Scanning laser polarimetry: »number« parameter sensitivity and specificity in glaucoma diagnostics
Abstract
Background: Scanning laser polarimetry (SLP) is a method that enables quantitative assessment of retinal nerve fibre layer (RNFL) thickness surrounding the optic nerve. The commercially available device GDx (GDx, Laser Diagnostics Technologies, San Diego, CA) yields an outprint consisting of a reflectance image, colour-coded retardation map, and the 14 parameters, of which the »Number« was shown to be the single best parameter to discriminate between glaucomatous and normal eyes. The »Number« is a probability score, ranging from 1 (low probability of glaucoma) to 100 (high probability of glaucoma). In our study we determined the sensitivity and the specificity of the »Number« at cutoff values of 23 and 30.
Methods: Thirty patients with different stage of glaucoma and 14 patients with typical glaucomatous changes of the ONH without visual field loss (preperimetric glaucoma) were included in the analysis. The control group was represented by 27 adults without ocular pathology with intraocular pressure of < 21 mmHg and normal visual fields. The sensitivity and specificity of the »Number« was determined at a cut-off level of 23 and 30.
Results: The sensitivity of the »Number« at a cut-off level of 30 for the glaucoma group was 74% at a specificity of 86%, at a cut-off of 23 the sensitivity increased to 83% at a specificity of 76%. The discriminating ability of the »Number« in the group with preperimetric glaucoma was low, with the sensitivities of 36% and 50% at a cut-off value of 30 and 23, respectively.
Conclusions: The parameter »Number« yielded good separation between normal eyes and eyes with moderate and advanced glaucoma. However, the sensitivity of the »Number« in eyes with mild glaucoma and especially with preperimetric glaucoma was low. Because of the great interindividual variability of the RNFL, the assessment of RNFL thickness change over time would be more appropriate to detect early glaucomatous changes.
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References
Quigley HA, Dunkelberger GR, Green WR. Retinal ganglion cell atrophy correlated with automated perimetry in human eyes with glaucoma. Am J Ophthalmol 1989; 107: 453–64.
Harwerth RS, Carter-Dawson L, Shen F, Smith EL, 3rd, Crawford ML. Ganglion cell losses underlying visual field defects from experimental glaucoma. Invest Ophthalmol Vis Sci 1999; 40: 2242–50.
Sommer A, Katz J, Quigley HA, Miller NR, Robin AL, Richter RC, et al. Clinically detectable nerve fiber atrophy precedes the onset of glaucomatous field loss. Arch Ophthalmol 1991; 109: 77–83.
Quigley HA, Katz J, Derick RJ, Gilbert D, Sommer A. An evaluation of optic disc and nerve fiber examinations in monitoring progression of early glaucoma damage. Ophthalmology 1992; 99: 19–28.
Lauande-Pimentel R, Carvalho RA, Oliveira HC, Goncalves DC, Silva LM, Costa VP. Discrimination between normal and glaucomatous eyes with visual field and scanning laser polarimetry measurements. Br J Ophthalmol 2001; 85: 586–91.
Poinoosawmy D, Tan JC, Bunce C, Hitchings RA. The ability of GDx nerve fibre analyser neural network to diagnose glaucoma. Graefes Arch Clin Exp Ophthalmol 2001; 239: 122–7.
Weinreb RN, Zangwill L, Berry CC, Bathija R, Sample PA. Detection of glaucoma with scanning laser polarimetry. Arch Ophthalmol 1998; 116: 1583–9.
Yamada N, Chen PP, Mills RP, Leen MM, Stamper RL, Lieberman MF, et al. Glaucoma screening using the scanning laser polarimeter. J Glaucoma 2000; 9: 254–61.
Funaki S, Shirakashi M, Yaoeda K, Abe H, Kunimatsu S, Suzuki Y, et al. Specificity and sensitivity of glaucoma detection in the Japanese population using scanning laser polarimetry. Br J Ophthalmol 2002; 86: 70–4.
Trible JR, Schultz RO, Robinson JC, Rothe TL. Accuracy of scanning laser polarimetry in the diagnosis of glaucoma. Arch Ophthalmol 1999; 117: 1298– 304.
Colen TP, Lemij HG. Sensitivity and specificity of the GDx: clinical judgement of standard printouts versus the number. J Glaucoma 2003; 12: 129– 33.
Choplin NT, Lundy DC. The sensitivity and specificity of scanning laser polarimetry in the detection of glaucoma in a clinical setting. Ophthalmology 2001; 108: 899–904.
Munkwitz S, Funk J, Loeffler KU, Harbarth U, Kremmer S. Sensitivity and specificity of scanning laser polarimetry using the GDx: Br J Ophthalmol 2004; 88: 1142–5.
Weinreb RN, Bowd C, Greenfield DS, Zangwill LM. Measurement of magnitude and axis of corneal polarization with scanning laser polarimetry. Arch Ophthalmol 2002; 120: 901–6.
Reus NJ, Lemij HG. Diagnostic accuracy of the GDx VCC for glaucoma. Ophthalmology 2004; 111: 1860–5.
Reus NJ, Colen TP, Lemij HG. Visualization of localized nerve fiber layer defects with the GDx with individualized and fixed compensation of anterior segment birefringence. Ophthalmology 2003; 110: 1512–6.
Reus NJ, Lemij HG. Scanning laser polarimetry of the retinal nerve fiber layer in perimetrically unaffected eyes of glaucoma patients. Ophthalmology 2004; 111: 2199–203.
Mohammadi K, Bowd C, Weinreb RN, Medeiros FA, Sample PA, Zangwill LM. Retinal nerve fiber layer thickness measurements with scanning laser polarimetry predict glaucomatous visual field loss. Am J Ophthalmol 2004; 138: 592–601.
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