Scanning laser polarimetry - a review

OCT-Based Quantification and Classification of Optic Disc Structure in Glaucoma Patients

PURPOSE

To objectively classify the optic discs of open-angle glaucoma (OAG) patients into Nicolela's four disc types, i.e., focal ischemic (FI), myopic (MY), senile sclerotic (SS), and generalized enlargement (GE), with swept-source optical coherence tomography (SS-OCT).

METHODS

This study enrolled 113 eyes of 113 OAG patients (mean age: 62.5 ± 12.6; Humphrey field analyzer-measured mean deviation: -9.4 ± 7.3 dB). Newly developed software was used to quantify a total of 20 optic disc parameters in SS-OCT (DRI OCT-1, TOPCON) images of the optic disc. The most suitable reference plane (RP) above the plane of Bruch's membrane opening was determined by comparing, at various RP heights, the SS-OCT-measured rim parameters and spectral-domain OCT-measured circumpapillary retinal nerve fiber layer thickness (cpRNFLT), with Pearson's correlation analysis. To obtain a discriminant formula for disc type classification, a training group of 72 eyes of 72 OAG patients and a validation group of 60 eyes of 60 OAG patients were set up.

RESULTS

Correlation with cpRNFLT differed with disc type and RP height, but overall, a height of 120 μm minimized the influence of disc type. Six parameters were most significant for disc type discrimination: disc angle (horizontal), average cup depth, cup/disc ratio, rim-decentering ratio, average rim/disc ratio (upper and lower nasal). Classifying the validation group with these parameters returned an identification rate of 80.0% and a Cohen's Kappa of 0.73.

CONCLUSION

Our new, objective SS-OCT-based method enabled us to classify glaucomatous optic discs with high reproducibility and accuracy.

Clinical Signs and Diagnosis of the Canine Primary Glaucomas

The diagnosis of glaucoma is highly dependent on a working understanding of the clinical signs and available diagnostic procedures. Clinical signs may be attributable to increased intraocular pressure and/or complex alterations in the physiology or molecular biology of the anterior segment, retinal ganglion cells, and optic nerve. Many diagnostic procedures seek to more fully characterize these alterations and to identify which clinical features increase the risk of overt primary angle closure glaucoma (PACG) occurring. Considerable progress has been made in identifying the anatomic features that predispose an eye to PACG, and in elucidating the role of reverse pupillary block.

Advances in retinal imaging modalities: Challenges and opportunities

Imaging in ophthalmology is playing an increasingly important role not only in screening, but also in monitoring and assessing response to treatment in an objective manner. Technical advances in various modes of imaging acquisition provide more detailed images. These can be combined and reviewed on one screen in the place of acquisition or sent for a remote assessment. Moreover, the machines are more user-friendly, which reduces the need for highly skilled technicians. In this article the authors describe currently available and experimental ophthalmic imaging modalities and their impact on clinical practice.

Visual electrodiagnosis in glaucoma screening: a clinical study

BACKGROUND

The aim of the present study was to investigate the value of pattern visual-evoked potentials (pVEP) and pattern electroretinograms (pERG) in early glaucoma diagnosis.

MATERIALS AND METHODS

Thirty-eight eyes of 38 patients were included. Patients were classified into normal control (NC) and glaucoma patient (GP) groups. Patients underwent a detailed clinical ophthalmic examination and an electrodiagnostic examination using steady-state pVEP and pERG. Differences between groups in the amplitudes of the second harmonic of the pVEP and pERG responses to 480' (A480) and 48' (A48) check sizes and the ratio of the above amplitudes (A48/A480) were examined.

RESULTS

Differences in the 48' and 480' pVEP between groups were not statistically significant. The pVEP A48/A480 ratio was significantly higher in NC than in GP. Differences in pERG between groups were statistically not significant for both 48' and 480' check sizes. In contrast, respective differences in pERG A48/A480 ratio were statistically significant.

CONCLUSIONS

Steady-state pVEP and pERG A48/A480 ratio may be of value in glaucoma diagnosis.

Associations with retinal nerve fiber layer measures in the EPIC-Norfolk Eye Study

PURPOSE

To describe GDxVCC retinal nerve fiber layer (RNFL) measures and associations in a predominantly white British population.

METHODS

The EPIC-Norfolk Eye Study is nested within a large multicenter cohort study, the European Prospective Investigation of Cancer. RNFL measurements were taken using the GDxVCC. Generalized estimating equation models were used to assess associations of RNFL measures with age, sex, body mass index (BMI), height, blood pressure, social class, education level, alcohol intake, smoking status, axial length, intraocular pressure, and lens status. Models were linearly adjusted for typical scan score to handle scans with atypical retardation.

RESULTS

There were complete data from 11,030 eyes of 6309 participants with mean age 68 years (48-90 years). Older age (-1.53 μm/decade [95% confidence interval {CI} -1.73, -1.33], P < 0.001), male sex (-0.44 μm [95% CI -0.04, -0.84], P = 0.031), shorter axial length (-0.15 μm/mm [95% CI -0.02, -0.28], P = 0.024), and pseudophakia (-0.49 μm [95% CI -0.94, -0.04], P = 0.033) were associated with thinner RNFL after adjustment for possible confounders. Higher BMI was associated with a thinner RNFL in men only (-0.30 μm/5 kg/m(2) [95% CI -0.58, -0.02], P = 0.039).

CONCLUSIONS

This analysis of associations with RNFL thickness in a largely healthy population may provide insight into the determinants of glaucoma, suggesting higher risk in those who are older, in men, and in men with a higher BMI.

Glaucoma versus red disease: imaging and glaucoma diagnosis

PURPOSE OF REVIEW

The use of ophthalmic imaging for documentation and diagnosis of ocular disease is rising dramatically. Optical coherence tomography (OCT), confocal scanning laser tomography (CSLT), scanning laser polarimetry (SLP) and photographic imaging of the optic nerve head (ONH) are currently used to document baseline characteristics of the ONH and for diagnosing glaucoma and glaucoma progression secondary to loss of retinal nerve fiber layer (RNFL). Imaging modalities typically provide information on ONH and RNFL characteristics which are outside of the normal (relative to normative databases) in red lettering or boxes, whereas ONH and RNFL characteristics within the normal range are presented in green.

RECENT FINDINGS

As imaging modalities have become more sophisticated and are validated in research studies, clinicians have come to rely upon data from these imaging devices to aid in differentiating between normal and glaucomatous states of the ONH and RNFL - typically by examining if the data are green or red suggesting normal or abnormal. However, normative databases can sometimes be flawed relative to atypical ONH or RNFL morphologies and imaging can provide artifacts which do not represent true ocular disease but secondary to limitations of imaging technology.

SUMMARY

Ophthalmic imaging is an important adjunct to clinical diagnosis but the results from imaging devices need to be assessed critically relative to artifacts of imaging and the limitations of the technology and its normative databases.

Imaging of retinal ganglion cells in glaucoma: pitfalls and challenges

Imaging has gained a key role in modern glaucoma management. Traditionally, interest was directed toward the appearance of the optic nerve head and the retinal nerve fiber layer. With the improvement of the resolution of optical coherence tomography, the ganglion cell complex has also become routinely accessible in the clinic. Further advances have been made in understanding the structure-function relationship in glaucoma. Nevertheless, direct imaging of the retinal ganglion cells in glaucoma would be advantageous. With the currently used techniques, this goal cannot be achieved, because the transversal resolution is limited by aberrations of the eye. The use of adaptive optics has significantly improved transversal resolution, and the imaging of several cell types including cones and astrocytes has become possible. Imaging of retinal ganglion cells, however, still remains a problem, because of the transparency of these cells. However, the visualization of retinal ganglion cells and their dendrites has been achieved in animal models. Furthermore, attempts have been made to visualize the apoptosis of retinal ganglion cells in vivo. Implementation of these techniques in clinical practice will probably improve glaucoma care and facilitate the development of neuroprotective strategies.

Assessment of Structural Glaucoma Progression

Purpose

To provide an update on the role of optic nerve head and peripapillary retinal nerve fiber layer imaging in monitoring glaucoma progression.

Methods

Review of literature.

Results

Imaging technologies, such as optical coherence tomography, scanning laser polarimetry, and confocal scanning laser ophthalmoscopy, objectively and quantitatively measure the structural change associated with glaucoma. Rates of retinal nerve fiber layer (RNFL) and rim area loss are significantly faster in progressing compared with nonprogressing subjects. A number of strategies to detect progression have been proposed. The precision of these methods is generally high. However, there is no agreement as to which instrument or parameter is most appropriate for the evaluation of structural progression associated with glaucoma at this moment. The agreement between structural and functional glaucoma progression is generally poor regardless of the strategies used. Structural progression analyses appear to complement visual field progression analyses, detecting a different subset of progressing subjects.

Summary

Imaging devices are promising tools for monitoring patients with glaucoma. Combining structural and functional analyses is useful for accurate monitoring of glaucoma progression.

How to cite this article

Miki A. Assessment of Structural Glaucoma Progression. J Current Glau Prac 2012;6(2):62-67.

Detection of retinal nerve fibre layer progression: comparison of the fast and extended modes of GDx guided progression analysis

PURPOSE

To compare detection of retinal nerve fibre layer changes using GDx guided progression analysis (GPA) fast mode (which assumes fixed variability of a reference population) and extended mode (which measures individual variability), and to determine how they compare with photography and conventional visual field-based methods for identifying glaucoma progression.

METHODS

172 eyes from 117 participants in the Diagnostic Innovations in Glaucoma Study (12 healthy, 108 glaucoma suspects and 52 glaucoma eyes) with ≥ 4 GDx VCC visits and ≥ 3 good quality GDx VCC scans at each visit were included.

RESULTS

Agreement between the GDx GPA fast mode and GDx GPA extended mode was limited. The GDx fast mode and extended mode detected 15 and 18 eyes, respectively, as 'likely progression', but only seven of them agreed. The conventional reference standard (stereophotograph-based optic disc and/or visual field progression) identified nine eyes as progressing, of which two eyes were also identified by the GDx fast mode and three eyes by the extended mode. In the GDx fast mode, we found that the progression detection varied depending on which two scans were included in the baseline and follow-up images.

CONCLUSION

There was limited agreement between the GDx fast mode and the GDx extended mode for progression detection, and between different scans included in the GDx fast mode progression analysis. Longer follow-up is needed to determine the proportion of eyes classified as 'likely progression' by the GDx analysis that are early change and the proportion that are false positive results.

Spectral-domain optical coherence tomography and scanning laser polarimetry in glaucoma diagnosis

PURPOSE

To evaluate glaucoma diagnostic capability of the retinal nerve fiber layer (RNFL) imaging by spectral-domain optical coherence tomography (Cirrus OCT) and scanning laser polarimetry (GDx VCC).

METHODS

We imaged 88 glaucomatous and 77 healthy eyes using both devices. Areas under the receiver-operating characteristic curves (area under the curves, AUCs) and sensitivities at fixed specificities of average, superior, and inferior RNFL thickness were compared. Likelihood ratios (LRs) and diagnostic agreement based on normative classifications yielded by both devices were determined.

RESULTS

The best performing parameter was the nerve fiber indicator (NFI) in GDx VCC and inferior RNFL thickness in Cirrus OCT (AUC = 0.912, 0.961, P = 0.045). The AUCs of the Cirrus OCT were significantly higher than those of GDx VCC in all parameters. Most of the parameters in Cirrus OCT were more sensitive than GDx VCC in the detection of glaucoma at fixed specificity values. Cirrus OCT had an infinite LR with abnormal classification results in both average and superior RNFL thickness. There was good agreement between the two instruments with respect to abnormal classifications (kappa, 0.611-0.766)

CONCLUSION

Both Cirrus OCT and GDx VCC RNFL measurements showed good glaucoma diagnostic capabilities. Cirrus OCT showed higher sensitivities than GDx VCC.