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Peripheral vision, or indirect vision, is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in the "corner of one's eye". The vast majority of the area in the visual field is included in the notion of peripheral vision. "Far peripheral" vision refers to the area at the edges of the visual field, "mid-peripheral" vision refers to medium eccentricities, and "near-peripheral", sometimes referred to as "para-central" vision, exists adjacent to the center of gaze.
Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness, it affects many adults over the age of 40. A common sign of presbyopia is difficulty reading small print which results in having to hold reading material farther away. Other symptoms associated can be headaches and eyestrain. Different people will have different degrees of problems. Other types of refractive errors may exist at the same time as presbyopia. This condition is similar to hypermetropia or far-sightedness which starts in childhood and exhibits similar symptoms of blur in the vision for close objects.
Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amblyopia is the most common cause of decreased vision in a single eye among children and younger adults.
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye influence the sharpness of an image on its retina. Neural factors include the health and functioning of the retina, of the neural pathways to the brain, and of the interpretative faculty of the brain.
A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862 as a measurement tool for the acuity formula developed by his professor Franciscus Cornelius Donders. Many ophthalmologists and vision scientists now use an improved chart known as the LogMAR chart.
The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina.
An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. Eye charts are often used by health care professionals, such as optometrists, physicians and nurses, to screen persons for vision impairment. Ophthalmologists, physicians who specialize in the eye, also use eye charts to monitor the visual acuity of their patients in response to various therapies such as medications or surgery.
Anterior ischemic optic neuropathy (AION) is a medical condition involving loss of vision caused by damage to the optic nerve as a result of insufficient blood supply (ischemia). This form of ischemic optic neuropathy is generally categorized as two types: arteritic AION, in which the loss of vision is the result of an inflammatory disease of arteries in the head called temporal arteritis, and non-arteritic AION, which is due to non-inflammatory disease of small blood vessels.
Visual or vision impairment is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment – visual impairment may cause the individual difficulties with normal daily tasks including reading and walking. The terms low vision and blindness are often used for levels of impairment which are difficult or impossible to correct and significantly impact daily life. In addition to the various permanent conditions, fleeting temporary vision impairment, amaurosis fugax, may occur, and may indicate serious medical problems.
The Landolt C, also known as a Landolt ring, Landolt broken ring, or Japanese vision test, is an optotype: a standardized symbol used for testing vision. It was developed by the Swiss-born ophthalmologist Edmund Landolt.
The LEA Vision Test System is a series of pediatric vision tests designed specifically for children who do not know how to read the letters of the alphabet that are typically used in eye charts. There are numerous variants of the LEA test which can be used to assess the visual capabilities of near vision and distance vision, as well as several other aspects of occupational health, such as contrast sensitivity, visual field, color vision, visual adaptation, motion perception, and ocular function and accommodation (eye).
Gordon Ernest Legge is currently the Distinguished McKnight University Professor and former chair of the Department of Psychology at the University of Minnesota. Legge is the director of the Minnesota Laboratory for Low-Vision Research.
Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the ciliary muscle in a relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and eye lens and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfectly sharp distance vision. A human eye in a state of emmetropia requires no corrective lenses for distance; the vision scores well on a visual acuity test.
A logMAR chart is a chart consisting of rows of letters that is used by ophthalmologists, orthoptists, optometrists, and vision scientists to estimate visual acuity. The chart was developed at the National Vision Research Institute of Australia in 1976, and is designed to enable a more accurate estimate of acuity than do other charts. For this reason, the LogMAR chart is recommended, particularly in a research setting.
Crowding is a perceptual phenomenon where the recognition of objects presented away from the fovea is impaired by the presence of other neighbouring objects. It has been suggested that crowding occurs due to mandatory integration of the crowded objects by a texture-processing neural mechanism, but there are several competing theories about the underlying mechanisms. It is considered a kind of grouping since it is "a form of integration over space as target features are spuriously combined with flanker features."
Jan E. Lovie-Kitchin is an Australian optometrist, former professor at Queensland University of Technology and founder of the university's Vision Rehabilitation Centre. She was the co-developer of the Bailey-Lovie visual acuity chart.
Vernier acuity is a type of visual acuity – more precisely of hyperacuity – that measures the ability to discern a disalignment among two line segments or gratings. A subject's vernier acuity is the smallest visible offset between the stimuli that can be detected. Because the disalignments are often much smaller than the diameter and spacing of retinal receptors, vernier acuity requires neural processing and "pooling" to detect it. Because vernier acuity exceeds acuity by far, the phenomenon has been termed hyperacuity. Vernier acuity develops rapidly during infancy and continues to slowly develop throughout childhood. At approximately three to twelve months old, it surpasses grating acuity in foveal vision in humans. However, vernier acuity decreases more quickly than grating acuity in peripheral vision. Vernier acuity was first explained by Ewald Hering in 1899, based on earlier data by Alfred Volkmann in 1863 and results by Ernst Anton Wülfing in 1892.
Childhood blindness is an important contribution to the national prevalence of the disability of blindness. Blindness in children can be defined as a visual acuity of <3/60 in the eye with better vision of a child under 16 years of age. This generally means that the child cannot see an object 10 feet away, that another child could see if it was 200 feet away.
Childhood cataract is cataract that occurs at birth or in childhood. It may be congenital or acquired.
Near visual acuity or Near vision is a measure of how clearly a person can see nearby small objects or letters. Near vision is usually measured and recorded using a printed hand-held card containing different sized paragraphs, words, letters or symbols. Jaeger chart, N notation reading chart and Snellen's near vision test are the commonly used charts for measuring and recording near visual acuity. Near vision testing is usually done after correcting the distance vision.
References
- 1 2 Altinbay, Deniz; Adibelli, Fatih Mehmet; Taskin, Ibrahim; Tekin, Adil (2016). "The Evaluation of Reading Performance with Minnesota Low Vision Reading Charts in Patients with Age-related Macular Degeneration". Middle East African Journal of Ophthalmology. 23 (4): 302–306. doi: 10.4103/0974-9233.194078 . ISSN 0974-9233. PMC 5141623 . PMID 27994393.
- ↑ Calabrèse, Aurélie; Cheong, Allen M. Y.; Cheung, Sing-Hang; He, Yingchen; Kwon, MiYoung; Mansfield, J. Stephen; Subramanian, Ahalya; Yu, Deyue; Legge, Gordon E. (1 July 2016). "Baseline MNREAD Measures for Normally Sighted Subjects From Childhood to Old Age". Investigative Ophthalmology & Visual Science. 57 (8): 3836–3843. doi: 10.1167/iovs.16-19580 . ISSN 1552-5783. PMC 4961000 .
- ↑ Calabrèse, Aurélie; To, Long; He, Yingchen; Berkholtz, Elizabeth; Rafian, Paymon; Legge, Gordon E. (19 January 2018). "Comparing performance on the MNREAD iPad application with the MNREAD acuity chart". Journal of Vision. 18 (1): 8. doi: 10.1167/18.1.8 . ISSN 1534-7362. PMC 5774869 . PMID 29351351.
- ↑ Calabrèse, Aurélie; Owsley, Cynthia; McGwin, Gerald; Legge, Gordon E. (1 April 2016). "Development of a Reading Accessibility Index Using the MNREAD Acuity Chart". JAMA Ophthalmology. 134 (4): 398–405. doi:10.1001/jamaophthalmol.2015.6097. PMC 5369600 . PMID 26868760.
- ↑ Radner, W. (14 April 2017). "Reading charts in ophthalmology". Graefe's Archive for Clinical and Experimental Ophthalmology. 255 (8): 1465–1482. doi: 10.1007/s00417-017-3659-0 . ISSN 0721-832X. PMC 5541099 . PMID 28411305.
- ↑ "MNRead-History | MN Lab for Low-Vision Research". gellab.psych.umn.edu.
- ↑ "MNREAD Acuity Charts | MN Lab for Low-Vision Research". gellab.psych.umn.edu.