Use of the ISNT rule for optic disc evaluation in 40 to 79 year old patients seen in optometric practice
The purpose this study was to investigate the association between intraocular pressure (IOP) and the outcome of ISNT rule assessment of the optic disc in healthy patients seen in mainstream optometric practice. Consecutive patients over the age of 40 years and with no known general- or ocular pathology were enrolled from 4 optometric practices in Norway and Sweden during a period of 9 months. The sample was stratified by age group (40-49, 50-59, 60-69 and 70-79 years) and ISNT rule outcome (obeyed or broken). Subjects underwent a full optometric examination including stereoscopic assessment of the optic disc with the use of the ISNT rule, followed by measurements of intraocular pressure (IOP), central corneal thickness (CCT) and vertical size of the optic disc. Odds ratio (OR) was used to assess the association between IOP and the outcome measure. Stratified and multivariable analyses were employed to investigate the effect of age, gender, CCT, refractive error and disc size on the association. IOP was dichotomized at a cut-off corresponding to the 75th percentile (18 mmHg), whereas numeric covariables were categorized at cut-offs corresponding to the 33rd (ONH 1.6 mm, CCT 545 μm) and 66th percentile (ONH 1.8 mm, CCT 571 μm), respectively. A total of 177 patients (F: 57%, age range 40-79 years) were included. IOP was significantly higher in patients with broken ISNT rule (16.6 vs. 15.5 mmHg, p = 0.046), corresponding to a crude OR of 2.0 (CI 0.95-4.24). In stratified and multivariable analyses the association between IOP and outcome of the ISNT rule was strengthened in males (OR 4.8) and in subjects with small discs (OR 2.2), however only the effect modification by gender reached significance. Further research is necessary to understand the possible implications of these findings on the assessment of optic discs with the use of the ISNT rule.
Bengtsson, B. (1981). The prevalence of glaucoma. British Journal of Ophthalmology, 65, 46-49.
Bourne, R. R., Foster, P. J., Bunce, C., Peto, T., Hitchings, R. A., Khaw, P. T.,… Garway-Heath, D.F. (2008a). The morphology of the optic nerve head in the Singaporean Chinese population (the Tanjong Pagar study): part 1--Optic nerve head morphology. British Journal of Ophthalmology, 92, 303-309. doi:10.1136/bjo.2007.123273
Bourne, R. R., Foster, P. J., Bunce, C., Peto, T., Hitchings, R. A., Khaw, P. T.,… Garway-Heath, D.F. (2008b). The morphology of the optic nerve head in the Singaporean Chinese population (the Tanjong Pagar study): part 2--Biometric and systemic associations. British Journal of Ophthalmology, 92, 310-314. doi: 10.1136/bjo.2007.123349
Budde, W. M., Jonas, J. B., Martus, P., & Grundler, A. E. (2000). Influence of optic disc size on neuroretinal rim shape in healthy eyes. Journal of Glaucoma, 9, 357-362.
Caprioli, J., & Miller, J. M. (1987). Optic disc rim area is related to disc size in normal subjects. Archives of Ophthalmology, 105, 1683-1685.
Crowston, J. G., Hopley, C. R., Healey, P. R., Lee, A., & Mitchell, P. (2004). The effect of optic disc diameter on vertical cup to disc ratio percentiles in a population based cohort: the Blue Mountains Eye Study. British Journal of Ophthalmology, 88, 766-770. doi: 10.1136/bjo.2003.028548
Garway-Heath, D. F., Ruben, S. T., Viswanathan, A., & Hitchings, R. A. (1998). Vertical cup/disc ratio in relation to optic disc size: its value in the assessment of the glaucoma suspect. British Journal of Ophthalmology, 82, 1118-1124.
Harizman, N., Oliveira, C., Chiang, A., Tello, C., Marmor, M., Ritch, R., & Liebmann, J. M. (2006). The ISNT rule and differentiation of normal from glaucomatous eyes. Archives of Ophthalmology, 124, 1579-1583.
Jonas, J. B., Fernandez, M. C., & Naumann, G. O. (1991). Correlation of
the optic disc size to glaucoma susceptibility. Ophthalmology, 98, 675-680.
Jonas, J. B., Grundler, A. E., & Gonzales-Cortes, J. (1998). Pressure-dependent neuroretinal rim loss in normal-pressure glaucoma. American Journal of Ophthalmology, 125, 137-144.
Jonas, J. B., Gusek, G. C., & Naumann, G. O. (1988). Optic disc, cup and neuroretinal rim size, configuration and correlations in normal eyes.[Erratum in Investigative Ophthalmology and Visual Science 1991, 32, 1893 and 1992 32, 474-475]. Investigative Ophthalmology and Visual Science, 29, 1151-1158.
Kahn, H. A., Leibowitz, H. M., Ganley, J. P., Kini, M. M., Colton, T., Nickerson, R. S., & Dawber, T. R. (1977). The Framingham Eye Study. II. Association of ophthalmic pathology with single variables previously measured in the Framingham Heart Study. American Journal of Epidemiology, 106, 33-41.
Klein, B. E., Klein, R., Sponsel, W. E., Franke, T., Cantor, L. B., Martone, J., & Menage, M. J. (1992). Prevalence of glaucoma. The Beaver Dam Eye Study. Ophthalmology, 99, 1499-1504.
Leske, M. C., Connell, A. M., Schachat, A. P., & Hyman, L. (1994). The Barbados Eye Study. Prevalence of open angle glaucoma. Archives of Ophthalmology, 112, 821-829.
Mackie, S. W., Jay, J. L., Ackerley, R., & Walsh, G. (1996). Clinical comparison of the Keeler Pulsair 2000, American Optical MkII and Goldmann applanation tonometers. Ophthalmic and PhysiologicalOptics, 16, 171-177. doi: 10.1046/j.1475-1313.1996.95000291.x
Mason, R. P., Kosoko, O., Wilson, M. R., Martone, J. F., Cowan, C. L., Jr., Gear, J. C., & Ross-Degnan, D. (1989). National survey of the prevalence and risk factors of glaucoma in St. Lucia, West Indies. Part I. Prevalence findings. Ophthalmology, 96, 1363-1368.
Mitchell, P., Smith, W., Attebo, K., & Healey, P. R. (1996). Prevalence of open angle glaucoma in Australia. The Blue Mountains Eye Study. Ophthalmology, 103, 1661-1669.
Ogbuehi, K. C. (2006). Assessment of the accuracy and reliability of the Topcon CT80 non-contact tonometer. Clinical and Experimental Optometry, 89, 310-314. doi: 10.1111/j.1444-0938.2006.00068.x
Ramrattan, R. S., Wolfs, R. C., Jonas, J. B., Hofman, A., & de Jong, P. T. (1999). Determinants of optic disc characteristics in a general population: The Rotterdam Study. Ophthalmology, 106, 1588-1596.
Tielsch, J. M., Sommer, A., Katz, J., Royall, R. M., Quigley, H. A., & Javitt, J. (1991). Racial variations in the prevalence of primary open-angle glaucoma. The Baltimore Eye Survey. Journal of the American Medical Association, 266, 369-374.
Varma, R., Tielsch, J. M., Quigley, H. A., Hilton, S. C., Katz, J., Spaeth, G. L., & Sommer, A. (1994). Race-, age-, gender-, and refractive error-related differences in the normal optic disc. Archives of Ophthalmology, 112, 1068-1076.