Abstract
Purpose: :
To evaluate whether scanning laser polarimeter GDx VCC is a valid tool for the detection of glaucomatous optic nerve damage.
Methods: :
This was a prospective, observational, cross-sectional, non-consecutive, population study that took place in Montreal, Quebec, Canada and focused on "high risk" groups for open angle glaucoma development. 240 (480 eyes) subjects were enrolled during a 12 months period. Subjects underwent these tests: FDT, GDx VCC, a standard ophthalmologic examination, including gonioscopy, intraocular pressure, central corneal pachymetry, optic disc grading and fundoscopy.Outcomes measures included positive/negative Likelihood Ratios (LR), sensitivities and specificities, as well as positive/negative predictive values (PPV) of the nerve fiber indicator (NFI) parameter at a cut-off value 30, 35 and 40. Gold-standard definitions of glaucoma (Gold Standart 1- positive vs probable, possible, negative; Gold 2 - positive, probable vs possible, negative; Gold 3 - positive, probable, possible vs negative) varied depending on whether suspects were classified with normals, suspects or glaucoma, based on optic nerve appearance and on FDT results.
Results: :
Of the original 240 patients examined, 19(8%) were found to have glaucoma. Depending on gold-standard definitions for glaucoma, Specificity ranged from 90% to 98%, Sensitivity from 10% to 100%, PPV from 14% to 65%, NPV from 56% to 100%.In all three test positive groups (NFI>=30,35,40) there was a good correlation between clinical based diagnoses:NFI>=30Gold 1 OS Khi=24, p<0.002; Gold 2 Khi=23, p<0.000, Gold 3 Khi=7, p<0.012Gold 1 OD Khi=27, p<0.001; Gold 2 Khi=14, p<0.005, Gold 3 Khi=3, p<0.072Gold 1 OS or OD Khi=37, p<0.000 Gold 2 Khi=32, p<0.000, Gold 3 Khi=5, p<0.028NFI>=35Gold 1 OS Khi=17, p<0.013 Gold 2 Khi=5, p<0.060, Gold 3 Khi=3, p<0.083Gold 1 OD Khi=33, p<0.001 Gold 2 Khi=18, p<0.003, Gold 3 Khi=4, p<0.037Gold 1 OS or OD Khi=18, p<0.005 Gold 2 Khi=17, p<0.001, Gold 3 Khi=3, p<0.099NFI>=40Gold 1 OS Khi=27, p<0.006 Gold 2 Khi=3, p<0.127, Gold 3 Khi=3, p<0.106Gold 1 OD Khi=19, p<0.011 Gold 2 Khi=5, p<0.084, Gold 3 Khi=2, p<0.143Gold 1 OS or OD Khi=11, p<0.029 Gold 2 Khi=7, p<0.030, Gold 3 Khi=2, p<0.172
Conclusions: :
This study suggests that a glaucoma screening program may be more effective in detecting POAG when targeting high risk populations. GDxVCC may prove to be a useful tool in detecting glaucomatous optic nerve damage, and could be used as part of a complete glaucoma screening protocol.