Bioengineering Aids to Reproductive Medicine
Sujoy K. Guba in Bioengineering in Reproductive Medicine, 2020
In order to maintain simplicity in the design and construction most rigid endoscopes have a fixed focus. Even so the design is such that objects within a certain range of distance from the objective are fairly well focused and this range is the depth of focus. Power of accommodation of the eye also helps in viewing objects at varying distances and the accommodation increases the range beyond the intrinsic depth of focus of the instrument. An older observer with reduced power of accommodation will obviously be able to clearly see objects over a smaller range of distance than a younger endoscopist with normal amplitude of accommodation which usually ranges from infinity to 25 cm in front of the eye. The difference between the intrinsic depth of focus of an endoscope and the effective range of focus as viewed by an observer has important bearing in photography through an endoscope. An observer may see an object clearly through an endoscope but the picture taken may come out as blurred. This may be because the observer has exerted his power of accommodation to bring the object into focus whereas the camera obviously does not have this provision. Modern endoscopic cameras are provided with focusing arrangement which is independent of the power of accommodation of the photographer’s eye.
Rehabilitation and management of visual dysfunction following traumatic brain injury
Mark J. Ashley, David A. Hovda in Traumatic Brain Injury, 2017
Patient B.B. was seen for examination 4 months postinjury. He had no light perception from his right eye due to optic nerve atrophy following his injury. His left eye was healthy and intact. He presented with decreased acuity (20/80 when reading a vertical column and 20/30 when reading horizontally). He had reduced contrast sensitivity for medium spatial frequencies. He also had a left hemianopia with macular sparing. He had difficulty reading. He watched his feet when walking and tended to veer leftward. Saccades were slow and pursuits were jerky. He had a reduced amplitude of accommodation and was already wearing a bifocal correction, which he found useful. He read at approximately 8 inches from his eyes for the additional magnification.
Impact of dual-focus soft contact lens wear on near work-induced transient myopia
Published in Clinical and Experimental Optometry, 2023
Raimundo Jiménez, Beatriz Redondo, Tomás Galán, Pedro Machado, Rubén Molina, Jesús Vera
All participants were examined at a baseline visit to determine the fulfilment of the following inclusion criteria: (i) between −0.50 D and −6.00D of spherical error and less than 1.00D of astigmatism, (ii) best-corrected distance visual acuity of at least 0.0 logMAR in each eye, (iii) a myopic anisometropia lower than 2.00D, (iv) free of any systemic/ocular disease or current use of systemic medication, (v) no history of strabismus or amblyopia, (vi) a normal range of amplitude of accommodation, as calculated by the Hofstetter’s formula,36 (vii) fusion in near and far vision, as assessed by the standard Worth-4-dot test (viii) 50 sec of arc of near stereoacuity, and (ix) belong to the asymptomatic group (score< 24) using the Conlon survey.37 The protocol was approved by the University of Granada Institutional Review Board (IRB approval: 1786/CEIH/2020) and adhered to the tenets of the Declaration of Helsinki. An individual informed consent was obtained from all participants.
Screening for convergence insufficiency in school‐age children
Published in Clinical and Experimental Optometry, 2018
Anne M Menjivar, Marjean T Kulp, G Lynn Mitchell, Andrew J Toole, Kathleen Reuter
Monocular amplitude of accommodation was assessed using a single column of letters of 6/9 equivalent at 40-cm and a near point rule. The first sustained blur was considered the endpoint. Accommodative amplitude was measured three times (right eye only, recorded to the nearest half‐centimetre) and the mean was used for analysis. Monocular accommodative facility was measured using ± 2.00-D lens flippers and a single column of letters of 6/9 equivalent on a hand‐held fixation target held at 40-cm. The subject was instructed to try to get the letters clear as quickly as possible, and to report (by saying ‘clear’) as soon as the letters were clear. Monocular accommodative facility (cycles/minute) was assessed only on the right eye. Binocular accommodative facility was also assessed using a Suppression Vectogram number 9 and Polaroid filter glasses (Stereo Optical, Chicago, Illinois, USA).
Does Hofstetter's equation predict the real amplitude of accommodation in children?
Published in Clinical and Experimental Optometry, 2018
Hassan Hashemi, Payam Nabovati, Mehdi Khabazkhoob, Abbasali Yekta, Mohammad Hassan Emamian, Akbar Fotouhi
According to McBrien and Millodot,1986 the higher AA in eyes with myopia is due to strong parasympathetic or weak sympathetic innervation to the ciliary muscle, while hyperopic eyes have lower AA values due to strong sympathetic or weak parasympathetic innervation. This theory is in agreement with the findings by Charman,1982 who reported stronger parasympathetic innervation in myopic individuals and presented this as a theory of myopic development. The findings of our study confirm the results of studies by Fledelius1981 and McBrien and Millodot1986 in a large sample. Another possible explanation for the higher amplitude of accommodation measured in children with myopia is blur adaptation. Myopes normally have reduced sensitivity to blur in comparison to hyperopes and emmetropes.2004 According to Rosenfield, Hong and George,2004 myopes have increased blur thresholds. This blur adaptation can be associated with reporting of sustained blur at closer distances during push‐up testing and higher estimated AAs. Also the possibility of underestimation of AA due to the latent hyperopia should be considered in interpreting the association of AA with refractive error.
Related Knowledge Centers
- Convergence Insufficiency
- Eye
- Presbyopia
- Eye Examination
- Negative Relative Accommodation
- Positive Relative Accommodation