Myopia is a refractive defect in which parallel rays of light are brought to focus in front of the retina when no accommodation is used (Grosvenor and Goss, 1999; Saw, et al., 1996). This causes distant objects to appear blurred while near objects can still be seen clearly.
Myopia can be classified in various ways: cause (axial or refractive) (Emsley, 1953), age of onset (congenital, youth onset, early adult-onset, or late adult-onset) or degree (low, intermediate or high) (Grosvener, 1987). When classifying myopia by degree, high myopia is indicated where myopia is greater than 6.00 dioptres, intermediate between 3 and 6D and low 0.50 to 3.00D (Fitzgerald, Chung, and Krumholtz, 2005).
Axial myopia is due to the axial elongation of the vitreous chamber meaning that the eye becomes too long for its refractive power. (Benjamin, 1998) Refractive myopia is caused by an error in the dioptric power of the eye either due to variation in the refractive index of lens (index myopia), increase in curvature of the refractive surface of cornea (curvature myopia) or abnormality in anterior chamber depth (anterior chamber myopia) (Borish, 1970). Further research (Strang, Winn and Bradley, 1998) showed that most cases of significant myopia are mainly due to axial myopia.
Theories about the cause of myopia are currently incomplete. It is thought there is some genetic aspect but it can also be induced by an excessive amount of near work stimulating accommodation. (ref) Systemic conditions may also have an influence in myopia and its progression. (ref)These include: Marfans syndrome, foetal alcohol syndrome, Crouzoan syndrome and cerebral palsy. Another influence proven to be associated with myopia and its progression is birth weight and ...
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Optometrists have accepted vision therapy, which is a medical treatment for optical muscle disabilities, as a feasible treatment used for eye related problems; claiming the treatment can strengthen vision and give the patient the opportunity to understand visuals quicker and clearer (Press). Vision therapy originated in the 1950s and over the past 25 years, has gained popularity, mainly because of new technological innovations in the field of treatment. Generally, vision therapy is prescribed as a measure mainly for people between the ages of 3 and 18. With the results from a comprehensive series of eye tests, the optometrist can work with the patient using special instruments—prisms, filters, occluders, and eye lenses—and strengthen the eye muscles, thus improving sight. According to optometrists in favor of vision therapy, these methods of treatment using these instruments function as safer routes to repair eye disabilities. Although vision therapy can yield favorable results, the practice as a treatment for innate eye disabilities has been in hot debate lately; as it can exceed $8000 and insurance companies do not cover the treatment. For decades, insurance companies have refused to accept vision therapy as a legitimate method for repairing eyesight (Boink). Concomitant with lack of insurance, the cost for a full treatment can exceed $8000, and doctors cannot guarantee a successful outcome. Recently, parents of children with eye related disabilities, such as amblyopia (lazy eye) and strabismus (cross-eye), and doctors have attempted to cooperate with public schools to allow families access to school-funded doctors to practice vision therapy. With a tight budget, most schools cannot afford to supply vision therapy, and a...
The ‘where visual pathway’ is concerned with constructing three dimensional representations of the environment and helps our brain to navigate where things are, independently of what they are, in space in relation to itself (Mishkin & Ungerleider & Macko, 1983).... ... middle of paper ... ... The 'Standard' of the 'Standard'.
The effects of perceptual load on the occurrence of inattentional blindness were demonstrated clearly by experiment. In an experiment conducted by Finch and Lavie in 2007, participants were given identical series of central cross-targets with two arms of clearly different color (blue and green) and slightly different length. Participants were split in two groups, one performing an easy task (low load condition) and the other a harder task (high load condition). The group performing the easiest task only had to make color discrimination between the tw...
According to Baily and Hall, while visual impairment early in life is associated with inherited congenital disorders, abnormal fetal devepment, and problems associated with premature birth, most eye conditions are associated with aging. They claim that over 70% of the visually impaired population in the United States is over 65. Age related maculopathy, also called macular degeneration, or AMD, impairs the center of vision in older individuals. The macula is the region in the back of the retina that surrounds and includes the fovea (Goldstein 1999). It is important to understand that when this degeneration progresses enough, the condition constitutes blindness because the foveal area is what is used to focus on something. Most cases do not progress this far, but between five and 20% do. Allikments and Shroyer claim that 11 million people in the United States alone suffer some degree of this impairment, with 75% of those individuals being 75 or older. Seven percent of this older age group reportedly suffer advanced forms. Freidman reports the disease as most common in developed countries.
Myopia is a condition in which visual images come into focus in front of the retina of the eye. This condition causes objects at a distance to appear blurry, while objects nearby are seen clearly. If not severe, myopia can be treated with contacts or glasses. Other treatments for myopia include photoreactive keratectomy (PRK), LASIK, and orthokeratology. Degenerative myopia is a quick progression of myopia and leads to complete loss of vision. The treatment for degenerative myopia is a combination of medication and laser surgery.
As humans age, they frequently develop a condition known as presbyopia. This condition decreases the person's ability to focus sharply on those object which are nearby and is the result of the lens of the eye hardening. In addition, astigmatism requires a person wear prescription eyeglasses and/or contact lenses. Astigmatism arises when the curvature of the eye is irregular. The eye is normally shaped liked a soccer ball or basketball. With astigmatism, it takes on a more oval shape and resembles a football. Due to the irregular curvature, the eye processes light differently and leads to blurred vision. The degree of blurriness is determined by the degree of
Vecera, S.P. & Gilds, K.S. (1998) What Processing is Impaired in Apperceptive Agnosia: Evidence from Normal Subjects. Journal of Cognitive Neuroscience, 10 (5), p.568
This is a representation of the eye's lens system. This eye has no eye condition, such as nearsightedness or farsightedness, and the lens is drawn in its relaxed position. The light rays are focused appropriately on the retina. The thickness of the cornea is 0.449 mm, the distance from the cornea to the lens is 2.
There are several types of amblyopia. Researchers must be aware of the various types of amblyopia because the effects for each are not always consistent. Strabismic amblyopia is caused when the two eyes are out of alignment due to weak musculature. Anisometropic amblyopia is a result of a large difference in refractive power of an individual's eyes. Another form of amblyopia results when visual information does not reach the retina. This is called stimulus deprivation amblyopia. Meridional amblyopia is a result of the diffused images caused by astigmatism. Researchers often discover that there are differences between groups of amblyopes based on type. For example, Levi and his colleagues (1994) discovered differences in vernier acuity between anisomet...
Muller, N. G., Bartelt, O. A., Donner, T. H., Villringer, A. & Brandt, S. A. (2003). A physiological correlate of the “zoom lens” of visual attention. The Journal of Neuroscience, 23(9): 3561-3565.
Macular degeneration also known as late, aged-related maculopathy is an eye disorder which causes a decrease in the visual field known as the retinal macula (Medical Encyclopedia, 2000). The majority of people who are affected are people over the age of 65, but occasionally it develops earlier in people 40-50 years old (Philippi, 2000). The majority of the visual loss is located in the central part of the visual field, while the peripheral vision is unharmed. There are also two types of macular degeneration, the "wet" and "dry" forms. The "dry" form of this disease is the most popular, affecting 90% of the cases (American Academy of Ophthalmology, 1997).
Regarding to the ocular examination, the patient's visual acuity without optical correction (spectacle) was good 20/20 in both eyes. IOP measurements was 18 mmHg on the right eye and 16 mmHg in the left eye. The pupil was equal, round and reactive to light with no afferent pupillary defect in both eyes. In extarocular movement test, there was limited downward gaze with
Heiting, Gary, and Mark Mattison-Shupnick. "Bifocals and Trifocals for Vision Over 40." All About Vision. All About Vision, 1 Jan. 2014. Web. 23 May 2014. .
There are many different Visual Perception principles in perception. The main principles are Gestalt. Gestalt is a German word meaning 'form' or 'shape'. Gestalt psychologists formulated a series of principles that describe how t...
The images formed on the two retinas are so unlike that they cannot be blended in the brain. Thus, a double image is perceived. The condition is known as diplopia, or double vision. Prismatic lenses are prescribed to correct this defect.Imperfections in the cones of the retina, resulting from heredity or disease, cause defective color vision. This is known as color blindness, or Daltonism. In total color blindness, everything appears in shades of gray.