Optimized Artificial Intelligence for Enhanced Ectasia Detection Using Scheimpflug-Based Corneal Tomography and Biomechanical Data.

PURPOSE: To optimize artificial intelligence (AI) algorithms to integrate Scheimpflug-based corneal tomography and biomechanics to enhance ectasia detection. DESIGN: Multicenter cross-sectional case-control retrospective study. METHODS: A total of 3886 unoperated eyes from 3412 patients had Pentacam and Corvis ST (Oculus Optikgeräte GmbH) examinations. The database included 1 eye randomly selected from 1680 normal patients (N) and from 1181 "bilateral" keratoconus (KC) patients, along with 551 normal topography eyes from patients with very asymmetric ectasia (VAE-NT), and their 474 unoperated ectatic (VAE-E) eyes. The current TBIv1 (tomographic-biomechanical index) was tested, and an optimized AI algorithm was developed for augmenting accuracy. RESULTS: The area under the receiver operating characteristic curve (AUC) of the TBIv1 for discriminating clinical ectasia (KC and VAE-E) was 0.999 (98.5% sensitivity; 98.6% specificity [cutoff: 0.5]), and for VAE-NT, 0.899 (76% sensitivity; 89.1% specificity [cutoff: 0.29]). A novel random forest algorithm (TBIv2), developed with 18 features in 156 trees using 10-fold cross-validation, had a significantly higher AUC (0.945; DeLong, P < .0001) for detecting VAE-NT (84.4% sensitivity and 90.1% specificity; cutoff: 0.43; DeLong, P < .0001) and a similar AUC for clinical ectasia (0.999; DeLong, P = .818; 98.7% sensitivity; 99.2% specificity [cutoff: 0.8]). Considering all cases, the TBIv2 had a higher AUC (0.985) than TBIv1 (0.974; DeLong, P < .0001). CONCLUSIONS: AI optimization to integrate Scheimpflug-based corneal tomography and biomechanical assessments augments accuracy for ectasia detection, characterizing ectasia susceptibility in the diverse VAE-NT group. Some patients with VAE may have true unilateral ectasia. Machine learning considering additional data, including epithelial thickness or other parameters from multimodal refractive imaging, will continuously enhance accuracy. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Traumatic cataract in a young patient with myopia.

A 36-year-old man was referred to our clinic because of traumatic cataract in his right eye, which had developed after being hit in the eye with a badminton shuttle as a child. He noticed that his vision in his right eye was gradually becoming worse. His refraction, corrected with spectacles, was -4.25 -2.00 × 115 in his right eye and -5.50 -1.50 × 57 in his left eye, with a corrected distance visual acuity of 20/32 and 20/20, respectively. Because of allergies, the patient never tolerated contact lens wear for more than 2 hours. On a slitlamp examination, we confirmed anterior subcapsular star-like cataract without any signs of zonulolysis. Optical biometry showed an axial length of 25.73 mm and 26.66 mm and an anterior chamber depth of 3.70 mm and 3.78 mm in the right and left eyes. Keratometric astigmatism measured by optical biometry was 1.56 diopters (D) at 30 degrees and 1.12 D at 138 degrees for the right and left eyes, and Scheimpflug tomography showed 1.1 D of regular astigmatism at 33 degrees in the right eye, and 0.9 D of regular astigmatism at 130 degrees in the left eye. The patient is a professional photographer and asked for a treatment that would still allow him to be able to perform his job: he wants to read all the buttons on the camera up close and focus on the scenery in the distance. What is your advice on this challenging case?

COVID-19 outbreak and increased risk of amblyopia and epidemic myopia: Insights from EUROCOVCAT group.

The most common cause of vision impairment in children is amblyopia. It is defined as impaired visual acuity in one or both eyes that is present with no demonstrable abnormality of the visual pathway and is not immediately resolved by wearing glasses. After the World Health Organization (WHO) recognized COVID-19 as a global pandemic on March 11, 2020, widespread changes and restrictions to social and sanitary practices have presented significant issues in access to eye care during the COVID-19 pandemic. A reduction of more than 80% in pediatric eye care volume up to its total cessation has been observed in different departments. In this scenario, reduced or absent eyesight, due to delay in timely treatment of amblyopic conditions, could create major, long-lasting effects on all aspects of life, including daily personal activities, interacting with the community, school and work opportunities and the ability to access public services. Processes coming out of lockdown should be gradually easing restrictions giving priority to ophthalmology and eye care facilities so that amblyopia does not remain unattended and irreversible as in adults due to lack of timely treatments. If not reversible, this process could lead to a dramatic increase in disability and unsustainable social costs for many governments.

Impact on refractive surgery due to increasing use of personal protection equipment: Insights from EUROCOVCAT group.

Since the World Health Organization declared COVID-19 to be a pandemic on 11th March 2020, changes to social and sanitary practices have included significant issues in access and management of eye care during the COVID-19 pandemic. Additionally, the fear of loss, coupled with social distancing, lockdown, economic instability, and uncertainty, have led to a significant psychosocial impact that will have to be addressed. In the current COVID-19 pandemic, personal protective equipment such as face masks or face coverings have become a daily necessity. While "mass masking" along with hand hygiene and social distancing became more widespread, new issues began to emerge - particularly in those who wore spectacles as a means of vision correction. As we began to see routine patients again after the first lockdown had been lifted, many patients visited our clinics for refractive surgery consultations with a primary motivating factor of wanting spectacle independence due to the fogging of their spectacles as a result of wearing a mask. In this article, we report on new emerging issues in eye care due to the widespread use of masks and on the new unmet need in the corneal and cataract refractive surgery fields.

Detection of postlaser vision correction ectasia with a new combined biomechanical index.

PURPOSE: To validate and evaluate the use of a new biomechanical index known as the Corvis biomechanical index-laser vision correction (CBI-LVC) as a method for separating stable post-LVC eyes from post-LVC eyes with ectasia. SETTING: 10 clinics from 9 countries. DESIGN: Retrospective, multicenter, clinical study. METHODS: The study was designed with 2 purposes: to develop the CBI-LVC, which combines dynamic corneal response (DCR) parameters provided by a high-speed dynamic Scheimpflug camera (CorVis ST; OCULUS Optikgeräte GmbH) and then to evaluate its ability to detect post-LVC ectasia. The CBI-LVC includes integrated inverse radius, applanation 1 (A1) velocity, A1 deflection amplitude, highest concavity and arclength, deformation amplitude ratio of 2 mm, and A1 arclength in millimeters. Logistic regression with Wald forward stepwise approach was used to identify the optimal combination of DCRs to create the CBI-LVC and then separate stable from LVC-induced ectasia. Eighty percentage of the database was used for training the software and 20% for validation. RESULTS: 736 eyes of 736 patients were included (685 stable LVC and 51 post-LVC ectasia). The receiver operating characteristic curve analysis showed an area under the curve of 0.991 when applying CBI-LVC in the validation dataset and 0.998 in the training dataset. A cutoff of 0.2 was able to separate stable LVC from ectasia with a sensitivity of 93.3% and a specificity of 97.8%. CONCLUSIONS: The CBI-LVC was highly sensitive and specific in distinguishing stable from ectatic post-LVC eyes. Using CBI-LVC in routine practice, along with topography and tomography, can aid the early diagnosis of post-LVC ectasia and allow intervention prior to visually compromising progression.

Comparability of an image-guided system with other instruments in measuring corneal keratometry and astigmatism.

PURPOSE: To test whether keratometry (K) and astigmatism measurements provided by the Verion Reference Unit (an image-guided system) compared well with the Tonoref II automated tonometer-refractometer, IOLMaster partial coherence interferometry (PCI) biometer, AL-Scan optical biometer, Pentacam rotating Scheimpflug camera, and OPD Scan III wavefront aberrometer. SETTING: Augenklinik am Neumarkt, Cologne, Germany. DESIGN: Retrospective case series. METHODS: Patients having routine cataract surgery had standard preoperative assessment including biometry measurement with all study devices. The K values, power of astigmatism, axis, and the lens power of an imaginary intraocular lens (IOL) were analyzed for each device. RESULTS: One hundred five eyes of 62 patients with a mean age of 68.5 years ± 11.9 (SD) (range 27.2 to 89.7 years) were included in the study. The mean differences in flat K readings between the image-guided system and the tonometer-refractometer, PCI biometer, optical biometer (2.4 and 3.2 mm), rotating Scheimpflug camera, and wavefront aberrometer were -0.03 mm, 0.00 mm, 0.01 mm (both 2.4 and 3.2 mm), -0.03 mm, and -0.01 mm, respectively (P < .001). Differences were slightly greater for steep K readings as follows: -0.04 mm, -0.01 mm, -0.02 (optical biometer 2.4 mm), -0.03 mm (optical biometer 3.2 mm), -0.04 mm, and -0.06 mm, respectively (P < .001). The calculated power of an imaginary IOL from the study devices fell within 0.28 diopter of one another (P > .05). CONCLUSIONS: The image-guided system compared well with and provided astigmatism measurements similar to those of currently available diagnostic measurement devices. This system can aid appropriate preoperative IOL power calculations. FINANCIAL DISCLOSURES: Drs. Schultz, Oberheide, and Kermani have received honoraria from Alcon Pharma GmbH for corporate presentations.

Rotation stability of the cachet angle-supported phakic intraocular lens.

PURPOSE: To evaluate the rotational stability of an acrylic angle-supported phakic intraocular lens (PIOL) 12 months after implantation in myopic eyes. METHODS: Patients with a history of moderate to high myopia underwent unilateral or bilateral implantation of an acrylic angle-supported PIOL (AcrySof Cachet; Alcon Laboratories, Inc., Fort Worth, TX). All were followed up for 12 months. IOL rotation was assessed using digital overlay of ocular photographs captured within 2 weeks of implantation and at postoperative month 12. The secondary outcomes of refractive power (spherical equivalent, refractive sphere, and cylinder) and uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) were assessed preoperatively and again at 3 months after implantation. RESULTS: Fifty eyes of 28 patients with a mean age of 32 years were included in this retrospective cohort study. All underwent successful IOL implantation and follow-up. A mean 12-month rotation of 11° was observed (standard deviation: 15.1°, range: 0 to 60°). All preoperative measures (mean) of refractive power improved by 3 months postoperatively (spherical equivalent = -0.35 ± 0.79 diopters [D], spherical refraction = 0.04 ± 0.82 D, and cylindrical refraction = -0.77 ± 0.91 D). Two percent of eyes requiring additional laser adjustment by postoperative month 12, primarily due to corneal astigmatism. CONCLUSION: The study findings suggest that AcrySof Cachet angle-supported PIOLs offer moderate 1-year rotational stability. Because this type of IOL also corrects myopia effectively, it appears to be a good treatment option for myopic eyes. However, the rotation that occurs makes it unsuitable for cylinder corrections.

Control of femtosecond thin-flap LASIK using OCT in human donor eyes.

PURPOSE: Thin-flap keratomileusis is a procedure that minimizes LASIK flap thickness to preserve both the corneal epithelium and the maximum residual stroma. This study investigated the usefulness of optical coherence tomography (OCT) as a tool in guiding the femtosecond laser in the creation of a thin flap in human eyes in a non-randomized case series. METHODS: In a private research laboratory, an in vitro investigation was performed on human autopsy eyes. Five human cadaver eyes, unsuitable for transplantation, underwent flap creation with a femtosecond laser. The laser procedure was controlled in real-time with an OCT system (Thorlabs HL AG) to ensure that the cut was placed just underneath Bowman's layer. The repetition rate of the femtosecond laser was 10 MHz with a single-pulse duration of <400 femtoseconds (pulse energy in the nJ range). As a control, all eyes underwent histological dissection and were examined using light microscopy. RESULTS: Video monitoring of the flap creation supported the feasibility of real-time OCT monitoring of the femtosecond laser flap creation process. A clear distinction of the corneal epithelium was possible in all eyes. Bowman's layer was not identified in all donor eyes at the given resolution of the OCT device used in this study. Light microscopy demonstrated flaps approximately 50-microm thick, confirming that the real-time monitoring assured a positioning of the cutting plane at minimum distance underneath Bowman's layer. CONCLUSIONS: This study of five human cadaver eyes shows that real-time OCT monitoring of the creation of thin-flaps in LASIK using a femtosecond laser is possible, thus ensuring that the flap is created at the desired depth.

Dual intraocular lens implantation: Monofocal lens in the bag and additional diffractive multifocal lens in the sulcus.

PURPOSE: To evaluate a new diffractive multifocal intraocular lens (IOL) as an additional (add-on) IOL for sulcus-based implantation. SETTING: Augenklinik am Neumarkt, Köln, Germany. METHODS: In this prospective study, cataract patients had phacoemulsification and IOL implantation. After phacoemulsification, an aspheric silicone monofocal IOL (MS 612 ASP-Y) with a power range of +4.00 to +27.00 diopters [D]) was implanted in the capsular bag. This was followed by sulcus placement of an add-on multifocal IOL (MS 714 PB) with a +3.50 D diffractive element for near but zero refractive power for distance. RESULTS: The study included 56 eyes of 30 patients. Three months postoperatively, the mean monocular uncorrected distance visual acuity was 0.10 logMAR +/- 0.11 (SD) (median 1.00 decimal; 20/20 Snellen), with a remaining mean postoperative spherical equivalent of 0.01 +/- 0.51 D. The mean uncorrected intermediate visual acuity was 0.20 +/- 0.15 logMAR (median 0.63 decimal; 20/30 Snellen) with a luminance of 500 lux at 1 m. The mean uncorrected near visual acuity (Early Treatment Diabetic Retinopathy chart) was 0.16 +/- 0.13 logMAR (median 0.80 decimal; Jaeger 2). No major complications (eg, iris chafing, iris capture, lens epithelial cell ingrowth, glaucoma) were associated with the add-on IOL in the sulcus. CONCLUSIONS: Combined implantation of an add-on diffractive sulcus IOL and a monofocal capsular bag IOL was safe and effective in improving far and near visual acuity in cataract surgery. Preliminary visual acuity results were similar to those in eyes with a single 1-piece diffractive multifocal IOL.

Outcomes of hyperopic LASIK with the NIDEK NAVEX platform centered on the visual axis or line of sight.

PURPOSE: To report refractive outcomes of hyperopic LASIK with automated centration on the visual axis compared with centration on the line of sight (LOS). METHODS: The NIDEK Advanced Vision Excimer Laser platform (NAVEX) was used to treat 181 hyperopic eyes with centration on the LOS (LOS group) and 64 hyperopic eyes with centration on the visual axis (visual axis group). The coordinates of the visual axis were digitally transferred to the excimer laser system based on the positional relationship between the LOS and the coaxially sighted corneal light reflex. All eyes were treated with a 6.5-mm optical zone and 9.0-mm transition zone. Three-month postoperative outcomes were retrospectively analyzed. RESULTS: The preoperative manifest refraction spherical equivalent (MRSE) was +2.57+/-1.26 diopters (D) (range: 0.13 to 5.63 D) in the visual axis group and +2.46+/-1.32 D (range: 0.38 to 5.63 D) in the LOS group. The postoperative MRSE was +0.29+/-0.70 D (range: -1.00 to 1.75 D) in the visual axis group and +0.19+/-0.57 D (range: -0.75 to 1.75 D) in the LOS group. Postoperatively, 81% (38/47) of eyes in the visual axis group and 64% (74/116) of eyes in the LOS group were +/-0.50 D. In the visual axis group, 91% (44/52) of eyes and 92% (102/109) of eyes in the LOS group maintained best spectacle-corrected visual acuity within one line compared with preoperatively. CONCLUSIONS: Initial experience with hyperopic LASIK centered on the visual axis indicated safe and predictable outcomes.

Comparative micromorphologic in vitro porcine study of IntraLase and Femto LDV femtosecond lasers.

PURPOSE: To assess flap creation and stromal bed quality of 2 femtosecond refractive surgery lasers in laser in situ keratomileusis. SETTING: Augenklinik am Neumarkt, Cologne, Germany. METHODS: Corneal flaps were created in 115 freshly enucleated porcine eyes using the 60 kHz IntraLase FS laser (Advanced Medical Optics) and a prototype model of the Femto LDV femtosecond laser (Ziemer Ophthalmic Systems AG). The parameters that were evaluated included actual versus intended thickness by subtraction pachymetry, cutting and total suction time, quality of flap edges, and smoothness of flap beds. Confocal microscopy (Atos PLmu [Altos GmbH]) was used to objectively determine the root mean square (RMS) of the surface roughness of the stromal bed. RESULTS: Cutting time was 31 seconds for the 60 kHz IntraLase FS laser and 38 seconds for the Femto LDV laser. With both lasers, the standard deviation in achieved versus intended flap thickness was small (136 microm +/- 10 and 130 +/- 9 microm, respectively). Under micromorphologic examination, stromal bed quality was slightly better with the IntraLase. The RMS of bed roughness was 1.6 +/- 0.5 microm with the IntraLase and 2.0 +/- 0.4 microm with the Femto LDV. Neither laser showed significant thermal or mechanical damage in adjacent tissue layers of the stromal bed. The laser-induced bubble layer was more pronounced with the IntraLase. CONCLUSION: The laser cuts of the IntraLase FS and Femto LDV femtosecond lasers were equally smooth and of excellent quality. The standard deviation of the flap thickness was small and equal in both systems.

Real-time optical coherence tomography-guided femtosecond laser sub-Bowman keratomileusis on human donor eyes.

PURPOSE: To determine the usefulness of optical coherence tomography (OCT) as a tool in guiding the femtosecond (fs) laser in the creation of a sub-Bowman keratomileusis (SBK) flap in human eyes. DESIGN: A nonrandomized case series. METHODS: In a private research laboratory setting, we performed an in vitro investigation on human autopsy eyes. Five human cadaver eyes, unsuitable for transplantation, underwent flap creation with a fs laser. The laser procedure was controlled in real-time with an OCT system (Thorlabs HL AG, Luebeck, Germany) to ensure that the cut was placed just underneath the Bowman layer. The fs laser worked at a repetition rate of 10 MHz with a single-pulse duration of < 400 fs (pulse energy in the nanoJoule range). As a control, all eyes underwent histologic dissection (toluidine blue) and were examined using light microscopy (LM). RESULTS: Video monitoring of the flap creation supported the feasibility of real-time OCT monitoring of the fs laser flap creation process. A clear distinction of the corneal epithelium was possible in all eyes. The Bowman membrane was not identified in all donor eyes at the given resolution of the OCT used in this study. Still, LM examination confirmed that the real-time monitoring assured a positioning of the cutting plane at minimum distance underneath the Bowman layer. CONCLUSION: This small laboratory test offers evidence that real-time OCT monitoring of creation of a SBK flap using a fs laser is possible, thus ensuring that the flap is created at the proper depth.

Topographic- and wavefront-guided customized ablations with the NIDEK-EC5000CXII in LASIK for myopia.

PURPOSE: To assess refractive outcomes, changes in the total higher order root mean square (RMS) aberration, and changes in higher order wavefront aberrations after LASIK for myopia and myopic astigmatism with the NIDEK Advanced Vision Excimer Laser platform (NAVEX) using either an aspheric or topography-based or whole eye wavefront ablation algorithm. METHODS: This was a retrospective study of 1459 eyes that underwent LASIK for myopia and myopic astigmatism. The mean preoperative spherical equivalent refraction was -4.68 diopters (D) (range: -0.50 to -9.63 D) with astigmatism up to -4.50 D. Treatments were classified into three categories depending on the type of ablation algorithm used--optimized aspheric transition zone (OATz) denoted eyes that underwent aspheric treatment zones; customized aspheric treatment zone (CATz) denoted eyes that underwent customized ablations based on corneal topography; and OPDCAT denoted eyes that underwent customized ablation based on the whole eye wavefront profile. Follow-up data are reported at 3 months (69%) and 12 months (17%) postoperatively. RESULTS: Three months after LASIK, the predictability (10.5 D from target refraction) was 80% for OATz, 91% for CATz, and 76% for OPDCAT. Of all eyes, 96% were within +/- 1.0 D of intended refraction 3 months postoperatively and 100% after 12 months (87% +/- 0.5 D). In the aspheric and custom groups, a notable improvement of uncorrected visual acuity was noted between 3 and 12 months after LASIK. No eye lost >1 line of best spectacle-corrected visual acuity. Mean higher order RMS increased in all groups. CONCLUSIONS: The data support that the treatment of myopia and myopic astigmatism is safe and effective with NAVEX. Customized ablation based on corneal topography rather than on total wavefront error was more predictable.

Automated visual axis alignment for refractive excimer laser ablation.

PURPOSE: To describe the use of new laser alignment and delivery software in the NIDEK Advanced Vision Excimer laser platform (NAVEX) that allows centration based on surgeon specification. METHODS: Descriptive article with a case report. RESULTS: The software allows specification via numeric entry of the exact placement of the laser tapered to the position of the visual axis or the line of sight. CONCLUSIONS: The ability to specify the exact location of the laser ablation based on pupil position is fundamental in patients undergoing custom ablation and those with eccentric fixation. A conservative treatment strategy is recommended for initial experience with this alignment software.

Hyperopic laser in situ keratomileusis with 5.5-, 6.5-, and 7.0-mm optical zones.

PURPOSE: To evaluate the results of laser in situ keratomileusis (LASIK) for the correction of hyperopia and hyperopic astigmatism using a large 7.0-mm optical zone and to compare them with treatments using a 5.5- and 6.5-mm optical zone. METHODS: One hundred sixty-one eyes of 89 patients with a mean preoperative spherical equivalent refraction of +2.44 +/- 1.32 diopters (D) (range: +0.00 to +5.62 D, cylinder 5.25 to 0.00 D) were treated for hyperopia and hyperopic astigmatism using a 7.0-mm optical zone and were analyzed retrospectively. Postoperatively, patients were examined after 1 day, 1 week, 1 month, 3 months, and 1 year. Eyes treated previously at the same center by the same surgeons with 5.5- and 6.5-mm optical zone applications were used as controls. All treatments were performed with the Nidek EC 5000 CXII excimer laser system (Nidek, Gamagori, Japan). A nasal hinged flap was created using the Nidek MK 2000 microkeratome in all cases. RESULTS: The mean postoperative spherical equivalent refraction after 1 month (n=89) was +0.12 +/- 0.72 D (range: -1.75 to +2.75 D), +0.13 +/- 0.74 D (range: -1.88 to +1.62 D) at 3 months (n=70), and +0.20 +/- 0.69 D (range: -1.62 to +1.12 D) at 1 year (n=33). Regression between 1 month and 1 year was 0.08 D in the 7.0-mm optical zone group. Regression was 0.25 D in the 5.5-mm group and 0.02 D in the 6.5-mm optical zone group between 1 month and 1 year. In both the 5.5- and 6.5-mm optical zone groups, 13% of eyes lost one line in visual acuity (2% in the 7.0-mm optical zone group). The gain of one or more lines in visual acuity was 19% in the 5.5-mm group, 17% in the 6.5-mm group, and 27% in the 7.0-mm optical zone group. All data represent primary cases without retreatment. CONCLUSIONS: Increasing the optical zone size from 5.5 mm to 6.5 mm and to 7.0 mm seems to improve refractive results, stability, and safety of hyperopic and hyperopic-astigmatic LASIK treatments. Although some hyperopic and astigmatic eyes are endangered by loss of lines in best spectacle-corrected visual acuity, more eyes gain one or more lines.

Alignment in customized laser in situ keratomileusis.

PURPOSE: To identify fundamentals of beam alignment in customized laser in situ keratomileusis (LASIK) with a special focus on the Nidek NAVEX system. METHODS: Analysis of Nidek specifications and recommendations for beam alignment with regard to a critical case example are presented. The potential impact of misalignment (tilt and defocus) is calculated. Cyclotorsional error evaluation in a normal LASIK population was performed by video image comparison. Potential problems of infrared-based eyetracking systems are discussed. RESULTS: The laser beam should be aligned with reference to the line of sight (LOS) when customized segmental laser ablation is applied. Only in cases with significant offset between the LOS and the visual axis it is recommended not to use segmental ablation and to manually align the beam toward the visual axis. Eye drift (tilt) as well as defocus should be avoided since undercorrection and irregular astigmatism can result. Almost 30% of eyes in a normal LASIK population showed a torsional error of 5 degrees to 10 degrees (9% more than 10 degrees) on video-based image comparison. Eye-trackers not only are defined by take-up speed and latency, but also by their sensibility (picking the real center of the pupil) and robustness (keeping it tracked during surgery). Errors due to parallax and reflex effects can systematically influence the performance of an eyetracker. CONCLUSION: Correct alignment is difficult to achieve but is of fundamental importance in customized LASIK. Strict standardization and further improvement in the alignment strategy is necessary to achieve more consistent results in customized LASIK.

Intrastromal refractive surgery with ultrashort laser pulses: in vivo study on the rabbit eye.

BACKGROUND: Femtosecond (fs) laser pulses may offer new possibilities in the field of refractive surgery, especially when using the laser as a microkeratome. By induction of nonlinear absorption processes the laser can be used to perform intrastromal cuts. The conventional microkeratome, associated with numerous potential side effects, can possibly be replaced. Furthermore, refractive lenticules can be prepared within the stroma and removed in a single-step operation. METHODS: In 10 rabbits, cuts were made to create both a lamellar flap and an intrastromal refractive lenticule. The flap was lifted, the lenticule was extracted and, finally, the flap was repositioned (intrastromal laser keratomileusis, ILK). The corneal samples were collected up to 120 days after treatment and processed for histopathological analysis. RESULTS: All flaps could be opened and prepared lenticules could be extracted in one piece by the surgeon. The treated corneas developed a mild wound healing reaction, comparable to that known from excimer laser in situ keratomileusis (LASIK) studies. The wound healing was restricted to the flap-stroma interface, most pronounced at the periphery of the flaps. CONCLUSIONS: The use of the fs-laser offers new possibilities in preparation of corneal flaps, possibly providing advantages over conventional microkeratomes. Furthermore, the fs-laser has the potential to create intrastromal refractive lenticules for complete refractive procedures (ILK).

Early results of nidek customized aspheric transition zones (CATz) in laser in situ keratomileusis.

PURPOSE: Standard ablation profiles for myopia and myopic astigmatism are spherical in shape and usually induce spherical aberration, often resulting in glare, halo, and other night vision problems. New ablation algorithms with aspheric transition zones may help reduce the amount of induced spherical aberrations in refractive surgery. METHODS: Between September and November 2002, 52 eyes were treated with bilateral laser in situ keratomileusis (LASIK) using a new ablation profile with customized aspherical transition zone (CATz). Results were analyzed from examinations performed 1 day, 1 and 3 months (if available) after surgery, and compared to a standard LASIK patient group. RESULTS: Refractive outcome of patients was within +/- 0.50 D of intended correction in 72% on day 1, and 82% at 1 month after surgery. At 1 month after LASIK, mean spherical equivalent refraction was changed from preoperative mean -6.73 +/- 2.04 D to postoperative mean -0.43 +/- 0.80 D (range -2.00 to +1.50 D). No eye lost more than 1 line of visual acuity; 10% gained 1 line and 80% remained unchanged 1 month after surgery. The topographically visible effective optical zone size was larger than in comparable treatments with standard ablation profiles. Spherical aberration was reduced and no patient complained about night vision problems after surgery. CONCLUSIONS: Customized aspheric transition zones may help reduce induction of spherical aberration in refractive surgical correction of myopia and myopic astigmatism.