Week 10 - Gonioscopy Flashcards
What does the aqueous humour do?
• The aqueous humor supplies nutrition and removes waste from the clear structures in the anterior eye - the cornea and the lens
• The balance between aqueous production and outflow determines the intraocular pressure
The ciliary body contains:
• Longitudinal muscles
- pull on the scleral spur
- open the trabecular meshwork
• Circular muscles
- accommodate the lens
• Forms part of the blood-aqueous barrier
• Forms hyaluronate for the vitreous
• Ciliary epithelium
- makes aqueous
• Circular epithelium
- makes aqueous
• In the ciliary processes
- There are ~80
Aqueous Humour:
• Made from plasma
• In the non-pigmented epithelium of the ciliary body
Made by:
1. Ciliary body stroma
- Highly vascular
2. Pigmented epithelium
3. Non-pigmented epithelium
4. Aqueous humour
Aqueous Humour production:
• Active transport (secretion)
• Ultrafiltration
• Diffusion
Aq humour production: Active transport:
• Active transport (secretion)
- energy expended
- sodium driven into the posterior chamber, water follows
- responsible for moving ascorbate and other large charged molecules
Aq humour production: Ultrafiltration
• Ultrafiltration
- passive
- via micropores in cell membrane
- movement along gradients
- pressure dependent
Aq humour production: Diffusion
• Diffusion
- passive
- lipid soluble materials
- driven by concentration gradients
Aqueous humour vs plasma
• Aqueous has virtually no protein
- Protein in the aqueous is seen as flare
• Aqueous has 10 - 50 x the levels of ascorbate
• Other differences are minor
Aqueous Outflow:
• Primarily through the trabecular meshwork into the episcleral venous system
- Pressure dependent
•Also through the ciliary body face and iris root into the suprachoroidal space
- Pressure independent
How can you assess the anterior chamber angle?
• Van Herick’s
• Smith’s Technique
• Gonioscopy
Van hericks or gonioscopy acceptable when referring:
• Refer irrespective of other signs refer if Van Herrick’s technique grade 2 as patient is at significant risk of developing acute closed angle glaucoma
• Using Gonioscopy, if ≥270 degrees of posterior pigmented trabecular meshwork is not visible.
Why is it important to do gonioscopy when viewing the angle?
• To determine if the angle is open or closed
• To determine which structures are visible in the angle
• Hence how adequately aqueous is being drained?
• To determine if angle structures are normal/abnormal
• To grade the angle in order to classify glaucoma patients
• To find signs which may be suggestive of a risk factor for the development of secondary glaucoma?
Why cant just Van Hericks be used?
Potential errors in Van Herick’s Grading due to:
• Room illumination not reduced
• Fixation in not stabilised in primary position (distance)
• Magnification too low
• Wide optic section (Reduced brightness of slit lamp)
• Illumination angle not 60°
• Reading not taken at limbus
• Peripheral corneal lesions such as ptergium or arcus senilus
• And it only tells you if the angle is open or closed, it doesn’t tell you anything about the appearance of the angle structures
Smiths technique
• Used when no gonioscopic lens
• Assesses anterior chamber depth by assessing the depth of the central anterior chamber
• Therefore useful in cases where there is an obscuration/opacity in the peripheral cornea making Van Herick’s difficult
• NOT listed as an acceptable way to refer patients under the SIGN glaucoma guideline
Why cant you see the angle using a slit lamp?
• The difficulty in viewing the iridocorneal angle is due to the critical angle of refraction at the corneal / air interface.
• The goniolens replaces the eye / air interface and the critical angle is eliminated by the steeply curved outer surface of the lens.
Normal Angle Structure:
• I - Iris
• Can - Ciliary Body
• See - Scleral Spur
• The - Trabecular Meshwork
• Line - Schwalbe’s Line
Iris processes:
• Small, usually tenuous extensions of the anterior iris surface that insert at the level of the scleral spur and cover the ciliary body to a varying extent
• Present in around a third of normal individuals, most prominent in brown eyes and in children
• Not to be confused with Peripheral anterior synechaie which can insert more anteriorly and are more substantial/broader
Ciliary Body
• Sits between the peripheral iris and the scleral sour
• Can be pink, brown or slightly grey
• It’s width depends on the position of iris insertion and tends to be narrower in hyperopes than myopes
• The angle recess represents the posterior dipping of the iris as it inserts into the ciliary body
• It may not be visible in all eyes
• May be irregular in appearance
Scleral Spur
• The scleral spur is the most anterior projection of the sclera and the site of attachment of the longitudinal muscle of the ciliary body
• On gonioscopy it can be seen posterior to the pigmented trabecular meshwork and anterior to the ciliary body base
• Appears as a narrow white band
The Trabecular Meshwork
• Sits between the scleral spur and Shwalbe’s line
• 90% of aqueous leaves via the trabecular meshwork
• Flow is pressure dependent
• The anterior portion bordering Schwalbes line is non pigmented and non-functional
• The posterior, functional portion borders the scleral spur, the level of pigmentation in this portion varies from pale to dark brown
Schlemm’s canal
• Positioned at the base of the scleral sulcus, most often not visible during gonioscopy
• Not a rigid structure, therefore at high intra ocular pressure the canal collapses and resistance to aqueous outflow increases
Schwalbe’s line
• Boundary between the trabecular meshwork and the corneal endothelium
• Can be some pigment settling in this area due to steeper curvatu than scleral sulcus
Principle of Gonioscopy:
• To view the angle during gonioscopy we need to overcome total internal reflection
• To methods
- Direct visualisation of the angle
- Indirect visualisation of the angle
Direct Gonioscopy: Advantages:
Direct lenses
• Patients lie supine
• Give a direct stereoscopic, panoramic view of the angle
Advantages
• Good magnification (1.5X)
Easy orientation for the observer
• Possible to simulaneously compare both eyes
• For high magnification need an illuminated loupe or a slit lamp
• Can be used in bedbound patients
• Very little corneal distortion
• Wide field of view for teaching
Direct Gonioscopy: Disadvantages:
Direct lenses
• Patients lie supine
• Give a direct stereoscopic, panoramic view of the angle
Disadvantages
• Time consuming
• Requires large working area
• May require assistant
• Requires separate illumination & magnification (or Handheld slit-lamp)
• Low magnification (depends on SL)
• Cannot create optic section to locate Schwalbe’s line
• Poor for detail (depends on SL)
• Technically difficult technique to master
Lenses for direct gonsioscopy:
Direct lenses eg Koeppe Lens
• +50D concave base curve; Convex outer surface.
• Diams of 17, 18, 19, 22.5mm.
• Magnification 1.5x
• Image: Erect, Virtual
• Saline/coupling fluid required to bridge the gap between the cornea and the lens
• Handheld slit lamp and external light source required to achieve view
Indirect gonioscopy: advantages
Advantages
• Focal illumination allows location of Schwalbe’s line
•Magnified view of angle
• Excellent for fine detail
•Stable image
•Technically simple to use
• Useful for laser treatment
• Can use ordinary SL
• Px sitting up (or gupine for surgical microscope)
•Photography (video) recording possible
• Variety of lenses available
•Surgical applications
Indirect gonioscopy: disadvantages
• Poor lateral view (stereopsis difficult)?
• Uncomfortable for Px. ?? (Use LA)
• Requires coupling fluid (Not always)
• Observations reversed
• Small field of view (use rotational scan technique)
• Cost of Lenses
• Reversed image
Indirect lenses:
• Optics
• All use a similar principle and mirors to
overcome total internal reflection
• Mag and degree of rotation required to view the entire angle depends of indirect lens used
• Lenses available
• Flange vs non flange
Different views afforded by using different
goniolenses
G1 Lens:
• Indirect lens
• Can view the angle by viewing in the mirror, and rotating through
360 degrees
• Flange and non flange designs available
• Highest mag of common gonio lenses (1.5x)
• 62 degree viewing angle
G2 lens
• Indirect lens
• 2 mirrors with slightly different angles hence slightly different views of the angle
• Can view the angle by viewing in the 2 mirrors, and rotating through 180 degrees
• Flange and non flange designs available
• Highest mag of common gonio lenses (1.5x)
G3 lens
• Indirect lens
• Can be used to view the angle and to view the peripheral fundus
• To view the whole angle need to rotate through 360 degrees
• Flange, no flange and mini non flange options
• Also known as the Goldmann lens
• Mag 1.06x
G4 lens
• 4 mirrors for viewing superior inferior, nasal and temporal angle
• All mirrors set at the same angel
• Can view the whole angle simply by viewing in the four mirrors, rotating 45 degree and viewing again
• Flange and non flange designs available
• Detachable handle
• Contact surface 9mm diameter
• Mag (1.0x)
Gonioscopy: Techniques, grading + recording
• Technique
- Basic
- Corneal Wedge
- Indentation
• Grading and Recording
- Shaffer (Sheie)
- Spaeth
- Comparison to other angle grading techniques (-Van Herricks and Smiths)
Gonioscopy Technique:
• Key Points
• Adequate anaesthesia required
• Short bright beam
• Room lights dim
•Coupling fluid required if using a flange lens
• Steady hand on the slit lamp, with a block/lens case if required
• Rotate lens appropriately to view the entire 360 degrees of the angle
• If using coupling fluid and a flange lens you will need to break the seal by putting a little pressure on the globe (through the lid) in order to safely remove the lens
Flange Lenses: Advantages and Disadvantages
• Advantages
• Easier to get an image initially
• View is more stable than lenses which don’t require coupling fluid
• Disadvantages
• Need coupling fluid to perform examination i.e. Celluvisc, Viscotears or Lacrilube (currently unavailable)
• Coupling fluid can impair ability of patient to complete visual fields and can degrade subsequent retinal images
• Cannot perform indentation to determine if angle is fully occludable
•Bubbles can form during the exam which can make viewing the angle difficult
• Messy
Corneal wedge:
• Helps to discriminate if an angle is open or closed
• Particularly useful in individuals with minimally pigmented angles, or angles with more pigment than average
Corneal Wedge technique:
• Very narrow beam
• Room dark
• Maximum beam brightness
• Beam displaced 5° - 10° (temporal or nasal)
Wedge tip denotes Schwalbe’s line
When is indentation gonsiocopy useful:
•When iris covers the trabecular meshwork it is
• easy to mistake:
-The non-pigmented TM for scleral spur
- The pigmented Schwalbe’s line for TM
- Apposition from synechiae
Rules to follow with indentation gonisocopy:
• Exert only sufficient pressure to maintain contact and expel bubbles
• Exerting a minimal amount of pressure (i.e. not indenting) then increasing the pressure (to indent) can show how the angle is in its everyday state and can give an idea if the angle can be opened with pressure and if therefore is suitable for certain surgical techniques
• NB. Exerting pressure on a no fluid goniolens can open the anterior angle and may give the impression that an angle is open when it is closed
Shaffer Grading Scale:
• Most commonly used gonioscopic grading scale
• Corresponds to Van Herricks grading scale
• Shaffer grade 4: 35°-45°
- Wide open angle in which all structures were visible up to the iris root and its attachment to the anterior ciliary body.
• Shaffer grade 3: 20°-35°
- Wide open angle up to the scleral spur, in grades 3 and 4, no risk of angle closure existed.
• Shaffer grade 2: 20°
- Angle was narrow with visible trabecular meshwork. In this angle width, a possible risk of closure existed.
• Shaffer grade 1: 10°
- Occurs when the angle was extremely narrow up to the anterior trabecular meshwork and the Schwalbe line, with a high risk of probable closure
• Shaffer grade 0: 0°
- The angle was closed with iridocorneal contact and no visibility of the ACA structures.
Spaeth Grading Scale:
• Detailed grading scale
• Provides detail on
- Level of iris insertion
- The width of the angle
- The peripheral iris configuration
- The number of iris processes
- Pigmentation of the pigmented trabecular meshwork
• Typically only used by specialists e.g. glaucoma specialist consultant ophthalmologists
Becker Goniogram
• A means of drawing gonioscopic findings
• Can add details such as
- Most posterior structure visible
- Iris processes, synechaie
- Pigmentation
- etc
Common way to record findings:
• Use Shaffer scale to grade angle in 4 quadrants
Add any details about findings
• Grade pigment in the angle grade 0-4 were zero has no discernible pigment in the angle and 4 is a very heavily pigmented angle
• Note any iris processes/synechaie and their position and extent
• Any other notable features
Physiological Variants:
• Variations in pigmentation of the trabecular meshwork
• Sampolesi’s line - can be physiological or pathological
• Iris processes - differential diagnosis peripheral anterior synechaie
Pathological Variations:
• Peripheral Anterior Synechaie
• Angle neovascularisation
• Pigment dispersion syndrome
• Pseudoexfoliation
