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The center of the pupil defines the origin of a Cartesian domain in which the pupil center coordinates can be computed. The corneal reflex « Apex » is a fixed landmark, wheras the pupil center can shift with pupil movements. Currently, there are no clinically available methods to locate the intercept of the visual axis and the corneal surface, which may correspond to the ideal point for laser ablation centering see this page for additional information about visual axis and other ocular axes for centering corneal refractive surgical treatments.
Because of the angle kappa, the corneal reflex appears usually located on the nasal side with respect to the pupil center. Optical zone centration in keratorefractive surgery. Entrance pupil center, visual axis, coaxially sighted corneal reflex, or geometric corneal center? Ophthalmology ; 8 In myopic eyes, the distance of the pupil center and the corneal reflex is usually low about microns or less.
However, in some eyes with hyperopia or high astigmatism , the distance between these points can be as high as to microns. This reflects the existence of a large angle Kappa, defined by the angle between the pupillary axis and the visual axis. Defining the proper axis for centration may become of critical importance in eyes which exhibit a large distance between the pupil center and the « Apex » corneal reflex.
Depending on the deviation between the pupillary axis and visual axis angle Kappa , the location of the visual axis intercept at the corneal plane may vary. A valid assumption is to consider that the visual axis may be located mid way between the corneal reflex and the pupil center.
Several examinations can be taken and averaged. Each examination is verified by the Topolyzer software, and must exceed a quality threshold to be valid for registration and integration in the treatment program sequence in which the desired correction, optical zone diameter, etc. The treatment sequence sphere and cylinder corrections and the anterior segment image data iris images, pupil center coordinates relative to the Apex are transferred to the EX laser system via local network.
It is displayed on the screen of the programming software. Several measurements are taken and provide information on the pupil diameter and location with respect to the apex Pupil Dec. A median value is computed from the various acquired examinations. In this example, due to large angle Kappa, the pupil center at registration with the Topolyzer is located micron temporally, and 60 micron inferiorly, to the apex.
Such variation can occur between the time and conditions of Topolyzer examinations to that of the excimer laser treatment, which follows flap creation or epithelial removal. This shift can be compensated for, provided that it is monitored with respect to a stable landmark.
Under the EX excimer laser, this landmark cannot be the corneal reflex anymore it is not clearly visible after flap lift since the exposed corneal stromal surface is dull , but can still be the limbal ring. It is therefore mandatory to accurately locate the limbus, and iris detail for optimal image matching and comparisons.
At the time of the surgery, after flap creation and lift LASIK surgery , or central epithelial removal PRK surgery , three steps must be completed to perform centration to the desired location after preventing from cyclotorsion and pupil shift:. The limbus diameter measured by the laser camera circle delineating the corneal periphery is compared to the reference image as captured by the Topolyzer and re-normalized to its value. The diameter of the limbus as seen by the laser camera is compared to the data recorded by the Topolyzer.
The diameter of the iris pupil is measured continuously under the laser, and the laser microscope illumination should be adjusted so that the live pupil diameter value gets as close as possible to that of the Topolyzer Vario referenced pupil image. Medical World News. Case Based Roundtable Series. Conferences Conference Coverage. Conference Listing. Conference Recaps. Publications Digital Edition. Europe Ophthalmology Times. Modern Retina. Supplements and Featured Publications.
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So, when is the best time to begin using DataLink Alcon Edition? Right from th e start — with our very first case! Get Brochure. Registration into DataLink Alcon Edition takes on a few minutes. A web-based in-service is scheduled with each surgeon to review the Synoptic Planner. Register today! Enroll Here. We look forward to working with you! Find out More New to the Alcon WaveLight Laser platform? Surgeons who are new to the WaveLight platform benefit from our large library of Starting Nomograms, so the best fit for your patient and surgical style is suggested right from the start — until your own Surgeon-Specific Nomograms have developed.
Been using the Alcon WaveLight Laser platform for some time? Surgeons who have been using the Wavelight platform quickly adapt to the Synoptic Planner and usually obtain Surgeon-Specific Nomograms within just a few days of starting. This aberration decreases the retinal blur circle and increases the depth of field.
In addition, surgeons have learned that they can induce negative spherical aberration by creating a prolate cornea with a negative Q-value of approximately This goal has been made possible by the development of scanning-spot lasers with excellent tracking, treating the peripheral cornea adequately by accounting for loss of laser ablation in the periphery by reflection and ovalization of the beam, and excimer lasers that can create seamless blend zones.
All of these characteristics were built into the initial design of the WaveLight Allegretto laser Alcon Laboratories, Inc.
Approximately 1. This is an off-label procedure in the United States, and appropriate informed consent needs to be obtained from the patient. We perform a myopic treatment at a 5. We then achieve a plano result through the opposite treatment at the different optical zone. This procedure is effective in emme-tropes as well, so its range of applications is greater than that of most other available laser treatments.
My colleagues and I have now treated patients, and surgeons at other centers around the country have operated on another or so patients. Other concerns such as night vision problems and glare have not been an issue and certainly no different than for our nonpresbyopic laser patients, according to data obtained from our postoperative questionnaire.
We achieve these results by creating a prolate shape with a negative spherical aberration and a negative Q-value Figure 4. Is the procedure the perfect solution to presbyopia? Of course not. Fortunately, surgeons are working with a physiologic optical system that is pliable and adaptable and allows for compromises.
He is a consultant to Alcon Laboratories, Inc. Gordon may be reached at mgordon aol. Search for:. End of Issue.
Customized Laser Refractive Surgery with Alcon WaveLight® Platform - Optimizing outcomes with topography-guided treatment Dr. Ik Hee Ryu, Korea - Trans-PRK . It’s a procedure in which an eye doctor uses a laser beam to reshape the surface of the eye, making it more effective at focusing light and ultimately leading to better vision. Today, we Missing: pearls. All of these characteristics were built into the initial design of the WaveLight Allegretto laser (Alcon Laboratories, Inc., Fort Worth, TX). PRESBY-LASIK Roberto Pinelli, MD, originally .