Topic 5 Gonioscopy

Overall yield:

Clinical exam:

Viva:

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Essay:

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MCQ:

"Gonioscopy is an evaluation of the AC angle." "And is based on the principle of total internal refraction ..." "There are 2 types of lens used to evaluate the angle."

Goniscopy

1. Principle

• Light from AC angle exceeds the critical angle at the cornea-air interface, undergoes total internal refraction and cannot be seen

• Goniolens has similar refractive index as the cornea and alters the cornea air interface to allow light to pass from AC through the cornea into the lens

• Critical angle of the new interface between lens and air is not exceeded and therefore images from the angle can be visualized

• Indirect goniolens provides mirror image of angle, while direct lens provides actual view of angle

2. Indirect goniolens

• Goldman goniolens

• Diameter of 12mm

• Stabilizes globe and therefore good for argon laser trabeculoplasty

• Needs coupling fluid

• 2 mirror lens angled at 62 degrees

• Largest mirror at 73 degrees (visualize posterior pole to equator)

• Second largest at 67 degrees (visualize equator to retinal periphery)

• Smallest (semicircular) at 59 degrees (visualize angles)

• Zeiss goniolens

• Diameter of 9mm and flatter than cornea

• Can be used for indentational gonioscopy

• No stability and therefore not good for argon laser trabeculoplasty

• 4 mirrors angled at 64 degrees

• Can see entire extent of angle

• No coupling fluid needed

• Better visualization

• Posner 4 mirror and Sussman 4 mirror lens (modified Zeiss with handle)

3. Direct goniolens

• Diagnostic

• Koeppe (prototype diagnostic goniolens)

• Can see entire extent of angle

• Barkan (prototype surgical goniolens), Medical Workshop, Thorpe and others

03 Exam tips:

* Candidates seldom answer the principle of gonioscopy well » The comparison between Goldman and Zeiss is another favorite question

<2D> How do you perform a gonioscopic examination?

"Gonioscopy is an evaluation of the AC angle."

"A systematic evaluation of the structures of the angle is done as follows ..."

Gonioscopic examination

1. Grade the angle (see below)

• Standard gonioscopy

• Indentational gonioscopy

• Differentiates appositional closure from synechiae closure

2. Assess the structures

• Anterior displacement of Schwalbe's line

• Posterior embryotoxon

• Trabeculum pigmentation

• P seudoexfoliation and pigment dispersion syndrome

• G laucoma (post angle closure glaucoma)

• M elanosis of angles (oculodermal melanosis)

• E ndocrine (diabetes and Addison's syndrome)

• Peripheral anterior synechiae

• Blood in Schlemm's canal (raised episcleral venous pressure)

• Carotid cavernous fistula

• Sturge Weber syndrome

• Superior vene cava obstruction

• Ocular hyopotony

• Post gonioscopy

IH Exam tips:

• The differential diagnoses for trabecular pigmentation can be remembered by the mnemonic "PIGMENT"!

NOTES

Compared to iris processes, peripheral anterior synechiae are denser, more irregular and extend beyond scleral spur

How is the angle clinically graded?

"The angle is graded according to classification systems such as ..." Grading of angle

Shaffer system (1 -4) Scheie's system (I—IV)

Grade 4 (40 degrees)

Grade I

Ciliary body seen

Grade 3 (30 degrees)

Grade II

Scleral spur seen

Grade 2 (20 degrees)

Grade III

Trabeculum seen

Grade 1 (10 degrees)

Grade IV

Schwalbe's line seen

Grade 0 (closed angle) Iridocorneal contact

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