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Optic Neuropathies Associated With Multiple Sclerosis (MS) and Neuromyelitis Optica Spectrum Disorders (NMO-SD)
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Optic neuritis associated with MS is one of the most common causes of acute/subacute unilateral visual loss in young individuals in temperate latitudes, where MS has the highest prevalence. The loss of color vision and contrast sensitivity may be early and out of proportion to the loss of visual acuity. MS-ON occurs more commonly in women as compared to men, usually in the age group of 15–45 years.
Contrast adaptation
Published in Pablo Artal, Handbook of Visual Optics, 2017
The classical way to determine contrast sensitivity (CS) of a subject is to find the threshold contrast for detection of a pattern. To determine CS at different spatial frequencies (leading to the contrast sensitivity function [CSF]), sine wave gratings of different spatial frequencies are used. The reciprocal of the threshold contrast (as a fraction, not in percent) is defined as CS. Figure 21.4 illustrates that CS varies with spatial frequency. On the left, sine wave gratings are shown with increasing spatial frequency from the left to the right. Contrast drops equally for all spatial frequencies from the bottom to the top. It can be seen that, for lower spatial frequencies, the sine wave grating appears to vanish earlier than for the mid spatial frequencies. Obviously, CS is higher in the middle of the spatial frequency range. At higher spatial frequencies, CS declines again, generating a CSF with the shape of an inverted “U” (Figure 21.4, right). Above detection threshold (in the bottom part of the figure), contrast at different spatial frequencies is seen similar even though one might expect more contrast in the mid spatial frequency range. This phenomenon is termed “contrast constancy.”
Rehabilitation and management of visual dysfunction following traumatic brain injury
Published in Mark J. Ashley, David A. Hovda, Traumatic Brain Injury, 2017
Contrast sensitivity is the ability to discriminate differences in luminance between adjacent areas. Low-contrast situations occur in fog, darkness, and when viewing through media opacities in the eye, such as cataracts. Reduced contrast sensitivity should be suspected when patients with good visual acuity complain of not seeing well. Neural damage in the visual system may also cause poor contrast sensitivity.120 Damage to the magno system results in a reduction of contrast sensitivity for middle to low spatial frequency (larger contours). Damage to the parvo system results in loss of contrast sensitivity in detailed targets and may result in decreased visual acuity. Patients with diminished contrast sensitivity in the high frequency range resulting in decreased visual acuity may find magnifying low vision aids helpful. Those with diminished contrast sensitivity for middle to low spatial frequencies are not helped by magnification. Printed material for these patients should be good quality and high contrast. In well-lit conditions, contrast-enhancing tints (usually yellow to amber tints that screen out blue light) or overlays may be used. The selection of tint is usually based on the patient’s subjective assessment of the quality of their vision. The Cerium Intuitive Colorimeter6 is an instrument that allows presentation of colored wavelength filters, which can be tested through the spectrum of hues, varying the saturation and brightness to find the lens tint that provides maximal comfort, efficiency, or contrast.
Binocular contrast sensitivity in patients with intermittent exotropia in relation to angle of strabismus and level of compensation
Published in Strabismus, 2023
Fatemeh Moradi, Ali Mirzajani, Mohammad Reza Akbari, Masoud Khorrami-Nejad, Jamileh Abolghasemi, Babak Masoomian
Intermittent exotropia (IXT) is one of the most common types of tropia that normal binocular vision with sensory fusion would occasionally disrupt; therefore, tropia and suppression will appear. Fatigue, illness, daydreaming, and looking to distance targets were known as common risk factors for induced tropia. It should be noted that blurred vision, eye strain, headache, diplopia, and photophobia are among the symptoms of these patients.1,2 The prevalence of photophobia in IXT was reported to be 54% to 65.5% in previous studies. The major cause of this symptom exactly has not been defined yet, but some studies have claimed that binocular photophobia and diplopia are related to the inability to suppress it in sunlight.2,3 On the other hand, others have reported that in outdoor activities, there is not enough stimulus to stimulate convergence, so the fusion is disrupted by the light and causes manifest strabismus. It is suggested that photophobia is a prevention method of diplopia and confusion.3,4 Some studies have evaluated photophobia by using contrast sensitivity (CS) measurement, which evaluates the reduction in visual function after exposure to a light stimulus with specific illuminance. Contrast sensitivity is the ability to detect a difference in brightness between adjacent objects or areas in space. It may be subnormal in optic neuritis, amblyopia, and glaucoma, but the presence of photophobia has a remarkable effect on it.4,5
Neuro-Ophthalmic Manifestations of HIV Infection
Published in Ocular Immunology and Inflammation, 2020
Lynn K. Gordon, Helen Danesh-Meyer
The neuroretinal disorder is seen in more than 10% of the patients at baseline up to a cumulative incidence of 50% of the patients examined over years and may be responsible for a significantly decreased vision-specific quality of life.50 Neuroretinal disorder may be secondary to microvascular ischemia, chronic immune activation, direct HIV infection of the neuroretinal tissue, or premature aging associated with HIV infection.51,52 HIV patients with more severe or advanced disease are more likely to develop the neuroretinal disorder. Optical coherence tomography (OCT) demonstrates retinal nerve fiber layer thinning as well as thinning of the ganglion cell and inner nuclear layers. There is some correlation with lower CD4 + T cell counts as well. These patients will demonstrate mild to moderate loss of vision and decreased contrast sensitivity.53 Concordantly the pattern electroretinogram (pERG) and multifocal electroretinogram (mERG) reveal abnormalities.54
Efavirenz-Associated Retinal Toxicity Presenting with Night Vision Defects in Patients with Human Immunodeficiency Virus
Published in Ocular Immunology and Inflammation, 2020
Sridharan Sudharshan, Kolli Dileep Kumar, Muna Bhende, Jyotirmay Biswas, Poongulali Selvamuthu
A 48-year-old female with HIV and Hepatitis B positivity, for 4 years, and on HAART with CD4 counts of 16 came with defective vision in both eyes for the last 20 days. She had been started on a combination of stavudine, lamivudine, efavirenz combination due to her dropping CD4 counts a month back. Her best corrected visual acuity was 6/12, N10 in the right eye and 6/60, N36 in the left eye. Slit lamp and fundus evaluation were clinically found to be within normal limits. Visual fields showed ceco-central scotoma in both eyes. Spectral domain OCT was normal in both eyes. In both eyes, flash visually evoked potential (VEP) showed reduced amplitudes and pattern VEP showed delayed latency and reduced amplitude. Contrast sensitivity was found to be reduced in both the eyes. Efavirenz was substituted with Atazanavir. Patient was followed up at regular intervals and she was feeling subjectively better. After 3 months of follow-up, her visual acuity was 6/6, N6 in both eyes, OCT in both eyes was normal and ERG showed normal photopic and scotopic responses. At 1-year follow-up, patient maintained normal visual acuity and did not have any fresh symptoms.