Sensitivity and specificity of scanning laser polarimetry using the GDx

[Glaucoma diagnosis using scanning laser polarimetry]

Scanning laser polarimetry (SLP) is another technology for early glaucoma diagnosis. This technique (represented in the GDx from Carl Zeiss Meditec, Jena, Germany) is based on polarimetry and measures the retinal nerve fiber layer (RNFL) thickness. Compared with previous instruments without customized corneal compensation, the variable corneal compensation technology enables improved differentiation between glaucoma and healthy eyes. Limitations are the atypical birefringence patterns that exist in some eyes, showing false high RNFL values. The newest software uses enhanced corneal compensation (ECC) technology to avoid these atypical patterns and to improve glaucoma diagnosis. Advantages of SLP include independence from drawing a contour line and a reference plane. Follow-up using SLP is limited, but with the use of the new ECC technology, trend and event analyses are possible. Long-term studies will determine the effectiveness of this method.

Scanning laser polarimetry - a review

Glaucoma is a leading cause of irreversible blindness worldwide. Retinal ganglion cells and their axons represent the selective target of the disease. When visual function is still intact on standard automated perimetry and optic disc appearance is suspicious, an early diagnosis may be supported by the identification of a retinal nerve fibre layer (RNFL) defect in the peripapillary area. At present days, computer-based, real-time imaging of the peripapillary RNFL is available through instruments of easy use and with high levels of accuracy and reproducibility. Scanning laser polarimetry is performed by a confocal scanning laser ophthalmoscope with an integrated polarimeter (GDx-VCC). There is a considerable amount of scientific evidence about the role of this imaging technique for glaucoma diagnosis. The aim of this review is to describe the principles of operation, the examination procedure, the clinical role, the results of main diagnostic studies and the future development of the software for the scanning laser polarimetry.

Combining nerve fiber layer parameters to optimize glaucoma diagnosis with optical coherence tomography

PURPOSE

To identify the best combination of Stratus optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness parameters for the detection of glaucoma.

DESIGN

Observational cross-sectional study.

PARTICIPANTS

Eighty-nine age-matched normal and perimetric glaucoma participants enrolled in the Advanced Imaging for Glaucoma Study.

METHODS

The Zeiss Stratus OCT system was used to obtain the circumpapillary RNFL thickness in both eyes of each participant. Right and left eye clock-hour data are analyzed together, assuming mirror-image symmetry. The RNFL diagnostic parameters were combined using either or-logic or and-logic approaches.

MAIN OUTCOME MEASURES

Area under the receiver operating characteristic curve (AROC), sensitivity, and specificity are used to evaluate diagnostic performance.

RESULTS

Overall average RNFL thickness has the highest AROC value (0.89) of all single parameters evaluated, followed by the inferior and superior quadrants (0.88 and 0.86, respectively). The clock hours with the best AROC values are in the inferior and superior quadrants. The highest AROC (0.92) was achieved by the or-logic combination of overall, inferior, and superior quadrant RNFL thicknesses. The 3-parameter combination was significantly better than the overall average alone (P = 0.01). The addition of more quadrants or clock hours to the combination reduced diagnostic performance.

CONCLUSIONS

The best stand-alone diagnostic strategy for Stratus OCT RNFL data is to classify an eye as glaucomatous if the overall, inferior quadrant, or superior quadrant RNFL thickness average is below normal.

Optic nerve head and retinal nerve fiber layer analysis: a report by the American Academy of Ophthalmology

OBJECTIVE

To evaluate the current published literature on the use of optic nerve head (ONH) and retinal nerve fiber layer (RNFL) measurement devices in diagnosing open-angle glaucoma and detecting progression.

METHODS

A search of peer-reviewed literature was conducted on February 15, 2006 in PubMed and the Cochrane Library for the period January 2003 to February 2006. The search was limited to studies of adults in English-language journals and yielded 442 citations. The panel reviewed the abstracts of these articles and selected 159 articles of possible clinical relevance for review. Of these 159 full-text articles, 82 were determined to be relevant for the first author and methodologist to review and rate according to the quality of evidence.

RESULTS

There were no studies classified as having the highest level of evidence (level I). The ONH and RNFL imaging instruments reviewed in this assessment were determined to be highly effective in distinguishing eyes with glaucomatous visual field (VF) loss from normal eyes without VF loss, based on level II evidence. In addition, some studies demonstrated that parameters from ONH or RNFL imaging predicted the development of VF defects among glaucoma suspects. Studies on detecting glaucoma progression showed that although there was often agreement on progression between the structural and functional (VF) tests, a significant proportion of glaucoma patients progressed by either the structural or the functional test alone.

CONCLUSIONS

The ONH and RNFL imaging devices provide quantitative information for the clinician. Based on studies that have compared the various available technologies directly, there is no single imaging device that outperforms the others in distinguishing patients with glaucoma from controls. Ongoing advances in imaging and related software, as well as the impracticalities associated with obtaining and assessing optic nerve stereophotographs, have made imaging increasingly important in many practice settings. The information obtained from imaging devices is useful in clinical practice when analyzed in conjunction with other relevant parameters that define glaucoma diagnosis and progression.

The future of glaucoma clinics

The number of patients seen with glaucoma related pathologies is predicted to increase significantly over the next few years as a result of an ageing population, increased optometric screening, and raised public awareness. In addition, the recent glaucoma literature proposes more aggressive management of ocular hypertension, open angle glaucoma, and narrow angle pathologies. This will overburden many glaucoma services and demands a reappraisal of current management strategies. Using a database of patients compiled from their tertiary referral glaucoma service as an example, the authors discuss the current controversies relating to each glaucoma subtype, encompassing issues relating to disease prognosis, efficacy of treatment, and resource management. They also suggest a range of strategies aimed at streamlining glaucoma clinics. Examples include shared care schemes, multidisciplinary teams, clinic guidelines/protocols, and alteration of clinic review times. The predicted effect of such schemes on clinic workloads is discussed, together with any existing validation.

Glaucoma screening: current trends, economic issues, technology, and challenges

PURPOSE OF REVIEW

Glaucoma is one of the leading causes of irreversible blindness worldwide. Early glaucoma detection and treatment are currently the only known methods for preventing blindness and low vision resulting from this frequently asymptomatic disease.

RECENT FINDINGS

New technologies for detecting early glaucomatous damage are important in diagnosing optic nerve disease, not only in community screening settings but also in clinics. Imaging of the optic nerve head and macula and retinal nerve fiber layer analysis can provide quick, automated, and quantitative measurements in agreement with clinical estimates of optic disc structure and visual function. In the area of perimetry, frequency-doubling technology is a promising and feasible mass-screening method with reasonable sensitivity for detecting visual field loss. Central corneal thickness has emerged as a new risk factor for the development and progression of glaucoma, thereby complicating the role of tonometry and measurement of intraocular pressure as screening parameters for glaucoma. Along with technological advances, strides are also being made with public policy and legislative efforts to bring glaucoma onto the national and global health care agenda. These initiatives incorporate vision-screening goals into national disease prevention programs emphasizing the need for early glaucoma detection and treatment.

SUMMARY

Glaucoma awareness needs to be increased through better education, and compliance with follow-up care needs to be improved to decrease the economic and social costs from glaucoma. In addition, screening models need to be developed that will be effective in developing countries where the risk of blindness from glaucoma is highest.

Discrimination between normal and glaucomatous eyes using Stratus optical coherence tomography in Taiwan Chinese subjects

BACKGROUND

We differentiated between normal and glaucomatous eyes in the Taiwan Chinese population based solely on the quantitative assessment of summary data reports from Stratus optical coherence tomography (OCT) by comparing their area under the receiver operating characteristic (ROC) curve.

METHODS

One randomly selected eye from each of the 62 patients with early glaucomatous damage (mean deviation -2.8 +/- 1.8 dB) and from each of the 62 age- and sex-matched normal individuals were included in the study. Measurements of glaucoma variables (retinal nerve fiber layer thickness and optic nerve head analysis results) were obtained by Stratus OCT. Twenty-one OCT parameters were included in a linear discriminant analysis (LDA) using forward selection and backward elimination to determine the best combination of parameters for discriminating between glaucomatous and healthy eyes based on ROC curve area.

RESULTS

The average RNFL thickness was the best individual parameter for differentiating between normal eyes and glaucomatous eyes (ROC curve area 0.793). The maximum area under the ROC curve of six input parameters (average RNFL thickness; 10, 11, and 12 o'clock segment thicknesses; cup area; and vertical integrated rim area) generated by the forward selection method was 0.881. Whereas the maximum area under the ROC curve of 15 input parameters (average RNFL thickness; 1, 3, 4, 6, 8-10, 12 o'clock segment thicknesses; vertical integrated rim area; horizontal integrated rim area; disc area; cup to disc area ratio; cup to disc horizontal ratio; and cup to disc vertical ratio) generated by backward elimination method was 0.929.

CONCLUSIONS

The performance of individual parameters obtained from Stratus OCT is fairly reliable for differentiating the early glaucomatous eyes from normal eyes. However, the discriminant power increases when LDA with forward selection and backward elimination methods is applied.