Glaucoma - Gonioscopy Flashcards
What is the principle of gonioscopy?
- 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)
Describe direct gonioscopy?
- 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
Describe direct gonioscopy lenses?
- 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
Describe indirect gonioscopy?
- 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
Describe indirect gonioscopy lenses?
- 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
Describe G1 indirect gonio lens?
- 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
Describe G2 indirect gonio lens?
- 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)
Describe G3 indirect gonio lens?
- 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
What are the techniques and gradings that can be used with gonioscopy?
- 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
Describe G4 indirect gonio lens?
- 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
What are key things to remember in gonioscopy technique?
- 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
What are the advantages/disadvantages of flange gonio lenses?
- 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
How do you use a 4-mirror gonio lens?
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