Absolute Glaucoma
Glaucoma is a generic term used to describe diseases in which the intraocular pressure is at a level sufficient to cause damage to the tissues within an individual eye, resulting in “glaucomatous optic neuropathy”. Around 30% of the globes received in the
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Absolute Glaucoma
Introduction Some 30 % of the globes received in the laboratory will have been enucleated in treatment of the complications and the intractable pain that are the features of secondary end-stage or “absolute” glaucoma. The commonest cause of secondary absolute glaucoma in the elderly patient was previously thrombotic occlusion of the central retinal vein (see Chap. 4), but, like diabetic eye disease, this is now less common due to effective suppression of intraocular neovascularisation by panretinal laser treatment (photoablation). Secondary “neovascular glaucoma” is brought about by proliferation of fibrovascular tissue in the chamber angle and this vasoproliferation is a response to transport, via the ocular fluids, of vasoformative biochemical agents synthesised in the retina in conditions in which there is underperfusion and hypoxia in the neural tissues. Ischaemic disease is often present in several tissue components in the elderly eye, and this is often the final stage in a process that may have been initiated by the primary and secondary glaucomas that will be described in this chapter. For the pathologist about to embark on the study of a glaucomatous eye, there is one important caveat. If, as is often the case in end-stage glaucoma, the cornea and lens are opaque, the clinician may not have been aware that an intraocular malignant melanoma (see Chap. 5) was the underlying cause of raised intraocular pressure (IOP). The presence of a tumour should be suspected if the globe is unusually firm on palpation, particularly in one quadrant. Thus, during this preliminary stage of the macroscopic examination, it is important to identify and retain the vortex veins, because these structures are much harder to find after the eye has been bisected.
The Functional Morphology of the Outflow System The corneoscleral envelope of the eye may be compared with the casing of an inflated football. Pressure within the inelastic collagenous casing is maintained at normal levels (13–21 mmHg) F. Roberts, C.K. Thum, Lee’s Ophthalmic Histopathology, DOI 10.1007/978-1-4471-2476-4_3, © Springer-Verlag London 2014
by a balance between the pressure of aqueous inflow and the resistance in the outflow system [1].
Aqueous Inflow Aqueous fluid is pumped into the eye by the ciliary epithelium utilising a bicarbonate pump mechanism. However, the inflow pressure is also dependent on the hydrostatic pressure in the fenestrated ramifying capillary bed in the ciliary processes. The anatomy of the two-layered epithelium of the ciliary processes is such that the inner, non-pigmented layer is united by tight junctions (zonulae occludentes). The inner part of the intercellular space is used for pumping anions and cations, which attract water by osmosis; and the ultrafiltrate, produced in the blood-aqueous barrier, consists of salts and low molecular weight substances [2].
Aqueous Outflow The Trabecular Meshwork Aqueous passes through the pupil to the chamber angle and leaves the eye via the outflow system or trabecular meshwork (
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