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Letting Go
Published in John William Yee, The Neurological Treatment for Nearsightedness and Related Vision Problems, 2019
An excessive “effort to see” can trigger asthenopia. Donders suggested that the phenomenon is prevalent in cases of farsightedness (Grosvenor, 2007). It contributes to headaches since most of our day-to-day work is in the near and midrange. It is also a factor to consider after experiencing an improvement by ortho C. The excess effort stems from applying 100% of the lens’ flexibility to bring a distant object into focus. If it becomes a habit, it can offset some of the gains from ortho C. I would often remind my participants to get into the habit of “letting go” of an object within a certain period of time.
Presenting data
Published in Antony Stewart, Basic Statistics and Epidemiology, 2018
The graph in Figure 4.1 is known as a pie chart, because it depicts each category as a slice of pie, with the size of each slice varying according to its proportion of the whole pie. This can be useful for comparing individual categories with the total. The pie chart in Figure 4.1 shows the distribution of different visual impairments in Swiss pathologists. It is easy to see that myopia (nearsightedness) was recorded most frequently, and that 8.6% of those with a visual impairment had hyperopia (farsightedness).
Adaptive optics ophthalmoscopes
Published in Pablo Artal, Handbook of Visual Optics, 2017
The optics of the human eye have been studied by learned men for many centuries, one of which was Ibn al-Haytham (known in the West as Alhazen), the most influential figure in the study of optics and vision in the Middle Ages (Alhazen and Sabra 1989). Although eyeglasses were introduced in the thirteenth century, it was not until the seventeenth century that Johannes Kepler formulated an accurate theory and the correction of myopia (positive defocus or nearsightedness) and hyperopia (negative defocus or farsightedness). Two centuries later, George Airy devised a cylindrical lens for the correction of astigmatism (Airy 1827; Levene 1966).
Optical mechanisms regulating emmetropisation and refractive errors: evidence from animal models
Published in Clinical and Experimental Optometry, 2020
Ranjay Chakraborty, Lisa A Ostrin, Alexandra Benavente‐perez, Pavan Kumar Verkicharla
Both the optical power in the anterior segment of the eye and axial length determine refractive state.2004 Emmetropisation is an active, visually guided mechanism whereby the axial length and the combined optical powers of the cornea and lens precisely match with each other to eliminate neonatal refractive errors, and bring the eye to perfect focus (also known as emmetropia). In non‐accommodating emmetropic eyes, visual images of distant objects are clearly focused at the retinal photoreceptors. Any disruption to this homeostatic mechanism of ocular growth results in the development of refractive errors. In myopia, or near‐sightedness, the eye is too long for the optical power of the cornea and lens, and images of distance objects focus in front of the photoreceptor plane. In hyperopia, or far‐sightedness, the eye is too short for the optics, and images of distant objects focus behind the photoreceptor plane.
Ophthalmologic Abnormalities in Children with Congenital Sensorineural Hearing Loss
Published in Journal of Binocular Vision and Ocular Motility, 2019
Sean Batson, Katherine Kelly, David Morrison, Frank Virgin
Multiple covariates were analyzed for our study with the following definitions. Congenital sensorineural hearing loss was defined as any sensorineural hearing loss due to genetic factors or without another identifiable cause (such as medication toxicity, trauma, etc.) Diagnosis of any ophthalmic abnormalities was determined by formal clinic evaluation by a pediatric ophthalmologist at the Vanderbilt Eye Institute. Ophthalmology examination notes were individually reviewed. These data were compiled and analyzed to evaluate disease prevalence and distribution, and to evaluate relevant associations such as syndromic disorders or history of premature birth. To determine clinical diagnosis of refractive error (need for glasses to correct nearsightedness, farsightedness, or astigmatism) and amblyopia risk factors, we utilized the American Academy of Ophthalmology’s preferred practice patterns guidelines for refractive correction in infants and young children12 (see Table 2). Our analysis of ophthalmic abnormalities considered more likely to be missed by automated screening included isolated diagnoses of pigmentary retinopathy, glaucoma, cortical visual insufficiency, optic atrophy, coloboma, and nystagmus.
Non-Orthogonal Refractive Lenses for Non-Orthogonal Astigmatic Eyes
Published in Current Eye Research, 2019
Ahmed Abass, Bernardo T. Lopes, Steve Jones, Lynn White, John Clamp, Ahmed Elsheikh
The existing system of prescribing a correction lens to a patient with an astigmatic eye consists of a combination of spherical and cylindrical lenses to form a single sphero-cylindrical lens.4 In this lens, the spherical component is responsible for correcting near or farsightedness and the cylindrical component is added to correct astigmatism. The current method of correcting the eye’s refractive error is based on the assumption that the lowest and highest power meridians in an astigmatic visual system are always at a right angle to each other (Figure 1). However, if the power axes of a patient are not orthogonal, there will be residual astigmatism even if the best possible orthogonal refractive lenses are used to correct the patient’s vision. Moreover, the software programs that control the operation of corneal topographers assume power axes are orthogonal in producing their power map outputs, making it impossible to assess the extent of non-orthogonal astigmatism present in individual eyes. Considering that up to 25% of the normal population have non-orthogonal astigmatism,3 it is important to revise the existing system of correcting astigmatism. This study addresses this need and presents a novel lens design method conceived to address the problem of residual astigmatism in non-orthogonal astigmatic eyes.