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Pinhole Occluder
A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light, as in a pinhole camera, temporarily removing the effects of refractive errors such as myopia. Because light passes only through the center of the eye's lens, defects in the shape of the lens (errors of refraction) have no effect while the occluder is used. In this way, the ophthalmologist, orthoptist or optometrist can estimate the maximum improvement in a patient's vision that can be attained by lenses to correct errors of refraction. This can be used to distinguish visual defects caused by refractive error, which improve when the occluder is used, from other problems, which do not. The pinhole occluder can also be used in testing visual acuity in mydriatic patients. In this case, the pinhole occluder compensates for the inability to contract the iris assisting the eye in obtaining ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Acuity
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal image within the eye, (2) the health and functioning of the retina, and (3) the sensitivity of the interpretative faculty of the brain. The most commonly referred visual acuity is the far acuity (e.g. 6/6 or 20/20 acuity), which describes the examinee's ability to recognize small details at a far distance, and is relevant to people with myopia; however, for people with hyperopia, the near acuity is used instead to describe the examinee's ability to recognize small details at a near distance. A common cause of low visual acuity is refractive error (ametropia), errors in how the light is refracted in the eyeball, and errors in how the retinal image is interpreted by the brain. The latter is the primary cause for low vision in people with a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinhole (optics)
A pinhole is a small circular hole, as could be made with the point of a pin. In optics, pinholes with diameter between a few micrometers and a hundred micrometers are used as apertures in optical systems. Pinholes are commonly used to spatially filter a beam (such as a laser beam), where the small pinhole acts as a low-pass filter for spatial frequencies in the image plane of the beam. A small pinhole can act as a lens, focusing light. This effect is used in pinhole cameras and camera obscura. This effect is also used in pinhole occluders, which are used by ophthalmologists, orthoptists and optometrists to test visual acuity. The same principle has also been applied as an alternative to corrective lenses: a screen of pinholes is mounted on an eyeglass frame and worn as pinhole glasses. Besides pinholes made by the point of a pin, precision commercial pinholes are often made by laser drilling Laser drilling is the process of creating thru-holes, referred to as “popped” hol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ophthalmologist
Ophthalmology ( ) is a surgery, surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a medical degree, a doctor specialising in ophthalmology must pursue additional postgraduate residency (medicine), residency training specific to that field. This may include a one-year integrated internship that involves more general medical training in other fields such as internal medicine or general surgery. Following residency, additional specialty training (or fellowship) may be sought in a particular aspect of eye pathology. Ophthalmologists prescribe medications to treat eye diseases, implement laser therapy, and perform surgery when needed. Ophthalmologists provide both primary and specialty eye care - medical and surgical. Most ophthalmologists participate in academic research on eye diseases at some point in their training an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optometry
Optometry is a specialized health care profession that involves examining the eyes and related structures for defects or abnormalities. Optometrists are health care professionals who typically provide comprehensive primary eye care. In the United States and Canada, optometrists are those that hold a Doctor of Optometry degree. They are trained and licensed to practice medicine for eye related conditions, in addition to providing refractive (optical) eye care. In the United Kingdom, optometrists may also practice medicine (and provide refractive care) for eye related conditions. The Doctor of Optometry title can also be used in the UK for those that hold the postgraduate O.D. degree. Within their scope of practice, optometrists are considered physicians and bill medical insurance(s) (example: Medicare) accordingly. Moreover, many participate in academic research for eye related conditions and disease. Optometrists are the only health care professionals with a first professional ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Acuity
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal image within the eye, (2) the health and functioning of the retina, and (3) the sensitivity of the interpretative faculty of the brain. The most commonly referred visual acuity is the far acuity (e.g. 6/6 or 20/20 acuity), which describes the examinee's ability to recognize small details at a far distance, and is relevant to people with myopia; however, for people with hyperopia, the near acuity is used instead to describe the examinee's ability to recognize small details at a near distance. A common cause of low visual acuity is refractive error (ametropia), errors in how the light is refracted in the eyeball, and errors in how the retinal image is interpreted by the brain. The latter is the primary cause for low vision in people with a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinhole Camera
A pinhole camera is a simple camera without a lens but with a tiny aperture (the so-called ''pinhole'')—effectively a light-proof box with a small hole in one side. Light from a scene passes through the aperture and projects an inverted image on the opposite side of the box, which is known as the camera obscura effect. The size of the images depends on the distance between the object and the pinhole. History Camera obscura The camera obscura or pinhole image is a natural optical phenomenon. Early known descriptions are found in the Chinese Mozi writings (circa 500 BCE) and the Aristotelian ''Problems'' (circa 300 BCE – 600 CE). Ibn al-Haytham (965–1039), an Arab physicist also known as Alhazen, described the camera obscura effect. Over the centuries others started to experiment with it, mainly in dark rooms with a small opening in shutters, mostly to study the nature of light and to safely watch solar eclipses. Giambattista Della Porta wrote in 1558 in his Magia Na ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refractive Error
Refractive error, also known as refraction error, is a problem with focus (optics), focusing light accurately on the retina due to the shape of the human eye, eye and or cornea. The most common types of refractive error are myopia, near-sightedness, hyperopia, far-sightedness, astigmatism, and presbyopia. Near-sightedness results in far away objects being blurred vision, blurry, far-sightedness and presbyopia result in close objects being blurry, and astigmatism causes objects to appear stretched out or blurry. Other symptoms may include double vision, headaches, and eye strain. Near-sightedness is due to the length of the eyeball being too long, far-sightedness the eyeball too short, astigmatism the cornea being the wrong shape, and presbyopia aging of the lens of the eye such that it cannot change shape sufficiently. Some refractive errors occur more often among those whose parents are affected. Diagnosis is by eye examination. Refractive errors are corrected with eyeglasses, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myopia
Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include headaches and eye strain. Severe near-sightedness is associated with an increased risk of retinal detachment, cataracts, and glaucoma. The underlying mechanism involves the length of the eyeball growing too long or less commonly the lens being too strong. It is a type of refractive error. Diagnosis is by eye examination. Tentative evidence indicates that the risk of near-sightedness can be decreased by having young children spend more time outside. This decrease in risk may be related to natural light exposure. Near-sightedness can be corrected with eyeglasses, contact lenses, or a refractive surgery. Eyeglasses are the easiest and safest method of correction. Contact lenses can provide a wider field of vision, but are associated with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mydriasis
Mydriasis is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of certain types of drugs. Normally, as part of the pupillary light reflex, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A ''mydriatic'' pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis. More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation. Fixed, unilateral mydriasis could be a symptom of raised intracranial pressure. The opposite, constriction of the pupil, is referred to as miosis. Both mydriasis and miosis can be physiological. Anisocori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycloplegia
Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation. Because of the paralysis of the ciliary muscle, the curvature of the lens can no longer be adjusted to focus on nearby objects. This results in similar problems as those caused by presbyopia, in which the lens has lost elasticity and can also no longer focus on close-by objects. Cycloplegia with accompanying mydriasis (dilation of pupil) is usually due to topical application of muscarinic antagonists such as atropine and cyclopentolate. Belladonna alkaloids are used for testing the error of refraction and examination of eye. Management Cycloplegic drugs are generally muscarinic receptor blockers. These include atropine, cyclopentolate, homatropine, scopolamine and tropicamide. They are indicated for use in cycloplegic refraction (to paralyze the ciliary muscle in order to determine the true refractive error of the eye) and the treatment of uveitis. All cycloplegics are also mydriat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinhole Glasses
Pinhole glasses, also known as stenopeic glasses, are eyeglasses with a series of pinhole-sized perforations filling an opaque sheet of plastic in place of each lens. Similar to the workings of a pinhole camera, each perforation allows only a very narrow beam of light to enter the eye which reduces the size of the circle of confusion on the retina and increases depth of field. In eyes with refractive error, the result is often a sharper image. However, a second effect may appear at the common bridge between each two adjacent holes, whereby two different rays of light coming from the same object (but each passing through a different hole) are diffracted back toward the eye and onto different places on the retina. Unlike conventional prescription glasses, pinhole glasses produce an image without the pincushion effect around the edges (which makes straight lines appear curved). While pinhole glasses are claimed to be useful for people who are both near- and far-sighted, they are not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amblyopia
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. The cause of amblyopia can be any condition that interferes with focusing during early childhood. This can occur from poor alignment of the eyes (strabismic), an eye being irregularly shaped such that focusing is difficult, one eye being more nearsighted or farsighted than the other (refractive), or clouding of the lens of an eye (deprivational). After the underlying cause is addressed, vision is not restored right away, as the mechanism also involves the brain. Amblyopia can be difficult to detect, so vision testing is recommended for all children around the ages of four to five. Early detection improves treatment success. Glasse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
