Gonioscopy
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(This Chapter is in development)
Introduction:
Gonioscopy is a technique used to visualize the anterior chamber angle of the eye including the trabecular meshwork, ciliary body and peripheral iris/cornea anatomy. Gonioscopy allows for the identification of structural abnormalities, which can cause or contribute to glaucoma. In this chapter, we will discuss the history, anatomy, techniques, lens types, diseases identified by gonioscopy, and surgical gonioscopy.
History:
Gonioscopy was first introduced by Albrecht von Graefe in 1858. The initial technique involved placing a goniolens on the eye and directing light onto the angle with a mirror. Over time, the technique evolved, and various types of lenses were developed to provide a more detailed view of the angle.
Anatomy of the anterior segment outflow system:
The anterior chamber angle is composed of the trabecular meshwork, Schlemm's canal, collector channels, and aqueous veins. The trabecular meshwork regulates outflow of aqueous humor into Schlemm's canal, which is a circular yet sometimes discontinuous canal that runs for 360 degrees between the scleral spur and peripheral cornea. Collector channels collect aqueous humor from Schlemm's canal and drain it into aqueous veins, which eventually empty into the bloodstream.
The anterior segment outflow system includes the structures responsible for the drainage of aqueous humor from the anterior chamber of the eye. These structures include the trabecular meshwork, Schlemm's canal, collector channels, and aqueous veins.
The anterior segment outflow system is a complex network that plays a crucial role in maintaining the intraocular pressure of the eye. Dysfunction of any of the structures within this system can result in increased intraocular pressure, which can lead to glaucoma.
Understanding the anatomy of the anterior segment outflow system is important for the diagnosis and treatment of anterior segment diseases, particularly those related to glaucoma. Gonioscopy, which involves the examination of the angle structures using a specialized lens, is an important tool for assessing the health of the anterior segment outflow system.
Techniques:
There are two primary techniques for performing gonioscopy: direct and indirect. Direct gonioscopy involves placing a contact lens on the eye, which provides a direct view of the angle. Indirect gonioscopy involves placing a hand-held lens in front of the eye and using a slit lamp to view the angle.
One technique is the Goldmann three-mirror lens technique, which uses a Goldmann three-mirror lens to examine the anterior chamber angle. This technique provides a wide-field view of the angle and allows for the examination of all four quadrants. The lens is placed on the cornea and the examiner uses the mirrors to visualize the angle structures.
Another technique is the Sussman four-mirror lens technique, which uses a Sussman four-mirror lens to examine the anterior chamber angle. This technique provides a high-magnification view of the angle and allows for the examination of all four quadrants. The lens is placed on the cornea and the examiner uses the mirrors to visualize the angle structures.
A third technique is the Zeiss four-mirror lens technique, which uses a Zeiss four-mirror lens to examine the anterior chamber angle. This technique provides a high-resolution view of the angle and allows for the examination of all four quadrants. The lens is placed on the cornea and the examiner uses the mirrors to visualize the angle structures.
In addition to these techniques, other specialized lenses may be used for specific situations. For example, the Koeppe lens may be used during surgical procedures to provide direct visualization of the anterior chamber angle.
When performing gonioscopy, it is important to properly prepare the patient and the equipment. The patient should be positioned comfortably and the examiner should ensure that the lighting is appropriate. The examiner should also ensure that the lens is properly cleaned and disinfected prior to use.
Additional Information on Lens types:
Gonioscopy lenses are available in both reusable and disposable forms. Reusable lenses are made of high-quality glass or plastic and can be sterilized and reused multiple times. They are more expensive than disposable lenses but offer better optical quality and durability. Some commonly used reusable lenses include the Goldmann, Sussman, and Zeiss lenses.
Disposable lenses are made of plastic and are designed for single use. They are less expensive than reusable lenses and eliminate the risk of cross-contamination between patients. Some commonly used disposable lenses include the Ocular Instruments Gonio Lens (Ocular Instruments, Bellevue, WA), the Volk 4 Mirror Gonio Lens (Volk Optical, Mentor, OH), and the Gonioscopy Prism Lens (Ophthalmic Instruments, Inc., Ontario, Canada).
Koeppe lenses are another type of reusable gonioscopy lens that is used for direct visualization of the anterior chamber angle during surgical procedures. They are designed to be used in conjunction with a microscope or other imaging device and are placed directly on the cornea. Some commonly used Koeppe lenses include the Barkan Gonioscopy Lens (Ocular Instruments, Bellevue, WA) and the K4 Gonioscopy Lens (Volk Optical, Mentor, OH).
It is important to choose a gonioscopy lens that is appropriate for the patient's anatomy and the intended use. Factors to consider include the lens size, angle of the mirror, and the degree of magnification. Proper lens selection and technique are essential for accurate diagnosis and treatment of anterior segment diseases.
Diseases identified by gonioscopy:
One of the most common abnormalities identified by gonioscopy is angle closure. Angle closure can be caused by several factors, including pupillary block, plateau iris syndrome, and iris bombé. Pupillary block occurs when the iris blocks the flow of aqueous humor through the pupil, leading to increased pressure in the posterior chamber of the eye. Plateau iris syndrome occurs when the iris root is abnormally anteriorly positioned, resulting in a shallower anterior chamber and an increased risk of angle closure. Iris bombé occurs when the iris bows forward, obstructing the trabecular meshwork and causing angle closure.
Peripheral anterior synechiae (PAS) can also be identified by gonioscopy. PAS occur when the iris adheres to the trabecular meshwork, blocking the outflow of aqueous humor and leading to elevated intraocular pressure. PAS can be caused by a variety of factors, including inflammation, trauma, and neovascularization.
Traumatic hyphema is another condition that can be identified by gonioscopy. Hyphema is the accumulation of blood in the anterior chamber of the eye, which can cause elevated intraocular pressure and damage to the optic nerve. Gonioscopy can help identify the extent of the hyphema and any associated angle abnormalities.
Surgical gonioscopy:
Surgical gonioscopy, also known as intraoperative gonioscopy, is a technique used during glaucoma surgery to visualize the anterior chamber angle and assess the patency of the trabecular meshwork. This technique differs from clinical gonioscopy in that it is performed intraoperatively with the patient under anesthesia and with the use of specialized instruments.
During surgical gonioscopy, a gonioscopy lens is placed directly onto the cornea, similar to clinical gonioscopy. However, the surgeon may use a microscope or other imaging technology to enhance visualization of the angle and surrounding structures. This technique can be particularly useful during minimally invasive glaucoma surgery (MIGS), which involves smaller incisions and less invasive approaches to treating glaucoma.
To enhance the success and quality of surgical gonioscopy during MIGS, here are some pearls for practice:
Use proper illumination: Adequate illumination is essential for good visualization of the angle. Use a bright light source and adjust the angle of the microscope or imaging device as needed to optimize illumination.
Use a high-quality lens: The quality of the gonioscopy lens can significantly impact visualization. Consider using a high-quality lens specifically designed for intraoperative use.
Use gentle pressure: Apply gentle pressure to the lens to prevent corneal indentation or distortion, which can affect visualization.
Be patient: Take the time to adjust the lens and microscope or imaging device to optimize visualization. A clear view of the angle is essential for proper assessment and treatment.
There are several approaches to MIGS, including trabecular micro-bypass stents, suprachoroidal shunts, and endoscopic cyclophotocoagulation. These techniques aim to improve aqueous outflow through the trabecular meshwork, suprachoroidal space, or ciliary body, respectively.
Conclusion:
Gonioscopy is a valuable technique for the identification and management of glaucoma. It provides a detailed view of the anterior chamber angle and allows for the identification of structural abnormalities that can contribute to elevated intraocular pressure. With ongoing research and development, new technologies and techniques will continue to enhance our ability to diagnose and manage glaucoma.
References:
Shields MB. Textbook of Glaucoma. 6th ed. Philadelphia, PA: Wolters Kluwer; 2016.
Shields MB. Gonioscopy. In: Yanoff M, Duker JS, eds. Ophthalmology. 4th ed. Philadelphia, PA: Elsevier; 2014:597-606.
Ritch R, Shields MB, Krupin T. The Glaucomas. 2nd ed. St. Louis, MO: Mosby; 1996.
Spaeth GL, Azuara-Blanco A, Araie M. Gonioscopy. In: Ritch R, Shields MB, Krupin T, eds. The Glaucomas. 2nd ed. St. Louis, MO: Mosby; 1996:49
Sheybani A, Reitsamer H, Ahmed IIK. Micro-invasive glaucoma surgery (MIGS): a review of surgical options. Saudi J Ophthalmol. 2017;31(4):217-224.
Gedde SJ, Vinod K. Surgical Techniques for Glaucoma. In: Yanoff M, Duker JS, eds. Ophthalmology. 5th ed. Elsevier; 2019:791-800.
Mosaed S, Dustin L, Minckler DS. Perioperative Gonioscopy in Minimally Invasive Glaucoma Surgery. J Glaucoma. 2017;26(4):272-276.
