PubMed · 15878084
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David Cockburn. 2005. Glaucoma detection.. https://doi.org/10.1016/j.ophtha.2004.11.004
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BACKGROUND: The detection of a slowly progressive loss of optic nerve fibres in patients with ocular hypertension is a very important task for confocal laser tomography. We compared changes of the parameters of the Heidelberg Retina Tomograph (HRT) with changes of static visual field measurements. METHODS: Since 1994, patients with ocular hypertension have been monitored prospectively every 6 months with visual field measurements (Octopus 123, dG1x) as well as examinations of the optic disc using the HRT. A progressive excavation of the optic nerve head was defined as a significant increase or decrease of the linear regression over time. We analysed the HRT parameters cup area (CA), cup volume (CV), cup shape measure (CSM), rim volume (RV), retinal nerve fibre thickness (RNFLT) and contour height variation (CHV) each circular and for six different sectors of 109 eyes (60 patients). A glaucomatous visual field defect and therewith the conversion from ocular hypertension (OHT) to open angle glaucoma (OAG) was defined as reproducible defect-cluster >20 dB of two or three single points at the same location. RESULTS: Nine of 109 eyes converted from OHT to OAG. A significant linear increase of the circular parameters occurred in two (CA), four (CSM), two (CV) and a decrease in three (CHV), two (RV) and four (RNFLT) eyes. The sectoral analysis increased the results of CA and CV in the temporal superior and temporal inferior sectors (ts/ti): five/four (CA), two/three (CV). Cup shape measure showed in the temporal superior, temporal inferior (ti) and nasal inferior (ni) sectors slightly increased hits [five (ts), five (ti), five (ni)]. CONCLUSIONS: The linear model for the progression of the optic disc parameters detected only a small amount of the converters. The hit rate could be increased with the sectoral based analysis. Cup shape measure showed the highest rate.
Optical coherence tomography, an important new tool in the investigation ofthe retina Recently optical coherence tomography (OCT) has been introduced into the field of ophthalmology to enhance visualization ofthe various retinal layers. OCT uses interference of near infra-red, low-coherent light reflected from the retina and from a reference mirror, to create transverse sections of the retina. The strength of the signal is a measure of the reflection of the retinal layer which is situated at the same distance from the light source as the mirror. Accurate placement ofthe mirror gives a transverse view of the retina with an axial resolution of 10 microm, with which the resolution of a histological section can be approximated. OCT is used in ophthalmic diseases such as macular oedema, macular holes and other abnormalities on the retinal-vitreous border, following photodynamic therapy and in treating glaucoma. OCT has been used to detect early glaucoma by measuring the thickness of the retinal nerve fibre layer. OCT and fluorescence angiography complement one another as diagnostic methods but OCT is superior in the diagnosis of macular oedema and macular holes. OCT provides images of retinal pathology which can easily be interpreted by both ophthalmologists and patients.
BACKGROUND: Age-related macular degeneration (ARMD) is the most prevalent cause of visual loss in patients older than 60 years in the United States. Observation of drusen is the hallmark finding in the clinical evaluation of ARMD. OBJECTIVES: To segment and quantify drusen found in patients with ARMD using image analysis and to compare the efficacy of image analysis segmentation with that of stereoscopic manual grading of drusen. DESIGN: Retrospective study. SETTING: University referral center.Patients Photographs were randomly selected from an available database of patients with known ARMD in the ongoing Columbia University Macular Genetics Study. All patients were white and older than 60 years. INTERVENTIONS: Twenty images from 17 patients were selected as representative of common manifestations of drusen. Image preprocessing included automated color balancing and, where necessary, manual segmentation of confounding lesions such as geographic atrophy (3 images). The operator then chose among 3 automated processing options suggested by predominant drusen type. Automated processing consisted of elimination of background variability by a mathematical model and subsequent histogram-based threshold selection. A retinal specialist using a graphic tablet while viewing stereo pairs constructed digital drusen drawings for each image. MAIN OUTCOME MEASURES: The sensitivity and specificity of drusen segmentation using the automated method with respect to manual stereoscopic drusen drawings were calculated on a rigorous pixel-by-pixel basis. RESULTS: The median sensitivity and specificity of automated segmentation were 70% and 81%, respectively. After preprocessing and option choice, reproducibility of automated drusen segmentation was necessarily 100%. CONCLUSIONS: Automated drusen segmentation can be reliably performed on digital fundus photographs and result in successful quantification of drusen in a more precise manner than is traditionally possible with manual stereoscopic grading of drusen. With only minor preprocessing requirements, this automated detection technique may dramatically improve our ability to monitor drusen in ARMD.