Assessing structure and function of the afferent visual pathway in multiple sclerosis and associated optic neuritis

The afferent visual pathway is commonly affected in MS. Assessment of the afferent visual pathway using clinical, imaging and electrophysiological methods not only provides insights into the pathophysiology of MS, but also provides a method of investigating potential therapeutic measures in MS. This review summarises the various assessment methods, in particular imaging techniques of the visual pathway. Retinal nerve fibre layer (RNFL) thickness is usually reduced following an episode of optic neuritis. Techniques such as optical coherence tomography, scanning laser polarimetry, and confocal scanning laser ophthalmoscopy are used to quantify RNFL thickness. MRI of the optic nerve is not routinely used in the diagnosis of MS or optic neuritis, but is valuable in atypical cases and in research. T2- weighted images of the optic nerve usually show the hyperintense lesion in optic neuritis and gadolinium enhancement is seen in the acute attack. Quantifying atrophy of the optic nerve using MRI gives an indication of the degree of axonal loss. Magnetization transfer ratio (MTR) of the optic nerve provides an indication of myelination. Diffusion tensor imaging (DTI) of the optic nerve and optic radiation provide information about the integrity of the visual white matter tracts. Functional MRI following visual stimulation is used to assess the contribution of cortical reorganisation to functional recovery following optic neuritis. Investigations including logMAR visual acuity, Sloan contrast acuity, Farnsworth- Munsell 100-hue colour vision tests and Humphrey perimetry provide detailed quantitative information on different aspects of visual function. Visual evoked potentials identify conduction block or delay reflecting demyelination. These collective investigative methods have advanced knowledge of pathophysiological mechanisms in MS and optic neuritis. Relevant ongoing studies and future directions are discussed.

Imaging of the retinal nerve fibre layer for glaucoma

BACKGROUND

Glaucoma is a group of diseases characterised by retinal ganglion cell dysfunction and death. Detection of glaucoma and its progression are based on identification of abnormalities or changes in the optic nerve head (ONH) or the retinal nerve fibre layer (RNFL), either functional or structural. This review will focus on the identification of structural abnormalities in the RNFL associated with glaucoma.

DISCUSSION

A variety of new techniques have been created and developed to move beyond photography, which generally requires subjective interpretation, to quantitative retinal imaging to measure RNFL loss. Scanning laser polarimetry uses polarised light to measure the RNFL birefringence to estimate tissue thickness. Optical coherence tomography (OCT) uses low-coherence light to create high-resolution tomographic images of the retina from backscattered light in order to measure the tissue thickness of the retinal layers and intraretinal structures. Segmentation algorithms are used to measure the thickness of the retinal nerve fibre layer directly from the OCT images. In addition to these clinically available technologies, new techniques are in the research stages. Polarisation-sensitive OCT has been developed that combines the strengths of scanning laser polarimetry with those of OCT. Ultra-fast techniques for OCT have been created for research devices. The continued utilisation of imaging devices into the clinic is refining glaucoma assessment. In the past 20 years glaucoma has gone from a disease diagnosed and followed using highly subjective techniques to one measured quantitatively and increasingly objectively.

Correlation of intraocular pressure measured with goldmann and dynamic contour tonometry in normal and glaucomatous eyes

PURPOSE

To compare intraocular pressure (IOP) values measured by both Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) in both normal and glaucomatous eyes, and to determine the relationship between these parameters and central corneal thickness (CCT).

PATIENTS AND METHODS

Forty-seven subjects with primary open-angle glaucoma and 38 normal subjects attended a 12-hour session during which IOP was assessed at 7 time points, every 2 hours, by both GAT and DCT. CCT was also assessed at the same visit. Mean IOP was calculated for each eye of each subject by each method from the 7 diurnal IOP measurements obtained.

RESULTS

Mean IOP was higher when measured by DCT than by GAT in both normal (by 1.1 mm Hg, P<0.0001) and glaucomatous (by 1.6 mm Hg, P<0.0001) eyes. IOP measurements by GAT and DCT were moderately correlated in both normal (r(2)=0.354, P<0.0001) and glaucomatous (r(2)=0.552, P<0.0001) eyes. In normal eyes, there was a weak positive correlation between GAT IOP and CCT (r(2)=0.088, slope=0.022 mm Hg/microm, P=0.009) and no correlation between DCT IOP and CCT (r(2)=0.007, slope=0.005 mm Hg/microm, P=0.468). In glaucomatous eyes, there was no correlation between GAT IOP and CCT (r(2)=0.006, slope=0.007 mm Hg/microm, P=0.473) and a weak inverse correlation between DCT IOP and CCT (r(2)=0.075, slope=-0.021 mm Hg/microm, P=0.008).

CONCLUSIONS

Both GAT and DCT are affected by CCT, albeit in different ways. Normal and glaucomatous eyes exhibit different relationships between CCT and IOP measured by either GAT or DCT. The relationships between CCT and transcorneal IOP measurements are complex and incompletely characterized, which limits the clinical interpretation of GAT and DCT measurements of IOP in both normal and glaucomatous eyes.

Effects of corneal thickness on intraocular pressure measured with three different tonometers

PURPOSE

To compare intraocular pressure (IOP) measured by a Goldmann applanation tonometer (GAT), a noncontact tonometer (NCT), and a portable noncontact tonometer (PNCT) in eyes of healthy volunteers, and to determine if a significant correlation exists between the IOP and the central corneal thickness (CCT).

METHODS

A total of 144 healthy participants were randomly assigned to one of two groups; in the first group, IOP was measured first with the NCT and then with the GAT. In the second group, IOP was measured first with the PNCT and then with the GAT. Subsequently, the CCT of all subjects was measured with an ultrasonic pachymeter.

RESULTS

The IOPs determined by the GAT and NCT and were strongly correlated, as were those determined by the GAT and PNCT, in both groups. However, a Bland-Altman plot showed that the correlations between the GAT and NCT and between the GAT and the PNCT measurements were not significant. With all three instruments, the IOP readings varied with the CCT. The mean IOPs obtained with the GAT increased by 0.23 mmHg with each 10-microm increase in CCT (0.23 mmHg/10 microm). The comparable value for the NCT was 0.29 mmHg/10 microm, and that for the PNCT was 0.31 mmHg/10 microm.

CONCLUSIONS

For measurements of IOP in normal eyes, the GAT is the tonometer least affected by the CCT, compared with the PNCT and NCT. A PNCT is more likely to be affected by variations in CCT than the GAT.

Most common mistakes in measuring intraocular pressure

<zakljucak> Zlatni standard za merenje IOP je tehnika GAT koja je tacna, ali ne i potpuno precizna, tako da ce se u cilju dobijanja sto preciznijih vrednosti IOP morati koristiti i druge tonometrijske tehnike.

Scan tracking coordinates for improved centering of Stratus OCT scan pattern

OBJECTIVE

To describe and evaluate a technique to optimize scan centering during the Stratus optical coherence tomography (OCT) image acquisition process using currently available scan tracking coordinates.

DESIGN

Observational clinical study.

PARTICIPANTS

Twelve eyes of six normal subjects were examined using the Fast retinal nerve fiber layer (RNFL) thickness and the Fast Optic Disc acquisition protocols.

METHODS

At visit 1, 3 consecutive measurements (trials) were taken by 2 different operators with the scan subjectively centered on the optic disc for the Fast RNFL thickness protocol and Fast Optic Disc protocol. At visit 2, 3 consecutive measurements were taken by positioning the scan using scan tracking coordinates. The scan coordinates were recorded twice by each operator and the limits of agreement and Bland-Altman plots were used to estimate agreement. The within subjects standard deviation (Sw) and the coefficient of variation (CV) were calculated for RNFL and optic disc parameters for each operator separately and differences by scan positioning method were evaluated using a 3-way (trial x operator x visit) analysis of variance for repeated measures.

RESULTS

The Sw and CV for the RNFL thickness parameters were generally higher when the scan was subjectively centered on the disc compared to when using the newly described coordinate system (eg, for operator 2, temporal sector Sw was 1.60+/-0.78 and 4.09+/-0.99 and CV was 2.2% and 5.7% with and without coordinate use, respectively). For the Fast RNFL protocol, the use of scan tracking coordinates resulted in significantly less variability than subjective placement of the scan circle using the landmark feature (currently recommended technique) in the temporal sectors only. No significant difference was found for any of the optic disc parameters. Bland-Altman plots showed good agreement within each operator for calculating scan coordinates suggesting this technique is reproducible.

CONCLUSIONS

Reproducibility of RNFL thickness measurements generally improves with the use of scan tracking coordinates, particularly in the temporal sector. However, small changes in the position of the scan do not significantly affect the reproducibility of optic disc parameters.

Learning effect of humphrey matrix frequency doubling technology perimetry in patients with ocular hypertension

AIM

To evaluate the learning effect of Frequency Doubling Technology (FDT) perimetry using the Humphrey Matrix-FDT perimetry (Matrix) 24-2 full-threshold program on patients with ocular hypertension experienced with standard automated perimetry.

METHODS

Twenty-four patients with ocular hypertension underwent 5 full-threshold Matrix tests at intervals of 5+/-2 days. Learning effect was defined as an improvement at results for duration, perimetric indices, foveal sensitivity, Glaucoma Hemifield Test, and the number of points with a P<5% and <1% in the total and pattern deviation maps. Eccentricity, hemifield, and quadrant sensitivities were also addressed as sources of differences in learning effect. Test-retest variability was also calculated for each repetition as the mean of the point-to-point interindividual standard deviations.

RESULTS

A learning effect was demonstrated for mean defect (P=0.031, analysis of variance) and foveal sensitivity (P=0.009) and it only affected the first test for both parameters. All the other parameters did not show any significant learning effect. The effect was independent from eccentricity and quadrant or hemifield sensitivities.

CONCLUSIONS

The results of this study demonstrate that the learning effect for Matrix-FDT is mild and it may affect only the first test. Caution is needed in the analysis of the first Matrix-FDT examination and retest may be advisable in the presence of low mean defect.

The relationship between Rarebit perimetry and OCT-derived retinal nerve fibre layer thickness in glaucoma

PURPOSE

To examine the association between measures of neuroretinal matrix integrity as determined with Rarebit perimetry and optical coherence tomography (OCT)-derived retinal nerve fibre layer thickness.

METHODS

One randomly selected eye of 30 White primary open-angle glaucoma patients (age: 60.9 +/- 11.7 years; MD: -3.2 +/- 5.1 dB) and 16 healthy White individuals (age: 33.2 +/- 6.4 years; MD: -0.8 +/- 0.8 dB) were included in the study. Participants underwent Rarebit perimetry testing (central field, software version 4) and an OCT fast retinal nerve fibre layer (RNFL) scan. Correlation was investigated between hemifield Rarebit scores and the corresponding RNFL values, as well as between global Rarebit scores and the respective RNFL measures.

RESULTS

Statistically significant correlations of average hit rate (HR) < 90 and mean hit rate (MHR) were detected with Max-Min and average thickness (Pearson's r ranging from 0.393 to 0.474). Number HR < 90 showed a moderate correlation only with Max-Min (r = -0.396, P = 0.030). Regarding the association between hemifield hit rates and the corresponding OCT thickness parameters, only inferior maximum correlated moderately with HR superior (r = 0.385, P = 0.035). A tendency was detected for the relationship of superior maximum with HR inferior (r = 0.345, P = 0.062). For the control group, no significant correlation was found for any of the global or hemifield indices and the corresponding thickness values.

CONCLUSION

Although Rarebit perimetry is based on a physiological principle distinctly different from conventional perimetry, it provides global indicators of neuroretinal matrix integrity that correlate with some OCT-derived RNFL thickness measures.

[Not Available]

Purpose of the study was to compare Rarebit Perimetry (RP) with Standard Automatic Perimetry (SAP) in patients with ischemic retrochiasmal lesions. Seventeen patients with homonymous hemianopia underwent SAP and RP. Correlation between the two techniques was evaluated, congruent defects were quantified in the spared hemifield and residual vision areas were investigated in the blind hemifield. A strong correlation was found between SAP and RP. In the spared hemifield, RP detected congruent defects in a higher percentage of cases. Residual detection function has been found at RP in 69,2 % of perimetrically blind visual field quadrants as assessed by SAP. In conclusion, RP appears to be useful to assess visual function in hemianopic patients. As compared to SAP, it seems able to detect small congruent defects in a higher percentage of cases. Finally, a certain residual function seems to be present at RP in the blind regions of the visual field, however, for this finding further demonstrations are required.

Diagnostic tools for glaucoma detection and management

Early diagnosis of glaucoma is critical to prevent permanent structural damage and irreversible vision loss. Detection of glaucoma typically relies on examination of structural damage to the optic nerve combined with measurements of visual function. To aid the clinician in evaluation of visual function and structure, computer-based devices such as confocal scanning laser ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography provide quantitative assessments of structural damage, and visual function testing includes standard automated perimetry as well as selective techniques, including short-wavelength automated perimetry and frequency-doubling technology perimetry are available. This article will review current literature on diagnostic modalities available for glaucoma with emphasis on the best evidence available in the literature to support their use in clinical practice.

Assessing the relationship between central corneal thickness and retinal nerve fiber layer thickness in healthy subjects

PURPOSE

To determine the relationship between central corneal thickness (CCT) and retinal nerve fiber layer (RNFL) thickness obtained by scanning laser polarimetry (GDx-VCC; Carl Zeiss Meditec, Dublin, California, USA), confocal scanning laser ophthalmoscopy (HRT II; Heidelberg Engineering, Heidelberg, Germany), and optical coherence tomography (Stratus OCT; Carl Zeiss Meditec).

DESIGN

Multicenter clinical trial, retrospective cross-sectional study.

METHODS

One hundred and nine healthy subjects from the Advanced Imaging in Glaucoma Study were enrolled in this study. All subjects had a standard clinical examination, including visual field (VF) and good-quality scans from all three imaging devices. CCT was measured using an ultrasonic pachymeter. A linear mixed-effects model was used to assess the relationship between RNFL thickness and CCT, accounting for clustering of eyes within subjects, testing site, ethnicity, family history of glaucoma, axial length intraocular pressure, and VF global indices.

RESULTS

For OCT and GDx, there was a slight nonstatistically significant positive relationship between CCT and RNFL thickness. For HRT, there was a slight nonstatistically significant negative relationship between CCT and RNFL thickness. Relationships for each device were found to differ between sites.

CONCLUSIONS

CCT was not statistically significantly related to RNFL thickness in healthy eyes.

Pascal, ICare and Goldmann applanation tonometry--a comparative study

PURPOSE

To compare intraocular pressure (IOP) measurements by Pascal, ICare and Goldmann applanation tonometry (GAT), to evaluate the effects of central corneal thickness (CCT) and curvature on IOP measurement and to estimate the intra-observer variability.

METHODS

A prospective, single-centre study of 150 eyes with a wide range of pressures. Six masked IOP measurements/method; corneal thickness and curvature were studied for each eye. GAT was the reference.

RESULTS

IOPPascal and IOPICare correlated with IOPGAT (r = 0.91, 0.89). Mean ICare measurement exceeded GAT by 2 mmHg. Pascal measured higher than GAT at low IOPs and lower at high IOPs. For every 10 mmHg increase in IOP above 31 mmHg, Pascal measured 2 mmHg lower than GAT and vice versa. CCT was correlated significantly with IOPGAT (r = 0.23) and IOPICare (r = 0.43) but not with IOPPascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOPGAT and IOPPascal were affected significantly by the CCT, whereas IOPGAT and IOPPascal were not. Corneal curvature was correlated significantly with IOPGAT (r = -0.27) and IOPPascal (r = -0.26) but not with IOPICare (P = 0.60). Intra-observer variability within each set of six measurements was approximately 2 mmHg, irrespective of method.

CONCLUSION

This study showed a reasonable overall correlation and concordance between the IOP obtained with the three instruments. None of the methods were completely independent of the biomechanical properties of the cornea. ICare showed a significant dependency upon CCT, whereas GAT and Pascal showed a significant dependency on corneal curvature. All methods showed intra-observer variability, which leaves room for further improvement of methods.

Effect of improper scan alignment on retinal nerve fiber layer thickness measurements using Stratus optical coherence tomograph

OBJECTIVE

Misalignment of the Stratus optical coherence tomograph scan circle placed by the operator around the optic nerve head (ONH) during each retinal nerve fiber layer (RNFL) examination can affect the instrument reproducibility and its theoretical ability to detect true structural changes in the RNFL thickness over time. We evaluated the effect of scan circle placement on RNFL measurements.

DESIGN

Observational clinical study.

METHODS

Sixteen eyes of 8 normal participants were examined using the Stratus optical coherence tomograph Fast RNFL thickness acquisition protocol (software version 4.0.7; Carl Zeiss Meditec, Dublin, CA). Four consecutive images were taken by the same operator with the circular scan centered on the optic nerve head. Four images each with the scan displaced superiorly, inferiorly, temporally, and nasally were also acquired. Differences in average and sectoral RNFL thicknesses were determined. For the centered scans, the coefficients of variation (CV) and the intraclass correlation coefficient for the average RNFL thickness measured were calculated.

RESULTS

When the average RNFL thickness of the centered scans was compared with the average RNFL thickness of the displaced scans individually using analysis of variance with post-hoc analysis, no difference was found between the average RNFL thickness of the nasally (105.2 microm), superiorly (106.2 microm), or inferiorly (104.1 microm) displaced scans and the centered scans (106.4 microm). However, a significant difference (analysis of variance with Dunnett's test: F=8.82, P<0.0001) was found between temporally displaced scans (115.8 microm) and centered scans. Significant differences in sectoral RNFL thickness measurements were found between centered and each displaced scan. The coefficient of variation for average RNFL thickness was 1.75% and intraclass correlation coefficient was 0.95.

CONCLUSIONS

In normal eyes, average RNFL thickness measurements are robust and similar with significant superior, inferior, and nasal scan displacement, but average RNFL thickness is greater when scans are displaced temporally. Parapapillary scan misalignment produces significant changes in RNFL assessment characterized by an increase in measured RNFL thickness in the quadrant in which the scan is closer to the disc, and a significant decrease in RNFL thickness in the quadrant in which the scan is displaced further from the optic disc.

An analysis of normal variations in retinal nerve fiber layer thickness profiles measured with optical coherence tomography

PURPOSE

To assess the normal variations in retinal nerve fiber layer (RNFL) thickness measured with optical coherence tomography (OCT).

SUBJECTS AND METHODS

Both eyes of 48 individuals (age 56.4+/-9.5 y) with normal vision and refractive errors between +/-6.0 D were tested with the fast RNFL scan protocol of the OCT3 (Zeiss Meditech). Their 256-point RNFL profiles were exported for analysis. The location and peak amplitude of the maxima of the RNFL profiles were measured. Intersubject and interocular variations were assessed with a coefficient of determination, R2. An R2 of 1.0 indicated that the average profile from all 48 individuals (or of the 2 eyes) accounted for 100% of the variation of an individual eye's profile.

RESULTS

The R2 for the interocular comparison was good, with averages of 0.91+/-0.07 (right eye) and 0.92+/-0.05 (left eye). The R2 for the comparison of the individual's profile to the mean group profile was only 0.61+/-0.29 (right eye) and 0.65+/-0.24 (left eye), with 27% of the R2 values below 0.5. Even after normalizing each individual's profile by its mean, R2 was only 0.75+/-0.16 (0.75+/-0.16) for the right (left) eye. The location of the peaks for the right (left) eye ranged over 91 degrees (88 degrees) for the superior peak and over 64 degrees (66 degrees) for the inferior peak. The range of peak amplitudes for the right (left) eye spanned a factor of 1.7 (1.8) and 2.0 (1.7) for the superior and inferior peaks, respectively.

CONCLUSIONS

There was a wide variation in the amplitude and shape of the individual RNFL profiles. However, the RNFL profiles of the 2 eyes of an individual were extremely similar. Adding an interocular comparison with OCT RNFL tests should help identify some false positives.

Effect of corneal thickness on intraocular pressure measurements with the Pascal dynamic contour, Canon TX-10 non-contact and Goldmann applanation tonometers in healthy subjects

PURPOSE

To investigate the effects of central corneal thickness (CCT) on intraocular pressure (IOP) measurements of the Pascal dynamic contour tonometry (DCT), Canon TX-10 non-contact tonometry (NCT) and Goldmann applanation tonometry measurements (GAT) in healthy subjects.

METHODS

IOP values of 135 eyes with normal corneas of 135 healthy volunteers were determined by DCT, NCT and by GAT. The CCT was measured using an ultrasonic pachymeter after all IOP determinations had been made.

RESULTS

When DCT measurements were compared (IOP = 17.52 +/- 2.0 mmHg) with NCT measurements (IOP = 16.54 +/- 2.77 mmHg) and GAT measurements (IOP = 15.07 +/- 2.35 mmHg), DCT measurements were significantly higher than NCT and GAT (p < 0.001). There was a significant correlation between CCT with both NCT (r = 0.260, p = 0.003) and GAT measurements (r = 0.257, p = 0.005). There was a weak correlation that was not statistically significant between CCT and DCT (r = 0.160, p = 0.079).

CONCLUSION

The IOP measurements with DCT seem to be less dependent on CCT. NCT appears to be more affected by variation in CCT than GAT.

Rarebit perimetry and frequency doubling technology in patients with ocular hypertension

PURPOSE

To test the capability of rarebit perimetry (RP), a recent non-conventional perimetric technique, in detecting early functional damage in subjects with ocular hypertension (OHT) and to compare RP findings with those obtained by frequency-doubling technology (FDT) perimetry.

METHODS

Thirty patients with OHT were matched with 30 healthy subjects. All were tested with RP and FDT. Frequency-doubling technology mean deviation (MD) and pattern standard deviation (PSD), as well as RP mean hit rate (MHR), of the two groups were analyzed. The agreement between the two techniques was tested by Kappa analysis.

RESULTS

In the OHT group the mean (SD) FDT MD was 0.5 (2.1), the mean (SD) FDT PSD was 4.2 (1.6), and the mean (SD) RP MHR was 81.4 (6.7). In the control group, corresponding values were mean (SD) FDT MD 1.1 (1.4), mean (SD) FDT PSD 3.0 (0.3), mean (SD) RP MHR 96.2 (2.0). The differences between the two groups were not significant for the studied indexes. Eleven (36.6%) out of the 30 OHT eyes had abnormal RP results; 12 (40.0%) eyes had abnormal FDT results. Five (16.6%) eyes had abnormal RP and FDT findings. Only 1 eye (3.3%) in the control group had abnormal RP results and 3 eyes (10.0%) had abnormal FDT results. RP and FDT showed a moderate agreement (Kappa=0.43; 95% CI: 0.42 to 0.51).

CONCLUSIONS

RP and FDT showed VF defects not shown in standard automated perimetry in the OHT group. This may be indicative of an increased risk in developing glaucoma, even if a gold standard for detecting subtle defects is not currently available. RP has the additional advantage of not requiring any expensive device to be used. The poor agreement between these techniques in identifying eyes with early damage warrants further investigations. Large longitudinal studies are needed before defining the role of RP in early glaucoma diagnosis.

Comparing glaucomatous optic neuropathy in primary open angle and primary angle closure glaucoma eyes by scanning laser polarimetry-variable corneal compensation

PURPOSE

To study the retinal nerve fiber layer thickness difference between high-tension primary open angle glaucoma (HT-POAG) and primary angle closure glaucoma (PACG) eyes using scanning laser polarimetry-variable corneal compensation (GDx VCC) in Taiwan-Chinese population; to evaluate the usefulness of the GDx VCC for detecting POAG and PACG eyes in Taiwan-Chinese population.

PATIENTS AND METHODS

The study comprised 88 early to moderate glaucomatous eyes (one randomly selected eye from 47 HT-POAG patients and 41 PACG patients) and the control group consisted of 45 age-matched eyes from 45 normal individuals. Each subject underwent retinal nerve fiber layer thickness measurement by GDx VCC and Humphrey Field Analyzer visual field testing. Measured GDx VCC parameters were compared among groups. We also calculated the area under the receive operator characteristic (AROC) curve, corresponding sensitivity/specificity and best cut off value for each parameter in differentiating normal from POAG and PACG eyes.

RESULTS

There was no significant difference between HT-POAG and PACG eyes in each parameter. The parameter with the best AROC curve for differentiating normal from POAG eye was nerve fiber indicator (AROC, 0.779; sensitivity=57.4%, specificity=100%; best cut off value >27). The parameter with the best AROC curves for differentiating normal from PACG eyes was temporal-superior-nasal-inferior-temporal average (AROC, 0.829; sensitivity=46.3%, specificity=100%, best cut off value <51.7).

CONCLUSIONS

There was no significant difference between the HT-POAG and PACG eyes as far as the various parameters were concerned. GDx VCC shows fair discriminating ability in distinguishing normal from POAG and PACG eyes in Taiwan Chinese population.

Perceived spatial frequency of sinusoidal gratings

PURPOSE

The "frequency-doubling" effect or illusion, in which the apparent spatial frequency of a grating appears to be doubled, is produced when a low spatial frequency sinusoidal grating is counterphase flickered at a high temporal frequency. This study examines changes in apparent spatial frequency of sinusoids of various spatiotemporal content after equating them for detectability.

METHODS

Detection contrast thresholds were determined for various spatiotemporal gratings. The perceived spatial frequency was then evaluated using stimuli that were four and six times detection threshold. Match ratios were determined for each spatiotemporal combination, whereby the periodicity of a stationary sinusoid was matched with that of a counterphase flickered grating. The same matching task was repeated under different matching task instructions for five randomly chosen spatiotemporal combinations.

RESULTS

Match ratios were fractional for many spatiotemporal combinations. Apparent spatial frequency ranged from less than veridical to greater than double depending on observer and spatiotemporal stimulus content. The effect of task instruction on match ratios was very small, yet significant.

CONCLUSIONS

The appearance of fractional spatial frequency percepts draws into question the notion that frequency-doubling is solely generated by spatially non-linear Y-type magnocellular ganglion cells.

Intraocular pressure measurements following Descemet stripping endothelial keratoplasty

PURPOSE

The effect of increased corneal thickness after Descemet stripping endothelial keratoplasty (DSEK) on intraocular pressure (IOP) measurement has not been previously studied. It is uncertain if this increase in corneal thickness would artificially elevate IOP reading by Goldmann tonometry [GAT] (Haag-Streit, Konig, Switzerland). Therefore the effect of DSEK-related thick cornea on IOP measurement was investigated using three different techniques.

DESIGN

Prospective cross-sectional study.

METHODS

Participants were recruited from a single tertiary referral center. Fifty eyes of 38 patients with successful DSEK at least three months prior to testing were evaluated. At the time of the study, none of the participants had clinically detectable corneal edema. IOP was measured with GAT, pneumatonometry, and dynamic contour tonometry (DCT) in an unmasked randomized sequence. Central corneal thickness (CCT) was measured by ultrasonic pachymetry.

RESULTS

Mean CCT was 701 +/- 68 microm. The mean IOP +/- standard deviation (SD) was 15.9 +/- 4.9 mm Hg for GAT, 20.3 +/- 4.5 mm Hg for pneumatonometry, and 19.8 +/- 4.4 mm Hg for DCT. Pneumatonometry and DCT IOP measurements were significant higher than GAT (P < .01). In contrast, the difference between pneumatonometry and DCT readings was not statistically significant (P = .28). The correlations between IOP and corneal thickness were not significant in this cohort (P > .05).

CONCLUSIONS

Falsely elevated GAT, as expected in thick corneas, was not demonstrated after DSEK. High IOP reading by GAT therefore should raise suspicion of elevated IOP in DSEK eyes.

Comparison of optical coherence tomography and scanning laser polarimetry in glaucoma, ocular hypertension, and suspected glaucoma

BACKGROUND AND OBJECTIVE

To compare the performance of the newest generation optical coherence topography (OCT) and scanning laser polarimetry with variable corneal compensation (SLP-VCC) in eyes with glaucoma, ocular hypertension, and suspected glaucoma.

PATIENTS AND METHODS

One eye each of 84 patients (30 with glaucoma, 26 with suspected glaucoma, and 28 with ocular hypertension) was included in the study. Retinal nerve fiber layer (RNFL) thickness was measured with both technologies and thickness parameters were compared in the three groups of eyes. The correspondence of RNFL thickness measurements with visual field function was also studied.

RESULTS

Average OCT-RNFL thickness was found to have a statistically significant difference between patients with glaucoma and either suspected glaucoma or ocular hypertension. A statistically significant correlation between the average RNFL thicknesses measured by the two different technologies was shown only in the glaucoma group. A significant correlation with visual field mean deviation was found for superior average RNFL thickness as measured by SLP and for nerve fiber indicator and average and inferior average RNFL thickness as measured by OCT in glaucomatous eyes. Regression analysis indicated nerve fiber indicator to be the most valuable factor in predicting mean deviation.

CONCLUSION

RNFL thickness measurements obtained with OCT and SLP-VCC correlate well only in eyes with more advanced glaucomatous damage. The nerve fiber indicator parameter derived by SLP correlated best with mean deviation.

Clinical comparison of the Icare tonometer and Goldmann applanation tonometry

PURPOSE

To compare a new method of intraocular pressure (IOP) measurement, using the Icare tonometer, with Goldmann applanation tonometry (GAT).

PATIENTS AND METHODS

Two observers obtained IOP readings in 292 eyes (143 right and 149 left) of 153 subjects, using the Icare without topical anesthetic. A GAT reading was subsequently obtained by a consultant ophthalmologist, without the knowledge of the Icare readings. Central corneal thickness (CCT) was obtained on all eyes with ultrasound pachymetry. Patient comfort after IOP measurement was assessed in a consecutive subset of patients.

RESULTS

The intraclass correlation coefficient between the 2 modalities of IOP measurement was r=0.95 for the right and r=0.93 for the left eye. The mean difference (Icare-GAT) between the IOP measured by the 2 methods was 0.4 mm Hg in the right eye (SD 3.0, 95% confidence interval -5.5 to 6.3), and 0.8 mm Hg in the left eye (SD 3.0, confidence interval -4.7 to 6.2). GAT measurements did not vary with CCT [correlation coefficient=0.09 (P=0.25) right and 0.14 (P=0.09) left eyes]. However, IOP measured with Icare tonometry increased with increasing CCT [correlation coefficient=0.16 (P=0.05) right and 0.21 (P=0.01) left eyes]. For every 100-microm increase in CCT, the difference (Icare-GAT) increased by 1 mm Hg. Of the 38 consecutive patients surveyed, 28 (73.7%) rated the Icare more comfortable than GAT, with only 2 (5.3%) rating it less comfortable (P<0.001).

CONCLUSIONS

There is good correlation between the 2 methods of IOP measurement, even at extremes of IOP. The Icare instrument was easy to use and recorded rapid and consistent readings with minimal training. It seems to be more comfortable than GAT and obviates the need for topical anesthesia.

Visual Field Changes after Transient Elevation of Intraocular Pressure in Eyes with and without Glaucoma

PURPOSE

To evaluate visual field (VF) changes in glaucomatous and nonglaucomatous eyes after transient elevation of intraocular pressure (IOP).

DESIGN

Prospective experimental study.

PARTICIPANTS

One hundred subjects (38 with glaucoma, 62 glaucoma suspects and controls).

METHODS

Intraocular pressure elevation was induced in the right eye of all subjects with a modified LASIK suction ring. Intraocular pressure was elevated to an average of 64 mmHg for <30 seconds. Humphrey Matrix perimetry 24-2 threshold tests were performed before and after the procedure. A cohort of patients who demonstrated significant deterioration in postprocedural perimetry was recalled for further testing.

MAIN OUTCOME MEASURES

Mean deviation (MD) and pattern standard deviation (PSD) from Humphrey Matrix perimetry.

RESULTS

A significant decline in MD of the right eye could be observed on immediate postprocedural perimetry amongst glaucoma and control patients, whereas no significant changes in PSD were seen in either group. Forty-five of 47 patients, whose immediate postprocedural perimetry showed a loss of MD > 2 decibels, attended for repeat perimetric testing with a median follow-up of 6 days. Both eyes among 28 control patients and the left eye among 17 glaucoma patients showed statistically significant improvement in MD. Similar improvement was seen in the right eye of glaucoma patients, but this failed to reach statistical significance. Six patients from the glaucoma group demonstrated deterioration in MD upon recall, compared with 3 in the control group (P = 0.046). These 6 patients were significantly younger than the rest of the group, but no other defining characteristics were identified.

CONCLUSIONS

Transient elevation of IOP in adult eyes with and without glaucomatous optic neuropathy did not lead to functional optic nerve change, as measured by Matrix perimetry, in the short term for the majority of patients. It is possible that a small cohort of patients with preexisting glaucomatous optic neuropathy may be more susceptible to transient increase in IOP, although the result is inconclusive. Prominent learning effects may have masked subtle worsening of visual function in our subjects; corresponding structural analyses of the optic nerve and longer-term follow-up may provide further information.

Poor agreement between Goldmann and Pascal tonometry in eyes with extreme pachymetry

AIM

To compare the intraocular pressure (IOP) measurements obtained using the Pascal dynamic contour tonometer (PDCT) with the standard Goldmann applanation tonometry (GAT) and to correlate them with the central corneal thickness (CCT) in a non-glaucomatous population.

METHODS

We prospectively measured IOP using PDCT and GAT in random order in 100 normal eyes. CCT was analysed with an ultrasonic pachymeter in each case. Statistical analysis of baseline and stratified data included intraclass correlation coefficient (ICC), Lin correlation, and Bland-Altman analysis to evaluate the agreement between both techniques.ResultsGAT was used first in 51 eyes and PDCT in 48 cases. Mean IOP was 14.8 mm Hg with GAT and 20.3 mm Hg with PDCT. Mean pachymetry was 553.23 micrometres (microm) (SD: 4.7 microm). Global agreement of IOP between GAT and PDCT was 0.09 by ICC and 0.170 by Lin correlation. When CCT values ranged between 540 and 545 microm, the agreement between both tonometers was optimal (ICC 0.54 and Lin 0.61). Outside these pachymetry values, agreement between both tonometers diminished dramatically.

CONCLUSION

Statistically significant agreement between both devices was reached only at intermediate pachymetry readings in contrast with other studies that show excellent global agreement between GAT and PDCT.

How robust is the optic chiasm? Perimetric and neuro-imaging correlations

OBJECTIVES

Analysis of form and function relationships with tumour-mediated dislocations and deformations of the optic chiasm.

MATERIALS AND METHODS

Results of magnetic resonance tomography and two forms of quantitative, computerized perimetry were contrasted in 31 patients with pituitary adenomata impinging on the chiasm, prior to treatment.

RESULTS

Perimetric abnormalities ranged from none to modest. High-pass Resolution Perimetry (HRP) produced abnormal results in 10 cases and RareBit perimetry (RBP) in 15 cases. Overall, field defects and qualitative stages of deformation and dislocation of the chiasm were well correlated. Among quantitative indices, the best correlations were obtained by a measure of the cranio-caudal position of the chiasm.

CONCLUSIONS

On average, an elevation of the chiasm by 6 mm will be associated with abnormal visual fields in 50% of the cases. An additional elevation of 5 mm will raise the incidence of field defects to 90%.

Diagnostic accuracy of the Matrix 24-2 and original N-30 frequency-doubling technology tests compared with standard automated perimetry

PURPOSE

To compare the diagnostic accuracy of the Matrix frequency-doubling technology (FDT) 24-2, first-generation FDT N-30 (FDT N-30), and standard automated perimetry (SAP) tests of visual function.

METHODS

One eye of each of 85 glaucoma patients and 81 healthy controls from the Diagnostic Innovations in Glaucoma Study was included. Evidence of glaucomatous optic neuropathy on stereophotographs was used to classify the eyes. Matrix FDT 24-2, first-generation FDT N-30, and SAP-SITA 24-2 tests were performed on all participants within 3 months. Receiver operating characteristic (ROC) curves were generated and used to determine sensitivity levels at 80% and 90% specificity for mean deviation (MD), pattern standard deviation (PSD), number of total deviation (TD), and pattern deviation (PD) points triggered at less than 5% and 1%. The tests were compared using the best parameter for each test (that with the highest area under the ROC curve) and with the PSD.

RESULTS

The best parameters were MD for SAP (0.680), PSD for FDT N-30 (0.733), and number of TD less than 5% points for FDT 24-2 (0.774). Using the best parameter, the area under the ROC curve was significantly larger for FDT 24-2 than for SAP (P = 0.01). No statistically significant differences were observed between SAP and FDT N-30 (P = 0.21) and FDT N-30 and FDT 24-2 (P = 0.26). Similar results were obtained when the PSD was used to compare the tests, with the exception that the area under the ROC curve for the FDT N-30 test (0.733) was significantly larger than that of the SAP-SITA (0.641; P = 0.03).

CONCLUSIONS

The performance of the Matrix FDT 24-2 was similar to that of the first-generation FDT N-30. The Matrix FDT 24-2 test was consistently better than SAP at discriminating between healthy and glaucomatous eyes. Further studies are needed to evaluate the ability of the Matrix FDT 24-2 to monitor glaucoma progression.

Stratus-OCT imaging in early glaucomatous and in ocular hypertensive patients with and without frequency-doubling technology abnormalities

AIM

To compare Stratus-OCT measurements in controls, ocular hypertensive (OHT) patients with (FDT+) and without (FDT-) frequency-doubling technology (FDT) abnormalities, and in patients affected with early primary open-angle glaucoma (POAG).

METHODS

Thirty-two controls, 78 OHT patients (38 FDT- and 40 FDT+), and 45 early POAG patients (six FDT- and 39 FDT+) underwent the following tests within 3 months: standard automated perimetry (SAP) HFA 30-2; FDT N-30-F; and, Stratus-OCT imaging with retinal nerve fibre layer (RNFL) and optic nerve head (ONH) scans. One eye per patient was considered. Differences among groups were evaluated using the Kruskal-Wallis, analysis of variance, and Duncan's tests.

RESULTS

There were no significant differences in all Stratus-OCT parameters between POAG and OHT FDT+ patients. Statistically significant differences were found between the control group and both the POAG and OHT FDT+ groups for 15 of the 21 Stratus-OCT parameters. Control eyes compared to OHT FDT- showed significant differences in 13 of the 21 parameters. The comparison between the OHT FDT- group, and both the POAG and OHT FDT+ group resulted in 13 of the 21 parameters to be significantly different.

CONCLUSIONS

Stratus-OCT seems to show a higher ability in detecting significant differences between healthy, OHT, and early POAG eyes when compared to SAP and FDT. This suggests that the Stratus-OCT could show structural abnormalities before SAP or FDT visual field defects appear in patients at risk of developing glaucoma, which may be beneficial in making therapeutic decisions, especially in OHT patients.

False negative results in glaucoma detection with Heidelberg Retina Tomograph II

Purpose

To evaluate the rate of false negative results with the Heidelberg Retina Tomograph (HRT II) in a glaucoma practice.

Design

Cross-sectional study.

Methods

We analyzed the HRTs taken between October 2002 and October 2003 in our glaucoma clinic, and selected the patients who had a good quality image (SD < 40 μ) with a normal Moorfield’s Regression Analysis (MRA). A masked independent observer classified those patients as normal, glaucoma suspect, or glaucomatous on the basis of optic disc stereo photos (ODP) and at least 2 consecutive reliable automated perimetries. The diagnosis of glaucoma was based on a glaucomatous optic disc with a congruent, reproducible visual field defect.

Results

Four hundred and fifty patients who had undergone an HRT examination were analyzed. One hundred and nine patients had an HRT classified as normal on the MRA, and a good quality image. Fifteen of those 109 patients (13.7%) were classified as glaucomatous on the basis of an abnormal ODP with corresponding visual field defect. Seven (6.4%) patients were classified as glaucoma suspect.

Conclusion

Fourteen percent of glaucoma patients with glaucoma remained undetected with the HRT II Moorfield’s regression analysis as a sole means to detect glaucoma.

Comparison of dynamic contour tonometry and goldmann applanation tonometry in deep lamellar and penetrating keratoplasties

PURPOSE

To compare the measurements of intraocular pressure (IOP) with dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in eyes with corneal graft and to evaluate the influence of corneal thickness (CCT), corneal curvature (CC), and astigmatism on these methods.

DESIGN

Prospective, observational cross-sectional study.

METHODS

Eighteen eyes of 18 patients after penetrating keratoplasty (PKP) and 14 eyes of 14 patients after deep lamellar keratoplasty (DLKP) underwent IOP evaluation with DCT and GAT, and measurements of CCT, CC, and astigmatism. Bland-Altman plots were used to evaluate the agreement between tonometers. Multivariate regression analysis was used to evaluate the influence of ocular structural factors and running suture on IOP measurements obtained with both tonometers.

RESULTS

IOP values obtained by DCT and GAT were strongly correlated in all eyes (r = .91; P < .001). DCT values measured 2.5 +/- 1.7 mm Hg higher than GAT readings (P < .001). A reduction of the mean IOP difference between DCT and GAT with an increase in IOP values (P < .001) was found. Regression analysis showed no effect of CCT, CC, astigmatism, and running suture on both DCT and GAT readings, either in DLKP or in PKP eyes.

CONCLUSIONS

We found a good overall correlation between both tonometers but the agreement between instruments differs in high or low IOP ranges. The wide and varying 95% limits of agreement between DCT and GAT indicates that DCT provides IOP measurements on deep lamellar and penetrating keratoplasties which can be used in the clinical practice.

Comparison of the iCare rebound tonometer and the Goldmann applanation tonometer over a wide IOP range

BACKGROUND

The aim of this study was to compare the intraocular pressure (IOP) results measured by the iCare rebound tonometer with those obtained by the Goldmann applanation tonometer (GAT) over a wide range of IOP values. Furthermore, the comfort level of the iCare measurement was evaluated.

METHOD

The study included 75 eyes of 75 patients. The patients were divided into three groups (7-15 mmHg n = 25, 16-22 mmHg n = 25, 23-60 mmHg n = 25). The measurements were taken by two independent observers in a masked fashion. All patients were asked about discomfort during the iCare measurement. To establish the agreement between the two devices, a Bland-Altman analysis was performed.

RESULTS

Overall, the 95% confidence interval of the differences between the two devices was -8.67 to 10.25 mmHg and in 62.7%, the iCare measurement was within +/-3 mmHg of the GAT measurements. The distribution of the differences in IOP was similar, from 7-22 mmHg. In the higher IOP range (23-60 mmHg), however, the deviation was almost twice as large. The measurement with the iCare tonometer was well tolerated; 100% of the patients denied any discomfort.

CONCLUSIONS

The iCare tonometer is a mobile alternative to GAT in a low to moderate IOP range, but our findings show a greater deviation than previously reported. In high IOP values, measurements with the iCare tonometer do not correlate well with GAT.

Clinical applications and new developments of optical coherence tomography: an evidence-based review

Optical coherence tomography (OCT) is a new imaging modality that has increasingly become an indispensable tool in clinical practice for the diagnosis and management of ocular diseases involving the macula, optic nerve and anterior segment. The instrument is an advanced imaging technique that provides unprecedented high resolution and cross-sectional tomographic images of the ocular microstructure in situ, and in real time. Since its introduction about four years ago, a multitude of advantages has made OCT an essential instrument in ophthalmic imaging. The technique has fast image acquisition speed and non-contact, non-invasive applicability, allowing a non-excisional 'optical biopsy' to be performed. The purpose of this paper is to provide an evidence-based review of the increasing role of OCT in the diagnosis and management of ocular disorders, particularly in age-related macular degeneration, diabetic macular oedema, macular hole, epiretinal membrane and glaucoma. Being one of the first users of OCT in Australia, our clinical experiences will be highlighted and clinical examples of various conditions will be presented to provide an overview of the immense implications of OCT in practice. The latest developments of the OCT revolution, in relation to combining OCT with fundus photography and scanning laser ophthalmoscopy, will also be described. New developments of three-dimensional visualisation of tissue morphology with future models of ultra-high speed, ultra-high resolution OCT may further enhance the early diagnosis, monitoring of disease progression and assessment of treatment efficacy, facilitated by this powerful technology.

Short-wavelength automated perimetry and frequency-doubling technology perimetry in glaucoma

Standard automated perimetry (SAP) is today still the clinical standard for the management of glaucoma and its progression, though it has been shown that it may detect the disease only after the death of a high number of retinal ganglion cells (RGCs). A number of "unconventional" perimetries have recently been evaluated by several clinical studies which showed their ability to identify the earliest glaucoma changes; the most promising of these techniques are short-wavelength automated perimetry (SWAP) and frequency-doubling technology perimetry (FDT). The applicability of these techniques is still limited by a number of factors: the limited economic resources allocated to perimetry; the paucity of well-conducted, prospective longitudinal studies showing the superiority of SWAP and FDT over SAP; and the lack of a consensus on the criteria to define test abnormality with these techniques. The aim of this article is to review the rationale, the limits, and the potentiality of SWAP and FDT for glaucoma management and to summarize the tasks required to improve the clinical usefulness of these two instruments in the future.

Diagnostic capability of scanning laser polarimetry with variable cornea compensator in Indian patients with early primary open-angle glaucoma

PURPOSE

To evaluate the diagnostic ability of scanning laser polarimetry (GDx variable corneal compensator [VCC]) for early glaucoma in Asian Indian eyes.

DESIGN

Cross-sectional observational study.

PARTICIPANTS

Two groups of patients (early glaucoma and normal) who satisfied the inclusion and exclusion criteria were included. Early glaucoma was diagnosed in presence of open angles, characteristic glaucomatous optic disc changes correlating with the visual field (VF) on automated perimetry (VF defect fulfilling at least 2 of 3 Anderson and Patella's criteria with mean deviation >or= -6 decibels). Normal subjects had visual acuity >or= 20/30 and intraocular pressure < 22 mmHg, with a normal optic disc and fields and no ocular abnormality.

METHODS

All patients underwent complete ophthalmic evaluation, including VF examination (24-2/30-2 Swedish interactive threshold algorithm standard program) and imaging with GDx VCC.

MAIN OUTCOME MEASURES

Sensitivity, specificity, positive predictive value and negative predictive value, area under the receiving operating characteristic curve, and likelihood ratios (LRs) were calculated for various GDx VCC parameters.

RESULTS

Seventy-four eyes (74 patients) with early glaucoma and 104 eyes (104 normal subjects) were enrolled. TSNIT Std Dev (temporal-superior-nasal-inferior-temporal standard deviation) had the best combination of sensitivity and specificity-61.3 and 95.2, respectively-followed by nerve fiber index score > 50 (sensitivity, 52.7%; specificity, 99%). Nerve fiber index score > 50 had positive and negative predictive values of 74.3% and 97.6%, respectively, for an assumed glaucoma prevalence of 5%. Nerve fiber index score > 50 had a positive LR (+LR) of 54.8 for early glaucoma.

CONCLUSIONS

GDx VCC has moderate sensitivity, with high specificity, in the diagnosis of early glaucoma. The high +LR for the nerve fiber index score can provide valuable diagnostic information for individual patients.

The quality of reporting of diagnostic accuracy studies in glaucoma using scanning laser polarimetry

PURPOSE

Scanning laser polarimetry (SLP) has been proposed as a useful diagnostic test for glaucoma. This study was conducted to evaluate the quality of reporting of published studies using the SLP for diagnosing glaucoma.

METHODS

A validated Medline and hand search of English-language articles reporting on measures of diagnostic accuracy of the SLP for glaucoma was performed. Two reviewers independently selected and appraised the manuscripts. The Standards for Reporting of Diagnostic Accuracy (STARD) checklist was used to evaluate the quality of each publication.

RESULTS

A total of 47 papers were identified of which the first 10 (from 1997 to 2000) and the last 10 articles (from 2004 to 2005) were appraised. Interobserver rating agreement of STARD items was high (85.5% agreement, kappa=0.796). The number of STARD items properly reported ranged from 3/25 to 19/25. Only a quarter of studies (5/20) explicitly reported more than half of the STARD items. Important aspects of the methodology were often missing such as participant sampling (reported in 40% of manuscripts), masking of the readers of the index test and reference standard (reported in 20% of manuscripts), and estimation of uncertainty (eg, 95% confidence intervals, reported in 25% of manuscripts). There was a slight increase in the number of STARD items reported with time.

CONCLUSIONS

The quality of reporting of diagnostic accuracy tests for glaucoma with SLP is suboptimal. The STARD initiative may be a useful tool for appraising the strengths and weaknesses of diagnostic accuracy studies.