Biomedical subjects

Qienyuan Zhou

Publications and source records attributed to Qienyuan Zhou.

4 recordsLinked to original sources

PubMed2006

Modeling of scanning laser polarimetry images of the human retina for progression detection of glaucoma.

The development of methods to detect slowly progressing diseases is often hampered by the time-consuming acquisition of a sufficiently large data set. In this paper, a method is presented to model the change in images acquired by scanning laser polarimetry, for the detection of glaucomatous progression. The model is based on image series of 23 healthy eyes and incorporates colored noise, incomplete cornea compensation and masking by the retinal blood vessels. Additionally, two methods for detecting progression, taking either one or two follow-up visits into account, are discussed and tested on these simulated images. Both methods are based on Student's t-tests, morphological operations and anisotropic filtering. The images simulated by the model are visually pleasing, show corresponding statistical properties to the real images and are used to optimize the detection methods. The results show that detecting progression based on two follow-up visits greatly improves the sensitivity without adversely affecting the specificity.

Algorithms↗

PubMed2006

Enhanced imaging algorithm for scanning laser polarimetry with variable corneal compensation.

PURPOSE: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Algorithms↗

PubMed2003

Effect of individualized compensation for anterior segment birefringence on retinal nerve fiber layer assessments as determined by scanning laser polarimetry.

PURPOSE: Scanning laser polarimetry estimates retinal nerve fiber layer (RNFL) thickness through measurement of retardation of a polarized laser light passing through the naturally birefringent RNFL and cornea. The commercial instrument, the GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies, Inc., San Diego, CA), uses an anterior segment compensator of fixed magnitude and slow polarization axis to eliminate the contribution of the cornea to the total signal. Previous studies have shown up to 30% of patients are not adequately compensated by this method. The aim of this study was to determine the effect of individualized anterior segment compensation using a newly designed variable compensator on estimates of retinal nerve fiber layer thickness compared with those as determined with the fixed compensator in the commercial device. DESIGN: Comparative, observational case series. PARTICIPANTS: Twenty-eight eyes from 14 normal participants and 24 eyes from 12 patients with bilateral glaucoma. METHODS: Using information derived from a scan of the macula, a newly designed variable anterior segment compensator for the GDx was set to neutralize anterior segment birefringence. Normal participants and patients with glaucoma underwent RNFL measurements using the standard (fixed) compensator and the variable compensator. The results were compared using Hotelling's generalized means test and Bonferroni's adjustment for multiple comparisons. MAIN OUTCOME MEASURES: Standard GDx modulation and thickness parameters as determined with the fixed and variable compensators. RESULTS: All thickness values were statistically significantly lower as determined with the variable compensator, with no discernible differences in any of the modulation parameters. CONCLUSIONS: Individualized anterior segment compensation lowers the RNFL thickness values as determined by scanning laser polarimetry compared with those determined with the standard fixed compensator. This may narrow the normal range and increase the discriminating ability of scanning laser polarimetry between normal and disease. However, modulation is less affected, and the modulation parameters may thus prove more useful for distinguishing between normal and glaucoma.

Aged↗

PubMed2002

Individualized compensation of anterior segment birefringence during scanning laser polarimetry.

PURPOSE: To describe a method for assessment and individualized compensation of anterior segment birefringence with scanning laser polarimetry. METHODS: A scanning laser polarimeter (GDx Nerve Fiber Analyzer; Laser Diagnostic Technologies, Inc., San Diego, CA) was modified to accommodate a variable compensator. The magnitude and axis of anterior segment birefringence of normal eyes were determined from a polarimetry image of the Henle fiber layer. The variable compensator was then adjusted to minimize anterior segment birefringence. Retinal nerve fiber layer (RNFL) and macular measurements were then obtained. Macular images with individualized compensation served to verify the effectiveness of the compensation. To demonstrate individualized compensation, two sets of three images each were obtained from four eyes of four normal subjects. One set was obtained with individualized compensation and another with fixed compensation, as used in the commercial polarimetry system. RESULTS: In the tested eyes, the magnitude of anterior segment birefringence ranged from 21.7 to 86.3 nm, and the slow axis ranged from 5.7 degrees nasally upward to 54.3 degrees nasally downward. The maximum residual retardation resulting from compensation was 70 nm for fixed compensation and 11.5 nm for individualized compensation. The compensation residual directly affected the assessment of the RNFL by scanning laser polarimetry. RNFL images obtained with individualized compensation were more consistent with the expected anatomy of the eye. In the eyes measured, the range of RNFL thicknesses appeared to be narrower with the variable corneal and lens compensator (VCC) compared with the fixed corneal compensator (FCC). CONCLUSIONS: In eyes with a normal macula, the magnitude and axis of anterior segment birefringence can be determined from a polarimetry image of the Henle fiber layer. Individualized anterior segment compensation can be achieved with the described method so that the measured birefringence largely reflects the RNFL birefringence. Whether and how macular diseases affect this method remain to be investigated.

Anterior Eye Segment↗