Glaucoma is a term that encompasses a group of conditions, which have in common the development of a potentially blinding optic neuropathy. The optic neuropathy is a result of a progressive loss of retinal ganglion cells, brought on by factors such as ganglion cell apoptosis, reduced blood flow to the nerve head or the physical effects of elevated intraocular pressure. Hence, glaucoma may be thought of as a disease of the retinal ganglion cells caused by a range of ocular conditions. Since the retinal ganglion cells and associated nerve fiber layer are visualized with difficulty in a standard clinical examination, diagnosis often relies upon detection of secondary changes in the optic nerve head and/or visual field. Glaucoma therapy is indicated if there is excessive intraocular pressure (IOP) or characteristic damage to the optic nerve, nerve fibre layer and/or visual field (VF). Since the condition is insidious in onset, risk factors requiring more frequent patient review include: mild increase in IOP, narrow anterior chamber angle, low central corneal thickness, family ocular history, and other possible signs.
Most glaucoma syndromes are insidious and asymptomatic. Fixation is not usually threatened until late in the disease process. The symptoms of acute angle closure are covered in the separate entry: Acute Angle Closure Glaucoma.
Classification and signs
This section acts as a signpost to the various conditions (in bold) in this series and book.
- Acute angle closure glaucoma: Risk factors are an anterior chamber central depth of less than 2mm, or gonioscopy failing to show the trabeculum angle structures. See also Plateau Iris.
- Primary open-angle glaucoma (see Glaucoma – Primary Open Angle). Usually has the triad of glaucomatous optic neuropathy (GON), VF loss and raised IOP, with open anterior chamber angles and the absence of other pathology or signs of inflammation.
- VF loss with static threshold perimetry, can be defined as significant loss at the 5% level in more than 3 contiguous points. The field loss should be repeatable. Field loss is most often in an arcuate zone between 10 and 20 degrees of fixation and characteristically respects (does not cross) the horizontal midline (See: Glaucoma – visual field assessment).
- GON features include: (a) thinner rim margin superiorly or inferiorly than the nasal or the temporal margins; (b) notching of the neuro-retinal rim; (c) increased cup-disc ratio over time or inter-ocular asymmetry more than 0.2 and (d) retinal nerve fibre layer defects (See: Glaucoma – neuro-retinal rim assessment)
- Risk factors may lead to glaucoma but are not necessarily a sign of the condition. They include: (a) Ocular hypertension: Defined in the Ocular Hypertension Treatment Study as an IOP in the range of 24–32 mmHg, with normal optic nerve appearance, normal VF findings, open anterior chamber angles and no other related ocular pathology. (b) nerve fibre layer (Drance) haemorrhage crossing the disc margin; (c) an enlarged vertical cup-disc ratio (>0.6); (d) thin central corneal thickness; (e) family ocular history of glaucoma
- Normal tension glaucoma: IOP is less than 21mmHg, in the presence of GON or VF defect or both. Exclude neurological cause including causes of optic atrophy, where the disc pallor is greater than the cupping. May be related to a thin cornea.
- Congenital glaucoma
- Pseudoexfoliation (PXF) glaucoma: white material deposited on the anterior crystalline lens, zonules and iris margin;
- Pigmentary glaucoma: iris transillumination, trabecular pigmentation, Krukenberg spindle;
- Neovascular glaucoma: abnormal blood vessels or fibrovascular membrane occluding anterior chamber angle;
- Steroid-induced glaucoma: e.g. more than 2 to 4 weeks of topical corticosteroids in susceptible people;
- Inflammatory glaucoma, Phacolytic glaucoma; Glaucomatocyclitic Crisis
- Angle recession glaucoma: Post-traumatic
- Malignant Glaucoma (Aqueous misdirection syndrome): Post-operative
- Associated conditions: Neurofibromatosis, Sarcoidosis
Other conditions associated with glaucoma covered in: Bruce AS and Loughnan MS. Anterior eye disease and therapeutics A-Z, Elsevier, Oxford 2003
Aniridia, Disciform keratitis, Epithelial and fibrous ingrowth, Filtering Bleb, Fuchs’ heterochromic iridocyclitis, Herpes Zoster Ophthalmicus, Iridocorneal dysgenesis (congenital anomalies), Iridocorneal endotheliopathy (ICE), Ocular cicatricial pemphigoid, Synechiae
Differential Diagnosis and other optic neuropathies, See also
see: Glaucoma – Differential Diagnosis And Management
Optic nerve head cupping, with suspect inferior temporal notching, is one of the risk factors for glaucoma.