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.
1Environmental Risk and Health, Flemish Institute for Technological Research (VITO), 2Centre for Environmental Sciences, Hasselt University, 3Transportation Research Institute, Hasselt University, 4Department of Public Health, Occupational and Environmental Medicine, Leuven University
1Institute of Nanoengineering and Microsystems, National Tsing Hua University, 2Taichung Veterans General Hospital
1Department of Therapeutics, Institut de la Vision, Sorbonne Universtés, UPMC Univ Paris 06, UMR_S 968, 2INSERM, U968, 3CNRS, UMR_7210
1Department of Biochemistry, Weill Cornell Medical College
Source: Laboratory of Jonathan Flombaum—Johns Hopkins University
In the back of everyone's eye is a small piece of neural tissue called the retina. The retina has photosensitive cells that respond to stimulation by light. The responses of these cells are sent into the brain through the optic nerve, a bundle of neural fibers. In each retina there is a place somewhere in the periphery where the outputs from retinal cells collect and the bundled optic nerve exits to the brain. At that location, there is no photosensitivity-whatever light reflects from the world and lands in that position does not produce a signal in the brain. As a result, humans have a blind spot, a place in the visual field for which they don't process incoming stimuli.
However, people are not aware that they have blind spots; there is not an empty hole in the visual images in front of the eyes. So what do people see in their blind spots? The brain actually fills-in missing input based on the surroundings.
This video demonstrates how to find a person's blind spot, and how to investigate the mechanisms of perceptual filling-in.…
Sensation and Perception
1Department of Cell and Molecular Biology, Tulane University, 2Department of Ophthalmology, Tulane University