GDx VCC 1

GDx VCC: 

GDx VCC Dr G Premnath

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• Uses diode laser light source (780 nm ) • 40 x 20 degree measurement area • Data displayed as 256 x 256 pixel grid Peripapillary region around ONH and macular region around fovea.

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• Artifact in NFL thickness measurement introduced by birefringence of other ocular structures – Cornea • Older generation of instrument adjusted for expected corneal birefringence - FCC Anterior segment birefringence - confounding factor.

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GDx VCC • Variable Corneal Compensation (VCC) – Allows measurement of individual corneal Birefringence. – Compensates for individual differences. – Improves reliability and detection of early glaucoma.

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GDx VCC • ECC – Enhanced Corneal Compensation new software method.

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INTERPRETATION OF GDx PRINTOUT

KEY AREAS: 

KEY AREAS Fundus image. RNFL thickness map. RNFL deviation map. TSNIT graph. Parameter table.

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Q score: 1-10 Acceptable quality: 8-10 Fundus image

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Phase shift of the polarised light passing through the RNFL which is proportional to thickness. 20 deg x 20 deg. Amount of phase shift - converted to a thickness measure and colour coded. Bright, warm colours: ( yellow , orange , red ) thicker areas. Dark, cool colours: ( black , blue )thinner areas. RNFL thickness map Hour-glass pattern

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Compare the retardation value of superpixels with corresponding areas the age and ancestry matched database . Each superpixel represent the average of 16 individual pixels (4x4). Makes it easy to see RNFL bundle defects and areas of abnormality. RNFL deviation map

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Peripapillary RNFL thickness along the measurement circle . (3.2 mm) Normal 95% range of the TSNIT plot is shown as shaded area. TSNIT Plots

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Average RNFL thickness around the entire calculation circle. Average RNFL thickness in the superior 120 ̊ region of t he calculation circle . PARAMETER TABLE

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Average RNFL thickness in the inferior 120 ̊ region of t he calculation circle . Modulation of the double-hump pattern. Peak – trough difference. Normal eye –high modulation. PARAMETER TABLE

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Measures deg of symmetry between eyes by correlating the TSNIT functions . Values range from -1 to +1. Normal eyes have values around 0.9. PARAMETER TABLE

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Nerve fibre indicator: Global measure based on entire RNFL thickness map. Output is a single value that ranges from 1-100. Indicates the overall integrity of the RNFL. Normal eyes: <35 Glaucoma: > 44 Borderline: 35-44 PARAMETER TABLE

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Image quality should be assessed. Systematic examination of print-outs. NFI – has best diagnostic ability.

NORMAL: 

NORMAL

BENEFITS TO THE CLINICIAN: 

BENEFITS TO THE CLINICIAN • Improved work flow efficiency. – Rapid scan time – Intuitive interpretation – Patient education tool – No dilation required • Most comprehensive RNFL analysis of any imaging device. • Accurate and repeatable RNFL analysis for early diagnosis and tracking change.

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• Useful diagnostic information with the first exam! • Screening Mode option (helps identify which patients need full glaucoma workup) • Offers new diagnostic information. • Compact and portable. • Effective even with mild cataracts and small pupils. Frenkel , Slonim , et al. Operator learning effect and interoperator reproducibility of the scanning laser polarimeter with variable corneal compensation. Ophthalmology. 2005 Feb;112(2):257-61

Benefits for the Patient: 

Benefits for the Patient • Fast and easy. • No learning curve. • Comfortable. • Easy to understand output. • Rapid examination (as little as 1 minute) • No dilation required.

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THANK YOU !