Source: Richard Glickman-Simon, MD, Assistant Professor, Department of Public Health and Community Medicine, Tufts University School of Medicine, MA
The simplest ophthalmoscopes consist of an aperture to look through, a diopter indicator, and a disc for selecting lenses. The ophthalmoscope is primarily used to examine the fundus, or the inner wall of the posterior eye, which consists of the choroid, retina, fovea, macula, optic disc, and retinal vessels (Figure 1). The spherical eyeball collects and focuses light on the neurosensory cells of the retina. Light is refracted as it passes sequentially through the cornea, the lens, and the vitreous body.
The first landmark observed during the funduscopic exam is the optic disc, which is where the optic nerve and retinal vessels enter the back of the eye (Figure 2). The disc usually contains a central whitish physiologic cup where the vessels enter; it normally occupies less than half the diameter of the entire disc. Just lateral and slightly inferior is the fovea, a darkened circular area that demarcates the point of central vision. Around this is the macula. A blind spot approximately 15° temporal to the line of gaze results from a lack of photoreceptor cells at the optic disc.
1Department of Ophthalmology, University of Bonn, 2Department of Ophthalmology, National University of Singapore, 3Geuder AG, 4Department of Ophthalmology, University of Münster, 5Section on Epithelial and Retinal Physiology and Disease, National Eye Institute/National Institutes of Health, 6Surgical Retina Department, Singapore National Eye Centre
Source: James W Bonz, MD, Emergency Medicine, Yale School of Medicine, New Haven, Connecticut, USA
Lateral canthotomy is a potentially eyesight-saving procedure when performed emergently for an orbital compartment syndrome. An orbital compartment syndrome results from a buildup of pressure behind the eye; as pressure mounts, both the optic nerve and its vascular supply are compressed, rapidly leading to nerve damage and blindness if the pressure is not quickly relieved.
The medial and lateral canthal tendons hold the eyelids firmly in place forming an anatomical compartment with limited space for the globe. In an orbital compartment syndrome, pressure rapidly increases as the globe is forced against the eyelids. Lateral canthotomy is the procedure by which the lateral canthal tendon is severed, thereby releasing the globe from its fixed position. Often, severing of the lateral canthal tendon alone is not enough to release the globe and the inferior portion (inferior crus) of the lateral canthal tendon also needs to be severed (inferior cantholysis). This increases precious space behind the eye by allowing the globe to become more proptotic, resulting in decompression. Most frequently, orbital compartment syndrome is the result of acute facial trauma, with the subsequent development of a retrobulbar …
Emergency Medicine and Critical Care
1Barbara & Donald Jonas Stem Cell Laboratory, and Bernard & Shirlee Brown Glaucoma Laboratory, Department of Pathology & Cell Biology, Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, 2Edward S. Harkness Eye Institute, New York-Presbyterian Hospital, 3Omics Laboratory, Byers Eye Institute, Department of Ophthalmology, Stanford University, 4Medical Scientist Training Program, University of Iowa, 5Department of Pediatrics, University of Iowa, 6Department of Neurology, University of Iowa, 7Department of Ophthalmology, Federal University of Sao Paulo (UNIFESP), 8Department of Ophthalmology, Federal University of EspÍrito Santo (UFES), 9Palo Alto Veterans Administration, Palo Alto, CA