gonioscopy Flashcards
from what degrees is the posterior pigmented trabecular meshwork not visible
Using Gonioscopy, if ≥270 degrees of posterior pigmented trabecular meshwork is not visible
normal angle structure in gonio
- I - Iris
- Can – Ciliary Body (pigmented tissue)
- See – Scleral Spur (white tissue)
- The – Trabecular Meshwork (there is pigmented then there is non pigmented)
- Line – Schwalbe’s Line (most anterior structure to the iridocorneal angle, differentiates the angle tissue from the peripheral cornea)
which structures in gonio have a different texture
Peripheral iris issue and ciliary body base (darkly pigmented) have a different texture, colour can be similar – depends.
what are healthy blood vessels that are seen in gonio
vessels travelling in the same direction of the iris tissue – not crossing any structures, – healthy eye
what are iris processes and who are they more common in
- 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 – lacy in appearance
- Present in around a third of normal individuals, most prominent in brown eyes and in children
what could iris processes be confused with
- Not to be confused with Peripheral anterior synechaie which can insert more anteriorly and are more substantial/broader – not lacey structure like iris processes
where is the ciliary body base/ face what colour is it
- Sits between the peripheral iris and the scleral spur
- Can be pink, brown or slate grey
what is the ciliary body base/ face dependant on and is it in everyone
- It’s width depends on the position of iris insertion and tends to be narrower in hyperopes than myopes (wider band in myopes)
- The angle recess represents the posterior dipping of the iris as it inserts into the ciliary body (change in curvature)
- It may not be visible in all eyes due to physiological anterior iris insertion
- May be irregular in appearance – might see in some areas and not others – means wider at those points
where is the scleral spur and what colour is it
- 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
- Becomes more yellow with age
where is the trabecular meshwork
- Sits between the scleral spur and Shwalbe’s line
the non pigmented trabecular meshwork purpose and location
- The anterior portion bordering Schwalbes line is non pigmented and it is non-functional
the pigmented trabecular meshwork purpose and location
- The posterior, (pigmented) functional portion borders the scleral spur, the level of pigmentation in this portion varies from pale to dark brown, allows drainage of aqueous
the flow of aqueous from the trabecular meshwork
- 90% of aqueous leaves via the trabecular meshwork via episcleral venous system
- Flow is pressure dependent, flow increases as IOP increases
- For aqueous to exit the eye by this route, the intraocular pressure must be higher than the episcleral venous pressure. At pressures below episcleral venous pressure (8 to 15 mm Hg), all aqueous outflow must be via nonconventional routes
schlemm’s canal location and purpose
- 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
- Traditional drainage through episcleral venous system, the aqueous is drained through the trabecular meshwork and is collected in Schlemm’s canal and exits
- Not visible in most eyes, some eyes it is a plexus rather than a single vessel
The longitudinal muscle of the ciliary body can open Schlemm’s canal by pulling on the scleral spur. Cholinergic drugs (by using this route) decrease resistance to outflow through this action.
what can happen to schlemms canal when the IOP is too high
- When there is high IOP the canal can collapse, the resistance to aqueous outflow can increase – problems with drainage – also problems when the pressure is too low (lower than the episcleral venous system then wont drain out)
location of schwalbe’s line and colour
- It is the Boundary between the trabecular meshwork and the corneal endothelium
- (It is a change in curvature)
- Can be some pigment settling in this area due to steeper curvature than scleral sulcus
lightly pigmented
aim for success in gonioscopy
need to overcome total internal reflection
what are the 2 methods of gonio
- Direct visualisation of the angle (not really used)
- Indirect visualisation of the angle
how is direct gonio done
- Patients lie supine
- Give a direct stereoscopic, panoramic view of the angle
- Were mostly use in children/ babies
- Direct gonioscopy is performed with a steeply convex lens, which permits light from the angle to exit the eye closer to the perpendicular at the interface between the lens and the air.
The Koeppe lens (3 6), which is a 50-diopter lens, is placed on the eye of a recumbent patient using saline to bridge the gap between lens and cornea (3 7).
The examiner views the angle through a hand-held binocular microscope, which is counterbalanced to permit ease of handling. Illumination is provided by a light source that is held in the other hand (3 8). The Koeppe lens magnifies ×1.5. This, in combination with the ×16 magnification of the oculars, yields a total magnification of ×24. There are Koeppe lenses in several sizes to suit infants to adults.
advantages of direct gonio
- Good magnification (1.5x)
- Easy orientation for the observer
- Possible to simultaneously compare both eyes
- For high magnificiation need an illuminated loupe or a slit lamp
- Can be used in bedbound patients
- Very little corneal distortion
- Wide field of view for teaching
disadvantages of direct gonio
- Time consuming
- Requires large working area
- May require assistant
- Requires separate illumination & magnification (or Hand-held slit-lamp)
- Low magnification (depends on SL), if slit lamp not used poor mag
- Cannot create optic section to locate Schwalbe’s line
- Poor for detail (depends on SL)
what is direct lens used for direct gonio eg the koeppe lens
- +50D concave base curve; Convex outer surface.
- Diameter of 17, 18, 19, 22.5mm.(can be used for different ages)
- 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 gonio advantages
- Focal illumination allows location of Schwalbe’s line (can do corneal wedge, technique can be used to see)
- Magnified view of angle
- Excellent for fine detail
- Stable image (seated on slit lamp)
- Technically simple to use
- Useful for laser treatment
- Can use ordinary slit lamp
- Px sitting up (or supine for surgical microscope)
- Photography (video) recording possible
- Variety of lenses available
- Surgical applications
disadvantages of indirect gonioscopy
- Poor lateral view (stereopsis difficult)?
- Uncomfortable for Px, same for direct
- Requires coupling fluid (Not always- depends on the lens)
- Observations reversed
- Small field of view (use rotational scan technique) – need to scan
- Cost of Lenses
- Reversed image
- Need to remember that view in superior mirror is of inferior angle
- Difficulty for patient to complete perimetry and have fundus photos taken after flange lens used due to coupling fluid
what is the mag and degree of rotation for an indirect lens dependant on
- Mag and degree of rotation required to view the entire angle depends of indirect lens used
which lenses are avaliable for indirect gonio
- Flange (coupling fluid needed) vs non flange
- Different views afforded by using different goniolenses
G1 lens features
- Can view the angle by viewing in the mirror, and rotating through 360 degrees
- Single mirror – need to move mirror to view everything
- Flange and non flange designs available
- Highest mag of common gonio lenses (1.5x)
- 62 degree viewing angle
G2 lens features
- 2 mirrors with slightly different angles hence slightly different views of the angle (one at 60 other at 64 degrees)
- Can view the angle by viewing in the 2 mirrors, and rotating through 180 degrees
- Flange (coupling fluid, wider corneal contact zone, stable view, doesn’t allow corneal indentation) and non flange (only saline used) designs available
- Highest mag of common gonio lenses (1.5x)
G3 lens features
- Can be used to view the angle and to view the peripheral fundus
- Versatile lens
- 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
- Through the central lens you can view the posterior pole
G4 lens features
- 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), can increase with slit lamp
what are the types of gonio techniques
- Basic
- Corneal Wedge
- Indentation
in a 4 mirror gonio what does the superior mirror show
a view of the inferior iridocorneal angle, deepest and most pigmented
Gonio basic technique
- Adequate anaesthesia required – ask px does it feel odd when blinking to check
- Short bright beam – no angle
- Room lights dim
- Coupling fluid required if using a flange lens – eg viscotears, celuvisc (so it couples with the eye)
- Steady hand on the slit lamp, with a block/lens case if required
- Rotate lens (when on eye) appropriately to view the entire 360 degrees of the angle (depending which lens used eg G4 only rotate 45degrees)
- 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 lens advantages
easier to get an image initally
viewing is more stable then lenses which dont require coupling fluid
disadvantages if flange lens
- 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
what is the corneal wedge technique in gonio and the benefits of it
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
how is corneal wedge in gonio done
Very narrow beam
Room dark
Maximum beam brightness
Beam displaced 5o – 10o (temporal or nasal)
Wedge tip denotes (points at) Schwalbe’s line, eg Schwalbes line is right next to iris tissue then closed angle
Very thin beam with slight angle
The corneal wedge points to Schwalbe’s line—the anterior border of the trabecular meshwork. The corneal wedge in this eye has a rounded contour that reflects the rounded interface between cornea and sclera.
what is indentation gonioscopy useful for
- 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 (not attached, with pressure from indentation helps open angle up) from synechiae (means adhesions between peripheral iris and corneal tissue) (helps differentiate)
what is the pressure like for indentation gonio and what does the pressure do
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
When you see corneal folds then cornea is being indented
most common grading scale of gonio
Shaffer Grading Scale
- Corresponds to Van Hericks grading scale
common way to record findings for gonio
- 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
what are the physiological variations seen in gonio
- Variations in pigmentation of the trabecular meshwork
- Sampolesi’s line - can be physiological or pathological
- Iris processes - differential diagnosis peripheral anterior synechaie
- Heavy angle pigment can accumulate in a line anterior to Schwalbe’s line as a Sampaolesi’s line. Sampaolesi’s line is a nonspecific finding in heavily pigmented angles, whether physiologic or pathologic.The corneal wedge can help in locating Schwalbe’s line and in defining whether the pigmentation is in the trabecular meshwork or anterior to it. Systems for grading angle pigmentation are discussed in Chapter 6
-Sampolesi’s line can be seen in PDS, pseudoexfoliation and normal angles
pathological variations in gonio
*Peripheral Anterior Synechiae (uveitis, allowed peripheral iris adhered to the peripheral cornea or angle structures
*Angle neovascularisation – leaky vessels – BV crosses over multiple structures, sign of px with DM maybe
* Pigment dispersion syndrome – transillumination in retro illumination, heavy pigment deposition on the angle structures (not only in PDS), Scheie’s stripe in the pigment dispersion syndrome. Pigment accumulates at the junction of the zonules and the posterior lens capsule (arrow). The trabecular meshwork is moderately pigmented
* Pseudoexfoliation – heavy deposition of pigment in the anterior chamber angle
