Glaucoma Flashcards
What are the parts of the ciliary body?
Pars plicata anteriorly
pars plana posteriorly
Where is aqueous humour produced?
by the ciliary processes of the pars plicata
What are the methods of secretion of the aqueous humour?
- Diffusion: due to a concentration gradient
- ultrafiltration: pressure gradient between oncotic and hydrostatic pressures (capillary verses intraocular pressures)
- Active (account for approx 80% of secretion): active transport is mediated by transmembrane aquaporin activated by Na+ / K+ ATPase enzye and carbonic anhydrase enzyme
how is aqueous humour secretion controlled?
by sympathetic (adrenergic innervation) system
B2 receptor stimulation = increases aqueous secretion and A2 receptor = decreased secretion
What is the composition of aqueous humour?
Water >99% of normal humour
Lower concentration of protein and glucose than plasma
higher concentration of ascorbic acid, chloride and lactate than plasma
similar concentration of sodium to plasma
Describe the different aqueous outflow routes
posterior –> Anterior
- trabecular out flow approx 70-90%%:
TM –> Schelmm’s Canal –> episcleral veins
-Uveoscleral outflow: ciliary muscle –> suprachoroidal space –> eventually drained by choroidal veins, emissary canal of sclera (vortex veins) or veins of ciliary body
What is the trabecular meshwork made up of?
inner –> outer
- uveal meshwork (innermost): contains relatively large holes
- corneosclera meshwork: contains smaller holes, accounting for greater resistance
Juxtacanalicular meshwork - connects the trabecular meshwork with Schlemm canals, contains narrow intercellular spaces supplies major part of the normal outflow resistance
What is Schlemm’s canal?
endothelial lined oval canal
situated circumferentially in the sclera sulcus
contains holes for collector channels which terminate in the episclera veins
What are the two parts of the optic nerve?
Neuroretinal Rim and Cup to Disc Ratio
What is the neuroretinal rim?
area of the optic disc
between margins of central cup and disc
contains retinal neuronal cells
Describe the neuroretinal rim
RIM IS THICKEST INFERIORLY, FOLLOWED BY SUPERIORLY, NASALLY AND THEN TEMPORALLY (‘ISNT’ RULE)
What happens to the neuroretinal rim during glaucoma?
it thins
What is the cup to disc ratio?
DEFINED AS THE VERTICAL DIAMETER OF THE OPTIC CUP DIVIDED BY THE VERTICAL DIAMETER OF THE OPTIC DISC
What is the normal cup to disc ratio?
NORMAL CD RATIO IS 0.3, SOME INDIVIDUALS MAY HAVE PHYSIOLOGICAL CUPPING OF 0.6 OR 0.7 WITHOUT GLAUCOMATOUS CHANGES
What is a trabeculectomy?
TRABECULECTOMY IS AN IOP-LOWERING SURGICAL TECHNIQUE
INVOLVES THE CREATION OF A FISTULA FOR AQUEOUS OUTFLOW FROM THE ANTERIOR CHAMBER TO THE SUB-TENON SPACE, CREATING A BLEB
What can be used to prevent bleb failure in a trabeculectomy?
ADJUNCTIVE USE OF ANTI METABOLITES MAY BE USED TO SLOW THE HEALING PROCESS IN ORDER TO PREVENT BLEB FAILURE
What are some examples of anti metabolites used?
F-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 hypertension?
IOP > 21MMhG WITHOUT GLAUCOMATOUS DAMAGE
What percentage of people with OHT were found to then develop open angle glaucoma?
9.5%
What are the risk factors for conversion of OHTN to Open angle glaucoma?
OLDER AGE
HIGHER IOP
LARGE CUP/DISC RAITO
THINNER CCT: PATIENTS WITH A RELATIVELY THIN CENTRAL CORNEAL THICKNESS HAD 3.4 TIMES HIGHER RISK OF CONVERSION THAN PATIENTS WITH CCT > 558 UM
OTHER RISK FACTORS:
- AFRICAN AMERICAN ORIGIN
- MALES
- HEART DISEASE
What is the management for ocular hypertension?
REGULAR MONITORING
MEDICAL TREATMENT IS INDICATED IN CASES WITH PERSISTENT IOP> 30 OR WITH HIGH-RISK PROFILE PATIENTS
What is primary open angle glaucoma?
CHRONIC DISORDER CHARACTERISED BY GLAUCOMATOUS VISUAL FIELD DEFECTS DUE TO OPTIC NERVE DAMAGE
What genes have the potential to cause POAG?
MYOC AND OPTN GENE MUTATIONS
What are the features of POAG? (4)
OPEN ANTERIOR CHAMBER ANGLE
HIGH C/D RATIO AND THINNING OF THE NEURORETINAL RIM
RAISED IOP > 21mmHg
GLAUCOMATOUS VF DEFECTS
What Ix are used in POAG?
FUNDOSCOPY: EVALULATE OPTIC DISC
GONIOSCOPY: ASSESSMENT OF ANGLE
PACHYMETRY: MEASURE CCT
PERIMETRY: VISUAL FIELD TESTING
What is the management for POAG?
TOPIC IOP-LOWERING AGENTS SUCH AS PRSOTAGLANDIN ANALOGUES OR BETA BLOCKER
LASER TRABECULOPLASTY
TRABECULECTOMY IF FAILURE OF OTHER TREATMENTS
What is normal tension glaucoma?
A FORM OF POAG WITH A PERSISTENLY NORMAL IOP <21mmHg
What did the collaborative normal-tension glaucoma study group find?
reducing IOP by 30% reduced the risk of progression of NTG (12% risk of progression in treated group vs 35% in the untreated group)
What are some risk factors for normal tension glaucoma?
AGE, COMMONLY OLDER PATIENTS WITH POAG
RACE: EAST ASIAN E.G
CCT: COMMONLY LOWER THAN PATIENTS WITH POAG
SYSTEMIC VASCULAR DISEASE: CONDITIONS SUCH AS RAYNAUD PHENOMENON, MIGRAINES AND SYSTEMIC HYPOTENSION ARE MORE ASSOCIATED WITH NTG RATHER THAN POAG
What are some features of normal tension glaucoma?
SIMILAR TO POAG
NOTABLE DIFFERENCES:
- OPTIC NERVE HEAD CAN BE LARGER IN PATIENTS WITH NTG
- FLAME SHAPED HAEMORRHAGES ON OPTIC NERVE RIM ARE MORE COMMON IN NTG
What is primary angle closure glaucoma?
OCCLUSION OF THE TM, CAUSING OBSTRUCTION OF AQUEOUS OUTFLOW WITH THE POTENTIAL OF CAUSING A RISE IN IOP AND OPTIC NERVE DAMAGE
What are some differences between primary angle-closure suspect, primary angle closure and primary angle closure glaucoma?
- PRIMARY ANGLE CLOSURE SUSPECT: A NARROW ANGLE IN WHICH THE PERIPERHAL IRIS IS ALMOST TOUCHING THE TM
NO PERIPERHAL ANTERIOR SYNCHIAE (PAS) PRESENT
(PAS REFERS TO THE ADHERENCE OF THE PERIPHERAL IRIS ANTERIORLY IN THE ANTERIOR CHAMBER) - PRIMARY ANGLE CLOSURE (PAC): PAS+ ELEVATED IOP
HOWEVER, NO GLAUCOMATOUS OPTIC NERVE CHANGES - PRIMARY ANGLE CLOSURE GLAUCOMA: PACG: PAS + ELEVATED IOP + GLAUCOMATOUS CHANGES AND VF DEFECTS
What are some risk factors for primary angle closure glaucoma?
INCREASING AGE
EAST ASIAN RACE
HYPERMETROPIA
FAMILY HISTORY
SHORT AXIAL LENGTH OF THE EYE