5. Bodnar Z, Clouser S, Mamalis N. Toxic anterior segment syn- drome: update on the most common causes. J Cataract Refract Surg 2012; 38:1902–1910 6. € Ozlem TY, Necati DM, Fatma YM, G€ ulsen Y, Ays ‚ e NB, Firdevs € O. Are cefuroxime and vancomycin really safe on the corneal endothe- lial cells? Graefes Arch Clin Exp Ophthalmol 2010; 248:415–420 7. Blomquist PH. Methicillin-resistant Staphylococcus aureus infections of the eye and orbit (an American Ophthalmological So- ciety thesis). Trans Am Ophthalmol Soc 2006; 104:322–345. Avail- able at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1809917/ pdf/1545-6110_v104_p322.pdf. Accessed February 9, 2014 8. Libre PE, Della-Latta P, Chin N-X. Intracameral antibiotic agents for endophthalmitis prophylaxis: a pharmacokinetic model. J Cataract Refract Surg 2003; 29:1791–1794 9. Hwang DG. Fluoroquinolone resistance in ophthalmology and the potential role for newer ophthalmic fluoroquinolones. Surv Ophthalmol 2004; 49(suppl 2):S79–S83 10. Villada JR, Vicente U, Javaloy J, Ali  o JL. Severe anaphy- lactic reaction after intracameral antibiotic administration during cataract surgery. J Cataract Refract Surg 2005; 31:620–621 11. Barry P, Cordov es L, Gardner S. ESCRS Guidelines for Prevention and Treatment of Endophthalmitis Following Cataract Surgery: Data, Dilemmas and Conclusions. Dub- lin, Ireland, European Society of Cataract and Refractive Surgeons, 2013, 2013; Available at: http://www.escrs.org/ downloads/Endophthalmitis-Guidelines.pdf. Accessed Feb- ruary 9, 2014 Epithelial thickness changes following realignment of a malpositioned free cap Dan Z. Reinstein, MD, MA(Cantab), FRCSC, FRCOphth, Timothy J. Archer, MA(Oxon), DipCompSci(Cantab), Marine Gobbe, MST(Optom), PhD, Richard C. Rothman, MD In 2006, we described a laser in situ keratomileusis (LASIK) patient in whom a free cap occurred, resulting in a loss of 3 lines of corrected distance visual acuity (CDVA) and the induction of 4.00 diopter (D) of re- fractive astigmatism despite no ablation having been performed. 1 Two free cap rotations using a formula based on refraction and topography 2 failed to realign the free cap into its original position. The patient was then scanned with a very-high-frequency digital ultrasound arc scanner to measure the thickness pro- files of the individual layers within the cornea. Using this information, the rotation required for anatomical realignment was determined by digitally generating a “lock and key” superimposition of the stromal component of the free cap (ie, without the epithelium) and residual stromal bed (RSB) thickness profiles. The free cap rotation was performed, and the eye regained preoperative CDVA and symmetrical corneal topography. The 4.00 D of induced refractive astigmatism was also neutralized, leaving the spher- ical equivalent C0.50 D from the original refraction. However, there was an interesting aspect of this case that we omitted in the original report: the epithelial thickness changes. It is known that the corneal epithelium has the abil- ity to alter its thickness profile to compensate for changes in stromal surface curvature to reestablish a smooth, symmetrical optical surface. Such compensa- tory epithelial thickness changes have been described after myopic excimer laser ablation, 3 hyperopic exci- mer laser ablation, radial keratotomy, orthokeratol- ogy, and in keratoconus and ectasia. 4 In cases of irregular astigmatism, epithelial thickness changes have a significant effect as they mask the true curva- ture of the irregular stromal surface from front surface topography. 5,6 In this case, the patient presented with an extremely irregular epithelial thickness profile, which was partially compensating for an underlying stro- mal surface irregularity. This irregularity stemmed from a nonuniform flap being misaligned with the RSB (Figure 1). Specifically, there was a localized re- gion in which the thickness of the stromal component of the free cap was about 60 mm, whereas the thick- ness was between 105 mm to 130 mm across the remainder. Inspection of the RSB thickness revealed a ridge similar in dimensions to the thin area of the free cap. Therefore, as the free cap and RSB were mis- aligned, this meant that the stroma was thicker than it should have been in the location of the ridge and thinner than it should have been in the location of the thin region of the free cap. This resulted in an irregular epithelial thickness profile with a minimum thickness of 42 mm and a maximum thickness of 82 mm within the central 4.0 mm zone. This compen- satory epithelial remodeling was masking a signifi- cant amount of the stromal surface irregularity from the corneal front surface topography. It is therefore not surprising that the correct rotation could not be calculated using a formula based on front surface topography. 2 The patient was scanned again 2 days after the flap rotation procedure; the thickness profiles are shown in Figure 1. The thin area of the free cap was well aligned with the ridge on the RSB. As the total stromal thick- ness profile was now back in its original state, the epithelial thickness profile had also changed to recom- pensate for the new, more regular stromal surface. The epithelial thickness profile was relatively uniform in thickness, ranging from 42 mm to 63 mm with a central thickness of 52 mm, which is the expected thickness for epithelium in an untreated cornea. 7 This represented a change in epithelial thickness of more than 20 mm within 2 days. This case demonstrates once more that the epithelial thickness compensatory mechanism occurs very quickly. This is similar to a previous report that 1237 CORRESPONDENCE J CATARACT REFRACT SURG - VOL 40, JULY 2014