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Ophthalmology > Day 10 (3): Evaluation of the Anterior Segment in Glaucoma > Flashcards

Day 10 (3): Evaluation of the Anterior Segment in Glaucoma Flashcards

1
Q

What is Gonioscopy?

A

A procedure that measures the iridocorneal angle using a goniolens or gonioscope together with a slit lamp or operating microscope

Direct: direct visualization using lenses
Indirect: indirect visualization using lenses WITH mirrors

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2
Q

Why can’t the ACA be visualized with a SL alone?

A

Due to total internal reflection at the tear film-air interface.

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3
Q

What are the different kinds of Gonioscopy lenses?

A

DIRECT
- provides an UPRIGHT image of the INTENDED angle

  1. Koeppe Lens: most commonly used
  2. Barkan Lens
  3. Swan Jacob
    - used with a handheld microscope or loupe with illuminator
    - pt should be supine

INDIRECT
- uses mirrors to view the INVERTED, slightly minified image of the OPPOSITE angle

  1. Goldmann 3-mirror or Posner
    - WITH suction cup effect thus NO coupling device needed
    - BROAD-based thus MORE stable
    - used to view the ACA only; NOT used in indentation gonioscopy because of image distortion due to suction cup effect
    - ask patient to look ahead and apply directly over the cornea
  2. Zeiss 4-mirror
    - NO suction cup effect thus NEEDS coupling device
    - NARROW-based thus LESS stable (can move with eye movement)
    - used in indentation gonioscopy: can determine occludability of ACA because there is NO image distortion from the ABSENCE of the suction cup effect
    - ask patient to look up, initially applying over the inferior sclera then sliding it over the cornea

Notes:
1. Angle width is generally proportional to the separation of the corneal beam and iris beam when they meet in the angle
2. Suction Cup Effect: prevents lens drift and bubble formation due to eye movement by encircling and pressing firmly on the entire cornea; can also DISTORT the anatomic relationships of angle structures

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4
Q

What is Indentation Gonioscopy?

A
  • Used to determine the occludability of ACA
  • Uses a narrow-based indirect goniolens like Zeiss 4-mirror WITH a coupling device
  • Indenting or applying varying amounts of posteriorly-directed pressure on the cornea in an attempt to open up the ACA
  • Increased pressure indents the central cornea and forces aqueous into the ACA, opening it wider

RESULTS:
1. Appositional closure
- angle OPENS up with visualization of the posterior pigmented TM

  1. Synechial closure
    - angle remains CLOSED with NO visualization of the posterior pigmented TM
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5
Q

What are the steps in performing gonioscopy?

A
  1. Anesthetize the cornea.
  2. Insert the goniolens with (Zeiss) or without (Goldmann) coupling device.
  3. Use a narrow and short beam of light (2 - 3 mm) directed away from the pupil.
  4. Ask patient to look in the direction of the mirror to view that aspect of the ACA.
  5. Do indentation gonioscopy if warranted using a Zeiss 4-mirror.
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6
Q

What are the normal angle structures visualized in gonioscopy?

A
  1. Schwalbe’s Line
  2. Anterior Non-pigmented TM
  3. Posterior Pigmented TM
  4. Scleral Spur
  5. Ciliary Body Band
  6. Iris Root
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7
Q

What is the Schwalbe’s Line?

A
  • ridge formed by the attachment of the TM to the peripheral cornea
  • junction of Descemet’s membrane and the uveal trabecular meshwork
  • located anterior to the apical part of the TM
  • delineates the peripheral border of the corneal endothelial layer and termination of Descemet’s membrane
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8
Q

What is posterior embyotoxon?

A
  • Displacement of Schwalbe’s line anterior to the limbus in the cornea
  • Associated with Axenfeld-Rieger Syndrome

Slit-Lamp:
- thin grey-white, arcuate ridge on the inner surface of the cornea, adjacent to the limbus.

Histology:
- central collagen core surrounded by a thin layer of Descemet’s membrane
- separated from the anterior chamber by a layer of endothelium

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9
Q

What is the Sampaolesi Line?

A
  • Abundance of brown pigment at or anterior to the Schwalbe’s line
  • More prominent at the inferior ACA
  • Associated with Pigment Dispersion Syndrome and Pseudoexfoliation Glaucoma
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10
Q

How does the trabecular meshwork appear in gonioscopy?

A
  • 2 parts:
    1. Anterior NON-pigmented TM: non-filtering
    2. Posterior Pigmented TM: filtering; immediately adjacent to the Schlemm’s canal
  • at birth: all NON-pigmented
  • acquires pigmentation with age which may be homogenous or irregular
  • OPEN: visualize the pigmented TM

Appearance:
Red: (+) blood reflux in the Schlemm’s canal
- Increased EVP: goniolens, lid squeezing, IJV pressure
- Decreased IOP: hypotony
- Iatrogenic: post-MIGS or trabeculectomy

Dark: (+) phagocytosed pigments
- Pseudoexfoliation glaucoma
- Pigment Dispersion Syndrome
- Uveitis

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11
Q

How is TM pigmentation graded?

A

Grading:
0: NON-pigmented (infants)
1: Trace
2: Light (adults)
3. Moderate
4. Dense/Dark (pathologic)

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12
Q

What is the Scleral Spur?

A
  • protrusion of the inner aspect of the anterior sclera into the anterior chamber
  • anterior-most projection of the sclera
  • appearance: prominent WHITE band
  • functions:
    1. posterior border of the scleral sulcus
    2. posterior attachment of corneoscleral TM
    3. origin of the longitudinal and circular fibers of the ciliary muscle
  • borders:
    + anterior: corneoscleral TM
    + posterior: longitudinal fibers of the CB
  • difficult to distinguish in:
    1. lightly-pigmented irides
    2. heavily-pigmented TM (PDS, PEG)
    3. (+) iris processes or PAS
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13
Q

What is the Ciliary Body Band?

A
  • Band formed by the anterior aspect of the ciliary body peeking between the root of the iris and the scleral spur
  • Wider INFERIORLY and TEMPORALLY: corresponds to wider ACA

Appearance:
- light irides: gray-white
- dark irides: brown or charcoal-gray

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14
Q

Differentiate Iris Processes from Peripheral Anterior Synechiae.

A

Iris Processes
- finer
- underlying structures can still be discerned
- upto the Scleral Spur
- follows concavity of the recess
- iris moves with indentation
- broken with angle recession

Peripheral Anterior Synechiae
- broader
- obscures other structures
- extends beyond the scleral spur
- bridges concavity of the recess
- tight thus resists movement
- intact even with angle recession

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15
Q

Describe the normal iris plane.

A

CONTOUR:
1. Normal
- slightly convex with (+) Fuch’s roll
2. Flat
- myopes (long AL) –> wide open ACA
3. Convex:
- hyperopes (short AL) –> smaller AC and ACA
- advancing age
- cataractous lens
4. Plateau Iris
- prominent peripheral iris roll blocking the view of the ACA due to anteriorly displaced CB processes

NO neovascular vessels crossing over the ACA
- if (+): Neovascular Glaucoma

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16
Q

What is the Shaffer Angle Grading System?

A
  1. Assess the angle in its NATURAL position with the patient looking STRAIGHT.

Grade 4
- Angle width: 40 degrees
- Configuration: wide open
- Visible structures: SL, TM, SS, CBB
- Chances of closure: IMPOSSIBLE

Grade 3
- Angle width: 30 degrees
- Configuration: open
- Visible structures: SL, TM, SS
- Chances of closure: IMPROBABLE

Grade 2
- Angle width: 20 degrees
- Configuration: slightly open
- Visible structures: SL, TM (esp. PTM)
- Chances of closure: POSSIBLE

Grade 1
- Angle width: 10 degrees
- Configuration: narrowed
- Visible structures: SL only (+/- ATM)
- Chances of closure: PROBABLE/SUSPECT

Grade 0
- Angle width: 0 degrees
- Configuration: closed
- Visible structures: none
- Chances of closure: CLOSED

  1. For Grades 0 - 2
    - Do indentation gonioscopy: determined if ACA can still be widened and if closure is appositional or synechial
    - Will benefit from Laser Peripheral Iridotomy
17
Q

When documenting the ACA, what aspects or findings are noted?

A
  1. ACA is divided into 4 quadrants:
    - Superior
    - Inferior
    - Temporal
    - Nasal
  2. Indicate the MOST POSTERIOR structure visualized.
  3. Indicate the TM pigmentation grading.
  4. Indicate additional findings:
    - angle recession
    - peripheral anterior synechiae
    - angle neovascularization
18
Q

What diagnostic modalities are used in OBJECTIVELY measuring the ACA?

A
  1. Anterior Segment OCT: more popular choice
    - A: scans angle to angle within one scan with good visualization of the angle recesses
    - A: can acquire images under dim conditions
    - A: performed in a non-contact fashion
    - D: can not image structures behind the iris
  2. Ultrasound Biomicroscopy
    - A: can visualize structures behind the iris
    - D: needs probe to contact the eye

Advantages over Gonioscopy:
1. BOTH provide cross-sectional angle images
2. BOTH allow quantitative measurement of the angle, iris & anterior chamber parameters

Disadvantages of Gonioscopy:
1. Needs an experienced ophthalmologist to do the test properly
2. Should be performed under dark conditions to minimize light entering the pupil
3. Requires patient’s cooperation because the goniolens needs to contact the eye
4. NOT suitable for massive screening

19
Q

What parameters are measured in UBM or ASOCT?

A
  1. Angle parameters
    - Angle Opening Distance
    - Angle Recess Area
    - Trabecular-Iris Space Area
    - Trabecular-Iris Contact Length
    - Trabecular-Iris Angle
  2. Iris parameters
    - Thickness
    - Curvature
    - Area
    - Volume
  3. Anterior Chamber parameters
    - Width
    - Depth
    - Area
    - Volume
  4. Lens Vault
20
Q

What angle parameters are measured in UBM/ASOCT?

A

Reference point: Scleral Spur

  1. Angle Opening Distance (AOD)
    - distance between the corneal endothelium and anterior iris along a line perpendicular to the TM at a specified distance from the SS
    - AOD500: 500 µm anterior to the scleral spur
    - AOD750: 750 µm anterior to the scleral spur
  2. Angle Recess Area (ARA)
    - area lying between the line taken for the AOD and the angle recess
  3. Trabecular-Iris Space Area (TISA)
    - trapezoidal area that excludes the nonfunctioning area posterior to the SS
    - TISA500: using AOD500
    - TISA750: using AOD750
    - boundaries:
    + anterior: AOD
    + posterior: line drawn from SS perpendicular to the plane of the inner scleral wall to the opposing iris
    + superior: inner corneoscleral wall
    + inferiorly: iris surface
  4. Trabecular-Iris Contact Length (TICL)
    - measured in closed angles
    - linear distance of iris contact with the corneoscleral surface
    - begins at the scleral spur and extending to the anterior-most point of contact
  5. Trabecular-Iris Angle (TIA)
    - angle measured with the apex in the scleral spur and the arms of the angle passing through a point on the trabecular meshwork 500 µm from the scleral spur and a perpendicular point on the iris
21
Q

What iris parameters are measured in UBM/ASOCT?

A

Reference point: Scleral Spur

  1. Iris Thickness
    - measured at a certain distance from the scleral spur
  2. Iris Curvature
    - draw a line from the most peripheral to the most central points of the iris pigment epithelium
    - then a perpendicular line is extended from this line to the iris pigment epithelium at the point of greatest convexity
  3. Iris Cross-Sectional Area
    - cumulative cross-sectional area of the full length of the iris from SS to the pupil margin
  4. Iris Volume
    - computed from the Pappus–Guldin centroid theorem using the iris cross-sectional area
22
Q

What anterior chamber parameters are measured in UBM/ASOCT?

A
  1. AC Width
    - horizontal distance between the temporal and nasal scleral spurs
  2. AC Depth
    - perpendicular distance between the anterior pole of the crystalline lens and the central corneal endothelium
  3. AC Area
    - area bordered by the corneo–scleral inner surface and the anterior iris and lens surfaces
  4. AC Volume
    - calculated based on the ACA
23
Q

How is the Lens Vault defined in UBM/ASOCT?

A

Perpendicular distance between the anterior pole of the crystalline lens and a horizontal line joining the temporal and nasal scleral spurs

Exaggerated LV
- iris appears to drape the anterior surface of the lens, giving rise to a “volcano-like configuration” without an increase in iris curvature
- defined as LV more than one-third the distance between the corneal endothelium and a line drawn to connect the nasal and temporal scleral spurs

24
Q

What is Angle Recession?

A
  • recession of the ACA following concussive ocular trauma
  • blunt trauma forces the aqueous posterolaterally against the iris and the angle, exerting traction on the iris root and causing a tear between the longitudinal and circular muscles of the CB

Gonioscopy: widened Ciliary Body band
- because of a tear between the circular and the longitudinal ciliary muscles

UBM/ASOCT: widened ACA
- increased AOD, ARA, TISA, TICL and TIA

25
Q

Differentiate Angle Recession, Cyclodialysis, Iridodialysis and Trabecular Damage.

A

Angle Recession
- tear between the longitudinal (base) and circular muscles (processes) of the CB
- gonioscopy: longitudinal muscles (widened CBB)

Iridodialysis
- separation of the iris from the ciliary body
- gonioscopy: ciliary processes (widened CBB)

Cyclodialysis
- tear between the scleral spur and the longitudinal muscles of the CB
- separation of the sclera from the CB and eventually from the choroid
- gonioscopy: suprachoroidal space (clefts)

Trabecular Damage
- tear in the anterior portion of the TM, creating a flap that is hinged at the scleral spur
- gonioscopy: Schlemm’s Canal

26
Q

What is Cyclodialysis?

A
  • tear between the scleral spur and the longitudinal muscles of the CB
  • separation of the sclera from the CB

(+) Cyclodialysis Clefts
- direct connection between the anterior chamber and the suprachoroidal space
- causes ciliochoroidal detachment
- increases aqueous outflow leading to hypotony

Gonioscopy:
- clefts showing the suprachoroidal space
- acute: red due to heme
- chronic: black

27
Q

What is a Nidek Gonioscope?

A
  • instantly documents the ENTIRE iridocorneal angle in high-resolution color photographs
  • acquires photographs in 16 directions (360 degrees) with 17 possible foci
  • digital format allows re-assessment any time
  • the gel immersion avoids contact of the prism with the cornea for maximum comfort

Ophthalmology (44 decks)

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