Despite the low number of patients with a follow-up longer than 3 years, results indicate long-term stabilization and improvement after collagen crosslinking. Thus, collagen crosslinking is an effective therapeutical option for progressive keratoconus.

Aim: The risk of regression after photorefractive keratectomy (PRK) and the tendency to develop keratectasia after laser-assisted in situ keratomileusis (LASIK) procedure is higher in women than men. Currently, interest is focused on the influence of oestrogen on corneal stability after corneal refractive surgery. The aim of this experimental study was to investigate the change in biomechanical properties of the cornea induced by oestrogen. Methods: The influence of oestrogen was investigated in 12 fresh porcine corneas incubated in culture medium with 10 mmol/l b-oestradiol for 7 days. A group of 12 porcine corneas incubated in culture medium without oestradiol for the same time served as a control group. Strips of cornea were cut and the stress-strain was measured in a biomaterial tester. The Young's modulus was calculated. Results: During incubation the thickness of the cornea changed in the control group by only 6.4% and in the oestradiol group by 12%. However, the difference in the biomechanical stress values at 10% strain was significantly larger. In the control group the stress value was 120.18¡28.93 kPa and in the oestradiol group 76.87¡34.63 kPa (p = 0.002), representing a reduction of the corneal stiffness by 36% due to the oestradiol treatment. Conclusion: Oestrogen is a modulating factor of the biomechanical properties of the cornea that is not explainable only by an increased swelling. The significance of the hormone status of patients and its influence on the biomechanical stability of the cornea, a determining factor after refractive surgery, have been underestimated and may contribute to the development of keratectasia.

CRF and CH changes may reflect structural changes of the cornea. Thus, the ORA provides valuable information for a better understanding and characterization of the biomechanical condition of the cornea, especially with regard to diseases such as keratoconus and glaucoma.

<h4>PURPOSE</h4><p> To investigate a correlation between cigarette smoking and keratoconus.</p> <h4>METHODS</h4><p>Patients with keratoconus who were treated with corneal collagen cross-linking from June 2006 to November 2007 were asked about their smoking habits. A person smoking a minimum of two cigarettes per day for more than 1 year was classified as a smoker.</p> <h4>RESULTS</h4><p>A total of 180 patients with keratoconus (mean age 28±9 years [range: 15 to 41 years]) were asked about their smoking habits. One hundred seventy-one (95%) were non-smokers and only 9 (5%) were smokers (95% confidence interval, 2.31 to 9.28). Using the chi-square test, a significant correlation was found between non-smokers and keratoconus (<i>P</i><.001). </p> <h4>CONCLUSIONS</h4><p>In this group of patients with keratoconus, few were smokers. Cigarette smoke contains toxic substances. Consequently, people are advised not to smoke. However, we speculate that the by-products of cigarette smoke may lead to cross-linking of collagen, which in the cornea, may prevent the development and progression of keratoconus. [<cite>J Refract Surg.</cite> 2008;24:S737-S740.]</p> <h4>ABOUT THE AUTHORS</h4> <p>From the Department of Ophthalmology (Spoerl, Raiskup-Wolf, Pillunat) and Institute of Medical Informatics and Biometry (Kuhlisch), Technical University Dresden, Germany.</p> <p>The authors have no commercial or proprietary interest in the materials presented herein.</p> <p>Presented in part at the International Congress of Corneal Cross-Linking; December 7-8, 2007; Zurich, Switzerland.</p> <p>Correspondence: Eberhard Spoerl, PhD, Dept of Ophthalmology, Carl Gustav Carus University Hospital, Fetscherstr 74, 01307 Dresden, Germany. Tel: 49 351 458 3763; Fax: 49 351 458 4335; E-mail: <a href="mailto:eberhard.spoerl@uniklinikum-dresden.de">eberhard.spoerl@uniklinikum-dresden.de</a> </p>

With regard to the size of our cohort and the follow-up time, no comparable data have been published in the literature. The results of this study indicate that collagen cross-linking appears to be an effective therapeutic option for progressing keratoconus. Besides the clinical benefit, there are enormous economic and psychosocial benefits. Cross-linking is an outpatient, minimally invasive, cost-effective treatment involving minimal effort for the persons concerned.