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Non-Organic Vision Loss
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Ashwini Kini, Mangayarkarasi Thandampallayam Ajjeya, Padmaja Sudhakar
In an ophthalmologist's clinic, the lenses may be used on a phoropter; however, this equipment is unavailable in a neurologist's office and may not always be feasible to do this test. A trial frame with a few loose plus and minus lenses could be kept in the clinic which may be handy in testing in such cases.
When There Are Symptoms But it All Looks Totally Normal
Published in Amy-lee Shirodkar, Gwyn Samuel Williams, Bushra Thajudeen, Practical Emergency Ophthalmology Handbook, 2019
Fogging: This is another method to try and demonstrate NOVL in patients with monocular vision loss. The patient is asked to read a vision chart with both eyes open. A trial frame is used with a neutral lens over the ‘bad’ eye, and a high power convex lens over the ‘good’ eye, obscuring the vision. Therefore, only the bad eye is being tested. By presenting the assessment as a binocular vision test, and by putting lenses over both eyes, the intention of the test is masked.
Wavefront sensors
Published in Pablo Artal, Handbook of Visual Optics, 2017
The subject looks at a point source of light about 1 m distant in a darkened room. The subject’s near prescription is placed in the trial frame. The lines in the central squares of the grid are seen as horizontal and vertical. Any change in spherical or cylindrical power causes a tilting of the grid lines. The subject is asked to memorize the grid’s pertinent features so that he or she can later sketch the grid with these features. The sketch is then analyzed quantitatively to estimate the wave aberration.
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
For each subject, the refraction starting point was taken from the orthogonal spectacle prescription and the visual acuity recorded, as well as a subjective assessment of the visual quality. There is currently no methodology in the literature aimed at non-orthogonal refraction and it is unknown how valid the visual tools available to assist in refraction of orthogonal astigmatism would be in refracting with non-orthogonal lenses. Thus, the refractive technique was kept as basic and as familiar to the subject as possible to avoid introducing unknown variables. In refracting subjects with irregular corneas, often the best way of establishing the optimal axis is to allow the subject to rotate the lens in the trial frame. Subjects will subjectively balance optimal contrast with minimal “ghosting” and “shadowing”. This method was used to attain the original orthogonal prescription, together with the use of spheres and cylinders lenses.
Effect of unifocal versus multifocal lenses on cervical spine posture in patients with presbyopia
Published in International Journal of Occupational Safety and Ergonomics, 2019
Rami L. Abbas, Mohamad T. Houri, Mohammad M. Rayyan, Hamada Ahmad Hamada, Ibtissam M. Saab
A repeated-measure design was used to compare the effect of unifocal lenses versus multifocal lenses on cervical posture in patients with symptoms of presbyopia. A digital pupillometer was used to measure the interpupillary distance (IPD) in order to adjust the trial spectacle accordingly, and a vision test was done to determine suitable corrective lenses for each subject. A measuring tape was used to adjust both the table and chair according to specific criteria. The chair seat, which had a lumbar pillow on it, was adjusted in such a way to allow the hips and knees to adopt 90° of flexion, while the feet were resting on the floor. The height of the table was set at 76 cm, which is similar to the standard desk used in the office [11]. The desk had paper placed on top, with letters in the Arial font and a font size of 14 [12]. The paper was 40 cm away from the candidate [13], with 50° inclination with respect to the surface of the desk [14]. To perform the tests, every subject wore a trial frame glass for mounting the related occluder and suitable trial lens for near vision.
Treatment of amblyopia: Part 3 Apparatus, exercise equipment and games (continued)
Published in Strabismus, 2018
The light-pointer cheiroscope consists of a housing with a light and a tapered tube. A diapositive can be inserted in the light housing. Its image then passes through the tube with a corresponding mirror guide through an aperture into the observer’s eye. Trial frame mountings are attached to either side of the aperture for the observer so that the original can be viewed with the right or left eye as required. The other eye looks at carbon paper, which is inserted into a metal holder while a sheet of paper can be inserted underneath. With a pointer with a light tip, the patient now traces the contours of the diapositive presented to the other eye on the carbon paper, which then appears on the underlying paper. In this way, it is never possible to see the same images with both eyes, since the drawing is concealed by the carbon paper. Therefore, only simultaneous vision is possible, not fusion.