a new direction: investigation of the impact of phaco- emulsification on corneal properties. They found a decrease in CH in the early postoperative period fol- lowed by a slight increase 3 months postoperatively. In their discussion, Kucumen et al. suggest this was due to the reconstruction of the eye after phacoemulsi- fication and intraocular lens implantation rather than to corneal edema. It is important to note that a distinct change in intra- ocular pressure (IOP) was detected during this period. Unfortunately, the data, as presented, do not pay suf- ficient attention to this detail. A tenet of CH consists of the registration of 2 inward and outward cornea ap- planations during dynamic changes in IOP. It is logical to assume that the initial IOP level can influence the fi- nal measurement. We would like to report 2 cases that demonstrate the influence of IOP on the outcome of such an investiga- tion. In March 2009, a 69-year-old man and a 65-year- old woman with glaucoma had uneventful glaucoma filtration surgery. Corneal hysteresis was examined twicedpreoperatively and postoperativelydusing the ORA. Preoperatively, the corneal compensated IOP (IOPcc) values in the 2 patients were 44.0 mm Hg and 30.0 mm Hg, respectively. The CH values were 2.3 mm Hg and 4.8 mm Hg, respectively. Four days after surgery, the IOPcc values were 8.0 mm Hg and 10.2 mm Hg, respectively. The CH levels increased to 8.6 mm Hg and 7.9 mm Hg, respectively. How can such a dramatic improvement in CH be ex- plained? Preoperative CH values of 3 mm Hg and 4 mm Hg are characteristic for keratoconus. Postoper- ative CH values of 8 mm Hg and 10 mm Hg refer to the normal biomechanical property of the cornea. It is highly unlikely that this shift was due to a deep biome- chanical change in the cornea during such a short pe- riod. Instead, we think it had been sequence of different levels of IOP in the moment CH was mea- sured. This factor of the unstable IOP may have played a role in the evaluation of the impact of phacoemulsi- fication on CH described by Kucumen et al. 1 Nikolai Sergienko, MD Irina Shargorodska, MD Kiev, Ukraine REFERENCES 1. Kucumen RB, Yeneral NM, Gorgun E, Kulacoglu DN, Oncel B, Kohen MC, Alimgil ML. Corneal biomechanical properties and intraocular pressure changes after phacoemulsification and intraocular lens implantation. J Cataract Refract Surg 2008; 34:2096–2098 2. Luce DA. Determining in vivo biomechanical properties of the cor- nea with an ocular response analyzer. J Cataract Refract Surg 2005; 31:156–162 REPLY: We have seen something similar to the out- comes described by Sergienko and Shargorodska in 2 cases with aphakic glaucoma. The first patient was a 75-year-old man with absolute glaucoma in the right eye caused by the pseudoexfoliation syndrome and spontaneous lens dislocation into the vitreous cavity. At presentation, the IOPcc without medication was 49 mm Hg and the CH was 1.4 mm Hg. After medical treatment was initiated, the IOPcc decreased to 27.3 mm Hg and the CH was 6.3 mm Hg. The fellow eye also had pseudoexfoliative glaucoma. With medica- tion, the IOPcc decreased from 30.9 mm Hg to 23.1 mm Hg and the CH increased from 6.1 mm Hg to 8.3 mm Hg. Since the difference between the pretreatment and posttreatment IOPcc was greater in the right eye than in the left eye, the CH improvement was more dra- matic in the right eye. The signal graphs before and after treatment showed short applanation peaks containing small oscillations. The central corneal thickness (CCT) was 505 mm in the right eye and 496 mm in the left eye. The second patient was a 27-year-old man with sec- ondary glaucoma caused by penetrating trauma; he had had vitrectomy and penetrating keratoplasty and was also aphakic. At presentation, the IOPcc in the right eye was 53 mm Hg without medication and the CH was 0.1 mm Hg. In the signal graphs before surgery, the air pulse curve did not intersect the appla- nation curve. Three days later, after Ahmed glaucoma valve surgery, the IOPcc decreased to 20.8 mm Hg and the CH was 6.2 mm Hg. The signal graph after surgery showed a more regular curve. The CCT was 811 in the right eye and 512 mm in the left eye. In both cases, the CH values recovered but not as well as expected in a normal eye. To explain this phenomenon, we can use the exam- ple of a ball. In a ball overfilled with air, it is difficult to indent the wall with a finger. When the ball is under- filled, it is easy to press the ball and change its shape. The eye is like a ball filled with liquid. Under high pressure, it is difficult to move the cornea inward by the air pulse. This initial applanation (peak 1) may have a small amplitude and therefore the outward movement of the cornea will be small; hence, the sec- ond applanation (peak 2). As both applanations are minimal, their amplitudes will be shorter and may not be high enough to intersect the air pulse curve. When the IOP normalizes, the cornea has more space to move inward and, consequently, outward so the biomechanical factors predominate. Also, one must not forget the influence of CCT on the measurements. In our opinion, corneal biomechanical properties are more valuable in normotonous eyes than in hyper- tonic eyes. If the IOP is extremely high, the signal graphs may not give ideal results and their interpreta- tion may be difficult and perhaps inaccurate. In our 2034 LETTERS J CATARACT REFRACT SURG - VOL 35, NOVEMBER 2009