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  • LETTERSBurst-shot infrared digital photography

    for measuring low-light pupilYang et al.1 recently reported the technique of burst-

    shot infrared digital photography for measuring thelow-light pupil diameter and compared this methodwith the Colvard pupillometer. The infrared-capableSony CyberShot video camera was used to captureimages that included an integral photographed ruler;the actual pupil diameter was measured against theruler standard using image-manipulation software.Dark adaptation was conducted at less than 0.1 luxfor 5 minutes, with ambient light measured by an illu-minance meter. Subjects were instructed to stare ata dark empty space behind the camera to suspendaccommodation. The authors compared the tech-niques using Bland-Altman plots.We have published several experiments25 on low-

    light pupil measurement with an identical photo-graphic technique using the Sony CyberShot; the firstwas in 2004. In 2005, we published an article6 compar-ing the Sony infrared photographic method with theColvard pupillometer, using Bland-Altmann analysis.It is always a pleasure to have ones work duplicated

    and confirmed by an independent investigation. Sincenone of our publications were included in Yang et al.sbibliography, we thought we would expand the use-fulness of their article by drawing attention torelated studies already in print in this journal.

    Sandra M. Brown, MDConcord, North Carolina, USA

    Arshad M. Khanani, MDJay C. Bradley, MDLubbock, Texas, USA

    REFERENCES1. Yang H, Lee M, Kim JB, Ahn J. Burst-shot infrared digital photog-

    raphy to determine scotopic pupil diameter. J Cataract Refract

    Surg 2006; 32:21132117

    2. Brown SM, Khanani AM, Xu KT. Day to day variability of the

    dark-adapted pupil diameter. J Cataract Refract Surg 2004; 30:

    639644

    3. Khanani AM, Brown SM, Xu KT. Six-month variability of the

    dark-adapted pupil diameter. J Cataract Refract Surg 2005; 31:

    987990

    4. Khanani AM, Archer SM, Brown SM. Horizontal versus vertical

    dark-adapted pupil diameters in normal individuals. J Cataract

    Refract Surg 2004; 30:25572558

    5. Brown SM, Khanani AM. Effect of brimonidine on pupil diameter

    [letter]. J Cataract Refract Surg 2005; 31:16861687

    6. Bradley JC, Anderson JE, Xu KT, Brown SM. Comparison of

    Colvard pupillometer and infrared digital photography for mea-

    surement of the dark-adapted pupil diameter. J Cataract Refract

    Surg 2005; 31:21292132

    REPLY: We thank Brown et al. for commenting onour work. In the article they mention,1 they used an

    Q 2007 ASCRS and ESCRS

    Published by Elsevier Inc.

    1502infrared-capable digital video camera to capture stillimages of the pupil, reviewed the images on a com-puter, and selected the clearest photograph for analy-sis. In contrast, we used an infrared-capable digital stillcamera to capture pupil images under the scotopiccondition.Compared with the capture function of a digital

    video camera, a digital still camera can acquire sharperstill images and obtain serial images at constantintervals (burst-shot function). We used the continu-ous-shot function of the camera so we could take7 well-focused serial images in 2.8 seconds at a con-stant interval of 400milliseconds.We did not select im-ages randomly according to image quality,1,2 butchose the image containing the largest pupil diameterfrom among the 7 serial images to overcome pupillaryunrest. The 400-millisecond interval of the serial pho-tographsmay not be sufficient to find the largest diam-eter of the pupil under the scotopic condition, andhigher-speed devices might be more accurate. Multi-ple-measurement digital infrared pupillometers thatcan acquire serial images at speeds up to 25 framesper second are available.3 Nevertheless, the largest re-corded pupil diameter might represent the scotopicpupil size better than an average or even a randomlyselected reading.4

    In the article by Bradley et al.2 comparing the infra-red photographic method with the Colvard pupillom-eter, the accuracy of the pupil diameter measurementusing the Colvard pupillometer was investigatedusing digital photography as a standard. The authorsused Bland-Altman analysis to compare the Colvardpupillometer and infrared digital photography, butthe repeatability of each device was not investigated.The purpose of our studywas to compare the accuracyof burst-shot infrared digital photography with theColvard pupillometer in terms of repeatability, so wecannot compare our data with the work by Bradleyet al.2 However, when using the Colvard pupillome-ter, the possible sources of errors they noted shouldbe considered.Again, we thank Brown et al. for drawing attention

    to articles related to our work and elucidating thedifferences between our study and those ofothers.dJaehong Aho, MD, Hongseok Yang, MD

    REFERENCES1. Brown SM, Khanani AM, Xu KT. Day to day variability of the

    dark-adapted pupil diameter. J Cataract Refract Surg 2004; 30:

    639644

    2. Bradley JC, Anderson JE, Xu KT, Brown SM. Comparison of Col-

    vard pupillometer and infrared digital photography for measure-

    ment of the dark-adapted pupil diameter. J Cataract Refract

    Surg 2005; 31:21292132

    3. Michel AW, Kronberg BP, Narvaez J, Zimmerman G. Compari-son of 2 multiple-measurement infrared pupillometers to

    0886-3350/07/$dsee front matter

    doi:10.1016/j.jcrs.2007.04.045

  • determine scotopic pupil diameter. J Cataract Refract Surg 2006;

    32:19261931

    4. Cheng ACK, Rao SK, Lam DSX. Determining scotopic pupil size

    [letter]. J Cataract Refract Surg 2005; 31:12671268; reply by

    SM Brown, 1268

    Pupil dilation with intracameral lidocaineduring phacoemulsificationThe concept of preoperative dilation of the pupil by

    intracameral injection of preservative-free lidocaine,described in the article by Nikeghbali et al.,1 appearsto be appealing. However, the effect of lidocaine onthe endothelium and other safety aspectsmust be stud-ied in detail. The following aspects need clarification:The pupil measurements were taken using a caliper.

    The authors did not mention whether the reportedpupil sizes were the actual pupil size or the measure-ment of pupil size over the cornea. A magnificationfactor has to be applied to ascertain the actual pupilsize from the measurement taken over the cornea.This magnification factor is dependent on the cornealpower, anterior chamber depth, and refractive indexof the aqueous. The measurement of pupil size overthe cornea will also have the inherent parallax error.For the sake of uniformity ofmeasurement, themag-

    nification of the microscope used during measure-ments should be uniform as well.The measurements over the cornea with the caliper

    have a potential of interobserver variability. The articledoes not mention whether all the measurements usinga caliper were taken by the same person.

    Chaitra Jayadev, DOMSBarun K. Nayak, MD

    Mumbai, India

    REFERENCE1. Nikeghbali A, Falavarjani FG, Kheirkhah A, et al. Pupil dilation

    with intracameral lidocaine during phacoemulsification. J Cata-

    ract Refract Surg 2007; 33:101103

    REPLY: We thank Drs. Jayadev and Nayak for theircritical analysis of our recent paper. As we mentionedin our article, preservative-free lidocaine was reportedto be safe for intracameral injection.13

    We measured the pupil diameters on the surface ofthe cornea. Since the measurement method was thesame in both groups, we did not consider the magnifi-

    measurements were performed by the same surgeonin all cases.dAminollah Nikeghbali, MD, KhalilGhasemi Falavarjani, MD, Ahmad Kheirkhah, MD,Pejman Bakhtiari, MD, Mohsen Bahmani Kashkouli, MD

    REFERENCES1. Anders N, Heuermann T, Ruther K, Hartmann C. Clinical and

    electrophysiologic results after intracameral lidocaine 1% anes-

    thesia; a prospective randomized study. Ophthalmology 1999;

    106:18631868

    2. Iradier MT, Fernandez C, Bohorquez P, et al. Intraocular lido-

    caine in phacoemulsification: an endothelium and blood-aqueous

    barrier permeability study. Ophthalmology 2000; 107:896900;

    discussion by JP Gills, 900901

    3. Heuermann T, Hartmann C, Anders N. Long-term endothelial cell

    loss after phacoemulsification: peribulbar anesthesia versus in-

    tracameral lidocaine 1%; prospective randomized clinical trial.

    J Cataract Refract Surg 2002; 28:639643

    Hydration behavior of porcine corneacrosslinked with riboflavin and ultraviolet AIn the recent article byWollensak et al.,1 it was inter-

    esting to note that the crosslinked portion of the corneawas minimally hydrated compared with the rest of thecornea and this effect was most pronounced in theanterior cornea where the maximum crosslinkingoccurred.We wonder whether a laboratory experiment could

    be conducted to extrapolate the above principle to cor-neas with faulty endothelium. If the crosslinked por-tion of the cornea is not vulnerable to hydration or isless vulnerable, the above principle could be appliedin a cornea with borderline endothelial function.When a cornea shows increasing guttae and pachyme-try, as in Fuchs endothelial dystrophy, but has notdecompensated, crosslinking can be expected to haltor reduce stromal hydration resulting from the faultyendothelium. As the crosslinking effect is seen moststrongly in the anterior cornea, at least bullae forma-tion, which is annoying to the patient because of painand distortion, might be prevented with crosslinking.If a laboratory experiment could be conducted as an

    extension of the one in the Wollensak et al. article, itmight show that crosslinking could benefit eyes thathave not yet decompensated but are endotheliallycompromised.

    Radhika Natarajan, FRCSPrema Padmanabhan, MD

    Sitalakshmi Gurus