This article is more than 5 years old. Information may no longer be current.
Digital imaging system an alternative to traditional process
New technology can be used to visualize structures in the anterior segment in a manner similar to direct gonioscopy.
Click Here to Manage Email Alerts
Although indirect gonioscopy is accepted as the current standard of care in angle evaluation, it does not appear to be performed regularly, even before laser or surgical glaucoma treatments, as found in recent studies.
Gonioscopy requires technical skills by the clinician, and increased time examining the patient, and it is often difficult. Patients are frequently uncomfortable and fidgety during gonioscopy, making it difficult for clinicians, particularly trainees, to gain an adequate visualization of all four angle quadrants.
Another issue with gonioscopy is inter- and intra-observer variability, which increases with narrow angles. Often, the examiner is unable to accurately document findings or compare structures before and after treatment, document patency of an internal ostium postoperatively or confirm precise placement of an implanted drainage device. Furthermore, gonioscopy is subject to artifact that can artificially reveal an angle to be more open than it truly is physiologically. Both indentation artifact from pressure on the cornea and light artifact from slit lamp illumination-induced miosis are capable of artificially opening the iridocorneal angle.
When an examiner wants photographic documentation of a gonioscopic view in a clinic setting, a slit lamp camera must be used. This is a cumbersome task, as the slit beam must be situated on a specific angle to minimize glare from the gonioscopic mirror. The resulting image often lacks adequate clarity and magnification. The skills required for gonioscopy and slit lamp photography are fairly sophisticated if one is to achieve a clear image. These challenges, coupled with patient discomfort, often make goniophotography a difficult task.
Additional imaging modalities to examine the anterior segment exist. Ultrasound biomicroscopy uses high frequency ultrasound for imaging the anterior segment and is particularly advantageous in its ability to assess structures posterior to the iris, such as the ciliary body. Recent use of anterior segment optical coherence tomography in the assessment of the angle has also shown promise. These devices provide high-resolution, cross-sectional representative scans of the angle and anterior segment, which can be done in a dark room with minimal to no corneal indentation. However, neither one of these technologies provides true color photographic examiner views of the angle that clinicians are accustomed to seeing during clinical gonioscopy. Pigment grading, neovascularization, subtle peripheral anterior synechia, pseudoexfoliation and other visual signs cannot be assessed with ultrasound biomicroscopy and anterior segment OCT.
|
|
|
|
|
|
|
Images: Calafati J, Naqi A, Ahmed IK |
What is the EyeCam?
The EyeCam (Clarity Medical Systems), distributed as the RetCam, is a new technology that was originally intended to yield focused, wide-field photographs of the fundus. With some modifications on optical technique and the use of a coupling gel, the RetCam can be used to visualize structures in the anterior segment in a manner similar to direct gonioscopy.
Of great interest to us within the anterior segment is the iridocorneal angle because accurate grading of patients’ angles is pivotal in the identification of closed-angle glaucoma, a disease process that seems to account for most blindness from glaucoma worldwide. EyeCam technology allows identification of critical angle components, namely Schwalbe’s line, the trabecular meshwork, the scleral spur and the ciliary body band, and thus allows magnified angle grading (Figures 1 to 5). It also enables visualization of physiologic and pathological signs in the angle (ie, iris processes, peripheral anterior synechia and neovascularization).
The EyeCam can help identify some etiologies of open-angle glaucoma such as pigment dispersion syndrome (Figure 6), pseudoexfoliation syndrome and neovascular glaucoma, as it produces a high magnification, true color view of the structures within the iridocorneal angle.
Furthermore, surgical manipulation of the angle and angle implants may be assessed pre- and postoperatively in cases of anterior chamber IOL implantation, goniosurgery, trabeculectomy ostium, trabeculo-Descemet’s window in non-penetrating surgery (Figure 7), new glaucoma angle devices (Figures 8 to 10) and tube shunt positioning (Figure 11). In the future, the EyeCam may be employed as an intraoperative visualization tool for anterior chamber approaches to new glaucoma angle and Schlemm’s canal surgery.
Moreover, in addition to evaluating the iridocorneal angle, the EyeCam may be employed to diagnose pathologies in the iris and lens.
Lastly, a trained ophthalmic technician can acquire images for each of the EyeCam applications. Then, the images can be either evaluated locally or sent remotely for evaluation by a clinician. The imaging system is designed to enable teleophthalmology applications via the Internet.
|
|
|
|
|
|
|
|
Techniques for EyeCam use
EyeCam is the anterior segment adaptation of existing RetCam technology. The most recent RetCam product is the RetCam Shuttle, which adds portability to the RetCam camera and software. The RetCam Shuttle system consists of three main parts, namely a light emitting control station, a computer hardware center and a digital camera. The camera is portable and is connected to the system by a cable. Users have the option to capture still images or extract images from the stream of video recording, which are saved to a DVD-RAM drive.
The lens that is used for the EyeCam is typically the 130· fundus lens, which images the posterior segment for conditions such as retinopathy of prematurity. With a different operating technique, the camera can be used to image the anterior segment in detail by using an angled approach (Figure 12).
The patient is positioned in a semi-reclined fashion, and topical anesthetic drops are used for patient comfort. A coupling gel such as viscous tear product is applied to the lens probe. This provides an optical interface between the camera’s lens and the cornea and eliminates the total internal reflection that naturally occurs at the corneal tear film-air interface, allowing rays of light coming from the iridocorneal angle to escape to the EyeCam. The gel essentially forms a Koeppe-style lens.
To image a particular angle, the patient is instructed to look in the direction of that angle to provide for the maximum apparition of images. For example, an examiner wanting to capture still frames of the nasal quadrant of the right eye would ask the patient to look in toward his left and would place the lens probe on the patient’s temporal limbus. The probe is positioned toward the angle of interest and then tilted downward to bring the angle structures into view.
The foot switch on the EyeCam provides users with control for light intensity and focus. In addition to a central button that can be pressed to capture still images, the apparatus has two additional pedals. One of these pedals functions to increase or decrease light accordingly, whereas the other pedal is used for focusing the image. With the ability to make these fine adjustments, it is possible to create an ideal environment that produces clear and detailed high-quality photos.
Preliminary investigations
A preliminary study that we performed comparing EyeCam “goniography” with gonioscopy in 60 eyes has demonstrated that results from the EyeCam are accurate and reliable.
In the study, we have included a myriad of patients who underwent EyeCam goniography. Angles range from a Shaffer grading of 0 to 4 on clinical gonioscopy. Specifically, we have been looking at the correlation of the EyeCam images with the angle measurements reported during gonioscopy.
In addition to examining correlations, we have been assessing the sensitivity and specificity of the EyeCam to detect narrow and occludable angles at risk of developing acute angle closure.
Advantages over gonioscopy
Perhaps the simplest yet most noticeable advantage of the EyeCam technology over traditional gonioscopy relates to patient comfort. Unlike gonioscopy, the EyeCam is applied lightly to the limbus and with the patient in a semi-recumbent position, which limits the patient’s natural reflex to move during an examination. The lens probe is placed on a coupling gel without direct contact onto the cornea, eliminating the concern of compression artifact. Light from the fiber optic probe is directed into the angle as opposed to the pupil to reduce light artifact.
We prefer using the EyeCam video capture mode to evaluate angles. This allows optimal still images to be extracted by scrolling through the stream of recorded video. By using video capture, patient motion has little effect on the quality of the examination by permitting the user to review the clip and select the best image.
Furthermore, gonioscopy relies on the premise that the examiner must evaluate the angle during slit-lamp visualization and does not allow for the documentation of angles using images. The EyeCam, however, is able to take still images that can be saved on a computer, thus allowing a basis of comparison to monitor angle changes if serial examinations are done over time. This monitoring would be useful to track both disease progression as well as treatment effects. In addition, access to these saved still images gives other health care professionals a view of that same angle, thus minimizing the potential discrepancies of inter-observer reliability. Overall, it is this ability to save images combined with the user-friendly nature of the equipment that makes the use of the EyeCam a realistic skill to acquire for most technicians with a basic ophthalmic background. Its portability and relative ease of use make it an important addition to screening programs worldwide.
Long-term implications
Our preliminary investigations using the EyeCam have yielded promising results in terms of angle correlation with clinical gonioscopy. We have found EyeCam goniography to be a useful adjunct to clinical gonioscopy — much like disc photos have become an important tool in glaucoma optic nerve evaluation and documentation. Further studies will be needed to determine its role compared with clinical gonioscopy and screening utility. Finally, EyeCam may have the potential to serve as a surgical visualization tool for intraoperative direct gonioscopy for goniotomy and new ab interno glaucoma devices.
References:
- Ahmed I, MacKeen L. A New Approach to Imaging the Angle. Glaucoma Today. 2007;4:1-3.
- Bruno CA, Alward W. Gonioscopy in primary angle closure glaucoma. Semin Ophthalmol. 2002;17(2):59-68.
- Coleman AL, Yu F, Evans SJ. Use of gonioscopy in Medicare beneficiaries before glaucoma surgery. J Glaucoma. 2006;15:486-493.
- Pavlin CJ, Foster FS. Ultrasound biomicroscopy. High-frequency ultrasound imaging of the eye at microscopic resolution. Radiol Clin North Am. 1998;36(6):1047-1058.
- Pavlin CJ, Harasiewicz K, Sherar MD, Foster FS. Clinical use of ultrasound biomicroscopy. Ophthalmology. 1991;98(3):287-295.
- Quigley HA, Friedman DS, Hahn SR. Evaluation of practice patterns for the care of open-angle glaucoma compared with claims data: the glaucoma adherence and persistency study. Ophthalmology. 2007;114(9):1599-1606.
- Tello C, Tran HV, Liebmann J, Ritch R. Angle closure: classification, concepts, and the role of ultrasound biomicroscopy in diagnosis and treatment. Semin Ophthalmol. 2002;17(2):69-78.
- Ike K. Ahmed, MD, FRCSC, is assistant professor at the University of Toronto and clinical assistant professor at the University of Utah in Salt Lake City. He can be reached at 905-820-3937; e-mail: ike.ahmed@utoronto.ca.
- Jennifer Calafati, MD, is a research fellow at the University of Toronto, under the supervision of Dr. Ahmed. She may be reached at 905-820-3937; e-mail: jennifer.calafati@hotmail.com.
- Abdulla Naqi, MD, is a clinical and research fellow at the University of Toronto, under the supervision of Dr. Ahmed. He may be reached at 905-820-3937; e-mail: abdullanaqi@hotmail.com.
- Dr. Ahmed is a consultant for Clarity Medical Systems.
- Dr. Calafati has no direct financial interest in the products discussed in this article, nor is she a paid consultant for any companies mentioned.
- Dr. Naqi has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.