Glaucoma

Glaucoma

AQUEOUS HUMOUR

• Normal range of intraocular pressure is 10-21 mm Hg (mean 16 ± 2.5 mm Hg).
• Normal amount of aqueous humour present in the anterior chamber is 0.25 ml and in posterior chamber is 0.06 ml.
• Normal aqueous production rate is about 2.3 µl/ minute.
• Aqueous humour is secreted by non-pigmented epithelium of pars plicata region of the ciliary body.
• Composition of aqueous is similar to plasma except that it has high concentration of ascorbate, pyruvate, and lactate; and low concentration of protein, urea and glucose. Concentration of ascorbate and bicarbonate is high and that of chloride is low in posterior chamber aqueous as compared to that in anterior chamber.
• Mechanisms concerned with aqueous production are diffusion, ultrafiltration and active secretion.
• Trabecular (conventional) outflow of aqueous humour accounts for 90 percent and uveoscleral outflow for 10 percent.

PRIMARY GLAUCOMAS

Primary congenital glaucoma

• In about 40% cases it presents since birth (True congenital glaucoma)
• In about 55% cases it manifests prior to the age of 2 years (Infantile glaucoma)
• In 5% cases it presents between 2 and 10 years of the age (Juvenile glaucoma).
• When it occurs before 3 years of age, eyeball usually enlarges, and so the term buphthalmos is used.

Prevalance and genetics

• Autosomal recessive inheritance with incomplete penetrance
• Affects 1 in 10,000 live births
• Male:female::3:2
• Bilateral in 75% cases

GlaucomaClinical features

• Lacrimation (first symptom), photophobia, blepharospasm and eye rubbing.
• Buphthalmos (occurs with onset before the age of 3 years), characterized by enlarged eyeball, corneal diameter more than 13 mm, corneal oedema (first sign), Haab’s striae (healed splits in Descemet’s membrane), deep anterior chamber, raised IOP, and variable optic disc cupping. Eye becomes myopic.
Gonioscopic examination may reveal: Mesodermal membrane (Barkan’s membrane), thickening of trabecular sheets, hypoplastic iris stroma and insertion of iris above scleral spur.

Treatment

Goniotomy is the surgery of choice (80% success rate).
Trabeculotomy is required when corneal clouding prevents visualization of angle for goniotomy.
Combined trabeculotomy and trabeculectomy (with antifibrotic treatment) is now-a-days the preferred sugery with better results.

Primary open-angle glaucoma (POAG)

Predisposing and risk factors

1. Heredity: POAG has  a polygenic inheritance. The approximate risk of getting disease in siblings is 10 percent and in offspring is about 40 percent.
2. Age: Affects 1 in 200 of population over 40 years of age. Risk increase in 50-70 years of age.
3. High myopes are more predisposed than the emmetropes.
4. Other risk factors include thyrotoxicosis, diabetes mellitus, and cigarette smoking.

Signs

1. IOP changes: Initially there is exaggeration of the normal diurnal variation. A difference of more than 6 mmHg is suspicious and over 8 is diagnostic (normal below 5). In later stages IOP is permanently raised and ranges between 30 and 45 mmHg.

2. Optic disc changes: Normal cup/disc ratio is 0.3. Asymmetry of more than 0.2 between two eyes and/ or notching of the neural rim is suspicious. Marked cupping (0.7 to 0.9) may occur in advanced cases.
• Nasal shift of blood vessels at the disc with appearance of being broken at the margin (Bayoneting sign)
• Increased pallor (area of disc lacking small vessels)
• Haemorrhages on the disc or disc margin
• Glaucomatous optic atrophy (white and deeply excavated disc) is the end result.

3. Visual field defects: These run parallel to the optic disc changes and progress in the following sequence:
• Baring of blind spot (earliest field defect)
• Paracentral scotoma between 10 and 20 degrees of visual field (Bjerrum’s area)
• Seidel’s sign (sickle-shaped extension of blind spot)
• Arcuate or Bjerrum’s scotoma
• Ring or double arcuate scotoma
• Roenne’s central nasal step
• Peripheral nasal step of Roenne’s
• Tubular vision with a temporal island of vision
• Advanced field loss with a temporal island of  vision only
• Complete loss of vision

Ocular associations

High myopia, Fuch’s endothelial dystrophy, retinitis pigmentosa, central retinal vein occlusion and primary retinal detachment.

Diagnosis

1. Established POAG: IOP more than 23 mmHg associated with definite disc cupping and visual field defects.

2. Glaucoma suspect or ocular hypertension. IOP more than 23 mmHg with no disc changes or visual field defects. These cases should be treated as cases of POAG under following circumstances:
• Significant diurnal variation (more than 8 mmHg)
• Significantly positive water drinking provocative test (more than 8 mmHg)
• More than 0.2 asymmetry of cup disc ratio in two eyes.
• Splinter haemorrhages over or near the disc.
• Family history of glaucoma.
• IOP constantly more than 30 mmHg.
• Diabetic and highly myopic patients.

3. Low tension glaucoma (LTG) or Normal tension glaucoma: IOP less than 21 mmHg with typical disc and/or visual field defects.

Primary angle-closure glaucma (PACG)

• It affects 1 in 1000 people over 40 years of age.

Etiology

Predisposing factors

• Hypermetropic eyes with shallow anterior chamber
• Eyes in which iris-lens diaphragm is placed anteriorly
• Eyes with narrow angle of anterior chamber due to small eyeball, relative large crystalline lens or bigger size of the ciliary body.
• Plateau iris configuration
• Sex; Male: Female is 1:4
• Nervous personality with unstable vasomotor system
• Positive family history
• Usually fifth or sixth decade of life

Precipitating factors

• Dim illumination
• Emotional stress
• Use of mydriatics

Clinical stages

1. Latent angle-closure glaucoma or primary angle- closure glaucoma suspect is the term used for the eyes which are anatomically predisposed to angle- closure glaucoma.

2. Subacute (intermittent) angle-closure glaucoma: It is characterised by intermittent attacks of transient rise in IOP, associated with transient blurring of vision, coloured halos around light and mild headache. Once clinically suspected diagnosis is confirmed by prone darkroom provocative test (positive if 8 mm of Hg pressure rise occurs in one hour). Treatment consists of laser iridotomy or surgical peripheral iridectomy.

3. Acute angle closure glaucoma (Acute congestive glaucoma): Sudden rise in IOP occurs due to total angle closure.

Surgical treatment is required after medical control of IOP

• Peripheral iridectomy/laser iridotomy – when peripheral anterior synechiae (PAS) are formed in less than 50 percent of the angle of anterior chamber.
• Filtration surgery (e.g., Trabeculectomy)- when PAS are formed in more than 50 percent of the angle.
• Peripheral Iridectomy/Laser iridotomy should also be considered for the fellow eye.

4. Postcongestive angle-closure glaucoma refers to the clinical status of the eye after an attack of acute PACG. It may be seen in following four clinical settings:
• Post-surgical post-congestive PACG,
• Postcongestive glaucoma with spontaneous angle opening.
• Chronic congestive angle-closure glaucoma, and
• Ciliary body shut down.

5. Chronic angle closure glaucoma – It may develop as a sequelae to sub-repeated subacute attacks (intermittent glaucoma) or due to gradual and progressive (creeping) synechial angle closure.

6. Absolute glaucoma – In this end stage, the eye is painful, completely blind, and IOP is very high.

SECONDARY GLAUCOMAS

1. Lens-induced glaucomas

• Phacomorphic: IOP is raised due to secondary angle closure and/or pupil block by lens intumescence or, anterior subluxation or dislocation of lens or spherophakia.
Phacolytic: An acute secondary open-angle glaucoma due to clogging of trabecular meshwork by macrophages laden with lens proteins in a patient with hypermature cataract.
Lens particle glaucoma: It occurs due to trabecular blockage by the lens particles.
Phacoanaphylactic: It occurs due to sensitisation of eye or its fellow to lens proteins. IOP is raised due to clogging of trabeculae by inflammatory material.

2. Glaucomas due to uveitis

• Non-specific hypertensive uveitis: IOP is raised due to clogging by inflammatory material and associated trabeculitis.
Specific hypertensive uveitis syndromes: These include: Fuch’s uveitis syndrome and glauc- omatocyclitic crisis.
Post-inflammatory glaucoma: It may result from annular synechiae, occlusiopupillae, angle closure following iris bombe formation or angle closure due to organisation of the inflammatory debris.

3. Pigmentary glaucoma

• About 35 percent of patients with pigment dispersion syndrome develop pigmentary glaucoma.
• Bilateral condition, typically affecting young myopic males.
• Glaucomatous features are similar to POAG with associated pigment deposition on corneal endothelium (Krukenberg’s spindle), trabecular meshwork, iris, lens and zonules.

4. Neovascular glaucoma

• It results due to formation of a neovascular membrane involving angle of the anterior chamber.
• Usually, stimulus to new vessel formation is retinal ischaemia as seen in diabetic retinopathy, CRVO, Eales’ disease. Other rare causes are chronic uveitis, intraocular tumours, old retinal detachment, CRAO and retinopathy of prematurity.
• Neovascularisation begins at pupil and spreads centrifugally.
• Management – Panretinal photocoagulation to prevent stimulus to new vessel formation.
– Glaucoma implant (e.g., Moltena tube) operation.
– Cyclocryotherapy.

5. Glaucoma associated with intraocular tumours

Intraocular tumours such as retinoblastoma and malignant melanoma may raise IOP by one or more of the following mechanisms:
• Trabecular block by tumour cells
• Neovascularization of the angle
• Venous stasis following obstruction to vortex veins

6. Pseudoexfoliative glaucoma (Glaucoma capsulare)

• Pseudoexfoliative syndrome (PES) refers to amyloid like deposits on pupillary border, anterior lens surface, posterior surface of iris, zonules and ciliary processes.
• 70 percent cases of PES are associated with raised IOP (secondary open-angle glaucoma).
• Other features and treatment is similar to POAG.

7. Glaucoma in aphakia

It implies association of glaucoma with aphakia.

Causes

• Raised IOP due to postoperative hyphaema, inflammation, vitreous filling the anterior chamber
• Angle closure due to flat anterior chamber
• Pupil block with or without angle closure
• Undiagnosed pre-existing POAG
• Steroid-induced glaucoma
• Epithelial ingrowth
• Aphakic malignant glaucoma.

8. Steroid-induced glaucoma

• Roughly, 5 percent of general population is high steroid responder (develop marked rise of IOP after about 6 weeks of steroid therapy), 35 percent are moderate and 60 percent are non-responders.
Pathogenesis: Probably mucopolysaccharides are deposited .in the trabecular meshwork
• Features are similar to POAG

Management

• Can be prevented by judicious use of steroids.
• IOP may normalise, in 98 percent of cases within 10 days to 4 weeks of discontinuation of steroids.
• Medical therapy with 0.5% timolol maleate is effective during normalization period.
• Filtration surgery is required in intractable cases.

9. Ciliary block glaucoma (Malignant glaucoma)

• It can occur as a complication of any intraocular operation.
• Classically, it occurs following peripheral iridectomy or filtration operation for primary narrow-angle glaucoma.
• Pathogenesis involves cilio-lenticular or cilio- vitreal block.

• Features

– Persistent flat anterior chamber with negative Siedel’s test
– Markedly raised IOP
– May be phakic, aphakic or pseudophakic

• Management:

1. Medical therapy (is useful in about 50 percent cases):

i) Atropine eye drops
ii) Acetazolamide 250 mg TDS
iii) 0.5% Timolol maleate eye drops BD

2 Surgical therapy: Anterior vitrectomy and injection of air in the anterior chamber.

10. Glaucoma associated with intraocular haemorrhage

• Haemolytic glaucoma: Acute open-angle glaucoma which occurs due to obstruction of the trabecular meshwork by macrophages laden with lysed RBC debris after hyphaema.
• Ghost cell glaucoma: It occurs in aphakic eyes with vitreous haemorrhage. RBCs converted into Khaki coloured ghost cells block the trabecular meshwork.
Red cell glaucoma: Caused by blockage ,of trabecular meshwork by RBCs following massive hyphaema.
• Haemosiderotic glaucoma: It occurs due to sclerotic changes in trabecular meshwork induced by iron from the haemoglobin.

11. Glaucoma associated with Iridocorneal- endothelial syndromes (ICE)
• ICE syndromes include progressive iris atrophy. Chandler’s syndrome and Cogan-Reese syndrome.
• IOP is raised due to endothelial membrane lining the trabecular meshwork.

MISCELLANEOUS POINTS

• The commonest hazard following surgery of narrow angle glaucoma is malignant glaucoma.
• The congenital anomaly most commonly associated with buphthalmos is facial haemangiomas.
• Sampaolesi’s line refers to heavy pigment deposition in a line above Schwalbe’s line in the angle of anterior chamber (a feature of exfoliative glaucoma).
• Vogt’s triad includes glaukomflecken (anterior subcapsular lenticular opacity), patches of iris atrophy and slightly dilated non-reacting pupil (due to sphincter atrophy); seen in the eye which has suffered an attack of acute congestive glaucoma.
• Pilocarpine and other miotics are contraindicated in inflammatory glaucoma, malignant glaucoma and glaucoma due to spherophakia.
• The most preferred site for filtering operation is superior nasal quadrant.
• Pilocarpine is the drug of choice for angle closure glaucoma.
• Argon laser trabeculoplasty is only the adjuvant to medical therapy of primary open-angle glaucoma.
• Miotics are not useful in a buphthalmos, aphakic glaucoma, glaucomatocyclitic crisis, glaucoma inversus and in epidemic dropsy glaucoma.
• Secondary glaucoma after perforation of the cornea is due to blockage of the drainage angle by anterior synechiae.
• In an acute-congestive glaucoma, the choice of surgery between peripheral iridectomy and filtering operation is decided by gonioscopic examination.
• The single most important test in diagnosing POAG and response to treatment is visual field testing.
• The earliest and most constant symptom in infantile glaucoma is lacrimation.