Glaucoma

Ocular hypertension

• Diagnosis

  • Normal IOP: mean IOP in the general population is 16 mm Hg; two standard deviations to either side of this gives a ‘normal’ IOP range of 11–21 mm Hg ( Fig. 10.1 ).

    

  • Definition: 4–7% of individuals older than 40 years have IOPs >21 mm Hg without detectable glaucomatous damage—‘ocular hypertension’ (OHT).

  • Risk factors for conversion of OHT to glaucoma: (a) higher IOP, (b) greater age, (c) lower central corneal thickness, (d) larger C/D ratio, and (e) higher ‘pattern standard deviation’ on perimetry.

• Management

  • Drug choice: as for primary open-angle glaucoma (POAG; see below), although regimen may be less aggressive.

  • Risk of conversion to POAG: after 5 years if untreated is 9.5%, and 4.4% if treated.

  • Other considerations: (a) individual patient profile (e.g. age/life expectancy, patient preference, and risk factors); (b) consider treating every patient with an IOP of ≥30 mm Hg.

Primary open-angle glaucoma

• Introduction

  • Definition: POAG is a generally bilateral disease of adult onset characterized by (a) IOP >21 mm Hg at some stage, (b) glaucomatous optic neuropathy, (c) open angle, (d) characteristic visual field loss as damage progresses, and (e) absence of signs of secondary glaucoma.

  • Risk factors: (a) elevated IOP, (b) greater age, (c) race (more common in black than white individuals), (d) family history (first-degree relatives) of POAG, (e) myopia, and (f) systemic vascular disease; elevation of IOP in response to topical steroid is more common in POAG than the general population.

• Diagnosis

  • History: usually asymptomatic until damage is advanced; (a) past ophthalmic history including refractive status, (b) family history, and (c) past medical history and current medication.

  • General examination: (a) pupils, (b) slit lamp, (c) tonometry, (d) pachymetry for central corneal thickness (CCT), (e) gonioscopy, and (f) optic disc examination with dilated pupils.

  • Perimetry : visual field defects include (a) small paracentral depression (70% of early defects), (b) arcuate-shaped defect, (c) nasal step, (d) ring scotoma, and (e) end-stage changes with a small residual island of central vision.

  • Imaging: of discs and peripapillary retinal nerve fibre layer (see below).

• Optic disc changes

  • Diffuse enlargement of the cup ( Fig. 10.2a ).

    

  • Focal notching, often inferior, of the neuroretinal rim (NRR) ( Fig. 10.2b ).

  • C/D ratio asymmetry may develop; comparison of overall disc diameter is critical.

  • Retinal nerve fibre layer defects.

  • Loss of nasal NRR.

  • ‘Sharpened’ disc edge as adjacent NRR is lost.

  • Lamina dot sign (exposed grey dot-like fenestrations in the lamina cribrosa; Fig. 10.2c ).

  • Vascular changes: (a) ‘splinter’ disc haemorrhages, (b) baring of circumlinear blood vessels (space between a superficial vessel and the disc margin), (c) bayoneting (double angulation of a vessel as it bends backwards due to loss of underling NRR), and (d) collateral disc vessels. Progression of peripapillary atrophy, particularly the inner (beta) zone ( Fig. 10.2d ).

• Imaging modalities: (a) stereo disc photography, (b) confocal scanning laser tomography (e.g. Heidelberg retinal tomograph), (c) scanning laser polarimetry (e.g. GDx glaucoma diagnosis), and (d) optical coherence tomography (OCT).

• Management: lowering IOP is the only proven method of slowing progression. A target IOP should be set, with subsequent monitoring and target resetting if progression occurs.

  • Initial medical therapy: with one drug in its lowest concentration, instilled as infrequently as possible consistent with the desired effect.

  • Review: after 4–8 weeks, when response is assessed against target IOP, and if satisfactory subsequently after a further 3–6 months.

  • Causes of failure: (a) poor compliance (25% of patients), (b) inadequate instillation technique, (c) inappropriate target pressure, and (d) IOP fluctuations including wide diurnal variation.

  • Ongoing monitoring: optic disc assessment, perimetry (annual in most low–moderate risk cases), and annual gonioscopy (angles narrow with age).

  • Laser trabeculoplasty: selective laser trabeculoplasty (SLT) or argon laser trabeculoplasty (ALT) can be used to replace or supplement medical treatment; indications include (a) patient preference, (b) intolerance of medical therapy, and (c) avoidance of polypharmacy or surgery.

  • Indications for surgery: (a) failed medical therapy, (b) intolerance of medical therapy, (c) avoidance of polypharmacy, (d) progressive deterioration despite seemingly adequate IOP control, and (e) as primary therapy in some patients.

  • Trabeculectomy: is the most common procedure, although nonpenetrating surgery is also widely performed. If significant lens opacity is present, phacoemulsification alone may be associated with a fall in IOP; alternatively, it can be combined with a filtration procedure (e.g. phacotrabeculectomy).

Normal-pressure glaucoma

• Introduction

  • Definition: (a) glaucomatous optic neuropathy, (b) IOP consistently ≤21 mm Hg, and (c) open angle.

  • Risk factors: (a) age (older than in POAG), (b) race (particularly prevalent in Japan), (c) family history of glaucoma, (d) CCT (thinner than in POAG), (e) systemic hypotension including nocturnal blood pressure dips, and (f) possibly abnormal vasoregulation (e.g. migraine, Raynaud phenomenon).

  • Differential diagnosis: (a) POAG with apparently normal IOP, (b) nocturnal IOP spikes, (c) previous secondary raised IOP (trauma, uveitis, steroids, resolved pigmentary glaucoma), (d) masking of elevated IOP by systemic treatment (e.g. beta-blocker), (e) previous acute optic nerve insult (e.g. anterior ischaemic optic neuropathy), (f) hypovolaemic or septicaemic shock, (g) progressive retinal nerve fibre defects not due to glaucoma (e.g. myopic degeneration, disc drusen), (h) congenital disc anomalies (e.g. disc pits, coloboma), and (i) chiasmal or optic nerve compression.

• Diagnosis

  • Specific points in the history: (a) migraine and Raynaud phenomenon, (b) episodes of shock, (c) headache and other neurological symptoms, and (d) systemic steroids and beta-blockers.

  • Specific points in the examination: (a) IOP is usually in the high teens but may be lower; (b) glaucomatous cupping is similar to POAG, although acquired optic disc pits, peripapillary atrophic changes, and disc splinter haemorrhages may be more frequent than in POAG.

  • Field defects : may be closer to fixation and more localized than in POAG.

  • Other investigations: as for POAG, but in certain patients consider assessment of systemic vascular risk factors, 24 h ambulatory blood pressure monitoring to exclude nocturnal systemic hypotension, blood tests for other causes of nonglaucomatous optic neuropathy, and cranial MR.

• Treatment

  • Indications: visual fields are stable in 50% over 5 years without treatment, so in mild cases it may be appropriate to demonstrate progression before treating; further IOP reduction is effective in reducing progression in at least some patients.

  • Topical: may include betaxolol thought to increases optic nerve blood flow.

  • Surgery (or laser trabeculoplasty): if progression occurs despite reduced IOP.

  • Systemic: (a) control of systemic vascular disease, (b) calcium channel blockers to counter vasospasm, and (c) if significant nocturnal dips in BP are detected, consider reducing antihypertensive medication (especially bedtime dosing).

Primary angle-closure glaucoma

• Introduction

  • Definition: ‘angle closure’ refers to occlusion of the trabecular meshwork by the peripheral iris—iridotrabecular contact (ITC), obstructing aqueous outflow. The condition is responsible for up to half of all cases of glaucoma globally and is typically associated with greater visual morbidity than POAG.

  • Mechanisms: (a) pupillary block—failure of aqueous flow through the pupil leading to anterior bowing of the iris ( Fig. 10.3 )—is relieved by peripheral iridotomy; (b) non pupillary block relating to a thicker or more anteriorly positioned iris ( Fig. 10.4 ), including plateau iris due to anteriorly positioned ciliary processes, is only partially relieved by iridotomy; and (c) plateau iris configuration characterized by a flat central iris plane with a normal central anterior chamber depth.

    
    

  • Risk factors: (a) age, (b) gender (female > male), (c) race (high Far Eastern prevalence), (d) family history, (e) hypermetropia, and (f) shorter ocular and anterior chamber dimensions.

• Diagnosis

  • Primary angle-closure suspect (PACS): (a) gonioscopy shows ITC in three or more quadrants but no peripheral anterior synechiae (PAS), and (b) normal IOP, discs, and fields.

  • Primary angle closure (PAC): (a) gonioscopy shows three or more quadrants of ITC ( Fig. 10.5 ), (b) raised IOP and/or PAS, and (c) normal discs and fields.

    

  • Primary angle-closure glaucoma (PACG): (a) gonioscopy shows ITC in three or more quadrants, and (b) glaucomatous optic neuropathy.

  • Chronic and subacute presentations: typically asymptomatic although episodic mild blurring may be present; (a) IOP elevation may be intermittent, (b) disc appearance depends on severity of damage, and (c) PAS may be broad (‘creeping’) or discrete (‘sawtooth’).

  • Acute presentation: acute onset of blurring and haloes, ocular pain and headache, sometimes malaise and gastrointestinal symptoms; (a) VA usually 6/60-HM, (b) IOP very high (50–100 mm Hg), (c) corneal epithelial oedema ( Fig. 10.6 ), (d) ciliary injection, (e) shallow anterior chamber ( Fig. 10.7 ), and (f) unreactive mid-dilated vertically oval pupil; fellow eye shows an occludable angle.

    
    

  • Resolved acute episode: (a) initially, folds in Descemet membrane ( Fig. 10.8 ), optic nerve head congestion, and choroidal folds; (b) later, iris atrophy with a spiral configuration, irregular pupil with posterior synechiae, glaukomflecken ( Fig. 10.9 ), and optic atrophy.

    
    

• Treatment

  • PACS: prophylactic laser iridotomy; if significant ITC persists, options include observation, laser iridoplasty, pilocarpine 1% prophylaxis, and lens extraction.

  • Chronic presentation of PAC and PACG: as for PACS, although subsequent medical treatment (as for POAG) may be required despite an opened angle.

  • Initial treatment of acute and subacute presentation: (a) intravenous acetazolamide 500 mg, (b) topical apraclonidine 1%, timolol 0.5%, prednisolone 1%, or dexamethasone 0.1% to the affected eye, and (c) pilocarpine 2–4% one drop to the affected eye, repeated after 30 min, with one drop of 1% as prophylaxis to the fellow eye; consider delaying pilocarpine until IOP begins to fall.

  • Subsequent treatment of acute and subacute presentation: (a) pilocarpine 2% four times daily to the affected eye and 1% to the fellow eye, (b) ongoing treatment according to IOP with timolol 0.5% twice daily, apraclonidine 1% three times daily, and oral acetazolamide 250 mg four times daily; once cornea is clear and eye quieter, bilateral laser iridotomy is performed and medical treatment tapered.

  • Options in unresponsive acute cases: (a) further topical pilocarpine, timolol, and apraclonidine, (b) intravenous mannitol or oral glycerol, (c) corneal indentation, (d) laser iridotomy or iridoplasty (clear oedema with glycerol 50% first), and (e) surgery (peripheral iridectomy, lens extraction, goniosynechialysis, trabeculectomy).

• Differential diagnosis of acute IOP elevation: consider alternatives to angle closure, particularly if the fellow eye's angle is open.

  • • Lens-induced angle closure due to an intumescent or subluxated lens.

    • Malignant glaucoma, especially if intraocular surgery has recently taken place.

    • Other causes of secondary angle closure, with or without pupillary block (see below).

    • Neovascular glaucoma sometimes presents acutely.

    • Inflammatory elevation with an open angle; iridocyclitis/trabeculitis, glaucomatocyclitic crisis (Posner–Schlossman syndrome), scleritis without angle closure.

    • Pigment dispersion.

    • Pseudoexfoliation.

    • Orbital/retro-orbital lesions (e.g. inflammation, retrobulbar haemorrhage).

Pseudoexfoliation

Pigment dispersion

Neovascular glaucoma

Inflammatory glaucoma