Maik Kaemmerer

Clinical results of wavefront-guided laser in situ keratomileusis 3 months after surgery

Purpose: To investigate the visual and refractive outcome of wavefront‐guided laser in situ keratomileusis (LASIK) to correct myopic astigmatism. Setting: Departments of Ophthalmology of the Universities of Dresden, Dresden, Germany, and Zurich, Zurich, Switzerland. Methods: This prospective study comprised 35 eyes of 28 patients who had a mean preoperative spherical refraction of –4.8 diopters (D) ± 2.3 (SD) and a cylinder of –1.1 ± 0.9 D. Preoperative and postoperative wavefront analysis was performed with a Tscherning aberrometer. A scanning‐spot laser with a 1.0 mm spot size and a 200 Hz repetition rate was used. The eye‐tracking system had a response time of less than 6 milliseconds. The treatment area diameter ranged from 6.0 to 7.0 mm with a transition zone of 1.0 mm. Results: At 3 months, 68.0% of the eyes were within ±0.5 D of emmetropia and 93.5% were within ±1.0 D. Uncorrected visual acuity was 20/20 or better in 93.5% of eyes. No eye lost more than 1 line of low‐contrast, glare, and best spectacle‐corrected visual acuity (BSCVA). Supernormal vision (BSCVA of 20/10 or better) was achieved in 16.0% of eyes. The correction of higher‐order aberrations (spherical aberration, coma) was insufficient, with an increase factor of the overall root‐mean‐square wavefront error of 1.44 ± 0.74. Coma was better corrected than spherical aberration. Conclusions: Wavefront‐guided LASIK is a promising technique that offers the potential to correct refractive errors, to improve visual acuity, and to increase the quality of vision, especially under mesopic conditions. Studies that include selective overcorrrection of different Zernike components are needed to achieve better correction of the aberrations. Prospective controlled clinical studies must clarify the major benefits of wavefront‐guided LASIK.

Increased higher-order optical aberrations after laser refractive surgery: A problem of subclinical decentration

Purpose: To study the clinical and theoretical effects of subclinical decentrations on the optical performance of the eye after photorefractive laser surgery. Setting: Department of Ophthalmology, University of Dresden, Dresden, Germany. Methods: Ocular aberrations were determined before and 1 month after uneventful photorefractive keratectomy (PRK) with the Multiscan laser (Schwind) in 10 eyes of 8 patients. The corrections ranged from –2.5 to –6.0 diopters, and ablation zones of 6.0 mm and larger were used. The measured wavefront errors were compared to numerical simulations using the individually determined decentrations and currently used ablation profiles. Results: The PRK‐induced aberrations were significantly greater than the preoperative aberrations. The numerically calculated increase in the higher‐order optical aberrations correlated with the clinical results, demonstrating a major increase in coma‐ and spherical‐like aberrations. Subclinical decentration (less than 1.0 mm) was found to be a major factor in increased coma‐like and spherical‐like aberrations after corneal laser surgery. Conclusion. To minimize higher‐order optical errors, special efforts to center the ablation zone are necessary; for example, by eye‐tracking systems that consider the visual axis.

Wavefront-guided Laser in situ Keratomileusis: Early Results in Three Eyes

PURPOSE Wavefront optical aberrations induced by refractive corneal surgery correction of myopia are probably the reason for deterioration of visual performance in some eyes after surgery. Customized photoablation of the cornea to correct both the sphero-cylindrical refractive error as well as individual optical aberrations may improve postoperative visual acuity and visual performance. METHODS In 3 eyes of 3 patients the wavefront deviations were measured by means of an aberrometer of the Tscherning-type. Based on these measurements an ablation pattern was determined and applied during a LASIK procedure using a Wavelight Allegretto scanning spot excimer laser with a spot size of 1 mm and a laser repetition rate of 200 Hz. The 3 eyes are part of a prospective study on wavefront-guided LASIK started in July 1999. RESULTS At 1 month after LASIK, all 3 eyes had gained up to 2 lines of best spectacle-corrected visual acuity. Best spectacle-corrected visual acuity improved to 20/10 in all 3 eyes, uncorrected visual acuity was 20/10 in two eyes, and 20/12.5 in 1 eye 1 month postoperatively. The wavefront deviations were reduced by 27% on average. At 3 months, best spectacle-corrected visual acuity was 20/10 in 2 eyes and 20/12.5 in 1 eye. CONCLUSION Wavefront-guided LASIK is a feasible approach in refractive corneal surgery. Optimized ablation patterns may further improve the visual results.

Principles of Tscherning Aberrometry

Higher-order optical errors of the human eye are often responsible for reduced visual acuity in spite of an optimal spherical or cylindrical refraction. These optical aberrations are of natural origin or can result from operations on the eye involving optical structures. The presented wavefront analyzer is based on Tschernings aberroscope. A collimated laser beam illuminates a mask with regular matrix pin holes which forms a bundle of thin parallel rays. These rays form a retinal spot pattern on the retina that is more or less distorted according to the optical errors of the eye. This retinal spot pattern is imaged onto the sensor of a low-light CCD camera by indirect ophthalmoscopy. The deviations of all spots from their ideal regular positions are measured by means of a personal computer, and from these values the optical aberrations are computed in the form of Zernike polynomials up to the 8th order.

Effects of photorefractive keratectomy and cataract surgery on ocular optical errors of higher order.

Abstract  · Background: This pilot study was carried out to assess the effects of photorefractive keratectomy (PRK) for myopia and myopic astigmatism and cataract surgery on the ocular optical aberrations of higher degrees.  · Methods: The optical aberrations were measured in 12 patients before and after PRK and in 10 patients after cataract surgery with a video aberroscope for clinical use (based on Tscherning’s aberroscope) designed by the authors. To characterize the optical performance of the eye the deviation of the wavefront of a foveal image point from its ideal (spherical) shape (wavefront aberration) was determined. The wavefront aberration is represented mathematically in Zernike polynomials. The first 14 Zernike coefficients Ki were determined and compared with data from normal eyes with full visual acuity. · Results: Most Zernike coefficients were considerably greater after PRK than before surgery. These changes differed significantly from the variability of repeated individual measurements. In particular, coefficients corresponding to astigmatism, spherical aberration or coma were highly significantly increased (P<0.001). After cataract surgery, the averaged Zernike coefficients exhibited no significant differences from normal values, except the coefficient K5 (astigmatism at 0° or 90°). However, coefficients showed a significant high variability, especially the coefficients for spherical aberration or astigmatism.  · Conclusion: Both PRK and cataract surgery are operations which may considerably increase the ocular optical errors of higher order. These aberrations are not predictable and can affect the visual acuity despite optimal sphero-cylindrical correction, in particular under mesopic conditions.

Meßplatz zur Bestimmung der monochromatischen Aberration des menschlichen Auges

Fragestellung: Nach refraktiven Eingriffen an der Hornhaut und nach Kataraktoperationen können okulare Bildfehler (Aberrationen) auftreten, die nicht mit sphärischen oder astigmatischen Linsen korrigierbar und wahrscheinlich der Grund dafür sind, daß der maximale retinal bedingte Visus trotz optimaler Korrektur häufig nicht erreicht wird. Die Erfassung dieser Bildfehler unter klinischen Bedingungen wäre ein erster wichtiger Schritt zur Dokumentation und Korrektion dieser Aberrationen mittels moderner photorefraktiver Verfahren.Meßprinzip: Die Erfassung der Bildfehler erfolgt unter Beachtung des Wellencharakters des Lichts als Aberration der realen Wellenfront eines zentralen retinalen Punkts von der idealen sphärischen Form (Wellenfrontaberration). Die Messung erfolgt analog dem Prinzip des Aberroskops nach Tscherning.Ergebnis: Das Meßproblem wird mit einem Geräteverbund gelöst, der aus einem Lasersystem, einer CCD-Funduskamera und einem PC besteht. Ein Bündel paralleler äquidistanter Einzelstrahlen wird mit einer Linse vor dem Auge so gebrochen, daß auf der Netzhaut ein entsprechendes Lichtpunktmuster entsteht, das gemäß der okularen Aberration mehr oder weniger verzerrt ist. Mit dem PC wird die Abweichung der einzelnen Punkte von ihrer idealen (äquidistanten) Position bestimmt und daraus die Wellenfrontaberration in Form von Zernike- bzw. Taylor-Polynomen formuliert. Erste Ergebnisse von gesunden emmetropen Augen werden vorgestellt.Schlußfolgerung: Das Verfahren erlaubt eine ausreichend genaue Bestimmung der Wellenfrontaberration und dürfte damit nach einigen technischen Verbesserungen für klinische Anwendungen geeignet sein.Background: After refractive or cataract surgery, ocular optical errors can occur that are not correctable with spherical or astigmatic lenses and are probably responsible for the fact that in many cases the best possible (retinal) acuity is not achieved in spite of an optimum refraction. Assessment of these aberrations in the clinical routine is an important first step towards documentation and correction of these errors with modern photorefractive methods.Principle of measuring: Ocular optical errors are assessed from the viewpoint of the wave property of light as an aberration of the real wavefront of a central retinal image point from the ideal spherical form (wavefront aberration). The measurement is based on the principle of the Tscherning aberroscope.Result: A test setup is presented consisting of a laser system, a CCD fundus camera and a PC. A bundle of parallel equidistant rays is refracted by means of a lens in front of the eye producing an equivalent pattern of light spots on the retina. This pattern is more or less distorted according to the ocular aberrations. The deviations of all spots from their ideal (equidistant) positions are measured by means of the PC and from these values the wavefront aberration is computed in the form of Zernike and Taylor polynomials. The first results of emmetropic eyes are presented.Conclusions: The method allows sufficiently accurate assessment of the ocular wavefront aberration and might be on principle suitable for clinical use, provided that some technical improvements are installed.

Improvement in photorefractive corneal laser surgery results using an active eye-tracking system

Purpose: To study the advantage of modern eye‐tracking systems for photorefractive surgery. Setting: Department of Ophthalmology, University of Zurich, Zurich, Switzerland. Methods: Photorefractive surgery (photorefractive keratectomy and laser in situ keratomileusis) for myopia and myopic astigmatism was performed in 40 eyes with a commercially available medical excimer laser system. The eyes were selected retrospectively from a larger group of patients treated at 1 clinic. In 20 eyes, the ablation was centered on the entrance pupil using the active, video‐based, eye‐tracking system (sampling frequency 50 Hz) of the laser. During laser treatment in the nontracker group (20 eyes), the active eye‐tracking system was switched off and centration was done manually by the surgeon. Preoperatively and 1 and 3 months after surgery, the patients had a standard ophthalmic examination as well as wavefront analysis by means of a custom‐designed wavefront analyzer. Results: After surgery, the visual acuity was significantly better (P < .05) in patients treated with the eye tracker. The increase in coma‐like (relative increase factor 0.4) and spherical aberrations (relative increase factor 1.1) was significantly smaller in these patients than in those in the nontracker group (spherical equivalents of 3.9 and 5.1, respectively; P < .05). The refractive outcome, however, was not significantly different in sphere and cylinder. Conclusion: The use of active eye tracking appeared to improve the optical and visual outcomes but did not affect the refractive outcome after photorefractive laser surgery.

Operative Correction of Ocular Aberrations to Improve Visual Acuity

PURPOSE Optical aberrations of the human eye degrade the quality of the retinal image and may, therefore, represent a major limit of visual acuity. METHODS In 15 eyes, ocular aberrations were corrected in addition to myopia and astigmatism by means of wavefront-guided laser in situ keratomileusis (LASIK). RESULTS At 1 month after surgery, a supernormal visual acuity of 20/10 and better was obtained in 4 eyes (27%). The increase in root mean square wavefront error ranged from 0.6 to 2.3 and was significantly correlated with the increase in visual acuity (R2 = 0.79; P = .03). CONCLUSION Although the correction of aberrations was not yet optimal, these results show that ocular optical aberrations limit visual acuity in humans and supernormal visual acuity can be achieved by operative correction.

Ocular optical aberrometer for clinical use

Higher-order optical errors of the human eye are often responsible for reduced visual acuity in spite of an optimal spherical or cylindrical refraction. These optical aberrations are of natural origin or can result from operations in the eye that involve optical structures. The ocular aberrometer presented is based on Tschernings aberroscope. A collimated laser beam (532 nm, 10 mW) illuminates a mask with a regular matrix of holes which forms a bundle of thin parallel rays of 0.3 mm diameter. These rays are focused by a lens in front of the eye so that their intraocular focus point is located a certain distance in front of the retina, generating a corresponding pattern of light spots on it. According to the existing ocular optical errors, this spot pattern is more or less distorted in comparison to the mask matrix. For a 6 mm pupil diameter 68 retinal spots are plottable for assessment of the optical aberrations. The retinal spot pattern is imaged onto the sensor of a low-light charge coupled device video camera by indirect ophthalmoscopy. Deviations of all spots from their ideal regular positions are measured by means of a PC, and from these values the intraocular wave front aberration is computed in the form of the sum of Zernike polynomials up to sixth order.

Clinical Experience With the Tscherning Aberrometer

PURPOSE With the aberrometer based on Tschernings principle, measurements of wavefront aberrations of human eyes with high accuracy and reproducibility are available for standard diagnostic investigations. METHODS During investigational and clinical trials, wavefront-aberrations of about 300 human eyes were measured and evaluated within the last few years. RESULTS measurements are presented in terms of Zernike coefficients and as height maps that can be converted directly to ablation profiles for wavefront-guided laser treatments. CONCLUSION The Tscherning aberrometer is a simple optical device with high accuracy appropriate for routine clinical investigations on optical aberrations of the human eye.