Week 4: Anterior Chamber Angle

Question 1

What is Lacrimal Patency?

Answer 1

• Making sure that tears are flowing correctly and the pathways is open (unblocked)
  Jones 1 test doesn’t tell us the location of the blockage

Question 2

What is sjogren’s syndrome?

Answer 2

Sjogren’s Syndrome
- Autoimmune disorder in which causes dry eye and dry mouth
- cause gland damage
Schirmer’s test is suited because it irritated the eye

Question 3

What is the function of the Aqueous Humor?

Answer 3

§ Constancy of globe shape
§ Nourish avascular cornea and lens
§ Contributes to optical function of eye

Question 4

What are the two mechanism for Aqueous Humor?

Answer 4

○ 80% - active secretion - by the non pigmented layer of the ciliary epithelium - independent of IOPS

○ 20 % - Passive secretion - produced by diffusion and ultrafiltration (affected by blood pressure, and IOP)

Question 5

What is the structures of the Anterior Chamber Angle (Posterior to Anterior)?

Answer 5

Ciliary body band
Scleral Spur
Pigmented trabecular meshwork 
Non - pigmented trabecular meshwork
Schwalbe's line

Question 6

What is the structures of the Anterior Chamber Angle (Anterior to Posterior)?

Answer 6

Schwalbe's line
Non-pigmented trabecular meshwork 
Pigmented trabecular meshwork 
Scleral Spur
Ciliary body band

Question 7

What are the 3 layers of the Trabecular Meshwork?

Answer 7

Uveal meshwork (inner) 
Corneo - Scleral Meshwork ( central ) 
Juxtacanalicular tissue (outer, cribriform)

Question 8

Describe the Uveal Meshwork

Answer 8

a. Large pores exists between tissue and lamellae
b. Contributes little resistance to outflow

Most variable between eyes

Question 9

Describe Corneo-scleral meshwork

Answer 9

a. Constructed from 10 - 15 perforated collagenous sheets suspended between Schwalbe’s line and ciliary muscle
b. Outer layer arise from scleral spur

c. Inner layer arise from ciliary muscle fibre insertions

Question 10

Describe the Juxtacanalicular tissue?

Answer 10

a. Outermost portion of the trabecular meshwork
b. Lies between Schlemm’s canal and the outer lamella of corneoscleral meshwork
c. Outer aspect formed by endothelial cells which line the inner wall of Schlemms’ Canal

d. Principle site of aqueous outflow resistance

Question 11

Describe Schlemm’s Canal

Answer 11

• Circular vessel considered to be a venous channel for aqueous drainage
  
  • Lies parallel to and continuous with the outer aspect of the trabecular meshwork
  • Ovoid in cross section
  • Outer wall is perforated by 30 - 35 collector channels draining to intrascleral venous plexus

Question 12

What are some substances found in the aqueous humor?

Answer 12

Electrolytes, ascorbic acid, sugars, sodium chloride, oxygen, amino acids, waste products (i.e. C)s, lactate acid)

Question 13

What is the rate of formation of Aqueous Humor?

Answer 13

○ Rate of formation 2 microlitres/min

Entire volume is replaced every 1 - 2 hours

Question 14

What is the drainage pathway for aqueous humor?

Answer 14

Trabecular (convectional) pathway

Uveoscleral (unconventional) pathway

Question 15

Describe the Uveoscleral (unconventional) pathway

Answer 15

a. 10 - 20% aqueous drained via this pathway
b. Independent of pressure at IOP level >7 - 10 mmHg
c. Aqueous passes through the ciliary muscle into supraciliary and suprachoroidal spaces
d. Drained by venous circulation in the ciliary body, choroid and iris (crypts allow aqueous to communicate with deep tissue)

e. Age related decline in uveoscleral outflow

Question 16

Describe the Trabecular (convectional) pathway

Answer 16

a. Pressure dependent, runs along a pressure gradient
b. 90% drained through TM into Schlemm’s canal
c. Schlemm’s canal feed to collector channels and the episcleral venous plexus
d. Exits the eye via episcleral veins
Episcleral venous pressure can affect the outflow

Question 17

How can be asses the Iridocorneal angle?

Answer 17

• Shadow test
  
  • Van Herrick
  • Gonioscopy
  • Imaging

Question 18

Why do we assess the Iridocorneal angle?

Answer 18

Before mydriatic (dilation) or a cycloplegic (cyclo) is instilled, the risks of allergic reaction, angle closure and increase in IOP are ascertained. Only when these risks are acceptably low is either class of drug used on a patient

6% of the population do have narrow anterior chamber angles, which predispose them to the possibility that angle closure may occur when these drugs are used.

Question 19

What are the 2 test we are mostly going to be using to assess narrow anterior chamber angles?

Answer 19

Van herick

Gonioscopy

Question 20

What is an outlayer for the iris shadow test?

Answer 20

The iris shadow test can be misleading when there is a plateau type iris .A plateau iris exists where the central portion of the iris is flat but the peripheral iris in the region of the angle is bowed .This results in a narrow angle with an apparently deep anterior chamber.

Question 21

How do you do the Iris Shadow test?

Answer 21

• Done by directing the light from a pen torch across the iris in a fronto-parallel plane the shape of the iris can be seen
  In eyes with a bowed iris and in narrower angles, the iris will be seen to bow forward and shadow will be cast into the opposite angle. The assumption that a bowed iris goes hand in hand with a narrow angle depends on the degree of forward bowing is similar at all regions across the iris. This assumption is not necessarily so

Question 22

What are the advantage of Iris Shadow Test?

Answer 22

Reliably indicate whether the iris is bowed and is good way of estimation the depth of the anterior chamber more centrally

Question 23

What are the disadvantaged of the iris shadow test?

Answer 23

Not reliable indicator of the open-ness of the anterior chamber angle

Not as reliable as van Herrick or gonioscopy

Question 24

What is the clinical indication for Gonioscopy?

Answer 24

for any patient whose Van Herick is estimated as 0.25 or less

Question 25

What are the main uses for Gonioscopy?

Answer 25

○ Determine the likelihood of angle closure before mydriatic or cycloplegic drugs are instilled
- The detection and/or management of ocular pathology

Question 26

Describe how gonioscopy works?

Answer 26

• Performed to examine the portions of the anterior chamber that are not visible with the biomicroscope due to total internal reflection (iridocorneal angle)
• The gonioprism replaces the cornea/air interface with a cornea/prism interface, allowing the light rays to be visualised via an angled mirror

Question 27

How do you record angle closure?

Answer 27

• An occludable angle is one where the pigmented )posterior) trabecular meshwork is not visible in more than one quadrant
  Record by writing the most posterior structure seen in each quadrant