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Gonioscopy: A necessary skill
Gonioscopy should be performed diagnostically in cases of suspected glaucoma and intraoperatively during MIGS or laser trabeculoplasty procedures.
Proficiency in performing gonioscopy is an asset not only to glaucoma specialists but also to cataract surgeons who undertake microinvasive glaucoma surgery.
Gonioscopy, which enables visualization and magnification of the iridocorneal angle through the use of a gonioscopic lens, “is very important for the diagnosis of glaucoma in terms of our major divisions of glaucoma, open angle and closed angle. The only real way you can ascertain that is through gonioscopy,” OSN Glaucoma Board Member Douglas J. Rhee, MD, said. “It should be done for anyone you suspect of having glaucoma or anyone with a shallow chamber.”
For therapeutic purposes, effective use of intraoperative gonioscopy is an important tool in the ophthalmologist’s armamentarium for performing MIGS as well as laser trabeculoplasty, according to Rhee.
“Many patients would probably undergo laser trabeculoplasty before undergoing anything more invasive,” Rhee said. “The number of people who might benefit or who are potential candidates for laser trabeculoplasty is even greater than the pool of people for MIGS procedures. In order to perform either MIGS or laser trabeculoplasty effectively, one needs to really know the landmarks in the angle and be able to perform gonioscopy well.”
Diagnosis
“I personally think everyone deserves gonioscopy simply because there is a condition that is pretty rare called plateau iris, in which the anterior chamber does not look shallow at all centrally but peripherally is very shallow,” Rhee said.
While anterior segment imaging and ultrasound biomicroscopy (UBM) are both useful imaging techniques to identify anatomic landmarks, gonioscopy remains the gold standard for documenting the angle, Rhee said. In cases of plateau iris syndrome, a “double hump” sign seen on gonioscopy is characteristic of the condition.
Whereas anterior segment OCT and UBM can be useful adjunct techniques for mapping out cyclodialysis clefts when IOP is low, gonioscopy can do the same and does not “require any expensive machinery or the technical skill involved for using either imaging platform,” Rhee said.
Technique
However, gonioscopy is a skill to be learned and does take practice. Every glaucoma book has a chapter on gonioscopy, which can help ophthalmologists improve gonioscopy techniques, develop diagnostic abilities and better understand the anatomy of a patient, Rhee said.
Particularly useful are online video resources. Wallace L.M. Alward, MD, of University of Iowa created a website, www.gonioscopy.org, that is “par excellence” for video tutorials and gonioscopy technique tutorials, Rhee said.
“Really understanding what you want to see scientifically and physiologically and looking at static images and looking at the videos will be helpful. That is not the only online resource. There are YouTube videos and other resources, but gonioscopy.org is comprehensive and organized,” he said.
Intraoperative gonioscopy
There is always an inadvertent chance for injury when there is an instrument in the eye and the patient is moving, so it is important for an ophthalmologist to be vigilant in the operating room, Rhee said.
When transitioning from cataract surgery to a MIGS procedure, Rhee suggested tilting the patient’s head and goniolens to achieve a 90° viewing angle.
“You want to tilt the microscope between 35° and 40°. You want to tilt it with the eyepiece toward you, the lens of the microscope tilted away, and the patient’s head tilted about 35° to 40° with the nose pointing away from you, not toward you. That will give you about a 90° viewing angle,” Rhee said.
Laser trabeculoplasty
“When people talk about the importance of gonioscopy, they often neglect to mention the importance of needing to know how to do gonioscopy for laser trabeculoplasty, whether selective or argon. From a therapeutic standpoint, more people will end up having laser trabeculoplasty than incisional surgery,” Rhee said.
“Even if you think to yourself, ‘Well, I’m not really planning on incorporating MIGS into my practice. I’ll refer it out to a specialist,’ you still should learn gonioscopy because most likely you are going to be doing laser trabeculoplasty.” – by Robert Linnehan
- References:
- eyewiki.aao.org/Plateau_Iris#Physical_examination. Accessed July 21, 2018.
- www.gonioscopy.org. Accessed July 12, 2018.
- For more information:
- Douglas J. Rhee, MD, can be reached at University Hospitals Eye Institute, LKS 5068, Cleveland, OH 44106-5068; email: dougrhee@aol.com.
Disclosure: Rhee reports he is a consultant for Ivantis and has received research grant support from Glaukos and Ivantis.
Perspective
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With the advent and popularization of microinvasive glaucoma surgery, it has become increasingly important for cataract surgeons to become more comfortable with intraoperative gonioscopy. Equally important is preoperative visualization of the angle during the initial cataract consultation, which helps assess candidacy for a particular MIGS device. As an implanter of an angle-based trabecular meshwork device, proper intraoperative visualization and identification of angle structures is vital in correct placement of the device. A simple mnemonic to remember the angle: I Cant see The Silly Line. This translates to Iris, Ciliary body band, Trabecular meshwork, Schwalbes Line. As there are various gonioscopic lenses available on the market, the key is to get comfortable with one and practice on normal eyes to identify anatomic landmarks. Once you are comfortable, you need to know where your MIGS device of choice is intended to be placed. There are many factors that can influence your intraoperative view for gonioscopy.
I find that it is important to fill the eye adequately with ophthalmic viscosurgical device and avoid undue pressure on the cornea with the gonioprism to avoid obscuration of the view secondary to corneal folds. Also, make sure to tilt the operating scope and the patients head to obtain the best view of the angle structures. As cataract surgeons become more familiar and comfortable with MIGS procedures, it is essential to be able to properly identify and target specific angle structures using intraoperative gonioscopy.