Accuracy of combined GDx-VCC and matrix FDT in a glaucoma screening trial

PURPOSE

To assess the advantage in glaucoma screening of the use of scanning laser polarimetry with customized cornea compensation (GDx-VCC) combined with Matrix Frequency Doubling Technology (M-FDT) testing.

METHODS

In a nonpopulation-based prepublicized trial, self-recruited white participants were screened for glaucoma with GDx-VCC, with M-FDT, and by independent clinical examination. Cases with possible glaucoma as found with any of the screening methods underwent a detailed clinical investigation to verify or exclude glaucoma. Sensitivity, specificity, accuracy, likelihood ratios, and predictive values were calculated using different threshold criteria for GDx-VCC alone, M-FDT alone, and for various combinations.

RESULTS

Of the 233 attendees, 181 participants (345 eyes) successfully underwent the GDx-VCC and M-FDT measurements. Thirty-nine eyes of 24 participants had glaucoma (11.3% prevalence among eyes tested successfully). All but 2 of the glaucomatous eyes had only early damage. Evaluated separately, the criterion GDx-VCC NFI (normal threshold < or =30) performed best, with 97.0% specificity, 88.8% accuracy, and 25.6% sensitivity; but with only 8.5 positive likelihood ratio (PLR). For paired criteria, the best combination of GDx-VCC-screening test with M-FDT-screening test provided 99.6% specificity, 91.3% accuracy, and 28.6 PLR. For NFI combined with GDx-VCC nerve fiber bundle defect criterion, specificity was 99.0%, accuracy 89.6%, and PLR 18.0. However, the sensitivities in the 2 cases fell to 12.0% and 18.0%. For a triple combination of M-FDT-screening test with the latter pair of criteria, sensitivity increased to 41.7% and PLR (13.6) still remained clinically useful.

CONCLUSIONS

In a self-recruited white population with relatively high risk for mild glaucomatous damage, a combination of GDx-VCC together with M-FDT could usefully be employed for mass glaucoma screening.

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.

Learning effect of Humphrey Matrix perimetry

BACKGROUND

Humphrey Matrix perimetry is a recent development in automated perimetry that uses frequency-doubling technology (FDT). We evaluated the learning effect of Humphrey Matrix perimetry with a full-threshold 30-2 strategy.

METHODS

Twenty-four patients with primary open-angle glaucoma and early visual field defects as assessed by standard automated perimetry and 24 healthy control subjects participated. All subjects had no prior experience with FDT visual field tests. Humphrey Matrix perimetry using a full-threshold 30-2 strategy was performed 3 times within 1 month. Various visual field indices were compared across multiple tests.

RESULTS

Mean deviation (MD) showed a larger defect at the first test than at the second and third tests (p < 0.001), and the mean total improvement of the MD was 2.80 decibels (dB) in the glaucoma group and 1.71 dB in the control group. Pattern standard deviations (PSDs) were decreased as the tests were repeated, but test duration, fixation losses, and false-positive or false-negative rate were not changed significantly. Additionally, the Glaucoma Hemifield Test (GHT) showed unstable results.

INTERPRETATION

In patients naive to the FDT test, Humphrey Matrix perimetry showed a large learning effect on MD and PSD among the various visual field indices. The GHT results of Humphrey Matrix perimetry showed a large instability.

Prevalence of myelinated retinal nerve fibres in urban and rural adult Chinese populations: the Beijing Eye Study

PURPOSE

To determine the prevalence of myelinated retinal nerve fibres in the elderly Chinese population.

METHODS

The Beijing Eye Study, a population-based, cross-sectional cohort study, included 4439 subjects out of the 5324 invited to participate (response rate 83.4%) with an age of > 40 years. The present investigation consisted of 8663 eyes of 4378 (98.6%) subjects for whom readable fundus photographs were available.

RESULTS

Myelinated retinal nerve fibres were detected in 35 eyes (29 subjects) with a prevalence rate of 0.4 +/- 6.3%[95% confidence interval (CI): 0.27, 0.54] per eye and 0.7 +/- 8.1% (95% CI: 0.42, 0.90) per subject. The myelinated nerve fibres were located most often in the temporal inferior region, followed by the temporal superior region and the nasal region. Prevalence of myelinated nerve fibres was not associated statistically with age, gender, refractive error, visual acuity (VA), intraocular pressure, cataract, glaucoma and age-related macular degeneration.

CONCLUSION

Myelinated retinal nerve fibres are present in about seven out of 1000 elderly Chinese in northern China, without association to VA, refractive error, glaucoma and macular degeneration.

Glaucoma detection with matrix and standard achromatic perimetry

BACKGROUND

Matrix perimetry is a new iteration of frequency-doubling technology (FDT) which uses a smaller target size in the standard achromatic perimetry presentation pattern.

AIM

To compare the performance of matrix and Swedish interactive thresholding algorithm (SITA) perimetry in detecting glaucoma diagnosed by structural assessment.

DESIGN

Prospective cross-sectional study.

METHODS

76 eyes from 15 healthy subjects and 61 consecutive glaucoma suspects and patients with glaucoma were included. All patients underwent optic nerve head (ONH) photography, SITA and matrix perimetries, and optical coherence tomography (OCT) within a 6-month period. Glaucoma diagnosis was established by either glaucomatous optic neuropathy or OCT by assessing retinal nerve fibre layer (RNFL) thickness. Mean deviation (MD), pattern standard deviation (PSD), glaucoma hemifield test and cluster of abnormal testing locations were recorded from matrix and SITA perimetries.

RESULTS

Similar correlations were observed with matrix and SITA perimetry MD and PSD with either cup-to-disc ratio or OCT mean RNFL. The area under the receiver operating characteristic (AROC) curves of MD and PSD for discriminating between healthy and glaucomatous eyes ranged from 0.69 to 0.81 for matrix perimetry and from 0.75 to 0.77 for SITA perimetry. There were no significant differences among any corresponding matrix and SITA perimetry AROCs.

CONCLUSIONS

Matrix and SITA perimetries had similar capabilities for distinguishing between healthy and glaucomatous eyes regardless of whether the diagnosis was established by ONH or OCT-RNFL assessment.

The influence of corneal properties on rebound tonometry

PURPOSE

To determine the influence of corneal thickness, corneal hysteresis (CH), and corneal resistance factor (CRF) on intraocular pressure (IOP) measurements obtained using the iCARE rebound tonometer.

DESIGN

Cross-sectional study.

PARTICIPANTS

One hundred twenty-five eyes of 125 normal healthy subjects.

METHODS

Intraocular pressure was determined in all subjects using the iCARE at both central and temporal corneal regions. Corneal thickness at these 2 regions was determined by ultrasonic pachymetry. Corneal hysteresis and corneal resistance factor were measured using an ocular response analyzer. Goldmann applanation tonometry (GAT) was also performed on all eyes.

MAIN OUTCOME MEASURES

Intraocular pressure, corneal thickness, corneal hysteresis, and corneal resistance factor.

RESULTS

Although the peripheral cornea was significantly thicker than the central cornea, IOPs obtained by the iCARE at the 2 regions were similar and significantly higher than GAT measurements. There were an overestimation at higher IOPs and an underestimation at lower IOPs relative to GAT measurements. Multiple regression analysis showed a significant correlation between the iCARE and CH (partial correlation r = -0.67, P<0.01) and CRF (partial correlation r = 0.82, P<0.01). The correlation between the iCARE and central corneal thickness was not significant.

CONCLUSIONS

Rebound tonometry is affected by corneal properties including CH and CRF but not corneal thickness.

Localized retinal nerve fiber layer defects and visual field abnormalities by humphrey matrix frequency doubling technology perimetry

PURPOSE

To investigate the ability of frequency doubling technology (FDT) perimetry to identify eyes with a localized retinal nerve fiber layer (RNFL) defect and normal Humphrey C30-2 SITA-Standard visual field (HVF).

DESIGN

Retrospective case-control study.

METHODS

Fifty-four eyes were divided into two groups, an abnormal (n = 29) and a normal (n = 25) FDT perimetry group. Approximation of the RNFL defect to the macula (angle alpha) and width of the defect (angle beta) were measured by RNFL photograph and compared between two groups.

RESULTS

Angle alpha and angle beta were significantly different between two groups (P < .001 by Mann-Whitney U test, respectively). A multivariate logistic regression analysis demonstrated that only angle beta was significantly associated with FDT perimetry abnormalities (P = .002).

CONCLUSIONS

Only 53.7% of the eyes with a localized RNFL defect and normal HVF had visual field abnormalities identified by FDT perimetry. Width of the RNFL defect was more strongly associated with FDT perimetry abnormalities than location of the defect.

Frequency Doubling Perimetry and Short-Wavelength Automated Perimetry to Detect Early Glaucoma

PURPOSE

To compare the ability of short-wavelength automated perimetry (SWAP) and frequency doubling perimetry (FDP) to detect early glaucoma damage.

DESIGN

Prospective case-control study using a comparative case series.

PARTICIPANTS

Forty-two patients with preperimetric glaucomatous optic nerve damage and a normal standard achromatic perimetry (SAP) in 1 eye, but with contralateral SAP abnormalities, and 35 normals.

METHODS

Forty-two patients and 35 normals underwent SWAP and FDP (Humphrey 24-2; Carl Zeiss Meditec, Inc., Dublin, CA). Correlations of mean deviation (MD) and pattern standard deviation (PSD) of the 2 groups were calculated. The number of defects at P<0.05 and P<0.01 on total deviation (TD) and pattern deviation (PD) plots were compared. Diagnostic precision and agreement on location of abnormalities were determined.

MAIN OUTCOME MEASURES

Correlations and comparisons of global indices between SWAP and FDP: MD, PSD, TD, and PD abnormal number of points.

RESULTS

Significant correlations in the glaucoma group were found between SWAP and FDP for MD (r = 0.54; P<0.008) and PSD (r = 0.49; P<0.001). Defects on the TD and PD plots were detected more frequently by FDP in the glaucoma group, although they were significant only for PD at P<0.01 (P = 0.024). Areas under receiver operator characteristic curves for MD of SWAP and PSD of FDP were 0.74 and 0.67, respectively (P = 0.37). Using defined defect criteria, FDP had a significantly higher sensitivity (72% vs. 54%; P = 0.02) and similar specificity (53% vs. 44%; P = 0.12) compared with SWAP. Agreement on defect location was moderate (kappa, 0.46). Testing time for SWAP was longer than for FDP in both glaucomatous and normal eyes (P<0.001).

CONCLUSIONS

Short-wavelength automated perimetry and FDP showed similar ability to detect visual dysfunction in patients with preperimetric glaucoma. Long-term follow-up is required to define their role in predicting subsequent SAP defects.

Comparison of the rebound tonometer with the Goldmann applanation tonometer in glaucoma patients

PURPOSE

To determine the agreement between the measurement of intraocular pressure (IOP) by the rebound tonometer (RBT) and by the Goldmann applanation tonometer (GAT) and to find out the effect of central corneal thickness (CCT) values on IOP measurements in glaucoma patients.

METHODS

IOP was measured with the RBT and GAT, respectively, in 61 eyes of 61 glaucoma patients. CCT was measured using an ultrasonic pachymeter after all IOP determinations had been made. The mean IOP measurement by the RBT was compared with the measurement by the GAT, by Student's t-test. Bland-Altman analysis was performed to assess the clinical agreement between the two methods. The effect of CCT on measured IOP was explored by linear regression analysis.

RESULTS

The mean patient age was 56.7+/-21.1 years (range: 30-80 years). There were 32 (52.46%) women and 29 (47.54%) men in the study group. The mean IOP readings were 18.70+/-4.76 mmHg using the RBT, and 18.27+/-3.49 mmHg using the GAT. The difference was not statistically significant (mean difference 0.43+/-2.55, P=0.2). A frequency distribution of the differences demonstrated that in more than 80% of cases the IOP readings differed by <2.3 mmHg between the RBT and GAT. There was a strong correlation between the RBT and GAT readings (r=0.852, P<0.0001). The IOP measurements with the two methods were correlated with CCT (r=0.40, P=0.02 for the RBT and r=0.48, P<0.0001 for the GAT). The IOP increased 1.1 mmHg and 8 mmHg for every 100-microm increase in CCT for the GAT and RBT, respectively.

CONCLUSION

The RBT slightly overestimated the IOP value by 0.43 mmHg on average when compared with the GAT. Nevertheless, the RBT readings appeared to be more affected by the various thicknesses of different corneas when compared with those obtained using the GAT.

Rebound Tonometer Compared With Goldmann Tonometer in Normal and Pathologic Corneas

PURPOSE

To compare the intraocular pressure (IOP) measurements obtained with the rebound tonometer (RT) and the Goldmann handheld tonometer (GT) in normal and altered corneas.

METHODS

A total of 208 normal corneas and 50 corneas with pathologies were included in this prospective study. All measurements were randomly obtained by 1 observer. The medians and interquartile range (IR) for both tonometers were compared. The median differences were assessed in IOP groups. Agreement between the tonometers was calculated using the Bland-Altman method.

RESULTS

The median IOP in all eyes was 17 mm Hg (IR, 13-22 mm Hg) with the RT and 16 mm Hg (IR, 13-21 mm Hg) with the GT (P < 0.001). The correlation was excellent between tonometers (r2 = 0.86; P < 0.001). The minimal differences between the two were obtained from 10 to 20 mm Hg (GT). The Bland-Altman scatterplot obtained good agreement between the instruments. In normal corneas, the median difference was < or =2 mm Hg in 77.4% of cases. In the altered corneas, the median difference was < or =2 mm Hg in 73% of cases (P = 0.21 compared with the normal group). In 10% and 2% of cases, the IOP could not be measured using the GT and RT, respectively.

CONCLUSIONS

The results were similar for both tonometers. In the altered corneas, the IOP could be difficult to obtain with the GT because of distorted half-circles. The 1-mm-diameter disposable RT tip facilitated obtaining measurements without anesthetic drops, which avoids infections. The RT could be useful in routine clinical settings when measuring IOP in corneas with pathologies.

Reproducibility and Tolerability of the ICare Rebound Tonometer in School Children

PURPOSE

To establish the intraobserver and interobserver reliability of the rebound tonometer (RBT) in healthy schoolchildren and to test patient tolerance in an unanesthetized eye.

SUBJECTS AND METHODS

To examine the reproducibility of the RBT, 2 experienced ophthalmologists undertook 3 consecutive intraocular pressure (IOP) measurements with the RBT without an anesthetic in 304 eyes of 152 healthy schoolchildren. Any pain or discomfort experienced by the children was recorded. Intraobserver and interobserver reliabilities were established by calculating correlation coefficients (r).

RESULTS

Of the 152 patients, 78 (51.3%) were males and 74 (48.7%) were females. The mean patient age was 11.2+/-2.6 years (range: 7 to 15 y). Mean IOP values obtained by examiners 1 and 2 were 16.48+/-2.82 mm Hg and 17.27+/-3.27 mm Hg for the right eyes and 17.15+/-3.36 mm Hg and 17.06+/-3.21 mm Hg for the left eyes. Intraobserver correlation coefficients for examiner 1 were 0.970 for the right eyes and 0.974 for the left eyes. For examiner 2, intraobserver correlation coefficients were 0.963 for the right eyes and 0.970 for the left eyes. The interobserver correlation coefficients were 0.798 for the right eyes and 0.858 for the left eyes (all P<0.0001). With the RBT, 98.6% of the subjects felt no pain and/or discomfort.

CONCLUSIONS

Measurement of IOP with the RBT is a highly reproducible method in schoolchildren showing high intraobserver and interobserver correlation and it seems to be very comfortable when performing IOP measurements in schoolchildren without an anesthetic.

Selective perimetry in glaucoma diagnosis

PURPOSE OF REVIEW

Selective perimetry evaluates visual function by using visual stimuli that attempt to target specific subpopulations of retinal ganglion cells, which is designed to improve sensitivity to detect glaucomatous functional loss. This paper reviews recent studies that have assessed the characteristics of new strategies/programs of selective perimetry.

RECENT FINDINGS

Selective perimetry is usually compared against an existing standard technique--standard automated perimetry. Recent studies did not consider standard automated perimetry results as part of inclusion/exclusion criteria, avoiding selection bias and permitting fair comparisons between perimetry techniques. Furthermore, the Swedish Interactive Threshold Algorithm is replacing Full-Threshold as the standard automated perimetry gold-standard strategy, and comparisons of the diagnostic performance of function-specific perimetry may be influenced by which standard automated perimetry technique is used as the reference. These factors may impact our perception about the role of selective perimetry in glaucoma management.

SUMMARY

The lack of a perfect gold-standard diagnostic test for glaucoma limits the interpretation of results from cross-sectional studies evaluating visual field tests. Nevertheless, evidence suggests that visual dysfunction in eyes with early glaucoma varies significantly between individuals and no single technique is superior to the others in all patients. A multimodal functional assessment may be more effective in detecting/quantifying visual impairment associated with early glaucoma.

Retinal nerve fibre thickness measured with optical coherence tomography accurately detects confirmed glaucomatous damage

AIM

To assess the accuracy of optical coherence tomography (OCT) in detecting damage to a hemifield, patients with hemifield defects confirmed on both static automated perimetry (SAP) and multifocal visual evoked potentials (mfVEP) were studied.

METHODS

Eyes of 40 patients with concomitant SAP and mfVEP glaucomatous loss and 25 controls underwent OCT retinal nerve fibre layer (RNFL), mfVEP and 24-2 SAP tests. For the mfVEP and 24-2 SAP, a hemifield was defined as abnormal based upon cluster criteria. On OCT, a hemifield was considered abnormal if one of the five clock hour sectors (3 and 9 o'clock excluded) was at <1% (red) or two were at <5% (yellow).

RESULTS

Seventy seven (43%) of the hemifields were abnormal on both mfVEP and SAP tests. The OCT was abnormal for 73 (95%) of these. Only 1 (1%) of the 100 hemifields of the controls was abnormal on OCT. Sensitivity/specificity (one eye per person) was 95/98%.

CONCLUSIONS

The OCT RNFL test accurately detects abnormal hemifields confirmed on both subjective and objective functional tests. Identifying abnormal hemifields with a criterion of 1 red (1%) or 2 yellow (5%) clock hours may prove useful in clinical practice.

Efficiency of Rarebit perimetry in the evaluation of homonymous hemianopia in stroke patients

AIMS

To compare the efficiency of Rarebit perimetry and the Humphrey field analyser (HFA) in detecting the homonymous hemianopia in stroke patients with occipital lobe infarcts.

METHODS

40 patients who suffered from visual complaints caused by acute occipital lobe infarcts underwent visual field analysis on the same day, in random order-first with either Humphrey perimetry 30-2, SITA standard program (Zeiss Humphrey Systems) or Rarebit perimetry. A visual field was classified into four quadrants for right and left eyes: superior temporal, superior nasal, inferior temporal, and inferior nasal. The entire mean hit rate numbers (MHR) and mean deviation and pattern standard deviation (PSD) values were compared for each quadrant of each eye.

RESULTS

The results of Rarebit MHR and HFA mean deviation values for each quadrant of the right and left eyes were highly correlated in all patients with homonymous hemianopia (Pearson's r correlation coefficients for superior temporal, superior nasal, inferior temporal and inferior nasal quadrants of right and left eyes were 0.827, 0.833, 0.843, 0851 and 0.746, 0821, 0882, 0.824, respectively (p<0.001 for all quadrants)). There was a strong correlation between Rarebit MHR and HFA PSD for each quadrant of both eyes.

CONCLUSIONS

Rarebit perimetry is rapid, reliable, and easily performed in patients with homonymous hemianopia. It can be done using a simple software program and simple hardware and it readily detects severe visual loss in patients with occipital lobe lesions.

Frequency-doubling perimetry: comparison with standard automated perimetry to detect glaucoma

PURPOSE

To compare second generation frequency-doubling perimetry (FDP) with standard automated perimetry (SAP) to detect glaucomatous visual field abnormalities.

DESIGN

Prospective, cross-sectional, controlled observational study.

METHODS

Fifty eyes of 50 patients with glaucoma with confirmed SAP visual field abnormalities and 42 eyes from 42 normal control subjects were studied. Swedish Interactive Thresholding Algorithm (SITA) standard 24-2 SAP and FDP visual fields were performed. The correlation of global indices and the number of defects on total deviation (TD) and pattern deviation (PD) plots were compared. The spatial concordance of FDP and SAP defect locations was determined.

RESULTS

In patients with glaucoma, significant correlations of mean deviation (MD) and pattern standard deviation (PSD) were found between SAP and FDP (P < .001 for MD and P < .001 for PSD), but not in the normal group. FDP had significantly greater defect scores than SAP on total deviation and PD plots in the glaucoma group (P = .028 and P = .01, respectively). In comparison with SAP, sensitivity and specificity of FDP were 92% and 98% with glaucoma hemifield test criteria and 98% and 93% with PSD <5% criteria, respectively. Similarly high diagnostic precision was found with MD and PSD (at 95% specificity; MD and PSD sensitivity was 82% and 90%, respectively). The location of defects within 12 hemifield clusters found with FDP agreed moderately well with those detected with SAP (kappa = .48).

CONCLUSIONS

FDP and SAP perform similarly in their ability to detect visual field defects in early to moderate glaucoma. Larger and deeper defects detected with FDP suggests the possibility of earlier detection at high specificity.

Ocular Hypertension Treatment Study Group, European Glaucoma Prevention Study Group, Gordon MO, Torri V, Miglior S, Beiser JA, Floriani I, Miller JP, Gao F, Adamsons I, Poli D, D'Agostino RB, Kass MA. Validated prediction model for the development of primary open-angle glaucoma in individuals with ocular hypertension

OBJECTIVE

To test the validity and generalizability of the Ocular Hypertension Treatment Study (OHTS) prediction model for the development of primary open-angle glaucoma (POAG) in a large independent sample of untreated ocular hypertensive individuals and to develop a quantitative calculator to estimate the 5-year risk that an individual with ocular hypertension will develop POAG.

DESIGN

A prediction model was developed from the observation group of the OHTS and then tested on the placebo group of the European Glaucoma Prevention Study (EGPS) using a z statistic to compare hazard ratios, a c statistic for discrimination, and a calibration chi2 for systematic overestimation/underestimation of predicted risk. The 2 study samples were pooled to increase precision and generalizability of a 5-year predictive model for developing POAG.

PARTICIPANTS

The OHTS observation group (n = 819; 6.6 years' median follow-up) and EGPS placebo group (n = 500; 4.8 years' median follow-up).

TESTING

Data were collected on demographic characteristics, medical history, ocular examination visual fields (VFs), and optic disc photographs.

MAIN OUTCOME MEASURE

Development of reproducible VF abnormality or optic disc progression as determined by masked readers and attributed to POAG by a masked end point committee.

RESULTS

The same predictors for the development of POAG were identified independently in both the OHTS observation group and the EGPS placebo group-baseline age, intraocular pressure, central corneal thickness, vertical cup-to-disc ratio, and Humphrey VF pattern standard deviation. The pooled multivariate model for the development of POAG had good discrimination (c statistic, 0.74) and accurate estimation of POAG risk (calibration chi2, 7.05).

CONCLUSIONS

The OHTS prediction model was validated in the EGPS placebo group. A calculator to estimate the 5-year risk of developing POAG, based on the pooled OHTS-EGPS predictive model, has high precision and will be useful for clinicians and patients in deciding the frequency of tests and examinations during follow-up and advisability of initiating preventive treatment.

Évaluation clinique du tonomètre dynamique Icare®

PURPOSE

The Icare dynamic tonometer (impact or Rebound tonometry) is a new tonometer based on making a moving object collide with an eye and on monitoring the motion parameters of this object following contact. The purpose of this study was to assess intra- and interobserver variability of IOP measurements with the Icare and their correlations with Goldmann applanation tonometry (GAT) and central corneal thickness (CCT).

MATERIAL AND METHODS

A prospective study including three groups of patients: group 1 (50 normal subjects), group 2 (50 patients with OHT or POAG and GAT IOP>22 mmHg), and group 3 (38 glaucomatous patients with GAT IOP< or =22 mmHg). In group 1, three consecutive IOP measurements were taken by three distinct observers with Icare followed by three GAT measurements by the same clinician. In group 2, the same procedure was followed from patients 1 to 25 and the reverse sequence from patients 25 to 50 after a 10-min break. In group 3, only one clinician took three GAT measurements followed by three Icare measurements after a 10-min break to exclude a tonographic effect in eyes with statistically normal-range IOPs.

RESULTS

: In group 1, intraobserver variability was about 6% for each observer (NS). There was no learning curve effect. The interobserver variation coefficient was 6.4%. Icare overestimated IOP compared to GAT (mean difference, 1.5-2.2 mmHg) (p<0.001). Icare IOP was 23.4 mmHg for observer 1 when GAT was 22 mmHg (95% individual CI, 18-28.9 mmHg). In group 2, intraobserver variation coefficients of the IOP ranged from 5% to 5.4% (NS). Icare overestimated IOP by mean 0.84 mmHg compared with GAT. In group 3, mean IOP was not different between Icare and GAT. Icare IOP of 20.7 mmHg corresponded to a value of 22 mmHg using GAT. In this group, correlations between CCT and IOP measurements were higher for Icare than for GAT (p=0.062).

CONCLUSION

Icare measures IOP in an unanesthetized sitting patient in a very brief time. Patient's minimal cooperation is needed. As long as the device is correctly positioned, the learning curve is short. Icare gives reproducible IOP measurements. Intra- and interobserver variability of IOP measurements are close to those of GAT. Icare overestimates IOP measurements an average 1.5 mmHg compared with GAT. Whatever the IOP level, Icare IOP measurements are well correlated with GAT. To a greater extent than for GAT, the reliability of IOP measurements is influenced by CCT. This tonometer can be used as a screening device for ocular hypertension as long as CCT measurements can be taken.

Perception of very small visual stimuli in the fovea: normative data for the Rarebit Foveal Test

BACKGROUND

Conventional visual tests are not sensitive enough to detect low degree neural damage, as 6/6 (1.0) visual acuity can be upheld with less than two-thirds of the normal number of optic nerve axons. The aim of the current study was to evaluate the physiologic properties of a new computerised test, the Rarebit Fovea Test (RFT), using very small stimuli, by quantifying the effect of age and binocular summation in relation to stimulus luminance.

METHODS

The RFT relies on the perception of very small (less than 0.5 minutes of arc) bright stimuli. Two different experiments were performed. 1. Thirty-five subjects (age 19 to 63 years) were tested with five different stimulus luminances, 158, 64, 53, 41 and 33 cd/m(2). 2. Nineteen subjects (age 19 to 63 years) were tested using binocular stimulation to define the binocular summation.

RESULTS

Significantly reduced median hit rates were observed at luminances of 53 cd/m(2) or below. Age and mean hit rate correlated negatively at all luminance levels below 158 cd/m(2). The mean hit rate from binocular stimulation, compared to the highest value from monocular stimulation in the same subject, was increased by a factor of 1.54 +/- 0.45 (SD). No age effect was found regarding binocular summation.

CONCLUSIONS

The results in the current study indicate that RFT can identify some of the well-known features of the visual system, that is, the effects of age and binocular summation, provided that the stimulus luminance is adequately selected.

Corneal thickness and visual field damage in glaucoma patients

PURPOSE

To verify whether there was a significant correlation between central corneal thickness (CCT) and visual field damage in patients with primary open angle glaucoma (POAG).

METHODS

A total of 99 eyes with POAG were consecutively recruited. Patients were classified as glaucomatous based on visual field and optic nerve head damage. All underwent applanation tonometry, Humphrey perimetry, and measurement of CCT with ultrasonic pachymetry. Based on CCT value, the sample was split at the mode in two groups (group 1<535 microm, n=49; group 2>or=535 microm, n=50).

RESULTS

Entire cohort: mean CCT 554 microm+/-45.03; mean deviation (MD) -6.68 dB+/-7.32; pattern standard deviation (PSD) 5.33+/-3.75; intraocular pressure (IOP) 17.91+/-4.16 mmHg with treatment. Group 1: CCT was 504.8 microm+/-30.8; MD -9.01 dB+/-8.72; PSD 6.38+/-3.99; IOP 18.02 mmHg+/-4.66. Group 2: mean CCT 574.6 microm+/-35.03; MD -4.39 dB+/-4.70; PSD 4.25+/-3.19; IOP 17.79 mmHg+/-3.57. A significant difference was found between the two groups for both MD and PSD. Linear regression analysis showed a significant correlation between CCT and PSD (P<0.001).

CONCLUSIONS

Our data show that patients with a thinner cornea had a worse MD and PSD. As a thinner CCT causes an underestimation of the true IOP, there may be a delay in the diagnosis of POAG or an inadequate estimate of the clinical course despite apparently desirable IOP applanation readings.

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.

Rarebit and frequency-doubling technology perimetry in children and young adults

PURPOSE

To describe the outcome of visual field examinations performed with rarebit (RB) and frequency-doubling technology perimetry (FDT) in children and young adults.

METHODS

Twenty-one children (aged 6.5-12 years) and 30 teenagers and young adults (aged 14-20 years), participated in the study.

RESULTS

Reliable RB examinations were carried out in 76% of the younger group and 90% of the older group. Corresponding values for FDT were 57% and 90-95%, respectively. The RB results were very similar to those previously obtained in adult subjects, while some subjects showed borderline values in FDT, depending on the criteria used. The RB perimetry was preferred by 88% of the examined subjects.

CONCLUSIONS

Rarebit perimetry seems useful for visual field examination in children aged 7 years and over, if age-corrected normative data are established; this test was also preferred by the tested subjects. No adaptation or special instructions were needed and the children found it rather amusing.