Factors affecting the sensitivity and specificity of the Heidelberg Retina Tomograph parameters to glaucomatous progression in disc photographs.

PURPOSE: To evaluate the factors affecting the sensitivity and specificity of the stereometric optic nerve head (ONH) parameters of the Heidelberg Retina Tomograph (HRT) to glaucomatous progression in stereoscopic ONH photographs. METHODS: The factors affecting the sensitivity and specificity of the vertical cup : disc ratio, the cup : disc area ratio, the cup volume, the rim area and a linear discriminant function to progression were analysed. These parameters were the best indicators of progression in a retrospective study of 476 eyes. The reference standard for progression was the masked evaluation of stereoscopic ONH photographs. RESULTS: The factors having the most significant effect on the sensitivity and specificity of the stereometric ONH parameters were the reference height difference and the mean topography standard deviation (TSD), indicating image quality. Also, the change in the TSD and age showed consistent, but variably significant, influence on all parameters tested. The sensitivity and specificity improved when there was little change in the reference height, the image quality was good and stable, and the patients were younger. The sensitivity and specificity of the vertical cup : disc ratio was improved by a large disc area and high baseline cup : disc area ratio. The rim area showed a better sensitivity and specificity for progression with a small disc area and low baseline cup : disc area ratio. CONCLUSION: The factors affecting the sensitivity and specificity of the stereometric ONH parameters to glaucomatous progression in disc photographs are essentially the same as those affecting the measurement variability of the HRT.

Clinical assessment of stereoscopic optic disc photographs for glaucoma: the European Optic Disc Assessment Trial.

PURPOSE: To determine the diagnostic accuracy of judging optic disc photographs for glaucoma by ophthalmologists. DESIGN: Evaluation of diagnostic test and technology. PARTICIPANTS: A total of 243 of 875 invited ophthalmologists in 11 European countries. METHODS: We determined how well each participant classified 40 healthy eyes and 48 glaucomatous eyes with varying severity of the disease on stereoscopic slides. Duplicate slides were provided for determining intraobserver agreement. All eyes were also imaged with the GDx with variable corneal compensation (GDx-VCC) (Carl Zeiss Meditec AG, Jena, Germany) and the Heidelberg Retina Tomograph (HRT) I (Heidelberg Engineering GmbH, Heidelberg, Germany). Diagnostic accuracies of clinicians were compared with those of the best machine classifiers. MAIN OUTCOME MEASURES: Accuracy of classification, expressed as sensitivity, specificity, and overall accuracy. Intraobserver agreement (kappa). RESULTS: The overall diagnostic accuracy of ophthalmologists was 80.5% (standard deviation [SD], 6.8; range, 61.4%-94.3%). The machine classifiers outperformed most observers in diagnostic accuracy; the GDx-VCC nerve fiber indicator and the HRT's best classifier correctly classified 93.2% and 89.8% of eyes, respectively. The intraobserver agreement (kappa) varied between -0.13 and 1.0 and was on average good (0.7). CONCLUSIONS: In general, ophthalmologists classify optic disc photographs moderately well for detecting glaucoma. There is, however, large variability in diagnostic accuracy among and agreement within clinicians. Common imaging devices outperform most clinicians in classifying optic discs. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

Conformal geometry of the retinal nerve fiber layer.

The nerve fiber layer of the human retina is made up of the retinal segments of ganglion cell axons. Its geometry can be described mathematically as a fibration of a 2D domain: a partition of a certain region into smooth curves. Here, we present a simple family of curves that closely models the observed geometry of the nerve fiber layer. For each retina, the pattern depends on 2 parameters, A and B: A computer program determines A and B for a given retina and the theory matches the retina with a standard deviation of approximately 6-8 degrees . These particular curves turn out to be the curves that would be generated if the growing ganglion cell axon tip moved down a gradient toward a source of diffusible neuroattractant at the disk and away from a weaker macular diffusible repellant. Thus, this model provides morphological evidence that diffusible substances provide positional information to the embryonic ganglion cell axons in finding their way to the optic nerve head.

Heidelberg retina tomograph parameters of the optic disc in eyes with progressive retinal nerve fibre layer defects.

PURPOSE: To determine the Heidelberg retina tomograph (HRT) parameters that identify glaucomatous changes in optic nerve head (ONH) topography associated with progression of retinal nerve fibre layer (RNFL) defects. METHODS: A total of 68 eyes with open-angle glaucoma were included in this retrospective study: 34 eyes showed progression of an RNFL defect during the follow-up period and 34 eyes did not. Successful RNFL photographs and scanning laser tomography examinations with the HRT were taken in all patients at each of three visits. The change in HRT parameter values during follow-up was calculated. RESULTS: Progression of the RNFL defect was statistically significantly correlated (p = 0.049) with only one topographic ONH parameter, the cup shape measure. The best combination of two parameters (p = 0.009) included the maximum cup depth and the linear cup : disc area ratio; the best combination of three parameters (p = 0.007) included the maximum cup depth, the linear cup : disc area ratio and the horizontal cup : disc area ratio. Sensitivity and specificity values were 52.9% and 73.5%, respectively, for the cup shape measure, 70.6% and 73.5%, respectively, for the two-parameter combination, and 76.5% and 79.4%, respectively, for the three-parameter combination. The areas under the receiver operating characteristic curve were 0.617, 0.724 and 0.753, respectively. CONCLUSIONS: The results indicate that the HRT parameters may be used to detect small ONH changes associated with progression of the RNFL defect. With the exception of the cup shape measure, the parameters which provide the best correlation with progression differ from those considered optimal for recognizing the presence or absence of glaucoma.

Placing the Molteno implant in a long scleral tunnel to prevent postoperative tube exposure.

PURPOSE: The purpose of this study was to retrospectively evaluate whether it is possible to decrease the risk of Molteno tube erosion through the conjunctiva by using a new technique where the silicone tube is inserted into a scleral tunnel instead of being covered only by the conjunctiva. METHODS: We reviewed Molteno implants carried out at the University Hospital of Oulu, in 332 patients who underwent traditional Molteno implantation between October 1986 and October 1998 and 92 patients who underwent surgery with the new technique between November 1998 and April 2001. RESULTS: With our former technique, conjunctival erosions occurred in 15 eyes of 15 patients (4.5%) after a median follow-up of 3.5 months (range 1-72 months); no conjunctival complications were discovered in patients who underwent surgery using the new technique during a median follow-up of 22 months (range 10-39 months). (p = 0.038, two-sample test of proportions). CONCLUSION: Inserting the Molteno tube into a scleral tunnel prevents tube extrusion through the conjunctiva in eyes with Molteno implants. The technique for making the scleral tunnel is described.

Efficacy and tolerability of the dorzolamide 2%/timolol 0.5% combination (COSOPT) versus 0.005% (XALATAN) in the treatment of ocular hypertension or glaucoma: results from two randomized clinical trials.

PURPOSE: To compare the efficacy of the fixed dorzolamide 2%/timolol 0.5% combination (COSOPT) versus latanoprost 0.005% (XALATAN). METHODS: Two 3-month, parallel group, randomized, observer-masked and patient-masked, multicentre, clinical trials were performed in patients with ocular hypertension or open-angle glaucoma. Study 1 (n=256) was conducted in the United States and Study 2 (n=288) was conducted in Europe/Israel. Patients could be included whether or not they were currently taking ocular hypotensive therapy, and regardless of the effectiveness of any previous therapy. Patients were washed out from their usual ocular hypotensive medications and then those with a baseline intraocular pressure (IOP) >/= 24 mmHg were randomized to either the dorzolamide/timolol combination eye drops twice daily or latanoprost eye drops once daily in both eyes. Efficacy was assessed by daytime diurnal IOP (the mean of measurements made at 0800, 1000, 1400 and 1600 h). RESULTS: At baseline, the mean daytime diurnal IOP was 26.1 mmHg in the dorzolamide/timolol combination group versus 25.6 mmHg in the latanoprost group in Study 1, and 25.3 mmHg in the dorzolamide/timolol combination group versus 24.7 mmHg in the latanoprost group in Study 2. After 3 months, the mean daytime diurnal IOP was 18.9 mmHg for the dorzolamide/timolol combination versus 18.4 mmHg for latanoprost in Study 1, and 17.4 mmHg for the dorzolamide/timolol combination versus 17.5 for latanoprost in Study 2. The difference between treatments in mean IOP change at 3 months was -0.04 mmHg [95% confidence interval (CI) -0.85, 0.77] in Study 1, and -0.57 mmHg (95% CI -1.31, 0.16) in Study 2. The probability that the true difference lay between -1.5 and 1.5 mmHg, the predefined bounds for equivalence, was >0.950 in both studies. Both treatments were well tolerated over 3 months, although ocular stinging occurred more frequently with the dorzolamide/timolol combination. CONCLUSIONS: The dorzolamide/timolol combination and latanoprost were equally effective at lowering IOP.

Optic disc biomorphometry with the Heidelberg Retina Tomograph at different reference levels.

PURPOSE: The Heidelberg Retina Tomograph (HRT) is a confocal scanning laser tomograph that produces high resolution optical section images of the optic disc and central retina. Measurement accuracy and reproducibility is good. Several of the stereometric variables depend on the definition of a reference plane level. The purpose of the present study was to evaluate the four different reference levels in terms of their advantages and disadvantages in clinical work. METHODS: Sixty-seven randomly chosen eyes belonging to 67 subjects were included in this study. Forty of the eyes were healthy and 27 had glaucoma. The HRT with software versions 1.09 and 1.11 was used to acquire and evaluate topographic measurements of the optic disc. Image analysis was performed at four different reference levels: 320 microm fixed offset reference level (REFd) (version 1.09), an individually determined reference level (REFi), a papillo-macular reference level (REFm) and a flexible reference level (REFf) (version 1.11). ANOVA was used to determine differences in the topographic parameters between the reference levels. RESULTS: In terms of the healthy eyes, all the variables using different reference levels give rather similar results. However, with advanced glaucoma the measurement values provided with REFd are clearly different to those of the other reference levels. The measurement values using REFm and REFf provide fairly similar results in all clinical groups. REFf indicates the lowest point in the segment between 350 degrees and 356 degrees along the contour line and thus provides the most stable and clinically useful reference level at present. CONCLUSION: At present, the flexible reference level REFf gives the most reliable and adequate HRT measurement values, both in normal and in glaucomatous eyes.