Glaucoma Flashcards
What are the tunica layers of the eye?
Tunica layers (3):
1) Sclera- fibrous layer, anteriorly continuous with cornea
2) Choroid- vascular layer, continuous with iris and ciliary body
• Cilary body = ciliary muscle + ciliary epithelium
• Ciliary muscle: attaches to lens via zonular fibred.
Cilary muscle contraction -> relaxation of zonluar fibers -> lens bulges out -> greater light refraction -> near accommodation
• Ciliary epithelium: creates aqueous humour
3) Retina- neural layer
Describe the anatomical segments of the eyeball?
Eyeball segments (2):
1) Anterior segment- in front of lens, contains aqueous humour (both chambers)
• Anterior chamber: between cornea and iris
• Posterior chamber: between iris and lens
• Angle between cornea and iris = iridocorneal angle
2) Posterior segment- behind lens, contains vitreous humour
Describe the physiology of aqueous humour production and outflow?
- Produced: ciliary epithelium of ciliary body
- Normal IOP: 12-22mmHg
Outflow via conventional trabecular path OR uvesceral outflow:
1) Conventional trabecular outflow (90%)
⇒ Travels between iris and lens in posterior chamber
⇒ Through the pupil into anterior chamber
⇒ Drains into trabecular meshwork (at angle between cornea and iris)
⇒ Canal of Schlemm -> aqueous veins -> episcleral veins
2) Uvescleral outflow (10%)
⇒ Travels straight through ciliary muscle
⇒ Scleral surface
What is the pathophysiology of glaucoma? Name the subtypes.
Glaucoma: a group of eye diseases resulting in optic nerve damage and vision loss
• Path:
⇒ Blockage of trabecular drainage system
⇒ Build up of aqueous humour in anterior chamber
⇒ Pressure transmits to posterior segment
⇒ Intraocular HTN
⇒ Optic nerve damage
Types of glaucoma:
- open angle glaucoma
- closed angle glaucoma
- normal tension glaucoma
- secondary glaucoma
Describe open-angle glaucoma?
Open-angle glaucoma (90%)
• Path: impaired drainage of aqueous humour through trabecular meshwork OR excessive aqueous humour production
- normal angle between cornea and iris
• Increased IOP -> optic nerve damage -> vision loss
• Clinical: painless, progressive vision loss (peripheral then central), no other symptoms (so often detected late)
• Risk factors: age >55yo, Caucasian, FMHx
Describe closed-angle glaucoma?
Closed-angle glaucoma (10%)
• Path: narrow angle between cornea and iris
⇒ Iris comes into contact with lens
⇒ Depending on extent of angle closure
-> reduced/complete obstruction of outflow of aqueous humour intor anterior chamber of eye AND any fluid entering anterior chamber unable to drain out through trabecular meshwork (due to complete obstruction by iris)
⇒ Raised IOP -> optic nerve damage
• Clinical: acute or chronic
o Acute- pupillary dilatation (pupillary block) -> lens pushes against iris and obstructs flow into anterior chamber -> surg emergency
- presents with severe eye pain, eye redness, mild pupil dilation, blurred vision, nausea/vomiting
• Risk factors: >60yo, Asian, far-sighted, FMHx
What is normal tension glaucoma?
Normal tension glaucoma
• Path: vascular compromise to optic nerve (assoc DM, metabolic syndromes) -> optic nerve damage
- nil increase IOP, normal iridocorneal angle, nil impaired aqueous humour drainage
• Rx: same as other glaucomas
What is secondary glaucoma?
Secondary glaucoma • Diabetes-related neovascularization • Trauma (e.g. post-surgical) • Drug-induced (e.g. corticosteroids) • Uveitis
List some risk factors for open-angle glaucoma?
Strongest evidence: o Intraocular HTN (note: 30% glaucoma has normal IOP) o FMHx o Age >55yo o Race (African descent) Less evidence: o Myopia o DM o HTN o Migraine
What investigations would you order for open angle glaucoma?
1) Tonometry- measures IOP
- screening tool for glaucoma risk
(note: 30% glaucoma has normal IOP)
2) Fundoscopy- measures cup to disc ratio (normal <0.3)
- assesses optic nerve damage
3) Gonioscopy- measures angle between iris and cornea
- differentiates between open and close angled glaucoma
4) Perimetry- assesses corneal thickness
5) Pachymetry- assesses visual fields
6) Optic coherence tomography (OCT) and retinal nerve fibre layer
- measures retina thickness to detection glaucoma progression and monitor treatment
Describe the treatment regime for open-angle glaucoma?
1) First line:
o Prostaglandin analogues (e.g. Lantaprost)
2) Second line:
o Alpha-2 agonist (Bromonide, Apraclonide)
o Carbonic anhydrase inhibitors (Dorzolomide)
o Non-selective B-blocker (Timolol)
3) Third line:
o Cholinergics (Pilocarpine, Carbachol)
Describe the indications, MAO and SE of prostaglandin analogues? Name an example.
E.g. Lantaprost (topical)
• MA: increasing the sclera’s permeability to aqueous humour -> promotes uveoscleral outflow
• Indications: chronic open angle glauma, ocular HTN
• SE:
- ocular (conjunctival hypaeraemia, foreign body sensation, eyelash lengthening, iris hyperpigmentation)
- systemic (headache, flu-like symptoms, chest pain, rash, MSK pain, asthma)
Describe the indications, MAO and SE of alpha-2 agonists? Name an example.
E.g. Brimonidine, Apraclonidine (topical)
• MA: promotes noradrenaline reuptake -> reducing sympathetic effect -> decreases production of aqueous humour and increases uveoscleral outflow
• SE: high allergy rate, conjunctival blanching, stinging, lid retraction, pupil dilation
• CI: pregnancy, children (central hypotension), MAOI
Describe the indications, MAO and SE of carbonic anhyrase inhibitors? Name an example.
E.g. Dorzolomide (topical)
• MA: decreasing bicarbonate production by ciliary epithelium
-> reduces humour production
• Indications: acute angle closure, chronic angle closure (treatment resistant)
• SE:
- ocular (allergical blepharoconjunctivitis)
- systemic (bitter metallic taste, anorexia, depression, short-lasting diuresis, kidney stones, UEC derangement, hypokalaemia, GI upset)
• CI: hepatic or renal failure, metabolic acidosis
Describe the indications, MAO and SE of non-selective B-blockers? Name an example.
E.g. Timolol (topical)
- note: used in combination w other agents
• MA: inhibits cAMP in ciliary epithelium -> reduces aqueous humour production
- very potent B-blocker
• Indications: chronic open angle glaucoma, ocular HTN
• SE: ocular (ocassional allergy, reduced tear production), systemic (brachycardia, hypotension, bronchospasm, lethargy, sleep disturbance, depression, reduced libido, reduced exercise tolerance)
• CI: asthma, severe COPD, bradycardia, do not add to system B-blocker
