EyeWorld Asia-Pacific December 2012 Issue

45 EWAP GLAUCOMA December 2012 stone. It should be re-evaluated and revised over time as the patient’s risk profile changes.” Central corneal thickness: Does it matter? As important as IOP is in the management of glaucoma, it is important to have the appropriate perspective when evaluating the IOP value. “True IOP does not exist in the clinic—it is just an estimate,” said Jose Morales, MD, King Khalid Eye Hospital, Saudi Arabia. AT A GLANCE • Lens softening with the femtosecond laser hopes to restore flexibility to the crystalline lens • Liquid crystal eyeglasses change power at the press of a button • Scleral expansion bands purport to help the posterior zonules work in changing lens shape • LaserACE restores the plasticity of the sclera, increasing the efficiency of Leonard YIP, MD Senior Consultant, Head of Glaucoma Service, Department of Ophthalmology, Tan Tock Seng Hospital 11 Jalan Tan Tock Seng, Singapore 308433 Tel. no. +65-63577726 Fax no. +65-63577718 Leonard_yip@ttsh.com.sg T he importance of intraocular pressure (IOP) as a risk factor for the development of glaucoma and progression of the disease is well established. The risk of glaucomatous damage rises with IOP increases. Lowering IOP reduced the risk of developing glaucoma and visual field loss in glaucoma patients. It is the only modifiable risk factor and thus is the basis of glaucoma therapeutic interventions. This article points out that IOP follows a circadian cycle and asks which matters more: Peak IOP or mean IOP? The practical problems in acquiring and using such information are highlighted well. To the general ophthalmologist, I would suggest that consideration be given to the circadian cycle when your patient is worsening on structural and functional assessments despite clinic visit IOPs attaining the target IOP. Under such circumstances, obtaining a diurnal curve may explain unexpected progression. The target IOP is a useful surrogate level for a good clinical outcome and is meant to be a pressure estimated to slow or halt disease progression. Even then, we try to be mindful that it should be appropriate to prevent significant visual damage in the patient’s lifetime, yet not overly aggressive in IOP lowering at the cost of the patient’s quality of life. The risks, costs and side effects of treatment need to be balanced against the risk of the pressure itself. Central corneal thickness (CCT), as part of glaucoma risk calculators, is useful in managing ocular hypertensive patients. I believe a risk estimate should be performed for most, if not all new ocular hypertensive patients. I do not routinely correct IOP on the basis of corneal thickness as target IOP is individualized to the patient’s own pretreatment IOP. In this way, any effect of that individual’s CCT on measured IOP will be accounted for in their treatment plan. Editors’ note: Dr. Yip has no financial interests related to his comments. Ivan GOLDBERG, AM, MBBS(Syd), FRANZCO, FRACS Clinical Associate Professor, University of Sydney Head, Glaucoma Unit, Sydney Eye Hospital Director, Eye Associates, Floor 4, 187 Macquarie Street, Sydney NSW 2000, Australia Tel. no. +61-0-2-92311833 Fax no. +61-0-1-92323086 eyegoldberg@gmail.com A long with increasing age and a positive family history, intraocular pressure (IOP) is the major risk factor for both onset and progression of primary glaucoma. Its reduction is what we achieve therapeutically. Both our knowledge about what needs to be accomplished and how best to do it are far advanced compared with ven a decad ago. We now know solitary IOP measurements as recorded at consultations separated by months offer little information on the continuous variable that is IOP and we know we need as many data points as possible at diagnosis and along the life-long pathway of treatment. IOP is relatively imprecise: besides the possible inaccuracies in its measurement, there are influences we need to keep in mind. Central corneal thickness is one for which we have no accurate corrective nomogram, but nonetheless influences our goals. Peak IOP is emerging as important and the water drinking test has been identified as a useful way to determine it for a patient both off and on treatment. As a profession, we need to employ it more often: it is relatively easy to use. We now know the gap our treatment creates between untreated and treated IOPs represent the visual safety margin we establish for each patient. How large that gap needs to be is influenced by the severity of the visual damage and its proximity to fixation (both of which affect significantly how badly the damage impacts on a patient’s quality of life and their ability to function independently) and the anticipated life expectancy of the patient (their general health status as well as their age—but remember how inexact this might prove to be). To this must be added an assessment of rate of progression of damage as the patient is followed on treatment. A rate of loss that indicates the patient is heading towards visual disability must be recognized so that treatment can be accelerated, target IOPs lowered and the visual safety gap widened. Flexibility in our approach is vital as we try therapeutically to use time intelligently. While the challenges remain large and ongoing, once a patient is placed on treatment, by saving sight, we have the chance to make a real difference to the quality of the rest of their lives. Editors’ note: Prof. Goldberg is a consultant for Alcon (Fort Worth, Texas, USA/Hünenberg, Switzerland), Allergan (Irvine, Calif., USA), and Forsight Labs, LLC (Menlo Park, Calif., USA), but has no financial interests related to his comments. Views from Asia-Pacific It is well known that the biomechanical properties of the cornea—of which central corneal thickness is just one—affect the validity of applanation tonometry. Acknowledging a frequent question about corneal thickness and IOP, Dr. Morales asked, “Can we correct IOP on the basis of corneal thickness? There are several formulas that have been proposed to do just this. They are mostly linear, however, and they ignore the reality that the relationship between corneal thickness and IOP is complex and nonlinear.” More importantly, he pointed out, “Adjusting IOP based on corneal thickness does not improve the prediction models for the development of glaucoma in the Ocular Hypertension Treatment Study.” Since the existing risk calculators allow inclusion of both IOP and central corneal thickness as risk factors, he recommended treating them separately unless future research suggests a better approach. EWAP Reference Gardiner SK, Johnson CA, Demirel S. Factors predicting the rate of functional progression in early and suspected glau- coma. Invest Ophthalmol Vis Sci. 2012 Jun 14;53(7):3598-604. Contact information Hoffmann: ehoffman@mail.uni-mainz.de Morales: jmorales@kkesh.med.sa Susanna: rsusanna@terra.com.br