The term ‘primary’ is used to describe idiopathic/isolated disease, where no precipitating trigger has been found. The term ‘glaucoma’ is used to describe characteristic optic disc changes alongside visual field defects. Therefore, ‘primary glaucoma’ refers to idiopathic/isolated optic disc changes and corresponding visual field defects. Primary glaucoma is further classified according to the state of the anterior chamber (AC) angle: open or closed.
Primary Open Angle Glaucoma (POAG)
Chronic glaucomatous change due to optic nerve damage with an open anterior chamber angle
Pathology
This is a ‘primary’ disease, meaning there is no identifiable cause of the glaucomatous change
Risk Factors
MYOC and OPTN gene mutations
Steroids
Smoking
Myopia
Afro-Caribbean race
Increasing age
People of Afro-Caribbean origin a more likely to be myopic (longer eyes) and are at risk of open-angle glaucoma, compared to east Asians who are more likely to be hyperopic (shorter eyes) and at risk of angle-closure glaucoma
Diagnostics
Presentation
Asymptomatic at first but will develop visual field defects
Typical presentation is a 60-year-old black myope with a history of vascular risk factors.
Investigations
Tonometry: IOP > 21mmHg
Slit-lamp examination: no signs of precipitating diseases
Gonioscopy: open angle
Fundoscopy: glaucomatous optic disc changes
Perimetry: visual field defects
Management
Treatment aims to control IOP.
Topical IOP lowering medications (1st line)
Topical prostaglandin or beta-blocker (other options are alpha-2 agonists, and carbonic anhydrase inhibitors)
Primary angle-closure glaucoma: ITC + Glaucomatous damage + elevated IOP or PAS or APAC episodes Acute angle-closure of the right eye. By James Heilman, MD, CC BY-SA 3.0
Pathology
Pupil block mechanism (Majority):
Apposition of iris to lens → abnormal aqueous flow through the pupil → increase in the pressure difference between the posterior and anterior chambers → anterior bowing of the peripheral iris leading → peripheral anterior synechiae (PAS) → angle closure → obstructed aqueous outflow → elevated IOP → glaucomatous optic nerve damage
Sudden Pain + blurred vision + nausea + worse in the dark + red eye An eye with acute angle closure. The pupil is irregular and mid dilated. The eye is red and the cornea is hazy. By Jonathan Trobe, M.D., CC BY 3.0, via Wikimedia Commons.
Episodes of APAC or same as APAC but with glaucomatous changes.
A more chronic state of disease
Investigations
Tonometry → IOP>21mmhg
Gonioscopy → closed-angle
A closed-angle on gonioscopy is indicative of angle closure. To diagnose angle-closure glaucoma, you must see glaucomatous optic disc changes and visual field defects
Management
APAC
The aim is to stabilize IOP quickly to prevent blindness
Monitor and consider systemic hyperosmotics (IV mannitol)
Definitive treatment is bilateral peripheral iridotomy, with either ND:YAG laser or surgery.
PACG
The aim is to control IOP over time
Bilateral peripheral iridotomy
The same medication protocol as POAG
Cataract extraction is effective in acute and chronic stages
Peripheral iridotomy is done bilaterally because angle closure in one eye, drastically increases the risk of angle-closure in the fellow eye (other eye).
Primary Congenital Glaucoma
Glaucoma in the first year of life due to malformed anterior chamber angles
Pathology
Mostly sporadic but can be AR
CYP1B1 gene mutation association
Diagnostics
Presentation
Hx: infant boy + haab striae + buphthalmos + large corneal diameter + epiphora
Investigation
Elevated IOP (normal in infants is 10–12 mmHg)
Widened corneal diameter
Management
Angle surgery: Goniotomy if the cornea is clear. If the cornea is cloudy, then trabeculectomy can be attempted.
Normal Tension Glaucoma (NTG)
NTG is POAG with persistently normal IOP (≤21 mmHg).
Pathology
Glaucomatous changes with normal IOP.
Risk factors for progression
Female sex
History of migraine
Disc haemorrhage at diagnosis
Diagnostics
Presentation
Asymptomatic
More common in elderly east Asian females
Symptoms of vascular dysregulation such as migraine, Raynaud's, and low BP.
Investigations
Tonometry → normal IOP
Gonioscopy → open angle
Fundoscopy → optic disc changes
Perimetry → visual field defects
Treatment follows the same protocol as POAG
Tonometry can be falsely low in people with thinner corneas. This can be picked up with pachymetry.
Ocular Hypertension (OHT)
Raised IOP (>21 mmHg) without glaucomatous damage.
Summary
Some OHT patients convert to primary open-angle glaucoma within several years.
