Recovery of Corneal Hysteresis After Reduction of Intraocular Pressure in Chronic Primary Angle-Closure Glaucoma

visual acuity (VA) and IOL Master testabilities than the Sydney cohort. In contrast, children in Sydney had better Randot stereoacuity testability than Singaporean children. We agree that these differences can be explained by variability in examiners between the 2 study centers as well as differences in testing protocols and population characteristics. When children in the SPEDS used the electronic visual acuity (EVA) instrument, testabilities were very similar to the STARS logMAR chart. The EVA tester was also utilized in the Multi-Ethnic Pediatric Eye Disease Study (MEPEDS),2 again leading to similar visual acuity testabilities to that of Singapore, substantiating the Sydney results. Furthermore, the fact that the SPEDS found no differences in testability between Caucasians and East Asians and the MEPEDS found no difference in testability between African Americans and Hispanics2– 4 supports the lack of a substantial influence of ethnic differences on variability in testability. There were a few subtle gender differences pointed out by Pai and associates between the Sydney and Singapore studies. Table-mounted autorefraction and Randot stereoacuity were significantly more testable in girls than boys in the STARS,1 whereas no gender differences were seen for these studies in the SPEDS. These differences are interesting, and highlight possible cultural differences in child development, behavior, and possibly testing conditions, which differentially influence testability of girls versus boys. MEPEDS found gender differences in certain age groups for visual acuity2 and IOL Master testability,3 which was not seen in STARS. In all cases, girls outperformed boys. Delineation by age groups of gender differences might demonstrate similar findings in the SPEDS. Collectively, the 3 studies—STARS, SPEDS, and MEPEDS—provide excellent data from large preschoolaged cohorts on testability of visual function for diverse populations in different countries and cultures. This information provides important insights for the minimum age for testing in future clinical screening programs and community-based research.

REFERENCES

1. Trager MJ, Dirani M, Fan Q, et al. Testability of vision and refraction in preschoolers: the strabismus, amblyopia, and refractive error study in Singaporean children. Am J Ophthalmol 2009;148:235–241 e6. 2. Cotter SA, Tarczy-Hornoch K, Wang Y, et al. Visual acuity testability in African-American and Hispanic children: the multi-ethnic pediatric eye disease study. Am J Ophthalmol 2007;144:663– 667. 3. Borchert M, Wang Y, Tarczy-Hornoch K, et al. Testability of the Retinomax autorefractor and IOLMaster in preschool children: the Multi-ethnic Pediatric Eye Disease Study. Ophthalmology 2008;115:1422–1425, 1425 e1. 4. Tarczy-Hornoch K, Lin J, Deneen J, et al. Stereoacuity testability in African-American and Hispanic pre-school children. Optom Vis Sci 2008;85:158 –163.

Recovery of Corneal Hysteresis After Reduction of Intraocular Pressure in Chronic Primary Angle-Closure Glaucoma EDITOR: WE READ WITH INTEREST THE PAPER BY SUN AND ASSOCI-

ates,1 which corroborates prior reports of rises in corneal hysteresis following reductions in intraocular pressure (IOP),2,3 but were surprised that they did not consider that the association they found could be related to their method of measurement. The ocular response analyzer uses an air puff to deform the cornea into a slight concavity and an electro-optical system to detect the timing of the corneal deflection from which the IOP can be determined. The air puff switches off shortly after the first applanation spike. This standardizes the degree of indentation but means that the pressure applied to the cornea is determined by a combination of the IOP and the structural resistance of the eye.2 By manually adjusting the pressure of the air puff, it is possible to induce artificial changes in hysteresis (Asaoka R, et al. IOVS 2008;49:ARVO E-Abstract 703). In our center, we examined consecutive records of 30 previously untreated subjects with glaucoma or ocular hypertension diagnosed by a single fellowship-trained glaucoma specialist (A.W.) and assigned to a 1-eye trial of either travoprost or bimatoprost. IOP and corneal biomechanical parameters were measured at baseline and at follow-up (mean 53 days) using a Goldmann tonometer, Pascal dynamic contour tonometer (DCT), and ocular response analyzer. Data for the first treated eye were analyzed using the corresponding eye as control. Using Student t tests, we found that our results were similar to those of Sun and associates. Significant decreases in Goldmann IOP (24 to 17 mm Hg, P ⫽ .0000003) in intervention eyes occurred alongside significant increases

MICHELLE TRAGER CABRERA

Durham, North Carolina MOHAMED DIRANI

Melbourne, Australia QIAO FAN PRABAKARAN SELVARAJ AUDREY CHIA SEANG-MEI SAW, PHD

Republic of Singapore GUS GAZZARD

Republic of Singapore, and London, United Kingdom TIEN-YIN WONG

Melbourne, Australia, and Republic of Singapore TERRI L. YOUNG

Durham, North Carolina, and Republic of Singapore ROHIT VARMA

Los Angeles, California 524

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in corneal hysteresis (8.06 to 9.04 mm Hg, P ⫽ .00007). However, when we modeled the data in a mixed model using Pascal DCT intraocular pressure and central corneal thickness as covariates we found that the change in corneal hysteresis did not reach conventional levels of statistical significance (P ⫽ .78). We conclude that the introduction of prostaglandin analogues increases corneal hysteresis as measured by the ocular response analyzer but not independently of IOP. Cross-sectional surveys have correlated corneal hysteresis with IOP,4 – 6 central corneal thickness,4 – 6 and axial length.6 The effect of IOP appears to be modest within the normal range, but these factors may be clinically relevant at high intraocular pressures, and research into air puff dynamics and hysteresis values at extremes of range is ongoing. It may be possible to use a correction factor to limit the influence of IOP on hysteresis measurement,2,4 but until one has been properly validated, it would seem prudent to consider inclusion of these variables as covariates in studies examining large variations in IOP.

We thank Dr Poostchi and his associates for sharing their findings on the associations between the corneal hysteresis and intraocular pressure. We are in agreement with their explanations that the associations may be related to the measurement of the ocular response analyzer (ORA), which was not considered in our article. We hope this exchange will stimulate further research.

ALI POOSTCHI

1. Sun L, Shen M, Wang J, et al. Recovery of corneal hysteresis after reduction of intraocular pressure in chronic primary angle-closure glaucoma. Am J Ophthalmol 2009;147(6): 1061–1066.

SIMON NICHOLAS ANTHONY P. WELLS

Wellington, New Zealand

REFERENCES

1. Sun L, Shen M, Wang J, et al. Recovery of corneal hysteresis after reduction of intraocular pressure in chronic primary angleclosure glaucoma. Am J Ophthalmol 2009;147(6):1061–1066. 2. Kotecha A, Elsheikh A, Roberts CR, Zhu H, Garway-Heath DF. Corneal thickness- and age-related biomechanical properties of the cornea measured with the ocular response analyzer. Invest Ophthalmol Vis Sci 2006;47(12):5337–5347. 3. Mangouritsas G, Morphis G, Mourtzoukos S, Feretis E. Association between corneal hysteresis and central corneal thickness in glaucomatous and non-glaucomatous eyes. Acta Ophthalmologica 2009;87(8):901–905. 4. Kamiya K, Hagishima M, Fujimura F, Shimizu K. Factors affecting corneal hysteresis in normal eyes. Graefes Arch Clin Exp Ophthalmol 2008;246(10):1491–1494. 5. Carbonaro F, Andrew T, Mackey DA, Spector TD, Hammond CJ. The heritability of corneal hysteresis and ocular pulse amplitude: a twin study. Ophthalmology 2008;115(9):1545– 1549. 6. Song Y, Congdon N, Li L, et al. Corneal hysteresis and axial length among Chinese secondary school children: the Xichang Pediatric Refractive Error Study (X-PRES) report no. 4. Am J Ophthalmol 2008;145(5):819 – 826.

REPLY IN THIS LETTER, WE REPLY TO THE ISSUES PRESENTED BY DR

Ali Poostchi and associates in their correspondence to the Editor regarding our article.1 VOL. 149, NO. 3

LEI SUN MEIXIAO SHEN

Wenzhou, Zhejiang, China JIANHUA WANG

Miami, Florida AIWU FANG AIQIN XU HAIZHEN FANG FAN LU

Wenzhou, Zhejiang, China

REFERENCE

Outcome of Raised Intraocular Pressure in Uveitic Eyes With and Without a Corticosteroid-Induced Hypertensive Response EDITOR: WE READ WITH GREAT INTEREST THE RECENTLY PUBLISHED

article “Outcome of raised intraocular pressure in uveitic eyes with and without a corticosteroid-induced hypertensive response” by Sallam and associates.1 We would like to highlight the following points. The authors have mentioned 2 causes of intraocular pressure (IOP) rise in the follow-up period of uveitis patients— either attributable to the disease process itself (uveitis) or attributable to steroid response. However, there may be other mechanisms of IOP rise, such as secondary angle closure.2 The gonioscopy findings of the study patients have not been mentioned. It is possible that some patients may have developed IOP rise attributable to progressive formation of peripheral anterior synechiae in the angle with consequent angle closure. Also, occurrence of other systemic and local side effects of steroids, such as deranged blood sugar levels or development of cataract in the study group, has not been mentioned. We would like to highlight that IOP elevation is a common and serious side effect of posterior sub-Tenon’s (PST) and intravitreal triamcinolone acetonide (IVTA) injection. Steroid-induced IOP rise in patients receiving intravitreal triamcinolone acetonide has been reported to

CORRESPONDENCE

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