The Water Drinking Test

The Water Drinking Test

outside the optical zone of the ICR. Additionally, the risk of making a stromal tunnel in a case of true PMD is probably very different than the risk ...

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outside the optical zone of the ICR. Additionally, the risk of making a stromal tunnel in a case of true PMD is probably very different than the risk involved in a case of central or paracentral keratoconus. This would be especially true for other ICR designs that require a larger optical zone. The authors should be commended for their excellent clinical results with a single large arc length ICR. The reader, however, should be cautioned that the cases cited are more typical of keratoconus and the recommendations in the article may not be applicable to classic PMD. MICHAEL W. BELIN

Marana, Arizona STEPHEN S. KHACHIKIAN

Rapid City, South Dakota RENATO AMBROSIO, JR.

Rio de Janerio, Brazil

REFERENCES

1. Kubaloglu A, Sogltlu E, Cinar Y, et al. A single 210-degree arc length intrastromal corneal ring implantation for the management of pellucid marginal corneal degeneration. Am J Ophthalmol 2010;150(2):185–192. 2. Kymionis GD, Aslanides IM, Siganos CS, Pallikaris IG. Intacs for early pellucid marginal degeneration. J Cataract Refract Surg 2004;30(1):230 –233. 3. Mularoni A, Torreggiani A, di Biase A, Lafi GL, Tassinari G. Conservative treatment of early and moderate pellucid marginal degeneration: a new refractive approach with intracorneal rings. Ophthalmology 2005;112(4):660 – 666. 4. Ertan A, Bahadir M. Intrastromal ring segment insertion using a femtosecond laser to correct pellucid marginal corneal degeneration. J Cataract Refract Surg 2006;32(10):1710 – 1716. 5. Luck J. Customized ultra-high-power toric intraocular lens implantation for pellucid marginal degeneration and cataract. J Cataract Refract Surg 2010;36(7):1235–1238. 6. Walker RN, Khackikian SS, Belin MW. Scheimpflug imaging of pellucid marginal degeneration. Cornea 2008;27(8):963–966.

REPLY I THANK DRS BELIN, KHACHIKIAN, AND AMBROSIO FOR

their interest in our article.1 They have reflected concern about topographical diagnosis of pellucid marginal corneal degeneration (PMCD) in our case series. PMCD is a rare, bilateral, noninflammatory, peripheral thinning disorder of the inferior cornea. It is characterized by high degrees of central against-the-rule astigmatism and with-the-rule astigmatism in the area of thinning. Although it is often misdiagnosed as keratoconus, PMCD has been distinguished from this more common condition on the basis of slit-lamp findings and corneal topographical examination. In our article,1 we clearly described this in the inclusion criteria: “The diagnosis of PMCD was based on slit-lamp VOL. 151, NO. 3

findings, including inferior corneal thinning and ectasia above the area of maximum thinning. The diagnosis was verified by corneal topography, which demonstrated a steep contour in the inferior peripheral cornea with high keratometric powers radiating from the inferior oblique meridians toward the center.” Our diagnosis was not based merely on the corneal topography. We have accepted the classical definition of pellucid marginal degeneration diagnosis as a combination of slit-lamp and corneal topography findings. Dr Belin and colleagues are basing their criticism in the pachymetric Orbscan map (Bausch & Lomb, Rochester, New York, USA), which does not show a typical inferior thinning, and this is probably because the device is unable to detect peripheral thinning in some cases, as that case showed. We insist on this, because the concern is that the pachymetric map of the Orbscan does not show peripheral thinnings. Probably this is an innate limitation of the Orbscan system. In previous publications about intracorneal ring segments in PMCD, the same trend was observed in the cases shown (no inferior flattening in the Orbscan pachymetric maps).2,3 Therefore, we emphasize that we agree in that the Pentacam (Oculus Optikgeräte, Wetzlar, Germany) has the best ability to reveal peripheral corneal thinnings. ES I˙N SOGUTLU SARI

Istanbul, Turkey

REFERENCES

1. Kubaloglu A, Sari ES, Cinar Y, et al. A single 210-degree arc length intrastromal corneal ring implantation for the management of pellucid marginal corneal degeneration. Am J Ophthalmol 2010;150(2):185–192. 2. Mularoni A, Torreggiani A, Di Biase A, Laggi GL, Tassinari G. Conservative treatment of early and moderate pellucid marginal degeneration. A new refractive approach with intracorneal rings. Ophthalmology 2005;112(4):660 – 666. 3. Rodríguez-Prats JL, Galal A, Garcia-Lledo M, De la Hoz F, Alió JL. Intracorneal rings for the correction of pellucid marginal degeneration. J Cataract Refract Surg 2003;29(7):1421–1424.

The Water Drinking Test EDITOR: WE READ WITH GREAT INTEREST THE EDITORIAL BY GOLD-

berg and Clement on the water drinking test.1 The authors reviewed relevant studies on this topic. We would like to highlight some important points that may complement their editorial and may be clinically relevant to your readership. First, it is important to emphasize that the reason for performing the water drinking test has changed from it being a test once thought useful in predicting which ocular hypertensive patients were more prone to develop visual field loss to a stress test to assess the capacitance of the trabecular meshwork. Similarly to other widely used stress tests (eg,

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4. Kumar RS, de Guzman MH, Ong PY, Goldberg I. Does peak intraocular pressure measured by water drinking test reflect peak circadian levels? A pilot study. Clin Experiment Ophthalmol 2008;36(4):312–315. 5. Susanna R Jr, Sheu WP, Latin American Glaucoma Society. Comparison of latanoprost with fixed-combination dorzolamide and timolol in adult patients with elevated intraocular pressure: an eight-week, randomized, open-label, parallelgroup, multicenter study in Latin America. Clin Ther 2004; 26(5):755–768. 6. Barkana Y, Anis S, Liebmann J, Tello C, Ritch R. Clinical utility of intraocular pressure monitoring outside of normal office hours in patients with glaucoma. Arch Ophthalmol 2006;124(6):793–797.

glucose tolerance test or cardiac stress test), the aim is to stress the trabecular meshwork and to observe how high the intraocular pressure rises and how long it takes to return to baseline. Rather than a specific numerical rise in intraocular pressure constituting a positive test, its interpretation depends on each patient’s baseline intraocular pressure, level of damage, and rate of progression. Although the physiology of the water drinking test is not fully understood, we have demonstrated that, at least in part, the intraocular pressure elevation may be caused by an increase in choroidal thickness resulting in a pressure gradient that is transmitted to intraocular compartments, causing aqueous to exit from the anterior chamber to the drainage system.2 Eyes may show a higher intraocular pressure elevation, depending on their outflow facility.3 Second, the water drinking test may prove very useful in assessing the efficacy of clinical or surgical therapy on the prevention of intraocular pressure spikes. As Goldberg and Clement described, intraocular pressure peaks detected during the water drinking test seem to correlate well with the peaks detected during diurnal tension curves.4 In this regard, the water drinking test may have an important role in the assessment of the quality of treatment and the probability of progression. Third, the water drinking test may differentiate between drugs that can produce equivalent intraocular pressure reductions in steady-state situations, but that may have different abilities to dampen intraocular pressure peaks, as showed by Susanna and associates.5 Medications capable of preventing greater or undetected intraocular pressure peaks, or both, may have an additional benefit in glaucoma treatment.6 Finally, we believe that there is an important potential role for the usefulness of this test in glaucoma management, and for this reason, it deserves to be investigated more widely.

REPLY WE THANK DE MORAES AND ASSOCIATES FOR THEIR

interest in our editorial1 and this contribution to the ongoing discussion of the water drinking test. The reasons to perform the WDT as well as its clinical usefulness in assessing the therapeutic effectiveness of intraocular pressure-lowering strategies, as we described,1 agrees totally with the points they raise. Since we wrote our editorial, De Moraes and associates have demonstrated choroidal thickening as a potential mechanism for the WDT-induced intraocular pressure response.2 It is a welcome contribution to the literature on the physiology of WDT, and we support this opportunity to highlight it for your readers. Even with this useful addition to our knowledge, our understanding of the physiological basis for the WDT remains incomplete. It bears repeating: further research into the WDT is needed to understand better its physiology and clinical application. IVAN GOLDBERG COLIN I. CLEMENT

Sydney, Australia

CARLOS GUSTAVO V. DE MORAES

New York, New York, and São Paulo, Brazil REFERENCES

REMO SUSANNA, JR.

São Paulo, Brazil

1. Goldberg I, Clement CI. The water drinking test. Am J Ophthalmol 2010;150(4):447– 449. 2. De Moraes CG, Reis AS, Cavalcante AF, Sano ME, Susanna R Jr. Choroidal expansion during the water drinking test. Graefes Arch Clin Exp Ophthalmol 2009;247(3):385–389.

ROBERT RITCH

New York and Valhalla, New York

REFERENCES

1. Goldberg I, Clement CI. The water drinking test. Am J Ophthalmol 2010;150(4):447– 449. 2. De Moraes CG, Reis AS, Cavalcante AF, Sano ME, Susanna R Jr. Choroidal expansion during the water drinking test. Graefes Arch Clin Exp Ophthalmol 2009; 247(3):385–389. 3. Phillips CI, Tsukahara S, Hosaka O, Adams W. Ocular pulsation correlates with ocular tension: the choroid as piston for an aqueous pump? Ophthalmic Res 1992;24(6):338 –343.

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AMERICAN JOURNAL

Enhanced Depth Imaging Optical Coherence Tomography of the Choroid in Idiopathic Macular Hole EDITOR: WE READ WITH INTEREST THE RECENTLY PUBLISHED ARTI-

cle by Reibaldi and associates, “Enhanced Depth Imaging OF

OPHTHALMOLOGY

MARCH

2011