China
Africa
Explore chapters and articles related to this topic
Contact lenses
Published in Pablo Artal, Handbook of Visual Optics, 2017
In a clinical setting, the optical power of the eye is typically determined by performing a subjective refraction. This procedure involves the iterative application of spherical and cylindrical lenses in front of the eye to determine the optimal visual acuity at distance. The lenses are mounted in front of the eye, in a trial frame, at a distance that replicates the position of a pair of spectacles to be worn by the patient. This is known as the spectacle plane, and the distance to the anterior corneal surface, typically 12–13 mm, is known as the vertex distance. When fitting a contact lens, clinicians must compensate for the vergence change that occurs from the spectacle plane to the anterior corneal plane to ensure the retinal image remains in optimal focus. While this can be calculated for each individual case, using the formula (Bennett 1974) K=F1−dF
Vecto-keratometry: determination of anterior corneal astigmatism in manual keratometers using power vectors
Published in Expert Review of Medical Devices, 2023
Raquel Salvador-Roger, Rosa Vila-Andrés, Vicente Micó, José J. Esteve-Taboada
Direct applications of power vector management in clinical practice have already been validated as well. Muñoz-Escribá and Furlan [36] formerly summarized the theoretical application of the power vector notation of several subjective refractive methods [24]. Continuing with that approach, Micó et al. [29] showed an alternative procedure to classical subjective refraction using power vector notation. Their purpose was to facilitate the obtention of an accurate refraction in irregular corneas as well as when dealing with regular astigmatism. By using spherical lens and a stenopaeic slit in four different positions, the maximum plus to maximum visual acuity (MPMVA) was found for each one of the orientations, namely: S0, S45, S90 and S135. According to the definition of power vector rectangular notation, sphero-cylindrical refraction can be obtained by those four spheres. This technique permits to achieve a final prescription even when there is a significant amount of high-order aberrations (not only regular ones). In this kind of cases, it is not possible to find the perfect refraction due to the presence of irregularities, therefore the main purpose is to find the best approximation that provides the best visual acuity for the patient.
Air shooting competition effects on visual skills depending on the sport level
Published in European Journal of Sport Science, 2022
Daniel Mon-López, Ricardo Bernardez-Vilaboa, Manuel Sillero-Quintana, Antonio Alvarez Fernandez-Balbuena
Two shooters were evaluated each session. No shooting activity was allowed before the visual measurement. The duration of the pre-competition simulation measurement was 50 min. Measurements were divided into five optometric tests that where realized in a sequential way, as described in the next paragraph. The first test was visual acuity: both monocular and binocular visual acuity were tested at five metres without glasses or contact lenses using the Sloan letter test protocol. The second test was the static retinoscopy with schiascopy ruler. The third was realized following the Donder’s method to obtain the patient’s subjective refraction. The fourth test consisted of measuring the far and near phoria with the Van Graëffe’s method. The next optometric test checked th accommodation function of the participant. Accommodative facility with values of 0.8 with sharpness was analyzed using ± 2 dioptric flippers at 40 cm. During this test, a close-up card of reduced Sloan letters was used to check the number of cycles per minute. The last test was other visual skills which included binocular vision time, binocular motor time and eye–hand coordination, which were measured using basic programme numbers 83 and 26 of a Wayne Saccadic Fixator device.
Repeatability and agreement of corneal thickness measurements by three methods of pachymetry in small incision lenticule extraction eyes
Published in Expert Review of Medical Devices, 2020
Liang Hu, Zhongli Hu, Giacomo Savini, Jinjin Yu, Haitao Zhou, Sisi Chen, Rui Ning, Yili Jin, Jinhai Huang
Our study was conducted at the Eye Hospital of Wenzhou Medical University, and conducted in accordance with the principles of the Declaration of Helsinki and approved by the Office of the Ethics Committee at Eye Hospital of Wenzhou Medical University. We explained the properties and requirements of the experiment to each research subject that signed the informed consent document. This was a prospective study in which subjects underwent a complete set of examinations prior to being included in this study: uncorrected visual acuity, autorefraction, subjective refraction, intraocular pressure, pupil size measurement, Topography (Pentacam), slit-lamp microscopy, and fundoscopy. The exclusion criteria were: corrected visual acuity less than 20/20, preoperative spherical power more than 8.00 diopters (D) or preoperative astigmatism power more than 3.00 diopters (D), irregular topography, history of using contact lenses (i.e. use of soft contact lenses has ceased less than two weeks, use of rigid contact lenses had ceased less than 4 weeks), previous eye surgery in addition to SMILE, and evidence of any diseases of the eye.