Faculty Bibliography

PURPOSE: To comparatively investigate the efficacy of the enhanced Athens Protocol procedure guided by novel Placido-derived topography with cyclorotation compensation (the cyclorotation adjusted group) to similar cases guided by Scheimpflug-derived tomography without cyclorotation compensation (the non-cyclorotation adjusted group). METHODS: Two groups were evaluated: the cyclorotation adjusted group (n = 110 eyes) and the non-cyclorotation adjusted group (n = 110 eyes). Analysis was based on digital processing of Scheimpflug imaging derived curvature difference maps preoperatively and 3 months postoperatively. The vector (r, vartheta) corresponding to the steepest corneal point (cone) on the preoperative surgical planning map (rp, varthetap) and on the curvature difference map (rd, varthetad) were computed. The differences between the peak topographic angular data (Deltavartheta = |varthetap - varthetad|) and weighted angular difference (WDeltavartheta = Deltavartheta x Deltar) were calculated. RESULTS: For the cyclorotation adjusted group, Deltavartheta was 7.18 degrees +/- 7.53 degrees (range: 0 degrees to 34) and WDeltavartheta was 3.43 +/- 4.76 mm (range: 0.00 to 21.41 mm). For the non-cyclorotation adjusted group, Deltavartheta was 14.50 degrees +/- 12.65 degrees (range: 0 degrees to 49 degrees ) and WDeltavartheta was 10.23 +/- 15.15 mm (range: 0.00 to 80.56 mm). The cyclorotation adjusted group appeared superior to the non-cyclorotation adjusted group, in both the smaller average angular difference between attempted to achieved irregular curvature normalization and in weighted angular difference, by a statistically significant margin (Deltavartheta: P = .0058; WDeltavartheta: P = .015). CONCLUSIONS: This study suggests that employment of the novel Placido-derived topographic data of highly irregular corneas, such as in keratoconus, treated with topography-guided profile with cyclorotation compensation leads to markedly improved cornea normalization. [J Refract Surg. 2015;31(11):768-773.].

PURPOSE: To evaluate corneal stromal thickness reduction and compare to attempted and achieved ablation depth in a consecutive case series study of myopic LASIK. METHODS: Stromal thickness reduction was retrospectively evaluated in 205 consecutive eyes of 205 patients undergoing myopic and myopic astigmatic LASIK. Anterior segment optical coherence tomography was performed preoperatively and 3 months postoperatively. Epithelial thickness remodeling was also accounted for to achieve objective stromal thickness reduction. The derived maximum stromal thickness reduction was then compared to the programmed (planned) maximum ablation depth. Deviation of planned versus achieved maximum stromal thickness changes was correlated with residual refractive error. RESULTS: The 3-month stromal reduction was 86.01 +/- 28.28 microm, compared to the average programmed maximum ablation depth of 88.48 +/- 26.05 microm. The attempted versus achieved thickness outliers correlated with deviations in achieved refractive correction. CONCLUSIONS: Actual objective stromal thickness reduction following myopic LASIK correlates well with the attempted versus achieved refractive change. [J Refract Surg. 2015;31(9):628-632.].

PURPOSE: To evaluate and investigate the distribution and repeatability of anterior corneal surface astigmatism measurements (axis and magnitude) using a novel corneal topographer. METHODS: Anterior corneal surface astigmatism was investigated in a total of 195 eyes using a novel multicolored spot reflection topographer (Cassini; i-Optics). Two patient groups were studied, a younger-age group A and an older-age group B. Three consecutive acquisitions were obtained from each eye. The repeatability of measurement was assessed using Bland-Altman plot analysis and is reported as the coefficient of repeatability. RESULTS: Group A (average age 34.3 years) had on average with-the-rule astigmatism, whereas the older-age group B (average age 72.3 years) had on average against-the-rule astigmatism. Average astigmatism magnitude measurement repeatability in group A was 0.4 diopters (D) and in group B 0.4 D. Average astigmatism axis measurement repeatability in group A was 5.4 degrees and in group B 5.5 degrees. The axis measurement repeatability improved with increasing magnitude of astigmatism: in the subgroups with astigmatism between 3.0 and 6.0 D, the axis repeatability was 1.4 degrees (group A) and 1.2 degrees (group B), whereas in the subgroups with astigmatism larger than 6.0 D, the repeatability was 1.1 and 0.6 degrees, respectively. CONCLUSIONS: This novel corneal topography device seems to offer high precision in reporting corneal astigmatism. This study reaffirms the established trend of a corneal astigmatism shift from an average "with-the-rule" to "against-the-rule" with aging.

PURPOSE: To evaluate the safety, efficacy, and refractive and keratometric stability of myopic femtosecond laser in situ keratomileusis (LASIK) with concurrent prophylactic high-fluence corneal collagen crosslinking (CXL) compared with the outcomes of standard femtosecond LASIK. SETTING: Private clinical practice, Athens, Greece. DESIGN: Consecutive randomized prospective comparative study. METHODS: Eyes that had myopic LASIK or myopic LASIK with concurrent high-fluence CXL were evaluated preoperatively and up to 2 years postoperatively for manifest refraction spherical equivalent (MRSE), refractive astigmatism, visual acuity, corneal keratometry (K), and endothelial cell count. RESULTS: One hundred forty consecutive eyes had myopic LASIK; 65 of the eyes were treated additionally with CXL. In the LASIK-CXL eyes, the mean postoperative MRSE was -0.18 diopter (D) +/- 17.0 (SD) from -6.67 +/- 2.14 D preoperatively. The postoperative flat K was 37.67 D from 43.92 D, and the steep K was 38.38 D from 45.15 D. The correlation coefficient of SE correction predictability was 0.975. In the LASIK-only eyes, the mean postoperative MRSE was -0.32 +/- 0.24 D from -5.49 +/- 1.99 D preoperatively. The flat K was 38.04 D from 43.15 D, and the steep K was 38.69 D from 44.03 D. The correlation coefficient of SE correction predictability was 0.968. The differences between the 2 groups at the 20/20 and 20/25 levels were statistically significant (P = .045 and P = .039, respectively). CONCLUSION: Two-year results indicate that the application of prophylactic CXL concurrently with high-myopic LASIK appears to improve refractive and keratometric stability, presumably by affecting corneal biomechanical properties. FINANCIAL DISCLOSURE: Dr. Kanellopoulos is a consultant to Alcon Surgical, Inc., Wavelight Laser Technologie AG, Allergan, Inc., Avedro, Inc., and i-Optics Corp. Dr. Asimellis has no financial or proprietary interest in any material or method mentioned.

BACKGROUND/AIMS: To evaluate ex vivo biomechanical and enzymatic digestion resistance differences between standard myopic laser in-situ keratomileusis (LASIK) compared with LASIK+CXL, in which high-irradiance cross-linking (CXL) is added. METHODS: Eight human donor corneas were subjected to femtosecond-assisted myopic LASIK. Group A (n=4) served as a control group (no CXL). The corneas in LASIK+CXL group B were subjected to concurrent prophylactic high-irradiance CXL (n=4). Saline-diluted (0.10%) riboflavin was instilled on the stroma, subsequently irradiated with UV-A through the repositioned flap. The cornea stroma and flap specimens were separately subjected to transverse biaxial resistance measurements; biomechanical differences were assessed via stress and Young's shear modulus. Subsequently, the specimens were subjected to enzymatic degradation. RESULTS: For the corneal stroma specimen, stress at 10% strain was 128+/-11 kPa for control group A versus 293+/-20 kPa for the LASIK+CXL group B (relative difference Delta=+129%, p<0.05). The stress in group B was also increased at 20% strain by +68% (p<0.05). Shear modulus in group B was increased at 10% strain by +79%, and at 20% strain by +48% (both statistically significant, p<0.05). The enzymatic degradation time to dissolution was 157.5+/-15.0 min in group A versus 186.25+/-7.5 min in group B (Delta=+18%, p=0.014). For the flaps, both biomechanical, as well as enzymatic degradation tests showed no significant differences. CONCLUSIONS: LASIK+CXL appears to provide significant increase in underlying corneal stromal rigidity, up to +130%. Additionally, there is significant relevant enzymatic digestion resistance confirmatory to the above. LASIK flaps appear unaffected biomechanically by the LASIK+CXL procedure, suggesting effective CXL just under the flap.

PURPOSE: To evaluate biomechanical changes induced by in situ corneal cross-linking (CXL) with stromal pocket delivered enhanced concentration riboflavin and high-fluence, high-energy UV-A irradiation. METHODS: Eight human donor corneas were subjected to intrastromal lamellar corneal tissue removal of anterior 140-mum deep, 80-mum thick x 5-mm diameter central stromal buttons, extracted through a 3.5-mm width tunnel, surfacing in the superior cornea periphery. Enhanced concentration riboflavin solution (0.25%) was instilled in the pocket. In study group A (CXL), superficial high-fluence UV-A irradiation was applied, whereas in control group B (no CXL), none. To comparatively assess changes in corneal rigidity, corneal specimens were subjected to transverse biaxial resistance measurements by application of a unidirectional tangential shear force. Biomechanical differences were evaluated through stress and Young shear modulus. RESULTS: Stress at 10% strain was 305 +/- 24 kPa in study group A versus 157 +/- 11 kPa in control group B (relative difference Delta = 107%, P = 0.021). Stress at 20% strain was 1284 +/- 34 kPa in study group A versus 874 +/- 29 kPa in control group B (Delta = 47%, P = 0.043). Average shear modulus in study group A at 10% strain was 6.98 +/- 1.12 MPa versus 4.04 +/- 0.85 MPa in control group B (Delta = 73%, P = 0.036). Average shear modulus in study group A at 20% strain was 11.46 +/- 0.75 MPa versus 8.80 +/- 0.72 MPa in group B (Delta = 30%, P = 0.047). CONCLUSIONS: Adjunct CXL in this ex vivo simulation refractive lens extraction procedure seems to provide significant increase in corneal rigidity, up to +107%. These findings also support our previous reported work on laser in situ keratomileusis combined with CXL.

PURPOSE/OBJECTIVE:To objectively define the effective centration of myopic femtosecond laser-assisted LASIK ablation pattern, evaluate the difference between achieved versus planned excimer laser ablation centration, and compare these results from two different generations of an excimer laser system. METHODS:The study retrospectively evaluated 280 eyes subjected to myopic LASIK. Digital image analysis was performed on Scheimpflug sagittal curvature maps (difference of preoperative to postoperative). Centration was assessed via proprietary software digital analysis of the coordinate displacement between the achieved ablation geometric center and the planned ablation center, which was the corneal vertex. Results from two different excimer laser generations (Eye-Q 400 [140 eyes] and EX500 [140 eyes]; Alcon/WaveLight, Fort Worth, TX) were compared. RESULTS:Radial displacement was on average 360 ± 220 µm (range: 0 to 1,030 µm) in the Eye-Q 400 laser group and 120 ± 110 µm (range: 0 to 580 µm) in the EX500 laser group (P < .01). The percentage of eyes with displacement of greater than 300 µm was 52% in the Eye-Q 400 laser group and 4% in the EX500 laser group. CONCLUSIONS:Displacement of ablation pattern may depend on the laser platform used. The improvement in the efficiency of centration indicates that newer generation excimer lasers with faster eye tracking and active centration control appear to achieve a significantly more accurate centration of myopic ablation patterns. The authors propose this novel, objective technique for laser refractive surgeon evaluation may point out significant outcome measures not currently used in standard metrics of refractive laser efficiency.

PURPOSE: To compare postoperative changes in apparent photopic and mesopic pupil size and centration in relation to cornea reflection landmarks after cataract surgery. SETTING: LaserVision.gr Clinical and Research Eye Institute, Athens, Greece. DESIGN: Prospective consecutive case study. METHODS: Pupils were imaged for pupil size and corneal vertex location before and 1-month after cataract surgery. Digital analysis of pupil images was used to determine the Cartesian coordinates (nasal-temporal, horizontal axis, superior-inferior, vertical axis) of the first Purkinje reflection point (approximating the corneal intersection of the visual axis [corneal vertex]) to the pupil geometric center (approximating the corneal intersection of the line of sight [corneal apex]). Pupil size changes were measured, and the correlation between vertex-to-apex shift changes and postoperative pupil centroid shift was evaluated. RESULTS: The study evaluated 40 eyes. The pupil size (diameter) change corresponded to a relative reduction of -9.8% for photopic pupils and -9.1% for mesopic pupils; the difference was statistically significant (P = .045 and P = .011, respectively). Also, there was a reduction in the centroid shift (all eyes) from a mean of 0.12 mm preoperatively to 0.05 mm postoperatively as a result of the postoperative minus temporal horizontal difference between the corneal vertex and the apex. CONCLUSIONS: Cataract extraction surgery appears to affect pupil size and centration. Specifically, a smaller pupil and less temporal shift were recorded. These data may have clinical relevance in targeted intraoperative intraocular lens centration. FINANCIAL DISCLOSURE: Dr. Kanellopoulos is a consultant to Alcon Surgical, Inc., Wavelight Laser Technologie AG, Allergan, Avedro, Inc., and i-Optics Corp. No author has a financial or proprietary interest in any material or method mentioned.