Primary open-angle glaucoma

What is glaucoma?

Glaucoma refers to a group of eye conditions that lead to damage to the optic nerve head, with progressive loss of retinal ganglion cells and their axons. This leads to a progressive loss of visual field. There are typical optic nerve changes on slit-lamp examination. Glaucoma is usually associated with an intraocular pressure (IOP) above the normal range. However:

• 20-52% (this varies between populations) of patients with glaucoma have intraocular pressure within the normal range. Patients with normal intraocular pressure who develop the characteristic changes associated with open-angle glaucoma are said to have low-tension or normal-pressure glaucoma.

• Many patients have raised IOP for years without developing the changes of glaucoma. This condition is referred to as ocular hypertension.

Prior to 1978, glaucoma was defined as intraocular pressure above 21 mm Hg in an eye (the normal range is considered to be 10-21 mm Hg with 14 being the average). More recently glaucoma has been understood as an abnormal physiology in the optic nerve head that interacts with the IOP, with the degree and rate of damage relating to both factors¹ .

Types of glaucoma

There are several glaucoma subtypes, although all are considered optic neuropathies.

• Glaucoma may be primary or secondary to other conditions.

• Glaucoma may be open-angle or closed-angle.

• Glaucoma may be acute, acute-on-chronic, intermittent or chronic.

• The end stage of glaucoma is referred to as absolute glaucoma. There is no functioning vision, the pupillary reflex is lost and the eye has a stony appearance. The condition is very painful .

Other separate articles that you may find relevant are Glaucoma and Ocular Hypertension, Angle-closure Glaucoma and Congenital Primary Glaucoma.

What is primary open-angle glaucoma?¹

Primary open-angle glaucoma (POAG) is a progressive, chronic condition characterised by:

• Adult onset.

• IOP at some point greater than 21 mm Hg (normal range: about 10-21 mm Hg).

• An open iridocorneal angle (between the iris and the cornea, where the aqueous flows out).

• Glaucomatous optic neuropathy.

• Visual field loss compatible with nerve fibre damage.

• Absence of an underlying cause.

• Being usually bilateral.

Pathophysiology²

The underlying problem in primary open-angle glaucoma is disease of the optic nerve. The pathophysiology is not fully understood but genetic factors have been identified. There is a progressive loss of retinal ganglion cells and their axons. In its early stages it affects peripheral visual field only but as it advances it affects central vision and results in loss of visual acuity, which can lead to severe sight impairment and complete loss of vision.

For most types of glaucoma, optic neuropathy is associated with a raised intraocular pressure. This has given rise to the hypothesis of retinal ganglion apoptosis, whose rate is influenced by the hydrostatic pressure on the optic nerve head and by compromise of the local microvasculature. The resulting optic neuropathy gives rise to the characteristic optic disc changes and visual field loss.

In primary open-angle glaucoma, flow is reduced through the trabecular meshwork (whose role is absorbing aqueous humour). This is a chronic degenerative obstruction which occurs painlessly.

The intraocular pressure is not always raised: in normal-tension glaucoma (NTG), IOP is in the normal range, which has led to other theories, including vascular perfusion problems or an autoimmune component. Others have postulated that the optic nerve head is particularly sensitive in these patients, with damage occurring at much lower IOPs than in normal individuals. This could explain why these patients benefit from IOP-lowering medication³ .

Epidemiology^{4 5}

• This is the most common form of glaucoma.

• Approximately 1-2% of the population aged over 40 are affected but about half are unaware of this.

• Prevalence increases with age, affecting about 8% of people aged over 80.

• It is responsible for 10-12% of all cases of registrations for severe visual impairment in the UK.

Risk factors for primary open-angle glaucoma¹

• Age - the incidence increases with age, most commonly presenting after the age of 65 (and rarely before the age of 40).

• Family history - there is a clear inherited component in many individuals (IOP, aqueous outflow facilities and disc size are inherited characteristics). However, it is thought that there is incomplete penetrance and variable expressivity of the genes involved. There are also several factors thought to contribute to the inheritance, and therefore the risk to relatives is currently only an estimate: 4% to children and 10% to siblings of an affected individual.

• Race - it is three to four times more common in Afro-Caribbean people in whom it tends to present earlier and is more severe.

• Ocular hypertension - this is a major risk factor for the development of glaucoma with about 9% of patients developing glaucoma over five years if left untreated⁶ .

• Other factors - myopia (short-sightedness) and retinal disease (eg, central retinal vein occlusion, retinal detachment and retinitis pigmentosa) can predispose individuals to primary open-angle glaucoma. Diabetes and systemic hypertension (and possibly also systolic hypotension) may also contribute to risk.

Primary open-angle glaucoma symptoms

Unfortunately, in the vast majority of cases of primary open-angle glaucoma, patients are asymptomatic. Because initial visual loss is to peripheral vision and the field of vision is covered by the other eye, patients do not notice visual loss until severe and permanent damage has occurred, often impacting on central (foveal) vision. By then, up to 90% of the optic nerve fibres may have been irreversibly damaged⁴ .

Primary open-angle glaucoma may be detected on checking the IOPs and visual fields of those with affected relatives. Suspicion may arise during the course of a routine eye check by an optician or GP, where abnormal discs, IOPs or visual fields may be noted.

Examination of primary open-angle glaucoma

An ophthalmologist will examine the eye thoroughly for evidence of glaucoma, comorbidity or an alternative diagnosis to the apparent findings. The details of a glaucoma assessment can be summarised as:

Before referral for further investigation and diagnosis of primary open-angle glaucoma and related conditions, patients should be offered the following in addition to a sight test:

• Central visual field assessment using standard automated perimetry (full threshold or supra-threshold). Visual field assessment requires the co-operation of the patient and can also be affected by fatigue, spectacle frames, miosis and media opacities. See also the separate Visual Field Defects article.

• Optic nerve assessment and fundus examination using stereoscopic slit-lamp biomicroscopy (with pupil dilatation if necessary), with optical coherence tomography (OCT) or optic nerve head image if available. Optic disc examination is a direct marker of disease progression. Optic disc damage is assessed by looking at the cup:disc ratio: normal is 0.3, although it can be up to 0.7 in some normal people:

  • Glaucoma is suggested by an increase in cupping with time, rather than by cupping alone. Marked but stable cupping may be hereditary.

  • The intra-observer variability in optic disc evaluation has been reduced by use of ocular coherence tomography (OCT), which produces excellent visual records and provides quantification of exact cup:disc ratio and areas of neuroretinal thinning.

• Intraocular pressure (IOP) measurement using Goldmann-type applanation tonometry. Tonometry is the objective measurement of IOP, usually based on the assessment of resistance of the cornea to indent. The normal range is considered to be 10 mm Hg to 21 mm Hg. (A decision to refer should not be based solely on IOP measurement using non-contact tonometry.)

• Peripheral anterior chamber configuration and depth assessments using gonioscopy or, if not available or the person prefers, the van Herick test or OCT. Gonioscopy measures the angle between the cornea and the iris to assess whether the glaucoma is open-angle or closed-angle.

National Institute for Health and Care Excellence (NICE) guidance states that at diagnosis all people with chronic open-angle glaucoma (COAG), suspected chronic open-angle glaucoma or ocular hypertension (OHT) should have⁴ :

• Visual field assessment using standard automated perimetry (central thresholding test), repeated if necessary to establish severity at diagnosis.

• Optic nerve assessment and fundus examination using stereoscopic slit-lamp biomicroscopy, with pupil dilatation.

• IOP measurement using Goldmann applanation tonometry (slit lamp mounted).

• Peripheral anterior chamber configuration and depth assessments using gonioscopy or, if not available or the person prefers, the van Herick test or OCT. The van Herick test involves comparing the depth of the peripheral anterior chamber to the thickness of the cornea, when a narrow beam is shone within the limbus at a 60° angle.

• Central corneal thickness (CCT) measurement.

NICE⁴ states that at each visit the following should be available:

• Records of all previous tests.

• Records of past medical history.

• Current medication list (systemic and topical).

• Glaucoma medication record.

• Allergies and intolerances.

For people with ocular hypertension, NICE⁴ recommends that risk of future visual impairment should be assessed, taking into account:

• Level of IOP.

• Central corneal thickness measurement.

• Family history.

• Life expectancy.

Referral⁴

NICE guidance offers recommendations for referral to secondary care services:

• Before deciding to refer, consider repeating visual field assessment and IOP measurement on another occasion to confirm a visual field defect or IOP of 24 mm Hg or more, unless clinical circumstances indicate urgent or emergency referral is needed.

• Refer for further investigation and diagnosis of open-angle glaucoma and related conditions, after considering repeat measures as above, if:

  • There is optic nerve head damage on stereoscopic slit-lamp biomicroscopy; or

  • There is a visual field defect consistent with glaucoma; or

  • IOP is 24 mm Hg or more using Goldmann-type applanation tonometry.

• Provide results of all examinations and tests with the referral.

• Advise people with IOP below 24 mm Hg to continue regular visits to their primary eyecare professional.

These referral guidelines apply to opticians who are equipped to monitor intraocular pressure and perimetry. GPs, unless they have a secondary speciality in ophthalmology, are unlikely to manage these patients alone⁴ .

Grading of primary open-angle glaucoma

Several staging systems have been developed over the years but while they may be of interest in scientific studies, they are of limited value in clinical management. Most systems currently in clinical use are modifications of the Hodapp-Parrish classification⁷ .

Broadly, glaucoma can be clinically classified as² :

• Mild - early visual field defects.

• Moderate - presence of an arcuate scotoma ('n'-shaped visual field loss arching over the central visual field) and thinning of neuroretinal rim (cupping).

• Severe - extensive visual field loss and marked thinning of the neuroretinal rim.

• End-stage - only a small residual visual field remains. There may be very little neuroretinal rim remaining (cup:disc ratio would be in the region of 0.9-1.0).

Treatment and management of primary open-angle glaucoma^{4 8 9}

Treatment aims^{4 10}

For people with ocular hypertension, assessment of the risk of developing problems with visual acuity should be considered before starting treatment (see Examination section, above).

For people with open-angle glaucoma, treatment is not necessarily started immediately on simple detection of an elevated intraocular pressure. Given the potential for variation of findings from one assessment to the next, the patient should be assessed on several occasions unless the findings are unequivocal - the diagnosis is significant and treatment is usually lifelong. Apparent disc cupping is considered in conjunction with visual fields and IOP. In some patients, the disease is obvious and advanced, in which case treatment should start promptly.

• Once a diagnosis and decision to treat have been made, a target IOP is set according to the degree of damage: this is the pressure below which further damage is considered unlikely. This is usually in the region of a 30% drop of IOP. It differs between patients and may be different in each eye.

• Regular monitoring to assess intraocular pressure, the optic disc and the visual fields. Some areas have schemes whereby trained opticians carry out all the monitoring.

• Patient education is essential, as this is a largely asymptomatic condition until it is very advanced, and medication compliance is often poor. Patients need to understand the irreversible nature of the disease, how to take drops correctly and their potential side-effects. They also need to be advised of the risk to other family members.

In 2022, NICE updated its guidelines to recommend that 360° selective laser trabeculoplasty (SLT) should be the first treatment of choice in appropriate patients with ocular hypertension and newly diagnosed open-angle glaucoma. For patients with advanced open angle-glaucoma, they recommend glaucoma surgery with pharmacological augmentation as indicated.

Initial treatment of ocular hypertension

NICE recommends the following:

• Offer 360° selective laser trabeculoplasty (SLT) to people with newly diagnosed ocular hypertension with IOP of 24 mm Hg or more (excluding cases associated with pigment dispersion syndrome) if they are at risk of visual impairment within their lifetime, taking into account the factors above.

• To help inform the patient's decision, the following should be discussed:

  • The fact that 360° SLT can delay the need for eye drops and can reduce but does not remove the chance they will be needed at all.

  • The likely timeframe for improvement of IOP after the procedure.

  • The side-effects and complications of 360° SLT.

  • The fact that a second 360° SLT procedure may be needed at a later date.

• A generic prostaglandin analogue (PGA) should be offered to people with ocular hypertension with IOP of 24 mm Hg or more if they are at risk of visual impairment within their lifetime and:

  • They choose not to have 360° SLT; or

  • 360° SLT is not suitable (for example, because they have pigment dispersion syndrome); or

  • As an interim measure for patients awaiting 360° SLT who need an interim treatment; or

  • They have had 360° SLT but need additional treatment to reduce their IOP sufficiently to prevent the risk of visual impairment.

Ongoing treatment of ocular hypertension^{4 8}

Offer another pharmacological treatment to people with an intraocular pressure of 24 mm Hg or more who are intolerant of current treatment. The first choice should be an alternative generic PGA, if available. If this is not tolerated, offer a beta‑blocker. If none of these options is tolerated, offer non-generic PGA, carbonic anhydrase inhibitors, sympathomimetics, miotics or a combination of treatments if IOP is 24 mm Hg or more and current treatment is not reducing IOP enough to reduce the risk of progression to sight loss.

Topical medicines from different therapeutic classes may be needed at the same time to control IOP. Refer people to a consultant ophthalmologist to discuss other options if their IOP cannot be reduced sufficiently with 360° SLT or pharmacological treatment or both to prevent the risk of progression to sight loss.

Note that for some drugs (eg, some generic PGAs and carbonic anhydrase inhibitors) this is an off-label use. Check with the British National Formulary¹¹ .

For people who have an allergy to preservatives or have clinically significant and symptomatic ocular surface disease, offer preservative-free eye drops, but only if they are at high risk of conversion to chronic open-angle glaucoma.

Treatment of chronic open-angle glaucoma
Do not offer treatment to people with suspected chronic open-angle glaucoma and IOP less than 24 mm Hg unless they are at risk of visual impairment within their lifetime. Advise them to continue regular visits to their primary eye care professional, at clinically appropriate intervals.

For people with advanced chronic open-angle glaucoma, offer glaucoma surgery with pharmacological augmentation (mitomycin C - an antimetabolite used during the initial stages of trabeculectomy to prevent excessive postoperative scarring and therefore reduce the risk of failure) as indicated.

Patients with advanced open-angle glaucoma should be given information on the risks and benefits of surgery. These patients should be offered interim treatment with a generic PGA while awaiting surgery.

NICE recommends offering 360° SLT to people with newly diagnosed chronic open-angle glaucoma, with exclusion criteria and additional recommendations to inform decision-making as for ocular hypertension above. A second 360° SLT should be considered for people with chronic open-angle glaucoma if the effect of an initial successful SLT subsequently reduces over time.

A generic PGA should be offered to people with COAG if:

• They choose not to have 360° SLT; or

• 360° SLT is not suitable (for example, because they have pigment dispersion syndrome); or

• As an interim measure for patients awaiting 360° SLT who need an interim treatment; or

• They have had 360° SLT but need additional treatment to reduce their IOP sufficiently to prevent the risk of visual impairment.

Correct eye drop installation technique demonstration should be provided, along with observation of the patient using the technique when eye drops are first prescribed.

Patients should be encouraged to continue with the same pharmacological treatment unless:

• Their IOP cannot be reduced sufficiently to prevent the risk of progression to sight loss.

• There is progression of optic nerve head damage.

• There is progression of visual field defect.

• They cannot tolerate the medicine.

It may be necessary to add drugs from another class (eg, beta-blockers, sympathomimetics, or carbonic anhydrase inhibitors) to control intraocular pressure. Generally, drugs are initiated one at a time. Treatment may be to one or both eyes.

If treatment with medicines from 2 therapeutic classes is inadequate to control IOP, consider 360° SLT or glaucoma surgery with pharmacological augmentation with mitomycin C as indicated.

• Prostaglandin analogues:
  

  • Action: increase aqueous outflow via the uveoscleral route.

  • Contra-indications: active uveitis, pregnancy and breastfeeding.

  • Caution: brittle or severe asthma, aphakia (patient with no lens), pseudophakia (patient with artificial lens); do not take within five minutes of using thiomersal-containing preparations.

  • Common ocular side-effects: change in eye colour: brown pigmentation, thickening and lengthening of eye lashes; more rarely: uveitis, ocular pruritus, photophobia and keratitis.

  • Systemic side-effects: rarely - hypotension, bradycardia.

• Beta-blockers:
  

  • Action: reduce aqueous secretion by inhibiting beta-adrenoceptors on the ciliary body.

  • Contra-indications: bradycardia, heart block, uncontrolled heart failure, asthma and history of chronic obstructive pulmonary disease (COPD).

  • Caution: depression, myasthenia gravis, possible interactions with other medication such as verapamil.

  • Common ocular side-effects: irritation, erythema, dry eyes, blepharo-conjunctivitis and allergy anaphylactic reaction possible.

  • Common systemic side-effects: bronchospasm, bradycardia, exacerbation of heart failure, nightmares.

• Carbonic anhydrase inhibitors:
  

  • Action: reduce aqueous secretion by ciliary body. Weak systemic diuresis when given orally.

  • Contra-indications: renal impairment, metabolite imbalance, severe hepatic impairment, sulfonamide sensitivity (acetazolamide), breastfeeding.

  • Caution: elderly, hepatic impairment, history of renal calculi, history of intraocular surgery, pregnancy and breastfeeding. Extravasation at infusion site of intravenous acetazolamide can cause necrosis.

  • Ocular side-effects: localised discomfort, lacrimation, topical allergy; more rarely: superficial punctate keratitis, uveitis, transient myopia.

  • Systemic side-effects: (particularly with systemic administration), taste disturbance, nausea/vomiting, headache, dizziness, fatigue, paraesthesia and sulfonamide-related side-effects.

• Sympathomimetics:
  

  • Action: reduce aqueous secretion and increase outflow through trabecular meshwork.

  • Contra-indications: angle-closure glaucoma (due to mydriatic effects), patients currently taking monoamine-oxidase inhibitors (possibility of hypertensive crisis).

  • Caution: hypertension, heart disease.

  • Common ocular side-effects: mydriasis, dry eye, severe smarting and redness of the eye.

  • Common systemic side-effects: lethargy, hypotension.

• Miotics:
  

  • Action: open up the drainage channels in the trabecular meshwork by ciliary muscle contraction.

  • Contra-indications: situations where pupillary constriction is undesirable (such as uveitis), presence of retinal holes.

  • Caution: darkly pigmented irides require higher concentrations but overdosage must be avoided, patients with retinal disease (especially previous detachment), cardiac disease, hypertension, asthma, peptic ulceration, urinary tract obstruction and Parkinson's disease.

  • Ocular side-effects: miosis - this can cause blurred vision which can affect driving and other skilled tasks, especially in the presence of a cataract. Accommodative spasm with brow ache (often causing intolerance in patients over 40), localised discomfort, pupillary block.

  • Systemic side-effects: sweating, bradycardia, gastrointestinal disturbance.

Laser treatment for open-angle glaucoma¹²

• Selective laser trabeculoplasty (SLT) - uses a laser at very low intensity, treating specific areas and leaving parts of the trabecular meshwork intact. It therefore, unlike argon laser trabeculoplasty, preserves the trabecular meshwork architecture and can be repeated.

• Cyclodiode laser trabeculoplasty - similar principle as above, using a higher laser power. This is often used in refractory cases and for relief of pain in end-stage glaucoma. However, a Cochrane review found that further research was needed to establish whether or not this method was more effective compared to other treatment options¹³ .

• Nd:YAG laser iridotomy - usually reserved for angle-closure glaucoma, a small hole is made in the iris in patients with angle-closure glaucoma, to enhance aqueous outflow.

• Diode laser cycloablation - part of the secretory component of the ciliary body is destroyed, so reducing aqueous secretion. This is used in intractable end-stage glaucoma.

Surgical therapy for primary open-angle glaucoma

A Cochrane review found that primary surgery lowers intraocular pressure more than primary medication but is associated with more eye discomfort. One trial suggested that visual field restriction at five years is not significantly different whether initial treatment is medication or trabeculectomy⁹ . However, the Cochrane review did not include recent trials that evaluated currently available drugs for glaucoma or modern surgical methods.

• Trabeculectomy. This procedure creates a fistula between the anterior chamber of the eye and the sub-Tenon space (immediately around the globe), so allowing aqueous outflow. Adjunctive antimetabolites such as mitomycin C may be used to prevent scarring over of the fistula. A deep sclerectomy is a variation of this procedure¹⁴ .

• Artificial shunts in the form of plastic devices connecting the anterior chamber to the sub-Tenon space can be inserted but are associated with many postoperative complications.

• New techniques and devices are being developed to minimise the complications of laser and surgical treatment. Examples include:
  

  • Canaloplasty whereby Schlemm's canal is artificially widened with a temporary tube and viscoelastic. Canaloplasty is not currently recommended by NICE¹⁵ .

  • Trabecular stent bypass microsurgery aims to reduce IOP by creating a bypass channel between the anterior chamber and Schlemm's canal to improve drainage. NICE states that, although there is evidence of short-term efficacy, this is based only on a small number of patients¹⁶ .

  • Trabeculotomy ab interno for open-angle glaucoma aims to reduce IOP by removing a portion of the trabecular meshwork to improve drainage. It avoids creation of the subconjunctival bleb associated with traditional trabeculectomy. NICE states that the current evidence on the safety and efficacy of trabeculotomy ab interno for open-angle glaucoma is adequate to support the use of this procedure¹⁷ .

Driving and glaucoma

A visual field defect counts as a 'relevant disability' (as opposed to the 'absolute disability' of a reduced visual acuity) in law. There are certain criteria set out and assessed by the Driver and Vehicle Licensing Agency (DVLA)¹⁸ .

The onus is on the patient to inform the DVLA (and it is important to document that you have advised them of this). It is the DVLA (and approved opticians) who will assess the visual fields and decide whether a patient can continue to drive. If you are concerned that the patient should not drive and has not told the DVLA (despite your clear advice to do so), it may be appropriate to inform the DVLA medical advisors. You will be breaching confidentiality in the public interest. If doing so you should inform the patient of your intentions and are best advised to liaise with your defence union to make sure that you have exhausted all other options and that in doing so your action is proportionate and defensible.

Complications

• Treatment side-effects - see 'Ongoing treatment of ocular hypertension'', above.

• Non-compliance - patient education and clear explanation of the risks, together with clear instructions on how to take medication, will reduce non-compliance.

• Steroid responsiveness - topical (to the eye) steroids have the potential to affect IOP in the long term (systemic steroids are generally less likely to do so). Broadly speaking, the population can be divided into three groups according to their IOP response to a six-week course of steroids¹⁹ :
  

  • High responders - they show a marked elevation (>30 mm Hg). This occurs in 5% of the general population but in 90% of the primary open-angle glaucoma population (and in 30% of their siblings and 25% of their offspring).

  • Moderate responders - 35% of the general population will show a modest elevation in IOP (22 mm Hg to 30 mm Hg), the figure dropping to 10% in primary open-angle glaucoma patients (and in 50% of their siblings and 70% of their offspring).

  • Non-responders - 60% of the population fall into this group. There are no primary open-angle glaucoma patients in this group (but 20% of their siblings and 5% of their offspring).

Prognosis

Unless treated, chronic open-angle glaucoma is progressive. Treatment aims to stall this progression but cannot reverse it. However, if treatment is timely, appropriate and maintained, useful vision can be expected to be maintained throughout the patient's lifetime.

Factors involved in more rapid progression include myopia, the presence of optic disc haemorrhages, vascular factors and genetic factors. Although there is not an associated mortality per se, studies have shown cardiovascular mortality tending to increase in people of African ethnicity with previously diagnosed/treated POAG and ocular hypertension^{20 21} .

Prevention⁴

Primary open-angle glaucoma cannot be prevented but its progression can be slowed if it is detected and treated. By and large, the patient will not notice symptoms relating to POAG until the visual field changes are very advanced, at which point very little can be done. For this reason, screening remains the only tool for detection, with shared care between optometrists and ophthalmologists underpinning the detection and management. It should involve tonometry (measuring the IOP), visual fields and an examination of the optic disc.

Where there is no family history, opportunistic screening can be performed (ideally every two years) when the patient goes for a routine visit to their optician. From the age of 65 this should be carried out yearly.

In patients with a first-degree relative with POAG, a full specialist optician or ophthalmologist review should be carried out at the age of 40, with further screening every two years until the age of 50, and yearly thereafter. Shorter inter-screening intervals are recommended for patients with raised IOPs and patients considered otherwise at risk of primary open-angle glaucoma.

Laser peripheral iridotomy was mooted as being a possible option for the prevention of POAG²² . However, a randomised controlled trial of 889 bilateral primary angle closure suspects aged 50-70 years has compared the impact of laser peripheral iridotomy in one randomly selected eye, with the other remaining untreated. Over a 72-month follow-up period, there were 19 episodes of acute angle-closure glaucoma in treated eyes compared to 36 in untreated eyes. Although the 47% relative risk reduction reached statistical significance, the low incidence of events in untreated eyes (0·97 per 1,000 eye-years in untreated eyes) led the authors to conclude that the benefit of prophylactic laser peripheral iridotomy is limited and that its widespread introduction cannot be recommended.

Dr Mary Lowth is an author or the original author of this leaflet.