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Editors Selection IGR 14-2

Intraocular pressure: CCT and IOP fl uctuation

Fabian Lerner

Comment by Fabian Lerner on:

20855 Association of Central Corneal Thickness and 24-hour Intraocular Pressure Fluctuation, Mosaed S; Chamberlain WD; Liu JHK et al., Journal of Glaucoma, 2008; 17: 85-88


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Several reports, have addressed the influence of central corneal thickness (CCT) on intraocular pressure (IOP).1 Although different nomograms have been proposed to 'correct' IOP based on CCT variations, there are other corneal factors that may influence IOP measurements like corneal biomechanics (elasticity and viscoelasticity).2,3

Nonetheless, pachymetry is readily available for clinicians, and knowing if the patient has a thin or a thick cornea may influence the management of glaucoma. Mosaed et al. (145) evaluated the correlation between CCT and 24-hour IOP fluctuation (defined as peak minus trough 24 hour IOP in the habitual body positions) both in untreated glaucoma patients and normal subjects. No difference between average 24-hour IOP, peak IOP or fluctuation was found between patients with glaucoma having thick or thin corneas. The authors have extensive experience in studying IOP variations in different types of patients housed in a sleep laboratory under controlled conditions.4-6 The present study was performed under the same strictly controlled setting. Based on observations in subjects with ocular hypertension,7 as well as patients with pre-perimetric glaucoma8 or advanced glaucomatous damage;9 it was suggested that CCT may be an independent risk factor for glaucoma. The present study indicates that a single measurement of CCT performed during office-hours is not correlated with 24-hour IOP fluctuation, and these two factors may play different roles in the pathophysiology of glaucoma. When analyzing factors that correlate with IOP fluctuation, the reader has to be aware that there are different types of IOP fluctuation; e.g.: 24-hour (subdivided into diurnal and nocturnal), as well as long-term fluctuation (usually defined as SD of the available IOP measurements). Attention to the definition of IOP fluctuation is essential. Also, it is important to note in which position the measurements were made. In the Mosaed et al. paper (as in other papers of the same lab), measurements were made in the habitual body positions, which reproduce a physiologic situation. More on this subject is available in the IOP Consensus book of the WGA.10

References

  1. Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocular pressure measures: A review and meta-analysis approach. Surv Ophthalmol 2000; 44: 367-408.
  2. Liu J, Roberts CJ. Influence of corneal biomechanical properties on intraocular pressure measurement: quantitative analysis. J Cataract Refract Surg 2005; 31: 146-155.
  3. Kotecha A, Elsheikh A, Roberts CR, et al. Corneal thickness and age-related biomechanical properties of the cornea measured with the ocular response analyzer. Invest Ophthalmol Vis Sci 2006; 47: 5337-5347.
  4. Liu JHL, Kripke DF, Hoffman RE, et al. Nocturnal elevation of intraocular pressure in young adults. Invest Ophthalmol Vis Sci 1998; 39: 2707-2712.
  5. Liu JHL, Kripke DF, Twa MD, et al. Twenty-four hour pattern of intraocular pressure in the aging population. Invest Ophthalmol Vis Sci 1999; 40: 2912-2917.
  6. Liu JHL, Zhang X, Kripke DF, et al. Twenty-four hour intraocular pressure pattern associated with early glaucomatous changes. Invest Ophthalmol Vis Sci 2003; 44: 1586-1590.
  7. Gordon MO, Beiser JA, Brandt JD, et al. Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol 2002; 120: 714-720.
  8. Medeiros FA, Sample PA, Zangwill LM, et al. Corneal thickness as a risk factor for visual field loss in patients with preperimetric glaucomatous optic neuropathy. Am J Ophthalmol 2003; 136: 805-813.
  9. Herndon LW, Weizer JS, Stinnett SS. Central corneal thickness as a risk factor for advanced glaucoma damage. Arch Ophthalmol 2004; 122: 17-21.
  10. Medeiros FA, Brandt JA, Liu J, et al. IOP as a risk factor for glaucoma development and progresión. In: Weinreb RN, Brandt JD, Garway-Heath DF, Medeiros FA (eds). Intraocular Pressure. Amsterdam: Kugler Publications 2007, pp. 59-74. (click here for more information)

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