malities were found. Her fundus appearance and renal abnormality led us to examine her parents. Both had normal fundus and no renal abnormalities. After obtaining informed consent, molecular genetic analysis of the PAX2 gene by direct sequencing of all coding regions revealed a heterozygous insertion of a G at position 619 (Figure 2). This substitution was not detected in the parents or 42 healthy volunteers, suggesting that this was a de novo mutation. The atypical coloboma in our patient is apparently different from a typical optic nerve head “coloboma” that results from defective closure of the embryonic fissure in the inferior part of the optic disk. This is consistent with a recent report that PAX2 is expressed in all cells of the optic stalk of developing mice. 2 We thus hypothesize that an abnormal development of the optic stalk led to the abnormal optic nerve head seen in congenital optic nerve anomalies caused by mutations in PAX2. Therefore, this is a dysplastic rather than a typical colobomatous disk, and “papillorenal syndrome” may be a more appropriate designation for the PAX2- associated optic disk anomaly. 3,4 Our findings suggest that we should consider renal abnormalities whenever an atypical round coloboma is observed, even if the patient has normal blood chemistry and urinalysis. Our study combined with other studies confirmed that exon 2 of PAX2, especially a sequence of seven Gs in the exon, may be particularly prone to mutations. 5 This would suggest that a common mutational mechanism may be involved, such as slippage during DNA replica- tion, irrespective of the race. The presence of a muta- tional hot spot would also suggest the diagnostic value of PAX2 gene. Molecular analysis of PAX2, especially exon 2 in combination with renal ultrasonography, may help in an earlier diagnosis at an early stage of the disease. REFERENCES 1. Sanyanusin P, Schimmenti LA, McNoe LA, et al. Mutation of the PAX2 gene in a family with optic nerve colobomas, renal anomalies and vesicoureteral reflux. Nat Genet 1995;9:358 –364. 2. Dakubo GD, Wang YP, Mazerolle C, Campsall K, McMahon AP, Wallace VA. Retinal ganglion cell-derived sonic hedge- hog signaling is required for optic disc and stalk neuroepithelial cell development. Development 2003;130: 2967–2980. 3. Parsa CF, Goldberg MF, Hunter DG. Papillorenal (“renal coloboma”) syndrome. Am J Ophthalmol 2002;134:300 –301; author reply 301. 4. Parsa CF, Goldberg MF, Hunter DG. No colobomas in “renal coloboma” syndrome. Ophthalmology 2003;110:251–252; au- thor reply 251. 5. The Human PAX2 Allelic Variant Database. Available at http://pax2.hgu.mrc.ac.uk. Accessed October 1, 2004. Comparison of Two Techniques of Marking the Horizontal Axis During Excimer Laser Keratorefractive Surgery for Myopic Astigmatism Jenna M. Burka, MD, Kraig S. Bower, MD, David L. Cute, DO, Richard D. Stutzman, MD, Prem S. Subramanian, MD, PhD, and Jeff C. Rabin, OD, PhD PURPOSE: To compare two methods of limbal marking used during laser refractive surgery for myopic astigmatism. DESIGN: Retrospective chart review. METHODS: Forty-two eyes of 42 patients who underwent photorefractive keratectomy (PRK) or laser-assisted in- situ keratomileusis (LASIK) for myopic astigmatism were marked preoperatively to identify the horizontal axis. In 18 eyes, marks were placed at the slit lamp (SL) with the slit beam set at 180 degrees as a reference. In 24 eyes, marks were placed in the laser room (LR) immedi- ately before reclining under the laser. All treatments were performed with the Alcon LADARVision excimer laser system. Vector analysis of postoperative cylinder and reduction in cylinder and uncorrected and best- corrected visual acuity were evaluated for both groups. RESULTS: The mean postoperative magnitude of error was – 0.19  0.44 diopters for the LR group and – 0.09  0.42 diopters for the SL group (P  .439, NS). Both groups had a mean angle of error indicating an overall counterclockwise rotation of axis with an angle of error of 6.3  8.7 degrees for the LR group and 8.0  10.2 degrees for the SL group (P  .562, NS). CONCLUSIONS: We found no significant difference in outcomes with an overall trend toward undercorrection of cylinder in both groups, leaving room for improvement after refractive surgery for myopic astigmatism (Am J Ophthalmol 2005;139:735-737. © 2005 by Elsevier Inc. All rights reserved.) A XIAL MISALIGNMENT MAY RESULT IN RESIDUAL ASTIG- matism after excimer laser keratorefractive surgery. 1–3 Misalignment by 15 degrees reduces efficacy, as measured by the flattening index, by 14%. A 50% reduction occurs with a misalignment of 30 degrees. The magnitude of postoperative astigmatism, however, is increased by 14% with an angle of error of only 4 degrees and by 50% with a 15-degree angle of error. 4 Limbal marking has been shown to improve surgical outcomes for 1.25 diopters of Accepted for publication Oct 4, 2004. From the Ophthalmology Service, Walter Reed Army Medical Center (J.M.B., K.S.B., D.L.C., R.D.S., P.S.S.), Washington, DC; School of Optometry, Pacific University, Forest Grove, Oregon (J.R.). Inquiries to Kraig S. Bower, MD, Ophthalmology Service, Walter Reed Army Medical Center, Room 2F-205, 6900 Georgia Avenue NW, Washington, DC 20307-5001; fax: (202) 782-4653; e-mail kraig.bower@ na.amedd.army.mil BRIEF REPORTS VOL. 139,NO. 4 735