glaucoma Flashcards
where is the ciliary body and what does it produce
pars plicata anteriorly and pars plana posteriorly.
The aqueous humour is formed by the ciliary processes in the pars plicata.
what are the mechanisms of secretion
Diffusion: Due to a concentration gradient.
Ultrafiltration: Pressure gradient between oncotic and hydrostatic pressures (capillary versus intraocular pressures).
Active (∼80%): Active transport is mediated by transmembrane aquaporin activated by Na+/K+ ATPase enzyme and carbonic anhydrase enzyme.
aqueous secretion is innervated by what
sympathetic (adrenergic innervation) system. β2 receptor stimulation increases aqueous secretion
however, α2 receptor stimulation decreases aqueous secretion.
function of the aqueous humour
Supplies essential nutrients for the cornea and lens.
● It fills the anterior chamber (volume of 0.25 mL; tends to become shallower
with age and in people with hypermetropia) and posterior chamber (smaller
than the anterior chamber).
composition of aqeous humor
- Water constitutes >99% of normal aqueous humour.
- Lower concentrations of protein and glucose than plasma.
- Higher concentrations of ascorbic acid, chloride and lactate than plasma.
- Similar concentration of sodium to plasma.
what are the aqeous outflow routes
● Trabecular outflow (∼70%): The conventional aqueous route in the eye going through the trabecular meshwork (TM) and Schlemm’s canal to the episcleral veins.
● Uveoscleral outflow: Aqueous humour passes through the ciliary muscle to the suprachoroidal space and is eventually drained by choroidal veins, emissary canals of the sclera (vortex veins) or veins of the ciliary body.
what are the three parts of the trabecular meshwork
● Uveal meshwork (innermost): Contains relatively large holes.
● Corneoscleral meshwork: Contains smaller holes, accounting for greater
resistance.
● Juxtacanalicular meshwork (outermost): Connects the trabecular meshwork
with the Schlemm canals. It contains narrow intercellular spaces, thus supplying the major part of the normal aqueous outflow resistance.
role of the schlemms canal
endothelial-lined oval canal situated circumferentially in the scleral sulcus. It contains holes for collector channels which terminate in the episcleral veins.
what is the neuroretinal rim
● Refers to the area of the optic disc, between the margins of the central cup and the disc, containing retinal neuronal cells.
● The rim is thickest Inferiorly, followed by Superiorly, Nasally and Temporally (the ‘ISNT rule’).
● During glaucomatous changes, thinning of this neuroretinal rim occurs.
what is cup to disc (C/D) Ratio
● Defined as the vertical diameter of the optic cup divided by the vertical diameter of the optic disc.
● The normal C/D ratio is 0.3. Some individuals may have physiological cupping of 0.6 or 0.7 without glaucomatous changes.
what is trabeculotomy
IOP-lowering surgical technique which involves the creation of a fistula for aqueous outflow from the anterior chamber to the sub-Tenon space, creating a bleb
what may be used to prevent bleb failure and examples of them
use of antimetabolites may be used to slow the healing process in order to prevent bleb failure. Such antimetabolites are:
- 5-fluorouracil (5-FU): A pyrimidine analogue which inhibits fibroblasts by blocking DNA synthesis.
- Mitomycin C: An alkylating agent which also inhibits fibroblasts.
what is ocular HTN
Raised IOP (>21 mmHg)
open angles
without glaucomatous damage.
RFS for ocular HTN goin to glaucoma
● Older age.
● Higher IOP.
● Large cup/disc ratio.
● A thinner CCT: Patients with relatively thin central corneal thickness (CCT)
(≤555 μm) had 3.4 times higher risk of conversion than patients with CCT
>588 μm.
● African American origin, males and heart disease.
- sterioid use
Mx for ocular HTN
● Regular monitoring.
● Medical treatment is indicated in cases with persistent IOP >30 mmHg or
with high-risk profile patients.
what is primary open-angle glaucoma
genetic causes
RFs
chronic disorder characterized by glaucomatous visual field defects due to optic nerve damage.
MYOC and OPTN gene mutations have the potential to cause POAG.
- age >40
- myopia
- Diabetes Mellitus
features
Sx
Signs
of primary open -angle glaucoma
- falling visual acuity
- difficulty moving from bright to dark rooms
● Open anterior chamber angle
● High C/D ratio and thinning of the neuroretinal rim
● Raised IOP (>21 mmHg)
● Glaucomatous VF defects
Ix for primary open-angle glaucoma
● Fundoscopy: Evaluate the optic disc.
● Gonioscopy: Assessment of angle.
● Pachymetry: Measure CCT.
● Perimetry: Visual field testing.
Mx for primary angle glaucoma
● Topical IOP-lowering agents, such as prostaglandin analogues or beta-blockers.
● Laser trabeculoplasty.
- minimally invasive glaucoma surgery
● Trabeculectomy if failure of other treatments.
what is normal tension glaucoma,Ix and Mx
progressive optic neuropathy despite a normal or low IOP
same as primary open-angle glaucoma
RFs of primary normal tension glaucoma
● Age: Commonly older than patients with POAG.
● Race: East Asian (e.g. Japanese).
● CCT: Commonly lower than patients with POAG.
● Systemic vascular disease: Conditions such as Raynaud phenomenon,
migraines and systemic hypotension (use beta-blockers carefully due to their effect on blood pressure) are more associated with NTG rather than POAG.
differences between NTG and POAG
● Optic nerve head can be larger in patients with NTG.
● Flame-shaped haemorrhages on optic nerve rim are more common in NTG. — Drance haemorrhages
what is primary angle-closure glaucoma
iris blocks the TM - 👈obstruction of aqueous flow with the potential of causing a rise in IOP and optic nerve damage.
peripheral anterior synaechiae + elevated IOP + glaucomatous changes adn VF defects
what is Primary angle closure suspect
A narrow angle in which the peripheral iris is almost touching the TM. No peripheral anterior synechiae (PAS) present (PAS refers to the adherence of the peripheral iris anteriorly in the anterior chamber).
What is PAS
peripheral anterior synaechiae + IOP
NO glaucomatous optic nerve changes
RFs of primary angle-closure glaucoma
● Increasing age ● East Asian race ● Hypermetropia ● Family history ● Short axial length of the eye
pathophysiology of primary angle closure glaucoma
● Relative pupillary block
Failure of the normal aqueous flow through the pupil causes an increase in pressure difference between the posterior and anterior chambers = anterior bowing of the peripheral iris (BOMBE) = subsequent TM obstruction
Risk is highest in a mid-dilated pupil due to maximum contact between iris and lens at this level.
● Plateau iris configuration (non-pupillary block): Important pathophysio- logical mechanism in the East Asian descents. Characterized by a flat iris, normal anterior chamber depth and anteriorly positioned ciliary processes which displaces the iris base leading to a narrow/closed angle.
Mx of primary angle-closure glaucoma
● Acute: Supine position - systemic acetazolamide - topical beta-blockers ± alpha-2 agonists ± topical prednisolone.
● Bilateral peripheral Nd: YAG laser iridotomies to be performed after resolution of acute attack.
● Cataract extraction has shown to be effective in lowering IOP in both acute and chronic stages of the disease.
what is neovascular glaucoma
known as 100 day glaucoma
cause of either secondary open- or closed- angle glaucoma.
NVG occurs due to proliferation of fibrovascular tissue in the anterior angle and results from rubeosis iridis
causes if neovascular glaucoma
● Ischaemic central retinal vein occlusion (CRVO) (NVG usually occurs about 3 months after onset of CRVO ‘100-day glaucoma’).
● Central retinal artery occlusion (CRAO).
● Diabetes mellitus.
● Ocular ischaemic syndrome.
● Retinal detachment.
