Gonioscopy

Introduction

It is not possible to view the structures of the anterior chamber angle with direct observation. The scleral tissue projects anterior to the angle and the curvature of the cornea creates internal reflection when one attempts to view the angle obliquely.
Gonio lenses permit observation of the angle by eliminating the cornea as a refracting surface by placing a concave surface against the cornea. This allows visualization of the angle using obliquely inclined mirrors.

Indications for Gonioscopy

To visualize the anterior chamber angle
To assess anterior chamber angle when it appears narrow with Van Herrick procedure -- (typically Grade 2 or less)
Historical evidence of Angle Closure
Classification of Glaucoma
To note extent of iris neovascularization
Assess Angle Recession
Evidence of neoplastic activity in the Anterior Chamber
History or evidence of Trauma
To assess Peripheral Anterior Syncheiae (PAS)

Instrumentation

Several different lenses are available for performing gonioscopy
Click on the following images for a larger image of each lens.

Goldmann 3 Mirror Lens

Goldmann 3 mirror gives both an erect virtual image of fundus as well as an indirect view in the angle as in a mirror.
-64 Diopter lens
BC 7.40 mm, (46.00 D), 18 mm OAD
Erect, virtual image of fundus
Only the "thumbnail" mirror is used for observing the angle the other mirrors provide views of the retina

Mirrors

Viewing the angle 180 degrees away from the mirror (view is inverted or reversed)
View II : 73 degrees, from posterior pole to equator, trapezoid
View III: 67 degrees, equator to beginning of ora, rectangular
View IV : 59 degrees, anterior chamber, ora serrata, thumbnail
* Use thumbnail mirror to view the AC angle

Goldman 4 mirror is also available with slightly different mirror angles for viewing Either lens may be obtained with flange or without a flange (lip). Personal preference only.

Procedure

Patient preparation
- Explain purpose in layman's terms
- Explain anesthetic and sensation (slight pressure)
- Wash hands before touching the patient
- Position patient at slit lamp
- Forehead against forehead rest
- * Patient should be comfortable
- Align lateral canthus with alignment mark on SL
  - Otherwise will not have enough vertical range
  - Check to make sure you have enough vertical range
- Scan cornea with cobalt light and fluorescein (make sure clear before instilling gtts) Can use Fluress or Fluorocaine
- Instill anesthetic
  - 1. One gtt proparacaine 0.5%
  - 2. Some persons allergic to proparacaine (Substitute Fluress instead)
    - a. Contains benoxinate and fluoroscein
    - b. No cross sensitivity to benoxinate
    - c. Fluorocaine
      - 1. Contains proparacaine and fluoroscein
      - 2. Persons allergic to proparacaine (typically will be allergic to fluorocaine)
- SL preparation
  - Adjust oculars for PD and RX so you are binocular
  - Illumination lamp and microscope at 0 degrees (perpendicular to pupil)
  - Low mag and low illumination (6-10X)
  - Parallelpiped (2 mm width and maximum height)
  - * Orient beam parallel to the axis of the mirror
  - Vertical for Superior and Inferior angles
  - Horizontal for Nasal and Temporal angles
- Lens preparation
  - Clean goniolens with soap and water and rinse with saline
  - Do NOT use alcohol, it can damage the lens
  - Instill gonio lens fluid (Goniosol or other viscous fluid)
  - Gonisol
    - Viscous solution (methylcellulose)
    - Allergic reaction to high % of BAK
    - Celluvisc is a better solution to use
  - Fill concave surface of goniolens to the black line
    - Use 4 to 6 drops
    - Remove bubbles
      - By tapping lens
      - Rolling kleenex to a point and popping bubbles (NOT A RECOMMENDED TECHNIQUE AS CONTAMINATION MAY OCCUR)
      - Do not use tip of gonio bottle or Celluvisc vial
      - Do not contaminate the bottle or vial
      - * Store gonio bottle upside down to help prevent bubbles
- Application of goniolens
  - Grasp goniolens with thumb and forefinger
  - Position lens such that the thumbnail mirror will be superior (12 o'clock position when placed on the eye)
  - For patient's right eye, hold lens in left hand
  - Have patient look down - Firmly grasp upper lid with thumb
  - Have patient look up
  - Pull down lid with fingers
  - Rest gonio lens on lower margin
  - Tilt lens up to meet cornea while asking patient to look straight ahead to meet gonio lens.
  - Place lens on cornea
  - Lower upper lid over the top of lens
  - Rotate lens with thumb and index finger until thumbnail mirror is in the proper position
  - Can hold lens with one hand and rotate with other hand
  - If lens forms a vacuum, will not rotate freely so rotate lens by using very small motions
- To view angle
  - Move SL beam into the appropriate mirror
  - SL beam should be exactly parallel to the axis of the mirror or perpendicular to the base of the mirror
  - To obtain a sharp optical image, tilt the lens slightly towards the light or move SL in/out in small increments
  - To remove glare
    - Try moving illum slightly to side (5-10 degrees)
    - Tilt lens along axis of base of mirror
    - When thumbnail is superior - Tilt lens Left to Right
    - When thumbnail is temporal - Tilt lens Up or Down
    - Glare may also be caused by bubbles
    - To see further into the angle
    - Rocking the lens
    - Away from mirror to see more posterior (CBB) or
    - Towards the patient's pupil to see more posterior (CBB)
    - To see more anterior, rock lens towards the mirror (towards SL)
    - Changing patient's fixation
    - To see more anterior, patient looks opposite the mirror
    - For lower angle, mirror is superior
    - To see more anterior, have patient look down
    - To see more posterior (CB), have patient look up
- Lens removal
  - To remove the goniolens
  - Rock gently back and forth till break the seal
  - Have patient look nasally, gently press temporal scleral region through the lid
  - Irrigate the eye if using goniosol
  - Stream saline in the cul-de-sac from nasal to temporal
  - Irrigate upper and lower cul-de-sacs
  - Irrigation is optional if using Celluvisc of CL solutions
  - Recheck corneal integrity with fluorescein
  - Normal to see negative staining (edema) Due to pressure of the lens begin held on cornea
  - Goniosol reaction: stippling over entire cornea
  - Proparacaine reaction: patchy punctate staining
  - Explain results to patient
  - Clean and disinfect lens
Structures to view while performing gonioscopy procedure.

Additional items to monitor and miscellaneous information