Roland Richter

Results of correction of myopic astigmatism with the VISX 20/20 excimer laser

SummaryThe advent of the excimer laser has brought about the potential for improved vision in many individuals with myopia and astigmatism. However, photoastigmatic refractive keratectomy (PARK) remains a matter of controversy. The purpose of our study was to determine the predictability of VISX 20/20 excimer laser photorefractive keratectomy in the treatment of myopic astigmatism. Patients and methods: Our study comprised 31 eyes of 22 patients with myopic astigmatism. All patients underwent treatment with a VISX 20/20 excimer laser and were followed up for 6 months. Complete 12-month follow-up data were available from 18 eyes. Park was performed in eyes with myopia between −1.5 and −10.0 D and with astigmatism between −0.5 and −5.5 D. Thus, the corresponding spherical equivalent ranged from −1.75 to −10.5 D. Results: Six months postoperatively, 21/31 (62 %) eyes were within ± 1.0 D of the target refraction and 13/31 (42 %) within ± 0.5 D of the target refraction. In 13 of 15 eyes (87 %) with myopia less than −6.0 D, an uncorrected visual acuity of at least 0.8 was noted. In eyes with myopia greater than −6.0 D, 9/16 (56 %) showed an uncorrected visual acuity of at least 0.5. Six months after PARK, an increase of one line on the Snellen Visual Acuity Chart was observed in 8/31 (26 %) and an increase of two lines was noted in eyes 3/31 (10 %). One of 31 eyes (3 %) showed an increase of three lines. A decrease in visual acuity of 1 line on the Snellen Visual Acuity Chart was found in 4/31 (13 %), and in 3/31 eyes (10 %) a decrease of 2–4 lines was noted. Overall, we observed a statistically significant reduction of astigmatism from 1.93 ± 1.43 D to 0.93 ± 0.63 D. Reduction of corneal astigmatism less than −1.25 D was not statistically significant. In eyes with astigmatism ranging from −1.25 to −2.5 D or greater than −2.75 D, a significant reduction of the mean astigmatism was noted. The postoperative regression of astigmatic correction was low. However, an axis shift of more than 15 ° was found in 42 %/35 % of eyes by subjective refraction (miosis/cycloplegia) and in 33 % in corneal topography. No central islands were noted. Conclusion: Photoastigmatic refractive keratectomy (PARK) constitutes a potential means of correcting myopic astigmatism. In eyes with astigmatism greater than −1.0 D a significant reduction of 60 % of the mean astigmatism was noted. However, the considerable proportion of eyes with a postoperative axis shift greater than 15 ° and a decrease in visual acuity of two or more lines indicates that further research is needed on excimer laser surgery to improve the reliability and safety.ZusammenfassungHintergrund: Die photo-astigmatisch-refraktive Keratektomie (PARK) mittels Excimerlaser bei myopem Astigmatismus ist eine noch kontrovers diskutierte Methode. Die Refraktionsergebnisse wurden 6 und 12 Monate postoperativ ermittelt, um die Genauigkeit und Stabilität der Behandlung eines myopen Astigmatismus mit dem VISX 20/20 Excimerlaser feststellen zu können. Patienten und Methode: Bisher wurden 31 Augen von 22 Patienten wegen eines myopen Astigmatismus behandelt. 6 Monatsergebnisse liegen von allen Augen, 12 Monatsergebnisse von 18 Augen vor. Es wurden gleichzeitig Korrekturen der Myopie und des Astigmatismus vorgenommen. Die Myopie wurde von −1,5 bis −10,0 dpt und gleichzeitig der Astigmatismus von −0,5 bis −5,5 dpt korrigiert, so daß sich Korrekturen mit einem sphärischen Äquivalent von −1,75 bis −10,5 dpt ergaben. Ergebnisse: Innerhalb des Zielrefraktionsbereiches von ± 1,0 dpt lagen 6 Monate postoperativ 21/31 (62 %) und innerhalb von ± 0,5 dpt 13/31 (42 %) der Augen. Bei Korrekturen unter −6,0 dpt erreichten 13/15 (87 %) der Augen eine unkorrigierte Sehschärfe von mindestens 0,8. Bei Korrekturen über −6,0 dpt hatten 9/16 (56 %) eine unkorrigierte Sehschärfe von mindestens 0,5. Nach 6 Monaten wurde eine Visusverbesserung um 1 Visusstufe bei 8/31 (25,8 %), um 2 Stufen bei 3/31 (9,7 %) und um 3 Stufen bei einem Auge (3,2 %) festgestellt. Visusverschlechterungen um mehr als zwei Visusstufen fanden wir bei 3/31 Augen (9,7 %). Der Betrag des Astigmatismus war im Mittel postoperativ statistisch signifikant von prä-operativ 1,93 ± 1,43 dpt auf postoperativ 0,9 ± 0,63 dpt vermindert. Bei Astigmatismuskorrekturen unter −1,25 dpt erreicht man keine signifikante Reduktion, bei einem Astigmatismus zwischen −1,25 bis −5,5 dpt ergab sich eine Reduktion um im Mittel 60 % des Ausgangswertes. Bei der Myopiekorrektur fand sich bis 6 Monate postoperativ bei 9/31 (29 %) Augen eine Regression zwischen 1,0 und maximal 3,375 dpt. Für den Astigmatismus zeigte sich 3 Monate postoperativ nur noch eine geringe Regressionstendenz. Änderungen der Astigmatismusachse größer 15 ° fanden wir 6 Monate postoperativ bei subjektiver Refraktion (Miosis/Zykloplegie) in 42 %/35 % und in der Hornhauttopographie (TMS) bei 33 % der Augen. Central islands traten bei diesen Behandlungen nicht auf. Schlußfolgerung: Die PARK eignet sich zur Reduzierung des myopen Astigmatismus. Bei Werten über −1,0 dpt ergibt sich im Mittel eine Verminderung um 60 % des Ausgangswertes. Der hohe Anteil an postoperativen Achsenabweichungen um mehr als 15 ° sowie die Rate der Visusverschlechterungen um zwei oder mehr Visusstufen erfordern jedoch eine Verbesserung der Achslagenkontrolle während der Behandlung, sowie eine Optimierung der Korrekturprogramme. Ob eine weiterentwickelte Lasertechnik (z. B. flying-spot laser) bessere Ergebnisse bringt, bleibt abzuwarten.UNLABELLED The advent of the excimer laser has brought about the potential for improved vision in many individuals with myopia and astigmatism. However, photoastigmatic refractive keratectomy (PARK) remains a matter of controversy. The purpose of our study was to determine the predictability of VISX 20/20 excimer laser photorefractive keratectomy in the treatment of myopic astigmatism. PATIENTS AND METHODS Our study comprised 31 eyes of 22 patients with myopic astigmatism. All patients underwent treatment with a VISX 20/20 excimer laser and were followed up for 6 months. Complete 12-month follow-up data were available from 18 eyes. Park was performed in eyes with myopia between -1.5 and -10.0 D and with astigmatism between -0.5 and -5.5 D. Thus, the corresponding spherical equivalent ranged from -1.75 to -10.5 D. RESULTS Six months postoperatively, 21/31 (62%) eyes were within +/- 1.0 D of the target refraction and 13/31 (42%) within +/- 0.5 D of the target refraction. In 13 of 15 eyes (87%) with myopia less than -6.0 D, an uncorrected visual acuity of at least 0.8 was noted. In eyes with myopia greater than -6.0 D, 9/16 (56%) showed an uncorrected visual acuity of at least 0.5. Six months after PARK, an increase of one line on the Snellen Visual Acuity Chart was observed in 8/31 (26%) and an increase of two lines was noted in eyes 3/31 (10%). One of 31 eyes (3%) showed an increase of three lines. A decrease in visual acuity of 1 line on the Snellen Visual Acuity Chart was found in 4/31 (13%), and in 3/31 eyes (10%) a decrease of 2-4 lines was noted. Overall, we observed a statistically significant reduction of astigmatism from 1.93 +/- 1.43 D to 0.93 +/- 0.63 D. Reduction of corneal astigmatism less than -1.25 D was not statistically significant. In eyes with astigmatism ranging from -1.25 to -2.5 D or greater than -2.75 D, a significant reduction of the mean astigmatism was noted. The postoperative regression of astigmatic correction was low. However, an axis shift of more than 15 degrees was found in 42%/35% of eyes by subjective refraction (miosis/cycloplegia) and in 33% in corneal topography. No central islands were noted. CONCLUSION Photoastigmatic refractive keratectomy (PARK) constitutes a potential means of correcting myopic astigmatism. In eyes with astigmatism greater than -1.0 D a significant reduction of 60% of the mean astigmatism was noted. However, the considerable proportion of eyes with a postoperative axis shift greater than 15 degrees and a decrease in visual acuity of two or more lines indicates that further research is needed on excimer laser surgery to improve the reliability and safety.