Rhonda Curtis, CRA, COT, FOPS
Washington University Medical Center
St. Louis, Missouri
Adapted from the Journal of Ophthalmic Photography, Spring/2004 Vol 26:1 pg 13
Some structures of the eye cannot be viewed directly with a slit lamp examination. The use of special lenses allows for those areas to be viewed indirectly by utilizing mirrors. Physicians perform gonioscopy - viewing the eye with use of mirrored lenses; photographers perform goniophotography, the photo documentation of the eye using mirrored lenses.
Goniophotography usually is the second step in photodocumentation, the first being slit lamp or external documentation. External, slit lamp images and gonio images produce a case presentation of the patient's condition. Look at it as telling a story photographically.
Goniophotographs are used for:
- Pre-Surgery Documentation
- Legal Documentation
Gonio lenses used for photo documentation are usually indirect lenses such as the three mirrored or four mirrored lenses, although other lenses may be used. These lenses provide visualization of the structures by neutralizing the refractive element of the cornea and giving an oblique view of the structures. Structures of the eye that are usually photographed with these lenses are the angle of the eye, an oblique view of the iris and angle, and the posterior vitreous and retina. Examination of the angle and iris should be undertaken with an undilated pupil. Examination of the ciliary body, retina or vitreous is usually done with the pupil dilated.
The angles of mirrors in the Goldmann lens are set at 59, 67 and 73 degrees. The smallest mirror is set at 59° and is used to view the angle of the eye. The next larger mirror is set at 67°, and is used to document the iris and angle in an undilated eye, or the iris and lens in a dilated eye. The largest mirror is set at 73° and is used to document the peripheral retina and ciliary body in a dilated eye. Stray reflections from the mirror or front surface of the contact lens can cause flare and unwanted artifacts. Because of this, lenses with anti-reflective coatings, such as those used in laser surgery are best for photography. The surface of the lens should be kept clean and free of scratches. (Illustration by David M. Yates)
In goniophotography it is important to establish a routine of preparation before the lens is placed on the patient's cornea. Determine what you need to photograph and how you intend to obtain the documentation. Communication with the physician is highly important. Determine what lenses and which mirror or mirrors will be used to visualize the pathology. Position the patient and photographer comfortably, center and pre-focus the pathology to be documented. Preset the flash, f/stop and magnification. Adjust the slit beam to the shape of the mirror to be used, (half moon shaped) and align the height to the area the mirror will be placed. Prepare the lens by filling the concave end one third to one half full with methylcellulose to provide the cushion between the lens and cornea. It is important that there are no bubbles in the methylcellulose as this will interfere with the ability to visualize the pathology. Check for bubbles by holding the lens up to the light. If there are bubbles, clean the lens and reapply. Prepare the patient by explaining the procedure. Obtaining good images are dependent on how the photographer relates to the patient. Explain the procedure in a confident, matter of fact manner, telling them exactly what will be expected of them.
Have the patient look up while gently pulling down the lower lid. Place the lens in the lower lid margin and have the patient look straight ahead as the lens is tilted on the cornea. The lens placement can also be accomplished by having the patient look down and holding the upper lid with the lens, rotating the lens down onto the cornea as the patient looks straight ahead. Usually the upper lashes will need to be held with the other hand to prevent from getting into the lens. The thumb, index and middle finger are used to hold and rotate the lens, the other two fingers are hooked on the forehead rest, leaving the other hand free to operate the slit lamp. An arm-rest may be used to support the examiner's arm and the two fingers braced on the patient's face to keep up with small movements of the patient's head. Pulling back on the lens by the examiner or the patient backing away from the lens will break the seal and cause bubbles to form in the methylcellulose, or the lens to come off the eye. Excessive pressure from pushing the lens on the cornea may cause corneal folds and possibly injure the eye.
Anterior chamber hemorrhage induced by pressure of gonio lens.
Determine which mirror will be appropriate for the pathology to be documented and position the mirror opposite. With the lens on and using a low magnification, swing the slit lamp housing to illuminate the mirror fully by slightly rotating the lens and making height adjustments as necessary. Center the pathology in the mirror and increase the magnification, checking for artifacts and reflections. Expose the image, using predetermined exposures from testing of your system. Goniophotos are easily overexposed and the use of a small aperture and lower flash are usually needed. Exposures also are dependent upon the reflectivity of the area to be documented. If in doubt, bracket! Use different magnifications, angles of view and mirrors for documentation. Diverting the patient's gaze slightly can improve the view of the pathology. Communication with the physician is critical as is familiarity with the pathology to be documented.
Establish standards for documenting different pathology:
- types of photos needed (external, slit lamp)
When following a condition, have the patient's chart available and try to repeat the magnification and exposure techniques for accurate comparison between visits. This example shows the same eye before and after treatment of this anterior chamber tumor.