Ziemer Group Research Articles

Biomechanical changes after keratorefractive lenticule extraction with CLEAR and after femtosecond LASIK, correlated with optical coherence tomography findings

The aim of this retrospective, comparative, single-eye study was to assess the biomechanical changes after laser correction of myopia by keratorefractive lenticule extraction (KLEx) and by femtosecond LASIK (FS-LASIK), correlating them with the stromal changes on anterior segment optical coherence tomography. Corneal biomechanical parameters, provided by the high-speed Scheimpflug camera CorVis-ST (Oculus Optikgeräte GmbH) and measured pre-operatively and 1 week post-operatively, were: stiffness parameter at first applanation (SP-A1), stress-strain index (SSI), inverse integrated radius (IIR), deformation amplitude ratio at 2 mm (DA ratio-2mm). A total of 79 eyes undergone KLEx (CLEAR, Ziemer Group) and 93 eyes undergone FS-LASIK were included. The mean residual stromal bed (RSB) was 271.36±17.22 µm after KLEx and 304.21±21.82 µm after FS-LASIK (p=0.00). All parameters in both groups showed statistically significant post-operative changes (p=0.00), except for SSI after FS-LASIK (p=0.39). The percent changes in all parameters were significantly higher in the KLEx group. Even in the eyes with equal RSB (300±5 µm; 19 eyes post-KLEx, 26 eyes post-FS-LASIK), changes were significantly higher after KLEx (SP-A1: -35.9%; SSI: -6.7%) than after FS-LASIK (SP-A1: -29.6%; SSI: -3.8%) (respectively, p=0.02, and p=0.00). In KLEx, reduction in stromal thickness had a weak correlation with reduction in SP-A1 (r=0.39), and poor correlation with reduction in SSI (r=0.26). In conclusion, stiffness parameters were significantly worse after KLEx than after FS-LASIK, even in eyes ending with similar RSB. These findings should be valued cautiously, as the CorVis-ST might not capture all the clinically significant alterations, especially in the post-KLEx bi-layered cornea.

Acoustic density of the sclera of keratoconus eyes and its clinical significance

Purpose: to assess the biophysical properties of the sclera by measuring its acoustic density in keratoconus, highly myopic, and healthy eyes. Material and methods. We examined 34 patients (67 eyes) aged 15–45 with keratoconus of various stages, 15 patients (30 eyes) aged 17–28 with high myopia and 15 people (30 eyes) aged 28–37 without ophthalmic pathology. The acoustic density of the sclera (ADS) was measured on the Voluson Е8 ultrasound device (GE Healthcare, USA) in the posterior eye pole (ADS-1) and in the equatorial area (ADS-2). The axial length (AL) of the eye, corneal thickness (CT), anterior chamber depth (ACD), and lens thickness (LT) were determined using Galilei G6 (Ziemer Group, Switzerland). The vitreal chamber depth (VCD) was calculated according to the formula: VCD = AL – СT – ACD – LT. Results. In keratoconus patients, the average ADS-1 value was 242.5 ± 7.4 conventional units (CU), ADS-2 averaged 234.1 ± 12.1 CU, AL was 24.6±1.1 mm long, and VCD was 17.1 ± 0.4 mm. In high myopia group, the average value proved to be significantly lower: ADS-1 was 210.3 ± 15.7 CU, ADS-2 — 201.2 ± 11,2 CU, while AL and VCD were higher: resp. 27.0 ± 0.7 mm and 19.2 ± 0.5 mm (p < 0,05). In the control group (healthy eyes), ADS-1 was 247.5 ± 2.8 and ADS-2 was 238.1 ± 0.6 CU, which practically showed no difference to the keratoconus group (p > 0.05). AL was 23.7 ± 0.6 mm, and VCD was 16.0 ± 0.6 mm. An insignificant tendency toward ADS drop in keratoconus eyes with AL over 25.0 mm was observed. Probably, we are dealing here with a combination of keratoconus with axial myopia. Conclusion. The acoustic density of the sclera of keratoconus patients approaches the respective parameter of healthy eyes and is significantly higher than that of highly myopic eyes. The analysis of acoustic density of the sclera and vitreal chamber depth may be considered as a method of additional differential diagnostics of keratoconus and congenital myopia with high corneal refraction and astigmatism.

Change in Stromal Thickness and Anterior Curvature After Refractive Corneal Lenticule Extraction With the CLEAR Application

To measure the changes in stromal thickness and anterior corneal curvature after corneal lenticule extraction for the correction of myopia and myopic astigmatism with the Corneal Lenticule Extraction for Advanced Refractive correction (CLEAR) application (Ziemer Group). The correlations between achieved correction on maximum myopic meridian and stromal thinning and spherical equivalent of achieved correction and anterior corneal flattening were evaluated by optical coherence tomography 6 months after CLEAR in 78 eyes of 78 patients in a retrospective, consecutive, non-comparative case series study. With an optical zone of 6.5 mm (52 eyes), the mean correction achieved was -5.80 ± 1.52 diopters (D) (range: -2.25 to -9.25 D), the mean stromal thinning was 104 ± 15 µm (range: 76 to 138 µm), and the regression line was: µm of thinning = 8.46 • D of correction + 55.25. With an optical zone of 6 mm (26 eyes), the mean correction achieved was -8.33 ± 1.61 D (range: -5.50 to -11.00 D), the mean stromal thinning was 114 ± 12 µm (range: 93 to 144 µm), and the regression line was: µm of thinning = 6.35 • D of correction + 60.92. With 6.5 mm, the mean corneal flattening was 4.27 ± 0.88 D, and the regression line was: D of flattening = 0.50 • D of correction + 1.60. With 6 mm, the mean corneal flattening was 6.40 ± 0.70 D, and the regression line was: D of flattening = 0.37 • D of correction + 2.36. Stromal thinning and anterior corneal flattening were correlated with the amount of myopic correction in a linear fashion. The thinning was significantly less than predicted by the laser software. [J Refract Surg. 2022;38(12):797-804.].

Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography.

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Effects of chalazia on corneal astigmatism

BackgroundA chalazion is a common eyelid disease that causes eye morbidity due to inflammation and cosmetic disfigurement. Corneal topographic changes are important factors in corneal refractive surgery, intraocular lens power calculations for cataract surgery, and visual acuity assessments. However, the effects of chalazia on corneal astigmatism have not been thoroughly investigated. The changes in corneal astigmatism according to chalazion size and location is necessary for better outcome of ocular surgery. The aim of this study is to evaluate changes in corneal astigmatism according to chalazion size and location.MethodsIn this cross-sectional study, a total of 44 eyes from 33 patients were included in the chalazion group and 70 eyes from 46 patients comprised the control group. Chalazia were classified according to location and size. An autokeratorefractometer (KR8100, Topcon; Japan) and a Galilei™ dual-Scheimpflug analyzer (Ziemer Group; Port, Switzerland) were utilized to evaluate corneal changes.ResultOblique astigmatism was greater in the chalazion group compared with the control group (p < 0.05). Astigmatism by simulated keratometry (simK), steep K by simK, total root mean square, second order aberration, oblique astigmatism, and vertical astigmatism were significantly greater in the upper eyelid group (p < 0.05). Astigmatism by simK, second order aberration, oblique astigmatism, and vertical astigmatism were significantly greater in the large-sized chalazion group (p < 0.05). Corneal wavefront aberration was the greatest in the upper eyelid chalazion group, whole area group, and large-sized chalazion group (p < 0.05).ConclusionsLarge-sized chalazia in the whole upper eyelid should be treated in the early phase because they induced the greatest change in corneal topography. Chalazion should be treated before corneal topography is performed preoperatively and before the diagnosis of corneal diseases.

Effect of femtosecond and microkeratome flaps creation on the cornea biomechanics during laser in situ keratomileusis: one year follow-up.

To compare the corneal biomechanical outcomes at one year after laser in situ keratomileusis (LASIK) with the flaps created by Ziemer and Moria M2 microkeratome with 110 head and -20 blade. Totally 100 eyes of 50 consecutive patients were enrolled in this prospective study and divided into two groups for corneal flaps created by ZiemerFemto LDV and Moria M2 microkeratome with 110 head and -20 blade. Corneal biomechanical properties including cornea resistance factor (CRF) and cornea hysteresis (CH) were measured before and 1, 3, 6, 12mo after surgery by ocular response analyzer. Central cornea thickness and corneal flap thickness were measured by optical coherence tomography. The ablation depth (P=0.693), residual corneal thickness (P=0.453), and postoperative corneal curvature (P=0.264) were not significant different between Ziemer group and Moria 110-20 group after surgery. The residual stromal bed thickness, corneal flap thickness, CH and CRF at 12mo after surgery were significant different between Ziemer group and Moria 110-20 group (P<0.01);Ziemer group gained better corneal biomechanical results. The CRF and CH increased gradually from 1 to 12mo after surgery in Ziemer group, increased from 1 to 6mo but decreased from 6 to 12mo in Moria 110-20 group. Both CRF and CH at one year after surgery increased with the increasing of residual cornea thickness; pre-LASIK CRF, CRF also increased with residual stromal bed thickness, while CH decreased with the increasing of pre-LASIK intraocular pressure and cornea flap thickness (P<0.01). In one year follow-up, femtosecond laser can provide better cornea flaps with stable cornea biomechanics than mechanical microkeratome.

Effect of suction on macular thickness and retinal nerve fiber layer thickness during LASIK used femtosecond laser and Moria M2 microkeratome.

To compare the effect of suction on the macular thickness and retinal nerve fiber layer (RNFL) thickness during laser in situ keratomileusis (LASIK) used Ziemer FEMTO LDV femtosecond laser (Ziemer group) and Moria M2 automated microkeratome (Moria group) for flap creation. Fourier-domain optical coherence tomography (FD-OCT) was used to measure macular thickness, ganglion cell complex thickness and (RNFL) thickness of 204 eyes of 102 patients with the Ziemer femtosecond laser (102 eyes) and the Moria M2 microkeratome (102 eyes) before surgery and 30min; 1, 3d; 1wk; 1, 3mo; 1y after surgery. The average foveal thickness and parafoveal retinal thickness 30min after the surgery were statistically more than that before surgery (Ziemer P<0.001, P=0.003 and Moria P=0.001, P=0.006) and the effect was less in the Ziemer group than that in the Moria group (P all<0.05). The ganglion cell complex thickness was not significantly changed in both groups (P all>0.05). The RNFL thickness was statistically less 30min after surgery in both groups (P=0.014, P<0.001), but the influence was less in Ziemer group than that in Moria group (P=0.038). However, the RNFL thickness had recovered to the preoperative level only 1d after surgery. The suction of femtosecond laser and mechanical microkeratome led to the increase in macular central fovea thickness and the decrease in RNFL thickness values at the early stage after LASIK. The effect of suction on macular and the RNFL thicknesses in Ziemer group is smaller than that in Moria group.

Small-aperture corneal inlay implantation to treat presbyopia after laser in situ keratomileusis

To evaluate the visual outcomes after implantation of a Kamra small-aperture corneal inlay into a femtosecond-created corneal pocket to treat presbyopia in patients who had previous laser in situ keratomileusis (LASIK). Private center, Tokyo, Japan. Prospective interventional case series. Post-LASIK presbyopic patients had inlay implantation into a corneal pocket created by a femtosecond laser at a depth of 200 μm or 250 μm a minimum of 80 μm below the previous LASIK flap interface in the nondominant eye. Uncorrected and corrected distance visual acuities, near visual acuity, and a patient questionnaire on satisfaction, the use of reading glasses, and visual symptoms were evaluated. The study enrolled 223 eyes (223 patients) with a mean age of 53.6 years (range 44 to 65 years) and a mean manifest spherical equivalent of -0.18 diopter (D) (range -1.00 to +0.50 D). The mean uncorrected distance visual acuity in the operated eye decreased 1 line from 20/16 preoperatively to 20/20 6 months postoperatively (P<.001). The mean uncorrected near visual acuity improved 4 lines from Jaeger (J) 8 to J2 (P<.001). At 6 months, significant improvements were observed in patient dependence on reading glasses and patient satisfaction with vision without reading glasses. The 6-month results suggest that implantation of a small-aperture inlay in post-LASIK presbyopic patients improves near vision with a minimal effect on distance vision, resulting in high patient satisfaction and less dependence on reading glasses. Drs. Tomita and Waring are consultants to Acufocus, Inc. Dr. Tomita is a consultant to Ziemer Group AG. No other author has a financial or proprietary interest in any material or method mentioned.

Contribution of posterior corneal astigmatism to total corneal astigmatism

To determine the contribution of posterior corneal astigmatism to total corneal astigmatism and the error in estimating total corneal astigmatism from anterior corneal measurements only using a dual-Scheimpflug analyzer. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Case series. Total corneal astigmatism was calculated using ray tracing, corneal astigmatism from simulated keratometry, anterior corneal astigmatism, and posterior corneal astigmatism, and the changes with age were analyzed. Vector analysis was used to assess the error produced by estimating total corneal astigmatism from anterior corneal measurements only. The study analyzed 715 corneas of 435 consecutive patients. The mean magnitude of posterior corneal astigmatism was -0.30 diopter (D). The steep corneal meridian was aligned vertically (60 to 120 degrees) in 51.9% of eyes for the anterior surface and in 86.6% for the posterior surface. With increasing age, the steep anterior corneal meridian tended to change from vertical to horizontal, while the steep posterior corneal meridian did not change. The magnitudes of anterior and posterior corneal astigmatism were correlated when the steeper anterior meridian was aligned vertically but not when it was aligned horizontally. Anterior corneal measurements underestimated total corneal astigmatism by 0.22 @ 180 and exceeded 0.50 D in 5% of eyes. Ignoring posterior corneal astigmatism may yield incorrect estimation of total corneal astigmatism. Selecting toric intraocular lenses based on anterior corneal measurements could lead to overcorrection in eyes that have with-the-rule astigmatism and undercorrection in eyes that have against-the-rule astigmatism. The authors received research support from Ziemer Group. In addition, Dr.Koch has a financial interest with Alcon Laboratories, Inc., Abbott Medical Optics, Inc., Calhoun Vision, Inc., NuLens, and Optimedica Corp.

Comparison of Central Corneal Thickness Measurements by Galilei Dual-Scheimpflug Analyzer ® and Ultrasound Pachymeter in Myopic Eyes

To compare the central corneal thickness (CCT) measurements by Galilei Dual-Scheimpflug analyzer (GSA) (Ziemer Group, Port, Switzerland) and ultrasound pachymeter (UP) in myopic eyes. In this prospective study, CCT of 161 myopic eyes of 81 refractive surgery candidates (35 female, 46 male; mean age: 23.18 ± 4.08 years) were measured by GSA and UP consecutively. The data were analyzed statistically by paired t test, Bland-Altman plot, and Pearson correlation test to assess the agreement of the measurements. The mean CCTs obtained by GSA and UP were 559.85 ± 30.87 and 560.41 ± 34.45 μm, respectively. No significant difference was found between the measurements (P = .684) and regression analysis showed a high correlation between the measurements obtained with both devices (r = 0.86; P < .001). A strong agreement between the two methods was also found by Bland-Altman plot. In myopic eyes, the CCT measurements of GSA and UP are similar and highly correlated. Because of high agreement between these devices, the GSA is a non-contact method that may be an alternative to UP for measurement of CCT.

Use of a Six-dimensional Eye-tracker in Corneal Laser Refractive Surgery With the SCHWIND AMARIS TotalTech Laser

To evaluate intraoperative six-dimensional (6D) eye movements and postoperative outcomes among aberrated eyes that underwent LASIK treatments with 6D eye-tracking using the SCHWIND AMARIS platform (SCHWIND eye-tech-solutions). Thirty-four patients (58 eyes) were enrolled in the study. Standard examinations and pre-and postoperative wavefront analyses with the Ocular Wavefront Analyzer (SCHWIND eye-tech-solutions) were performed. Treatments were planned using the Custom Ablation Manager and ablations (aspheric ablation [35 eyes] and ocular wavefront [23 eyes]) were performed using the SCHWIND AMARIS TotalTech laser. Laser in situ keratomileusis flaps were cut using the LDV femtosecond laser (Ziemer Group) in all cases. Eye movements were evaluated in terms of cyclotorsion, rolling, and axial movements. Clinical outcomes were evaluated in terms of predictability, refractive outcome, safety, wavefront aberration, and contrast sensitivity. Registration rate was 100% for cyclotorsion, and 90% for rolling and axial movements. Static cyclotorsion was within ±4° in 69% of eyes. Dynamic cyclotorsion was within ±2° in 72% of eyes. Z-movement was within ±0.5 mm in 69% of eyes. At 3-month follow-up, 70% of eyes were within ±0.25 diopters (D) of emmetropia. Mean defocus was -0.12±0.17 D and astigmatism was 0.15±0.25 D. Corrected distance visual acuity improved in 19% of eyes. Laser in situ keratomileusis with active compensation of 6D eye-movements with a 6D eye-tracker using the SCHWIND AMARIS is safe, predictable, and yields excellent outcomes. Refraction and higher order aberrations were reduced to subclinical values postoperatively without applying additional nomograms.

Six-month clinical outcomes after hyperopic correction with the SCHWIND AMARIS Total-Tech laser

Purpose To evaluate postoperative clinical outcomes, and corneal High Order Aberrations, among eyes with hyperopia up to +5 D of spherical equivalent, that have undergone LASIK treatments using the SCHWIND AMARIS laser system. Methods At six-month follow-up, 100 eyes with preoperative hyperopia or hyperopic astigmatism up to +5 D of spherical equivalent were retrospectively analysed. Standard examinations, pre- and postoperative wavefront analysis with a corneal-wavefront-analyzer (OPTIKON Scout) were performed. Aberration-Free aspheric treatments were planned with Custom Ablation Manager software and ablations performed using the SCHWIND AMARIS flying-spot excimer laser system (both SCHWIND eye-tech-solutions). LASIK flaps were created using a LDV femtosecond laser (Ziemer Group) in all cases. Clinical outcomes were evaluated in terms of predictability, refractive outcome, safety, and wavefront aberration. Results At six month, 90 % of eyes achieved ≥ 20/25 UCVA and 44 % achieved ≥ 20/16 UCVA. Seventy-four percent of eyes were within ± 0.25D of spherical equivalent and 89 % within ± 0.50D, with 94 % within 0.50D of astigmatism. Mean spherical equivalent was −0.12 ± 0.51D and 0.50 ± 0.51D for the astigmatism. Fifty-two percent of eyes improved BSCVA vs. only 19 % losing lines of BSCVA. Predictability slope for refraction was 1.03 and intercept +0.01 D. On average, negative corneal spherical aberrations were significantly increased by the treatments, no other aberration terms changed from pre- to postoperative values. Conclusions LASIK for hyperopia and hyperopic astigmatism with SCHWIND AMARIS yields very satisfactory visual outcomes. Preoperative refractions were postoperatively reduced to subclinical values with no clinically relevant induction of corneal HOA.

Posterior Corneal Elevation After LASIK with Three Flap Techniques as Measured by Pentacam

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). 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. 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). 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.

Bilateral Symmetry before and Six Months after Aberration-Free™ Correction with the SCHWIND AMARIS TotalTech Laser: Clinical Outcomes

Purpose To compare the preoperative and postoperative bilateral symmetry between OD and OS eyes that have undergone femto-LASIK using the Ziemer LDV femtosecond laser system, the SCHWIND AMARIS Excimer Laser and the Aberrationfree™ profiles implemented in the SCHWIND Custom Ablation Manager software. Methods A total of 25 LASIK patients were bilaterally evaluated at the six-month follow-up visit. In all cases standard examinations, pre- and postoperative analysis with corneal wavefront topography (OPTIKON Scout) were performed. Aberration-free™ aspheric treatments were devised using the Custom Ablation Manager software and ablations were performed by means of the SCHWIND AMARIS flying-spot excimer laser system (both SCHWIND eyetech- solutions). In all cases LASIK flaps were created using an LDV femtosecond laser (Ziemer Group). The OD/OS bilateral symmetry was evaluated in terms of corneal wavefront aberration. Results Preoperatively, 11 Zernike terms showed significant bilateral (OS-vs.-OD) symmetry, and only 6 Zernike terms were significantly different. Overall, 23 out of the 25 patients showed significant bilateral symmetry, and only 2 out of 25 patients showed significant differences. None of the aberration metrics changed from pre- to postoperative values by a clinically relevant amount. At the 6-month postoperative visit, 12 Zernike terms showed significant symmetry, and 8 terms were significantly different. Overall, 22 out of 25 patients showed significant bilateral symmetry (OS vs. OD), and only 3 out of 25 patients showed significant differences. Also, this postoperative examination revealed that 6 Zernike terms lost significant OS-vs.-OD symmetry, but 4 Zernike terms gained significant symmetry. Finally, 4 patients lost significant bilaterality, and 2 patients gained significant bilaterality: bilateral symmetry between eyes was better maintained in those patients with a clear preoperative bilateral symmetry. Conclusions Aberration-Free Treatments with the SCHWIND AMARIS did not induce clinically significant aberrations, maintained the global OD-vs.-OS bilateral symmetry, as well as the bilateral symmetry between corresponding Zernike terms (which influences binocular summation).

Relationship of Intraocular Pulse Pressure and Spontaneous Venous Pulsations

To determine the influence of intraocular pulse pressure (IOPP) on the presence of spontaneous venous pulsations (SVP) in patients with normal intracranial pressure. Clinic-based cross-sectional study. Forty-seven patients without signs and symptoms of elevated intracranial pressure were recruited from a general ophthalmology clinic. Patients with glaucoma or retinal vascular disease were excluded from the study. IOP was determined by applanation, and IOPP was measured with the Pascal Dynamic Contour Tonometer (Ziemer Group, Port, Switzerland). SVP were assessed by undilated (direct) and dilated indirect ophthalmoscopy. Other variables assessed included age, cup-to-disc ratio, and refractive error (spherical equivalent). The main outcome measure was the presence of SVPs with normal IOPP. The incidence of SVPs declined with increasing age in a nonlinear manner. Dilated examinations yielded the greatest sensitivity for detecting SVPs, with 91.5% of subjects having SVPs. However, in subjects with IOPP of 1.2 mm Hg or more in at least one eye, the incidence of SVPs was 100%. A significant correlation exists between the amplitude of IOPP and the presence of SVPs, with SVPs detected in one or both eyes of all patients with IOPP of 1.2 mm Hg or more. When IOPP is 1.2 mm Hg or more, absent SVPs may be more predictive of elevated intracranial pressure than previously recognized.

Comparison of Flap Adhesion Strength Using the Amadeus Microkeratome and the IntraLase iFS Femtosecond Laser in Rabbits

To compare adhesion strength of flaps created with a mechanical microkeratome and the IntraLase femtosecond laser as well as to analyze the effect of different side-cut configurations. A flap was created in four groups of New Zealand white rabbits--microkeratome group (Amadeus II microkeratome, Ziemer Group AG [5 eyes; 9-mm suction ring and 140-microm head]), and three IntraLase groups (IntraLase iFS 150 kHz femtosecond laser, AMO Inc [9-mm diameter and 120-microm flap each]): normal energy side-cut (4 eyes; side-cut angle 70 degrees, side-cut energy 0.8 microJ); high energy side-cut (4 eyes; side-cut angle 70 degrees, side-cut energy 1.6 microJ); and inverted side-cut (4 eyes; side-cut angle 140 degrees, side-cut energy 0.8 microJ). Flap adhesion strength was measured 75 days after surgery using a tension meter to dehisce the flaps. In the microkeratome group, mean force was 210+/-89 g (range: 151 to 360 g); 492+/-46 g (range: 439 to 540 g) in the normal energy side-cut group; 444+/-13 g (range: 426 to 455 g) in the high energy side-cut group; and 687+/-105 g (range: 552 to 797 g) in the inverted side-cut group. Differences between the microkeratome and all IntraLase groups were highly significant (P=.001), and differences between the inverted side-cut group and the standard 70 degrees side-cut groups were statistically significant (P=.01). Flap adhesion is significantly stronger with the IntraLase femtosecond laser than with the Amadeus mechanical microkeratome, and an inverted side-cut increases flap adhesion significantly compared with a standard side-cut.