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Abstract The diagnosis of primary glaucomas is always a summary of all the clinical information available. In diagnosing this disease one should not consider lOP measurement alone, visual field evaluation alone, optic disc evaluation alone. the role and importance of each examination may VaI)’ with several patient related factors as age, optical media, stage of the disease, optic disc size and other eye diseases. The ONH changes in glaucoma include: 1- Optic disc cupping: which is usually measured by the elD ratio but measurement of the neuroretinal rim area is more specific and sensitive in differentiating normal from glaucomatous eyes but still large overlap between normal and glaucomatous values are present. The rim contour is affected by glaucoma in the form of saucerization, shelving and excavation. There is no standard pattern of glaucomatous cupping. It may occur in the form of concentric enlargement of the cup, temporal unfolding, vertical ovalness, nasal cupping, notching, APON or over pass cupping. 2- Optic disc pallor: It should not be mistaken as cupping. It increases in glaucoma. Pallor due to glaucoma must be differentiated from non glaucomatous causes. 3- Vascular changes: In the form of nasal shift of vessels, change in shape or position of bend of the retinal vessels at the cup edge, baring of circumlinear vessels, vascular loops on the disc and optic disc Hges. 4- Peripapillary changes in the form of peripapillary chorioretinal atrophy or RNFL defects. For evaluation of the ONH changes many methods are used. The direct ophthalmoscope provides excellent magnification but the view is monocular making assessment of contour changes difficult. The standard binocular indirect ophthalmoscope does not provide significant magnification for routine ONH examination but provides stereoscopic view. To obtain stereoview with high magnification, the fundus contact lens, high power convex lens or Hruby lens used with the slit lamp biomicroscope can be used. - 178- n ONH changes can be documented by ONH drawing or high magnification stereo disc photos so that fme details can be studied and documentation for patient follow up can be available. ONH drawing can not replace the precision of photographs but forces the examiners to focus their observations. and usually capture the major features of the ONH and is mandatory in the absence of photographic capability. Flicker analysis and stereochronoscopy of the stereophotographs are more sensitive than side by side comparisons of disc slides. But flicker chronoscopy is preferred over stereochronoscopy for more accurate and quantitative analysis. Electronic digital subtraction of 2 aligned disc photos is superior to Judging stereoscopic photographs without any comparison devices but it is less sensitive than flicker chronoscopy. Planimetry is technique applied to the optic disc stereophotographs to provide one dimensional (vertical, horizontal axes) or area measurements only, leaving the third dimension (depth) to another technique (stereophotogrammetry). They were found to be accurate and reliable methods and add sensitivity to the non qualitative ”., clinical methods but they need experienced observers especially stereophotogramrnetry . B-scan ultrasonography is especially valuable in eyes with opaque media.!t is used to calculate the elD ratio. The ONH is also quantified using automated systems including ONH analyzers and confocal scarming laser ophthalmoscopes. This table shows some important difference between different types of ONH analyzers: hem HRA I Image net Rodenstock ONH Glaucoma-scope I analyzer Method of con- Stereoscopic videographic imaging stereoscopic videographic Raster stereograph, struction of the (assess the brightness distribution in the imaging (assesses deviation of ”assesses the deviation of 3-dimensional red free image projected blue stripes on the projected lines on the topography ONH ”cross-correlation ONH. between light segments” Image only direct direct and slide acquisition image only direct only direct acquisition - 179- n I I Number of pomts marking 8 4 4 the disc edge by -- the operator Reference plane disc edge disc edge or SOO Stable retinal reference plane Mean depth of 2 vertical f’ beyond the at the periphery of the image lines 350 f’ out side the disc edge temporal and nasal Distance of cup border of the ONH margin below the 120 f’ 150 f’ ISO f’ 120 f’ reference planetcu ONH 2 minutes for 3-5 minutes for 4 minutes for image 2 minutes for topographic image acquisition-I 2- the stereometric acquisition and recording and measurements of mapping time 18 minutes from analysis to be 12 minutes for image analysis topographi,: analysis marking the disc completed edge to complete to hic rnannin~ Operator high small small small variabilitv Instrument smaIl absent high high variabilitv The printouts of ONH analyzers in general are: 1) Topographic maps: In the form of numerical depth map, colour coded topographic map, contour map, cross sectional profiles and wire grid map, 2) Values of topographic parameters including vertical and horizontal disc diameters and cup/disc ratios, cup area, disc area, cup volume, cup area/disc area, minimum vertical and horizontal cup diameter ratios and relative RNFL height. 3) Pallor maps and pallor values. Limitations for the ONH analyzers include the need for pupillary dilatation, clear media (like photography) and experienced technician. The confocal laser scanning ophthalmoscope which produces optical sections of the retina and the ONH in a coronal plane have higher axial resolution and reproducibility than the ONH analyzers and can be used through undilated pupil less than 2 mm and even in the presence of20/60 cataract. Like ONH analyzers it have higher resolution and reproducibility than the stereo disc photos. The axial resolution of the laser scanning ophthalmoscope is limited by ocular aberrations and pupil aperture. Fluorescein angiography of the optic disc can detect areas of hypofluorescence of the disc and abnormal transit time in glaucomatous patients but it is invasive method. Laser Doppler velocimeter is non invasive technique measuring the ONH circulation. RNFL changes may precede detectable changes in the ONH and visual field ’. loss so it is very important in early diagnosis of glaucoma. The RNFL thinning due to glaucoma appears in the form of : • Localized or diffuse RNFL defects by red free ophthalmoscopy and photography. The dynamic scanning laser ophthalmoscopy allows better identification of these defects. • Decrease in the RNFL surface height by ONH analyzers. • Retardation (delay of polarized laser light) by laser scanning polarimetry and fourier ellipsometry. Decrease of the RNFL thickness by OCT which provides high resolution crosssectional images of the retinal structure in vivo depending on the delay of reflected or backscattered light using low coherence interoferometry. It has higher axial resolution than the laser scanning ophthalmoscope and tomograph. OCT by measuring the RNFL thickness has future in earlier detection of glaucoma before visual field defects, ONH changes and RNFL defects (by ophthalmoscopy or photography) can be detected. |