Enhanced Corneal Compensation Research Articles

Scanning Laser Polarimetry With Variable and Enhanced Corneal Compensation in Normal and Glaucomatous Eyes

To investigate whether correction for atypical birefringence pattern (ABP) using scanning laser polarimetry with enhanced corneal compensation (SLP-ECC) reduces the severity of ABP compared with variable corneal compensation (SLP-VCC) and improves the correlation with visual function. Prospective observational study. Normal and glaucomatous eyes enrolled from four clinical sites underwent complete examination, automated perimetry, SLP-ECC, and SLP-VCC. Eyes were characterized in three groups based upon the typical scan score (TSS): normal birefringence pattern (NBP) was defined as TSS > or = 80, mild ABP as TSS 61 to 79, and moderate-severe ABP as TSS < or = 60. For each of four SLP parameters, the area under the ROC curve (AUROC) was calculated to compare the ability of SLP-ECC and SLP-VCC to discriminate between normal and glaucomatous eyes. Eighty-four normal volunteers and 45 glaucoma patients were enrolled. Mean TSS was significantly (P < .001) greater using SLP-ECC (98.0 +/- 6.6) compared with SLP-VCC (83.4 +/- 22.5). The frequency of moderate-severe ABP images was significantly (P < .001, McNemar test) higher using SLP-VCC (18 of 129, 14%) compared with SLP-ECC (one of 129, 0.8%). Two SLP-ECC parameters (temporal superior nasal inferior temporal [TSNIT] average and inferior average) had significantly (P = .01, P < .001) higher correlation (r = .45, r = .50, respectively) with MD compared with SLP-VCC (r = .34, r = .37). Among eyes with moderate-severe ABP (n = 18), inferior average obtained using SLP-ECC had significantly (P = .03) greater AUROC (0.91 +/- 0.07) compared with SLP-VCC (0.78 +/- 0.11). SLP-ECC significantly reduces the frequency and severity of ABP compared with SLP-VCC and improves the correlation between RNFL measures and visual function.

Enhanced Imaging Algorithm for Scanning Laser Polarimetry with Variable Corneal Compensation

To describe and investigate a method of improving assessment of retinal nerve fiber layer (RNFL) morphology with scanning laser polarimetry (SLP) with variable corneal compensation (VCC). By neutralizing anterior segment birefringence with a variable compensator, the current VCC method allows direct measurement of RNFL retardation. In the new method, enhanced corneal compensation (ECC), the variable compensator was set to introduce a "bias" birefringence. This bias was removed mathematically for each individual pixel to produce the RNFL image. In 177 eyes of healthy subjects, patients with glaucoma, and subjects with ocular hypertension, retardation images were obtained with both VCC and ECC. In the tested eyes, images obtained with ECC showed the expected RNFL appearance better than those obtained with VCC. In addition, the typical scan score, which quantifies the amount of atypia, was higher with ECC than with VCC. The amount of residual anterior segment birefringence dropped significantly with ECC in the various groups. Measurements of peripapillary RNFL retardation showed reduced temporal and nasal values with ECC, whereas superior and inferior values were not significantly different between VCC and ECC. The dynamic range appeared to have increased with ECC. The accuracy of the TSNIT (temporal, superior, nasal, inferior, temporal) average and inferior average for detecting glaucoma was higher with ECC than with VCC. RNFL morphology may be better assessed with the presented ECC method than with standard VCC. ECC may be implemented in the current VCC systems by means of a software upgrade. It may enhance the clinical utility of the GDx VCC in glaucoma management.

Evaluation of Enhanced Corneal Compensation in Scanning Laser Polarimetry

To investigate the potential advantages of an enhanced corneal compensation algorithm (ECC) compared with variable corneal compensation (VCC), in scanning laser polarimetry. One eye of 15 healthy ametropic subjects was imaged immediately before and 7 days after uncomplicated LASIK surgery. Anterior segment birefringence was assessed at each measurement session. For post-LASIK calculations, either actual post-LASIK corneal retardation (VCC and ECC groups), or the pre-LASIK corneal retardation (VCC* and ECC* groups) was used. The typical scan score-value was higher for ECC both before and after LASIK (P < 0.01), and it was not influenced by LASIK in either compensation method. Both the axis and the magnitude of corneal birefringence altered after LASIK (P < 0.01). After LASIK, with VCC* all eyes showed uncompensated birefringence, but with ECC* none did. LASIK had no effect on retinal nerve fiber layer measurements in VCC and ECC methods. In VCC* the LASIK-induced retinal nerve fiber layer thickness change was significant (P < 0.01) in the temporal, superior, and nasal quadrants. After LASIK, the number of significantly altered sectors along the TSNIT plot showed no difference when comparing VCC and ECC, VCC and ECC*, or ECC and ECC*. In contrast, significantly more sectors were altered in VCC* than in either VCC or ECC* (P < 0.001). The new ECC software is more effective than VCC in neutralization of atypical polarization pattern and the uncompensated corneal retardation.

Influence of Myelinated Retinal Nerve Fibers on Scanning Laser Polarimetry Using Variable and Enhanced Corneal Compensation Methods

Five eyes with myelinated retinal nerve fibers were imaged using a scanning laser polarimeter with variable corneal compensation and with enhanced corneal compensation (a new research software). Using variable corneal compensation, areas of myelinated retinal nerve fibers uniformly appeared as areas of increased retardation. Using enhanced corneal compensation software, the same myelinated retinal nerve fiber areas adjacent to the optic nerve head appeared as areas of clinically significant thinning of the retinal nerve fiber layer in the superior and inferior quadrants, and as areas of increased retinal nerve fiber layer thickness nasally and temporally. Wedge-shaped myelinated retinal nerve fibers along a retinal nerve fiber bundle and discontinuous to the optic nerve head caused increased retardation with both compensation methods. The results show that influence of myelinated retinal nerve fibers on scanning laser polarimetric results varies according to the compensation method and the retinal location of the myelinated retinal nerve fibers.