Ophthalmology: Amblyopia, Lazy Eye
Amblyopia: Reduced visual acuity in the absence of sufficient eye or visual pathway disease to explain the level of vision.
Anisometropia: Difference in refractive error of the eyes.
Refraction: (1) Deviation in the course of rays of light in passing from one transparent medium into another of different density. (2) Determination of refractive errors of the eye and correction by lenses.
Refractive error (ametropia): An optical defect that prevents light rays from being brought to a single focus on the retina.
Refractive index: The ratio of the speed of light in a vacuum to the speed of light in a given material.
Visual acuity: Measure of the optical resolution of the eye.
Levin L. A. - Adler’s Physiology of the Eye (11th ed.) - 2011
Amblyopia is a developmental disorder of spatial vision usually associated with the presence of strabismus, anisometropia or form deprivation early in life.
Amblyopia is clinically important because, aside from refractive error, it is the most frequent cause of vision loss in infants and young children, and it is of basic interest because it reflects the neural impairment which can occur when normal visual development is disrupted. The damage produced by amblyopia is generally expressed in the clinical setting as a loss of visual acuity in an apparently healthy eye, despite appropriate optical correction; however, there is a great deal of evidence showing that amblyopia results in a broad range of neural, perceptual, and clinical abnormalities. Currently there is no positive diagnostic test for amblyopia. Instead, amblyopia is diagnosed by exclusion: in patients with conditions such as strabismus and anisometropia, a diagnosis of amblyopia is made through exclusion of uncorrected refractive error and underlying ocular pathology.
In humans, amblyopia occurs naturally in about 2–4 percent of the population and the presence of amblyopia is almost always associated with an early history of abnormal visual experience: binocular misregistration (strabismus), image degradation (high refractive error and astigmatism, anisometropia), or form deprivation (congenital cataract, ptosis). The severity of the amblyopia appears to be associated with the degree of imbalance between the two eyes, and to the age at which the amblyogenic factor occurred. Precisely how these factors interact is as yet unknown, but it is evident that different early visual experiences result in different functional losses in acuity and contrast sensitivity amblyopia, and a significant factor that distinguishes performance amongst amblyopes is the presence or absence of binocular function. Amblyopes who lack binocularity (primarily strabismic amblyopes) show much greater losses in Vernier and Snellen acuity than in grating resolution.
Ophthalmology, Fourth Edition- Myron Yanoff & Jay S. Duker
Amblyopia is a ‘developmental defect of spatial visual processing that occurs in the central visual pathways of the brain.’1 It presents most dramatically as loss of visual acuity in one or, rarely, both eyes, but amblyopia is more than this; certain forms of amblyopia also present with diminished contrast sensitivity, vernier acuity, grating acuity, and spatial localization of objects. These defects may be explained by the mechanism of lack of use of an eye because of media opacity or extreme refractive errors that cause a chronically blurred image to form on the fovea of that eye; however, the cause of amblyopia in an eye that has strabismus is not as straightforward and is the result of abnormal binocular interaction.
[A. K. Khurana] Comprehensive Ophthalmology (4th Ed.)
Uniocular vision. When refractive error in one eye is of high degree, that eye is suppressed and develops anisometropic amblyopia.
It implies a partial loss of sight in one or both eyes, in the absence of ophthalmoscopic or other marked objective signs. It may be either congenital or acquired. Acquired amblyopia may be organic (toxicamblyopia) or functional.
Functional amblyopia results from the psychical suppression of the retinal image. It may be anisometropic, strabismic or due to stimulus deprivation (amblyopia ex anopsia) (see page 319).
Anisometropic amblyopia occurs in an eye having higher degree of refractive error than the fellow eye. It is more common in aniso-hypermetropic than the anisomyopic children.
Even 1-2D hypermetropic anisometropia may cause amblyopia while upto 3D myopic anisometropia usually does not cause amblyopia.
У меня на тесте А, если видеть левым глазом только левую картинку, а правым правую только правую одновременно, то левая будет размыта, глаз расфокусирован, а по отедльности если смотреть то все четко. Если я закрою в этот момент правый глаз то начнет фокусироваться левый.
Clinical Ophthalmology - 6th ed (Kanski), page 655
Amblyopia is uncommon but may develop when there is a significant difference in myopia between the two eyes.
Anisometropic amblyopia is causcd by a dilTcrcncc in refrm:tivc crror bctwccn thc cycs and may rcsult from a diffcrcncc of ,IS littlc as I D sphcrc. Thc morc amctropic cyc rcccivcs a blurrcd imagc which is a mild limn of visual dcprivation. It is frcqucntly associatcd with microtropia and may cocxist with strabismic amblyopia.
Ophthalmology at a Glance, Second Edition - Olver, Jane, Cassidy, Lorraine
Amblyopia = ‘lazy eye’: amblyopia occurs in 2% of the population, and it occurs from insufficient use of the eye(s) during visual development (birth–7 years), commonly due to the presence of a manifest strabismus and/or refractive error. The brain suppresses the image from a deviating or defocused eye, particularly under 2 years of age—the sensitive period—when visual development is especially vulnerable to disruption.
Vaughan & Asbury’s General Ophthalmology, 18th Edition - Riordan-Eva, Paul & Cunningham, Emmett
The most common causes of amblyopia are strabismus, in which the image from the deviated eye is suppressed to prevent diplopia, and anisometropia, in which an inability to focus the eyes simultaneously causes suppression of the image of one eye. High degrees of hypermetropia or astigmatism, in which both eyes may become amblyopic because of failure to form a focused image in either eye, are less common causes of amblyopia.
Natural History of Refractive Errors
Most babies are slightly hyperopic, mean refractive error at birth being 0.5 D. The hyperopia slowly decreases, with a slight acceleration in the teens, to approach emmetropia. The corneal curvature is much steeper (6.59-mm radius) at birth and flattens to nearly the adult curvature (7.71 mm) by about 1 year. The lens is much more spherical at birth and reaches adult conformation at about 6 years. The mean axial length is short at birth (16.6 mm), lengthens rapidly in the first 2 or 3 years (to 21.8 mm), then moderately (0.4 mm per year) until age 6, and then slowly (about 1 mm total) to stability (24 mm) at about 10 or 15 years. Presbyopia becomes manifest in the fifth decade.
Refractive errors are inherited. The mode of inheritance is complex, as it involves so many variables. Refractive error, although inherited, need not be present at birth any more than tallness, which is also inherited, need be present at birth. For example, a child who reaches emmetropia at age 10 years will probably soon become myopic. Myopia usually increases during the teens. Factors influencing progression of myopia are poorly defined but probably include close work. Optical and pharmacological treatments to retard progression of myopia in children have not yet been shown to have long-term benefit.
Anisometropia is a difference in refractive error between the two eyes. It is a major cause of amblyopia because the eyes cannot accommodate independently and the more hyperopic eye is chronically blurred. Refractive correction of anisometropia is complicated by differences in size of the retinal images (aniseikonia) and oculomotor imbalance due to the different degree of prismatic power of the periphery of the two corrective lenses. Aniseikonia is predominantly a problem of monocular aphakia. Spectacle correction produces a difference in retinal image size of approximately 25%, which is rarely tolerable. Contact lens correction reduces the difference in image size to approximately 6%, which can be tolerated. Intraocular lenses produce a difference of less than 1%.
Correction of Refractive Errors
Spectacles continue to be the safest method of refractive correction. To reduce nonchromatic aberrations, the lenses are made in meniscus form (corrected curves) and tilted forward (pantascopic tilt).
- Currently there is no positive diagnostic test for amblyopia
- Diagnosed by exclusion, exclusion of uncorrected refractive error and underlying ocular pathology.
- бинокулярное зрение.
- осмотр глаз и глазного дна.
- extreme refractive errors
- form deprivation
- Levin L. A. et al. (eds.) - Adler’s Physiology of the Eye (11th ed.) - 2011
- 161. Helveston EM. Visual training: current status in ophthalmology. Am J Ophthalmol
- 162. Horton JC. Vision restoration therapy: confounded by eye movements. Br J Ophthalmol 2005; 89(7):792–794.
Treatment of amblyopia involves appropriate correction of refractive error and then, if necessary, initiating occlusion therapy (patching) of the sound eye several hours a day, or the use of atropine penalization (pharmacologic blurring of the sound eye) daily for several weeks. No matter what the therapy instituted, visual acuity of both eyes must be monitored.
- 161. Helveston EM. Visual training: current status in ophthalmology. Am J Ophthalmol
refractive error https://en.wikipedia.org/wiki/Amb
loss of visual acuity in an apparently healthy eye
broad range of neural, perceptual, and clinical abnormalities
- [Using Stereoscopic 3D Technologies for the Diagnosis and Treatment of Amblyopia in Children pdf]