الفهرس 
Embryology of the vitreousOnly 14 pages are availabe for public view
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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.
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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
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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.