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Cortical Visual Loss
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
In a three-dimensional world, the distance of objects from the observer is another visuospatial perception. This has been less studied after lesions, however. In frontally eyed creatures like humans, one important clue to distance is stereovision, the disparity between the retinal images of the object in the two eyes. Patients with astereopsis may complain that the world looks flat and that they cannot tell how far away an object is, and they may misreach for objects in depth but not in direction. This occurs after bilateral occipito-parietal lesions (422, 425), sometimes in milder form with unilateral lesions. Impaired depth perception may reflect more than just astereopsis. Monocular clues to depth exist, and include relative differences in object size and color intensity (which artists exploit), and differences in the movement of near versus far objects as the observer's head moves sideways (motion parallax). It is not known if these are also dysfunctional in patients with complaints of impaired depth perception. Stereopsis can be tested with commonly available 3-D tests in eye clinics (426).
Treating the Loss of Depth Perception
Published in John William Yee, The Neurological Treatment for Nearsightedness and Related Vision Problems, 2019
The loss of depth perception can be demonstrated horizontally. During the onset of myopia, depth perception is mainly lacking in the distance. Initially, the near range (at 16 in. or 40 cm away) and the midrange or computer range (at 20 in. or 50 cm away) is clear. After the spasm of the ciliary muscle sets in, objects in the near range, in the midrange, and in the distance are equally blurred. It is along a gradient according to the minus lens’ power. The spasm of the ciliary muscle and the seizure of the crystalline lens as a result induce the uniform blurriness.
Perceptual-cognitive development and cognition of movement
Published in Michael Horvat, Ronald V. Croce, Caterina Pesce, Ashley Fallaize, Developmental and Adapted Physical Education, 2019
Michael Horvat, Ronald V. Croce, Caterina Pesce, Ashley Fallaize
Depth perception is defined as the ability to judge how near or far away one or more objects are from a person. Depth perception also allows an individual to see three-dimensionally. Movement perception involves the ability to perceive that an object is moving. Together, depth perception and movement perception constitute two of the more important visual-perceptual abilities in children.
Posterior cortical atrophy: clinical, neuroimaging, and neuropathological features
Published in Expert Review of Neurotherapeutics, 2023
John Best, Marianne Chapleau, Gil D. Rabinovici
Individuals with PCA frequently initially present to optometrists and ophthalmologists. Evaluation will typically reveal normal visual acuity and fundoscopic examination. In a case registry of PCA patients presenting initially to neuro-ophthalmology, visual field defects were the most common finding, most frequently a left sided homonymous hemianopia [13]. The Hardy-Rand-Rittler and Ishihara color plates are used to assess for deficits in color vision. These involve a variety of hidden figures or numbers hidden within a grid of variable sized and colored dots. Color plate is abnormal in a vast majority of patients [13]. The titmus stereoacuity test, which is a measure of depth perception, is also frequently abnormal. Additional tests include tests for simultanagnosia, such as describing a complex visual scene (e.g., the commonly utilized ‘Boston Cookie Theft’ image). Central vision crowding can also be assessed by displaying single letters vs flanked letters, with individuals with PCA frequently having difficulty distinguishing with the flanked letters [13].
A 2020 Update on 20/20 X 2: Diplopia after Ocular Surgery Diplopia after Iatrogenic Monovision
Published in Journal of Binocular Vision and Ocular Motility, 2021
A 64-year-old female complaining of depth perception problems and an increase in her eye misalignment presents to our clinic. She states that before her cataract surgery she had one eye that drifted out intermittently, but she could control it and it did not bother her. Now, her eye drifts out all the time and is very bothersome to her. She had iatrogenic monovision pseudophakia 5 months prior to presentation. She had a preexisting strabismus prior to her pseudophakia surgery. She otherwise has a normal past ocular history and medical history. She never had surgery or treatment for her strabismus but notes it has been there for a long time. On her exam without correction, she has 20/20 distance vision in the right eye and 20/50 distance vision in the left eye. She reports no stereopsis on the Titmus test, and she has a large constant exotropia on her motility exam at distance and near. She has significant post-operative anisometropia with a refractive error of −0.50 + 0.25 × 135 in the right eye and −2.50 + 0.25 × 136 in the left eye. We recommended a trial of full time wear of the manifest refraction found on her exam. At her 2 months follow-up, she notes an improvement in depth perception with the glasses on, but the eye is still drifting out and she cannot control it like she did before her cataract surgery. She has a large intermittent, but poorly controlled exotropia on her exam in her full correction. Strabismus surgery was recommended to improve her symptoms from her decompensated strabismus.
Advances in the tools and techniques of vitreoretinal surgery
Published in Expert Review of Ophthalmology, 2020
Ashish Markan, Aman Kumar, Jayesh Vira, Vishali Gupta, Aniruddha Agarwal
Endoscopy allows surgery for vitreoretinal disorders that are impossible to observe with transpupillary imaging because of retropupillary location or ocular media opacities [19]. Endoscopic vitrectomy involves an endoscopic probe with a video camera, light source, and endolaser which is inserted into the eye, allowing direct visualization of the posterior ocular structures allowing the surgeon to operate. The endoscope can visualize structures like ciliary processes, pars plana, and anterior retina without scleral depression, thus making surgical maneuvers on these structures possible. To begin with, the surgeons might feel difficult to operate using endoscopes in view of a smaller surgical field of view, low resolution and low illumination. Surgeon is required to hold the instrument close to the ocular structure for visualization. Also it is important to hold the probe correctly to avoid rotating the camera in the endoscopy probe. This can cause disorientation of the image leading to iatrogenic injury to the ocular tissues. It is important to adapt to lack of depth perception during surgery.