations were performed before retreatment and 3 and 6 months postoperatively. No eye was lost to follow-up.

MAIN OUTCOME MEASURES

Micropachymetry, Orbscan II scanning-slit PCC data, and visual acuity (VA).

RESULTS

The groups did not differ in age, intraocular pressure, or retreatment ablation depth, but the UAF eyes had a lower mean pre-retreatment RBT (270.7+/-25.4 microm) than conventional enhancement eyes (353.0+/-41.5 microm) (P = 0.001). Eyes undergoing UAF had no significant change in PCC, whereas eyes undergoing conventional retreatment had an increase in the posterior corneal power within the central 3-mm zone (P = 0.008) 3 months after retreatment. No significant changes occurred thereafter. The amount of change in posterior corneal power within the 3-mm central zone from before to after retreatment differed significantly between the groups (mean difference, 0.135 D; 95% confidence interval, 0.022-0.248 D; P = 0.02). No keratectasia developed clinically, and no retreated eye lost or gained > or =2 lines of best-corrected VA. Six months after retreatment, the efficacy and safety indices for the UAF procedure were 0.96 and 1.01, respectively, and 1 and 1.06 for conventional LASIK enhancement.

CONCLUSION

Undersurface ablation of the flap retreatment appears to have less potential for changing the posterior corneal surface than conventional LASIK enhancement and can help reduce the likelihood of retreatment-induced keratectasia.

Correlations Between Central and Peripheral Changes in Anterior Corneal Topography After Myopic LASIK and Their Implications in Postsurgical Contact Lens Fitting

PURPOSE

To investigate the changes in central and peripheral anterior corneal curvatures after myopic laser in situ keratomileusis (LASIK) and to correlate them with the manifest refractive change to discuss how such results could affect post-LASIK corneal topography profiles and midterm stability and their implications in postsurgical contact lens fitting.

METHODS

Topographic and refractive data from 18 eyes of 11 patients that had undergone myopic LASIK were collected for 6 months after surgery. Short-term and midterm topographic responses were investigated and correlated with spherical equivalent manifest refractive changes.

RESULTS

There was a strong correlation between eccentricity changes and manifest refractive change 15 days after surgery (r = 0.753, P < 0.001), with no significant changes thereafter for the following 6 months (r = 0.148, P = 0.114). A strong linear relationship was found between baseline manifest refraction and changes in corneal curvature at the center (r = 0.810, P < 0.001), 4-mm chord (r = 0.895, P < 0.001), and 6-mm chord (r = 0.696, P < 0.001). Statistically significant changes were also found after the first 15 days (P < 0.005) and showed a regression effect that affects the three zones. In this case, a weaker relationship was found between curvature regression and the final refractive change for the central location (r = 0.412, P = 0.004), 4-mm chord area (r = 0.430, P = 0.003), and 6-mm chord area (r = 0.283, P = 0.023). CONCLUSIONS.: After myopic LASIK, the anterior corneal dioptric power is expected to change, on average, approximately 77% of the attempted spherical equivalent correction at the center; 60% at the 4-mm chord region, where the stronger correlation between topographic and refractive change is found; and 30% at the 6-mm chord area. The paracentral area 4 mm from the center seems to be more likely to predict baseline corneal curvature from manifest refractive change. Some degree of regression in the midterm period is expected to occur after myopic LASIK, which shows a significant correlation with the manifest refractive change. Again, this effect is more evident and more accurately predicted at the 4-mm chord area. The results of the current study are of interest for those fitting contact lenses after myopic LASIK.

Avoidance, recognition, and management of LASIK complications

PURPOSE

To provide important concepts of the latest developments in laser in situ keratomileusis (LASIK) complication avoidance, recognition, and management.

DESIGN

A perspective.

METHODS

A comprehensive literature search and review of a total of 816 publications that discussed LASIK complications from 1992 to 2005 was conducted.

RESULTS

The risk of visually threatening complications is inherent in any ophthalmologic surgical procedure. Not only does LASIK require the use of several complex medical devices, but there can be significant human variation in response to this surgical intervention. As a result, many potential complications can occur after LASIK. The risk of many complications can be mitigated by appropriate patient selection and preoperative, surgical, and postoperative care. Unforeseen complications will occur, despite meticulous planning, and must be managed. Important current developments in the avoidance, recognition, and management of LASIK complications are reviewed.

CONCLUSIONS

Complications as a result of LASIK can threaten vision and may cause debilitating symptoms in an otherwise healthy eye. Advancing our understanding of the prevention and management of the complications of LASIK is an endeavor that must be continued as long as refractive surgery is performed.

Management of a post-ELLKAT keratectasia with a gas permeable contact lens

BACKGROUND

The Excimer laser keratoplasty of augmented thickness for keratoconus (ELLKAT) has been proposed for the refractive management of keratoconus.

CASE REPORT

A 41-year-old man with a history of bilateral keratoconus came to the clinic for a contact lens. He had undergone an ELLKAT procedure in his right eye some months earlier in an attempt to obtain acceptable unaided vision. As the result in this eye was not positive, the surgery in the fellow eye was cancelled. On examination, I diagnosed a centrally located keratectasia (KE) in his RE. After surgery, the corneal shape presented some complications in relation to contact lens fitting. The patient was able to achieve 6/9.6 acuity with adequate comfort with a Soper lens using a "modified three-point touch" relationship.

CONCLUSIONS

The surgical procedure of ELLKAT can exhibit some advantages with regard to the penetrating keratoplasty. In this case, because a keratectasia was induced, a contact lens fitting was needed to restore vision. A gas permeable contact lens with a Soper design and with a "modified three-point touch" fitting was a viable clinical solution. The fitting of contact lenses in cases of keratectasia can be a practical solution that may avoid the need for further surgery.