Corneal cylinder in cataractous eyes

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LETTERS

REFERENCES 1. Osher RH. Initial report of IOL-induced accommodation [letter]. J Cataract Refract Surg 2008; 34:2009 2. Marchini G, Pedrotti E, Visentin S. Reply to letter by Osher RH, Initial report of IOL-induced accommodation. J Cataract Refract Surg 2008; 34:2009 3. Marchini G, Pedrotti E, Modesti M, Visentin S, Tosi R. Anterior segment changes during accommodation in eyes with a monofocal intraocular lens: high-frequency ultrasound study. J Cataract Refract Surg 2008; 34:949–956 4. Schachar RA, Kamangar F. Proper evaluation of accommodating IOLs. J Cataract Refract Surg 2006; 32:4–6

REPLY: I do not think Schachar’s findings are completely right. In fact, analyzing the cited images, I do not find a thicker central optic in Figure 1. In Figure 2, the anterior curvature of the IOL appears to be flatter during accommodation, but that is explained by the tilt of the IOL consequent to the contraction of the ciliary muscles, whose action deforms the profile of the IOL loops, as shown by the arrows; it is evident that contraction of ciliary muscles determines movement of the IOL and that appearance is not due to a variation in the UBM imaging acquisition plane between the nonaccommodative state and the accommodative state. These phenomena are even more evident in Figure 3, in which IOL tilting is more pronounced. In that image (Figure 3, B), the IOL optic disc appears thicker because the imaging acquisition plane is slightly diagonal because the IOL moved during accommodation.dEmilio Pedrotti, MD

Corneal cylinder in cataractous eyes The recent article by Ferrer-Blasco et al.1 reporting levels of astigmatism in a large group of bilateral cataractous eyes (4540) was very informative. The authors stated, ‘‘Currently, we know of no reports of systematic data about the prevalence of the degrees of corneal astigmatism in large population cohorts. . . .’’ A simple literature search would have shown that the largest series on this subject (7500 eyes) was published in 1980.2 This information has been available for 29 years ‘‘to anticipate levels of need for toric lenses in the population.’’ The 1980 publication reported that the mean corneal power of 6950 bilateral phakic cataractous eyes (mean age 74 years G 10 [SD]) was 43.81 G1.60 diopters (D) in contrast to the mean corneal power (of 4540 similar eyes; mean age 61 G 10 years) of 43.78 G 1.60 D reported in the 2009 study. Although the population of the current study was 13 years younger, the insignificant 0.03 D difference (with exactly the same SD) is remarkable so many years later and in a different population (European versus United States). The 1980

study reported a mean cylinder of 1.00 G 1.00 D compared with the ‘‘mean corneal astigmatism (1.02 D)’’ (although it is listed as 0.86 G0.93 D in Table 1) in the 2009 study. Again, the results are not that different. The 1980 report evaluated the effect of axial length on these values and found a mean corneal power of 44.43 G 1.56 D in hyperopic eyes, 43.58 G 1.23 D in emmetropic eyes, and 43.13 G 1.52 D in myopic eyes and a corneal cylinder of 1.00 G 1.06 D (maximum 9.50 D), 0.92 G 0.88 D (maximum 6.30 D), and 1.00 G 1.00 D (maximum 9.50 D), respectively. Only 4.2% were reported as ‘‘no cylinder’’ compared with the cylinder of 13.14% reported in the 2009 study. This can be affected by the definition of ‘‘no cylinder.’’ The 1980 study used a measurement of 0.00 D and reported that an equal amount (18%) had 0.25 D and 0.25 to 0.50 D of cylinder, yielding a total of 40% of eyes with a cylinder less than or equal to 0.50 D compared with the 58.8% reported in the 2009 study. The 1980 study reported only 10% of eyes with a cylinder greater than 2.00 D, exactly the same as in the 2009 study. It also reported only 3% with greater than 3.50 D compared with 2.55% in the 2009 study. The 1980 study reported 50% with a cylinder between 0.50 and 2.00 D and the 2009 study, 33%. The mean difference in cylinder between bilateral eyes was 0.87 G 0.83 D. It would be interesting if the authors added the values of both studies to report the combined results for more than 12 000 eyes. New means can be easily calculated by multiplying the individual means by the totals from each study, adding the total, and then dividing that by the total number of the combined studies. The authors should be congratulated for publishing this extensive study. Kenneth J. Hoffer, MD Santa Monica, California, USA REFERENCES 1. Ferrer-Blasco T, Monte´s-Mico´ R, Peixoto-de-Matos SC, Gonza´lez-Me´ijome JM, Cervin˜o A. Prevalence of corneal astigmatism before cataract surgery. J Cataract Refract Surg 2009; 35:70–75 2. Hoffer KJ. Biometry of 7,500 cataractous eyes. Am J Ophthalmol 1980; 90:360–368; correction, 890

REPLY: When we noted the absence of current literature on the prevalence of astigmatism prior to cataract surgery, we probably failed to explain clearly that we meant the absence of recent reports. In fact, there is no recent report evaluating the prevalence of corneal cylinder before cataract surgery in such a large cohort of patients. We were misled by the title of Hoffer’s article1 and did not, therefore, include it; we

J CATARACT REFRACT SURG - VOL 35, JUNE 2009