Eyeworld

48 | EYEWORLD | JULY2019 C ORNEA epithelium-off accelerated corneal crosslinking, 9 mW/cm 2 for 10 minutes (total fluence 5.4 J/ cm 2 ). Six months after bilateral crosslinking, the right eye Kmax was lowered by 5.5 D with 20/16 visual acuity, and the left sided Kmax was lowered by 6.1 D with 20/16 visual acuity. "There is a strong similarity between tibolone, a selective estrogen activity regulator, and estrogen," Dr. Torres-Netto explained. "It is not only similar in the chemical structure but also as a result of metabolism is rapidly con- verted into components with estrogenic effects, such as 3alpha-hydroxy-tibolone and 3beta-hy- droxy-tibolone. Although there was nothing published on tibolone specifically, it has been shown that estrogen receptors are present in the corneal stroma." Estrogen receptors are thought to modify collagen and glycosaminoglycans biosynthesis. Such components play a central role in corneal composition and therefore in biomechanics. More evidence is needed, however, to prove the effects of estrogen on these molecules and to demonstrate how other factors like pregnancy, hypothyroidism, age, and smoking affect the cornea and the eye overall. According to an unrelated in vitro study on the subject, estrogen was seen to reduce corneal stiffness by 36%. 2 The authors noted that the significance of hormone status and its influence on the biomechanical stability of the cornea were largely underestimated. 2 Another investi- gation demonstrated clinical evidence that hor- monal changes occurring during gestation had an impact on keratoconus progression. 3 In yet another study, a stable patient experienced cor- neal steepening following both of her pregnan- cies, despite the corneal stabilization from CXL that was performed after the first pregnancy. 4 "Usually we expected to find a remodeling effect around 2 D, according to the Dresden protocol, which is the most effective proto- col for corneal crosslinking. Accelerated CXL normally has a lower stiffening effect and is less effective than the Dresden protocol. In our case, however, it flattened the corneas up to 6 D, up to 9 months post-CXL [Figure 2]," Dr. Torres-Netto said. continued from page 47 References 1. Torres-Netto EA, et al. Late-onset progression of keratoconus after therapy with selective tissue estrogenic activity regulator. J Cataract Refract Surg. 2019;45:101–104. 2. Spoerl E, et al. Oestrogen-in- duced changes in biomechanics in the cornea as a possible reason for keratectasia. Br J Ophthalmol. 2007;91:1547–50. 3. Hoogewoud F, et al. Transi- tory topographical variations in keratoconus during pregnancy. J Refract Surg. 2013;29:144–6. 4. Hafezi F, Iseli H. Pregnancy-re- lated exacerbation of iatrogenic keratectasia despite corneal collagen crosslinking. J Cataract Refract Surg. 2008;34:1219–21. Financial interests Torres-Netto: None Figure 2. Scheimpflug image showing large bilateral flattening after CXL Source: Emilio Torres-Netto, MD Kmax 5.5 D Kmax 6.1 D –1.50 –1.75 @ 170 (20/16) –2.75 –1.25 @ 180 (20/16)

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