Glaucoma - Gonioscopy

Question 1

What is the principle of gonioscopy?

Answer 1

• To view angle during gonioscopy, need to overcome total internal reflection
  o When use gonioscopic lens, it reduces the difference in refractive index between cornea & air
• Two methods:
  o Direct visualisation of angle
  o Indirect visualisation of angle (via a mirror which is part of the lens system)

Question 2

Describe direct gonioscopy?

Answer 2

• Directly visualise the structures through lens
  o Steeply curved convex lens – allows the light from the angle to exit closer to the perpendicular (at the interface between lens and air)
• Direct lenses
  o Px lies supine
  o Give a direct stereoscopic, panoramic view of the angle
• Advantages:
  o Good magnification (1.5x)
  o Easy orientation for the observer
  o Possible to simultaneously compare both eyes
  o For high magnification need an illuminated loupe or a slit lamp
  o Can be used in bedbound patients
  o Very little corneal distortion
  o Wide field of view for teaching
• Disadvantages: - key reasons why they are not used
  o Time consuming – in child may need to sedate px
  o Requires large working area – need to fully walk round pxs head to view 360°
  o May require assistant
  o Requires separate illumination & magnification (or Hand-held slit-lamp)
  o Low magnification (depends on SL)
  o Cannot create optic section to locate Schwalbe’s line
  o Poor for detail (depends on SL)
  o Technically difficult technique to master

Question 3

Describe direct gonioscopy lenses?

Answer 3

• E.g. Koeppe Lens
• +50D concave base curve; Convex outer surface.
• Diameters of 17, 18, 19, 22.5mm  allowing it to be used on babies through to adults
• Magnification 1.5x
• Image: Erect, Virtual
• Saline/coupling fluid required to bridge the gap between the cornea and the lens
  o Then placed on eye
• Handheld slit lamp and external light source required to achieve view & get adequate magnification

Question 4

Describe indirect gonioscopy?

Answer 4

• Advantages:
  o Focal illumination allows location of Schwalbe’s line – can do corneal wedge/optic section
  o Magnified view of angle
  o Excellent for fine detail
  o Stable image – px seated on SL
  o Technically simple to use
  o Useful for laser treatment – e.g. SLT on glaucoma px
  o Can use ordinary SL
  o Px sitting up (or supine for surgical microscope)
  o Photography (video) recording possible
  o Variety of lenses available
  o Surgical applications
• Disadvantages:
  o Poor lateral view (stereopsis difficult)?
  o Uncomfortable for Px?? (Use LA)
  o Requires coupling fluid (Not always – depends on lens)
  o Observations reversed
  o Small field of view (use rotational scan technique)
  o Cost of Lenses
   Lenses are expensive, no more expensive than direct lens but a significant cost for something you won’t use on every px
  o Reversed image
• Difficulty for px to complete perimetry & have fundus photos taken after flange lens used due to coupling fluid
• Need to remember that view in superior mirror is of inferior angle

Question 5

Describe indirect gonioscopy lenses?

Answer 5

• Optics:
  o All use similar principle & mirrors to overcome total internal reflection
  o Mag & degree of rotation required to view entire angle depends on indirect lens used
• Lenses Available:
  o Flange vs non-flange
   Non-flange lens: make contact with central 10mm of cornea – use saline on the lens and don’t need coupling fluid
• Use little vit of saline
• Not as stable a view – can be more difficult to learn but does allow corneal indentation
   Flange lens: need coupling fluid, wider diameter of contact zone which cover entire cornea with  becomes relatively firmly attached to eye – get stable view
• Disadvantage: doesn’t allow you to do corneal indentation – so cannot fully assess how anterior chamber responds to slight pressure on cornea
  o Different views of peripheral anterior chamber angle afforded by using different goniolenses

Question 6

Describe G1 indirect gonio lens?

Answer 6

• Single mirror
• Can view angle by viewing in mirror, & view entire angle by rotating through 360°
• Flange and non-flange designs available
• Has highest mag of common gonio lenses (1.5x)
• 62 degree viewing angle which allows to view peripheral anterior chamber angle

Question 7

Describe G2 indirect gonio lens?

Answer 7

• 2 mirrors with slightly different angles hence slightly different views of angle – one at 60 & 64°
• Can view angle by viewing in 2 mirrors, and view entire angle by rotating through 180°
• Flange and non-flange designs available
• Has highest mag of common gonio lenses (1.5x)

Question 8

Describe G3 indirect gonio lens?

Answer 8

• Can be used to view angle & to view peripheral fundus
  o Through central lens you can view posterior pole
• To view whole angle need to rotate through 360°
• Flange, non-flange & mini non flange options
• Also know as Goldmann lens
• Lower level of mag: 1.06x

Question 11

What are the techniques and gradings that can be used with gonioscopy?

Answer 11

• Technique
  o Basic
  o Corneal Wedge
  o Indentation
• Grading and Recording
  o Shaffer (Sheie)
  o Spaeth
  o Comparison to other angle grading techniques (-Van Herricks and Smiths)
• Normal VS Abnormal appearance on Gonioscopy

Question 11

Describe G4 indirect gonio lens?

Answer 11

• 4 mirrors for viewing superior, inferior, nasal & temporal angle
• All mirrors set at same angle
• Can view whole angle simply by viewing in 4 mirrors, rotating 45° & viewing again
• Flange and non-flange designs available
• Detachable handle – can use handle to keep it stable in non-flange design
• Contact surface 9mm diameter
• Mag (1.0x) – can increase this with a SL

Question 12

What are key things to remember in gonioscopy technique?

Answer 12

• Adequate anaesthesia required – ask px if it feels odd when they blink then know if anesthetised
• Short bright beam – and direct beam (no angle on light)
• Room lights dim
• Coupling fluid required if using a flange lens – typically viscotears
• 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 – depends on lens (if 4-mirror lens then only 45°)
• 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 (usually bottom lens)) in order to safely remove the lens – allows air under lens to remove it

Question 13

What are the advantages/disadvantages of flange gonio lenses?

Answer 13

• Advantages:
  o Easier to get an image initially
  o View is more stable than lenses which don’t require coupling fluid
• Disadvantages:
  o Need coupling fluid to perform examination i.e. Celluvisc, Viscotears or Lacrilube (currently unavailable)
  o Coupling fluid can impair ability of patient to complete visual fields and can degrade subsequent retinal images
   May want to do gonioscopy last
  o Cannot perform indentation to determine if angle is fully occludable
  o Bubbles can form in coupling fluid during the exam which can make viewing the angle difficult
  o Messy

Question 14

How do you use a 4-mirror gonio lens?

Answer 14

If using 4-mirror lens start in centre then move superior to view inferior angle & scan left and right to see as much of it as possible.
Then move inferior to view superior angle & scan.
Then move back to centre & change beam horizontal & move beam to view temporal & nasal angles then do same on diagonals. Turn beam to 45 degrees and move angle up & down to view these positions

Question 15

Describe the corneal wedge technique in gonioscopy?

Answer 15

• 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
  o Can then be difficult to determine if posterior pigmented trab meshwork is visible or not
• Corneal Wedge technique:
  o Very narrow beam
  o Room dark
  o Maximum beam brightness
  o Beam displaced 5o – 10o (temporal or nasal)
• Wedge tip denotes Schwalbe’s line
  o If tip of wedge is right next to iris tissue – you know that none of the structures are visible as they are all hidden by the iris tissue – closed angle
  o If tip of wedge is further away from iris – you know between tip & iris tissue – posterior pigmented trab meshwork is visible – wide open angle
  Very thin beam, with slight angle – to view junction between cornea & sclera

Question 16

Describe indentation gonioscopy?

Answer 16

• Helps determine if patient has appositional or synechiael angle closure
  o Synechiael angle closure for e.g. from uveitis – adhesions between peripheral iris & corneal tissure
   Even with additional pressure (corneal indentation) it will not open the angle up
  o Appositional angle closure – not attached and when perform indentation (put pressure on corneal tissue) it will force some aqueous humour into peripheral angle & open the angle up
• When iris covers trab meshwork it is easy to mistake
  o The non-pigmented TM for scleral spur
  o The pigmented Schwalbe’s line for TM
  o Apposition from synechiae
• Indentation gonioscopy is particularly useful in these cases
• 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

Question 17

Describe Shaffer Grading Scale - gonioscopy?

Answer 17

• Most commonly used gonioscopic grading scale
• Corresponds to Van Hericks grading scale – Shaffer grade 4 is wide open angle, shaffer grade 0 is closed angle
• Easiest way to grade is to decide which structures you can see next to iris
• If first structure youcan see next to iris is anterior ciliary body then it is wide open grade 4 angle
• If first structure can see next to iris is scleral spur it is grade 3 angle
• If first structure can see next to iris is pigmented trabecular meshwork (& neither ciliary body & scleral spur are visible it is grade 2 angle
• If can only see anterior non-pigmented trab meshwork & no visibility of the pigmented bands then this is grade 1 angle
• Grade 0 is where only see Schwalbe’s line
• Other way to grade is done by width of peripheral anterior chamber in degrees

Question 18

What are the 5 grades of Shaffers grading scale - gonio?

Answer 18

Shaffer Grade 4: 35-45° - wide open angle with all structures visible up to iris root & its attachment to anterior ciliary body
Shaffer Grade 3: 20-35° - wide open angle up to scleral spur.
In grades 3&4 - no risk of angle closure
Shaffer Grade 2: 20° - narrow angle with visible trab meshwork. Possibility of angle closure
Shaffer Grade 1: 10° - occurs when angle extremely narrow up to anterior trab meshwork & Schwalbe line, with high risk of probable closure.
Shaffer Grade 0: 0° - closed angle with iridocorneal contact & no visibility of ACA structures

Question 19

Describe Spaeth Grading Scale - gonioscopy?

Answer 19

• Detailed grading scale – often used in secondary care
• Provides detail on
  o Level of iris insertion
  o The width of the angle
  o The peripheral iris configuration
  o The number of iris processes
  o Pigmentation of the pigmented trabecular meshwork
• Typically only used by specialists e.g. glaucoma specialist consultant ophthalmologists

Question 20

Describe Becker Goniogram method of gonioscopy grading?

Answer 20

• A means of drawing gonioscopic findings
• Can add details such as
  o Most posterior structure visible
  o Iris processes, synechiae
  o Pigmentation

Question 21

What is the common way to record gonioscopy findings?

Answer 21

• Use Shaffer scale to grade angle in 4 peripheral quadrants – inferior, superior, nasal & temporal
  o Grading often different in the quadrants – often inferior is widest open
• Add any details about findings:
  o Grade pigment in the angle grade 0-4 where zero has no discernible pigment in the angle and 4 is a very heavily pigmented angle
  o Note any iris processes/synechaie and their position and extent
  o Any other notable features

Question 22

What are the physiological variations in anterior chamber angles seen on gonioscopy?

Answer 22

• Variations in pigmentation of the trabecular meshwork
• Samapolesi’s line - can be physiological or pathological
  o Heavy angle pigment can accumulate in a line anterior to Schwalbe’s line as a Sampaolesi’s line
  o Sampaolesi’s line is a nonspecific finding in heavily pigmented angles
  o Sampaolesi’s line can be seen in PDS, pseudoexfoliation and normal angles
  o Corneal wedge can be useful in locating Schwalbe’s line & determining if pigment in angle is on trab meshwork or anterior to it
• Iris processes – common incidental finding – differential diagnosis peripheral anterior synechaie

Question 23

What are the pathological variations in anterior chamber angle that can be seen on gonioscopy?

Answer 23

• Peripheral Anterior Synechiae
• Angle neovascularisation
• Pigment dispersion syndrome
• Pseudoexfoliation

Question 25

Describe peripheral anterior synechiae on gonioscopy?

Answer 25

Usually uveitis which has caused inflammation in iris and caused it to be sticky & causes peripheral iris tissue to adhere to peripheral corneal tissue or angle structures
Iris processes are more lacy and tend to insert more posterior than anterior
When do corneal indentation in eye with peripheral anterior synechiae and put pressure on cornea forcing aqueous into the angle – will find that in an eye with peripheral anterior synechiae, during indentation process there will be areas where cornea & iris remain attached (shows there is angle closure which is not relieved by pushing on angle so not appositional angle closure)

Question 25

Describe angle neovascularisation on gonioscopy?

Answer 25

Difference between normal BVs that will see in some angles & angle neovascularisation is that angle neovasc will likely cause bleeding to occur – leaky vessels where see a few haemorrhages. Leaky vessels tend not to follow the normal structures so tend to bridge across structures.
Can sometimes see BV crossing over multiple structures – could be a sign of px with diabetes or have 100-day glaucoma

Question 26

Describe Pigment Dispersion Syndrome on gonioscopy?

Answer 26

Will see transillumination of iris tissue when doing retro illumination. May see pigment deposition on zonules (which can see in this pic) during gonioscopy and may see Krukenberg spindle on cornea.
When look at peripheral angle – one of key finding is they would have heavy pigment deposition on the angle structures (don’t only see this in pigment dispersion syndrome but will tie in with other findings) – e.g if on gonioscopy see heavily pigmented angle, go back and check if iris transillumination or Krukenberg spindle

Question 28

Describe pseudoexfoliation on gonioscopy?

Answer 28

Can also lead to heavy deposition of pigment in the anterior chamber angle – then go back & look for signs of pseudoexfoliative material on anterior lens surface.
When see extra pigmentation in anterior chamber angle – go back & look for the other signs to make sure no other signs of pathology.