Color Vision Impairment

Complaints of color vision disturbances are common with both digoxin and digitoxin, but color vision impairment can often be detected even in patients without... 

Occupational exposure to mercury (0.08) and chemical solvents, including styrene (2.95), tetrachloroethylene (3.40), /j-hexane (3.90), toluene (2.73), and carbon disulfide (1.94), has been shown to impair color vision in exposed workers J48l Color vision impairment was also observed for those exposed to solvent mixtures at levels below TLV values. I49l No explanation was offered by the authors for the observed mixture effect. 

Gobba F, Cavalleri A. Color vision impairment in workers exposed to neurotoxic chemicals. Neurotoxicology 2003 24(4-5) 693-702. 

A. Ethambutol is associated with retrobulbar neuritis, resulting in loss of central vision and impaired red-green discrimination. Ethionamide (B) is an analogue of isonicotinic acid and is associated with GI intolerance and peripheral neuropathy, but not the optic neuritis or color vision discrimination problems. Aminosalicylic acid (C) can cause GI irritation and bleeding problems, so caution is required in peptic ulcer patients. It has no neurological side effects. Rifampin (D) is associated with red-orange discoloration of saliva, tears, and urine but not the color vision problems. Isoniazid (E) is associated with peripheral neuritis in chronic alcoholics and malnourished individuals and requires pyridoxine supplements. It is not associated with optic neuritis. 

Candidates must be in excellent health and have no conditions that would restrict their ability to safely do fire suppression and rescue work. Weight (body fat content) must be proportionate to height for men and women. Uncorrected distance visual acuity of at least 20/100 in the poorer eye and 20/40 in the better eye, correctable to at least 20/40 in one eye and 20/20 in the other eye, is required. Regarding refractive surgery, most persons who have had these procedures will be passed. However, some may be deferred for several months or disqualified based on an individualized assessment of the surgical outcome. Color vision Candidates must be able to accurately and quickly name colors and must be free of other visual impairments that would restrict the ability to perform firefighter duties. 

In adults maintained on vitamin A-deficient diets for a period of months, there are a number of early signs, apparent before the impairment of dark adaptation impairment of the senses of taste, smell, and balance and distortion of color vision, with impaired sensitivity to green light. With the exception of the effects on color vision, these can all be attributed to dedifferentiation of ciliated epithelia (Sauberlich et al., 1974 Hodges et al., 1978). 

Characteristics of the vision loss can aid in the diagnosis of demyelinating optic neuropathy. The vision loss is progressive, is maximal in 1 week, and achieves variable recovery within 4 to 6 weeks. The reduction in vision frequently is accompanied or preceded by periocular pain on movement of the eye. Color vision often is severely impaired, and visual fields most commonly reveal a relative central scotoma. The ophthalmoscopic picture is usually one of a normal optic nerve head, because most commonly the optic neuropathy is behind the globe and thus is called retrobulbar optic neuritis. When there is optic disc swelling, it is known as papillitis. 

The presence of systemic disease can alter the way an individual detoxifies or excretes a drug. Liver and kidney disease, in particular, can markedly influence drug response by allowing the drug to accumulate to toxic levels. The rate of excretion of digoxin, for example, is reduced considerably in patients with renal impairment, thus causing an increased risk of alterations in color vision in these patients. 

Retinal pigmentary changes, visual field defects, color vision loss Retinal pigmentary changes, disturbances of dark adaptation, color vision loss, visual field defects Impairment of dark adaptation, visual field defects, vascular attenuation Color vision disturbances, entoptic phenomena Color vision disturbances... 

The most common symptoms reported by patients are changes in color vision and impaired vision. These symptoms can take many forms and include the visual phenomena listed in Box 35-4. A common symptom is snowy vision (objects appear to be covered with frost or snow), and this observation is intensified in brightly illuminated environments. There is also evidence that digoxin may contribute to rhegmatogenous retinal detachment by decreasing the normal adhesion of the retina to the RPE. 

Mild toxic reactions are characterized by slight reduction of visual acuity, flickering of vision, color vision decrease, impaired night vision, tinnitus, weakness, or confusion. In more severe cases, symptoms consist of sudden complete loss of vision, dizziness, and even deafness. Coma with circulatory collapse characterizes the most severe form of quinine toxicity. Patients may complain of impairment of night vision, but color vision is usually normal. The visual fields usually demonstrate concentric constriction. Improvement of the visual fields after the acute episode may require days or months, but the field loss may show no recovery and become permanent. 

Color vision deficiencies are probably the most sensitive indicator of early ethambutol optic neuropathy and can occur even before visual acuity and visual fields are affected. Sometimes, contrast sensitivity can be affected before either visual acuity or color vision becomes impaired. 

Amiodarone can cause impaired color vision associated with keratopathy (SEDA-12, 153) (104). Of 22 patients taking long-term amiodarone, two who had otherwise healthy eyes had abnormal blue color vision (101). Otherwise, color vision, contrast sensitivity, and visual fields were normal or could be explained by eye diseases such as cataract. 

The resulting functional defects are varied difficulty in reading, scotomas, defective color vision, photophobia, light flashes, and a reduction in visual acuity. Symptoms do not parallel the retinal changes. By the time that visual acuity has become impaired, irreversible changes will have taken place. 

In aluminium-overloaded dialysis patients, acute visual impairment can occur after only the first or second intravenous test dose of 40mg/kg deferoxamine (42-44). Visual symptoms are of retinal origin and include impairment of color vision, night bhndness, and reduced visual acuity serious and persistent visual loss can occur... 

Quinidine rarely affects vision, but can cause scotomata, impaired color vision, and toxic amblyopia (20), altered vision (21), sicca syndrome (22), keratopathy (23), and granulomatous uveitis (24). 

Studies of chronic exposure of those working in dry cleaning plants have reported some CNS effects, some liver function abnormalities, renal dysfunction, and some definite central and peripheral neurotoxicity. Other effects from chronic exposure to PERC include cardiac arrhythmias, reduced color perception, impaired memory, peripheral neuropathy, impaired vision, confusion, disorientation, fatigue, personality changes, and agitation. 

Some neurotoxic effects of exposures to organic solvent mixtures are not anticipated. Solvent mixture exposures to lipophilic/hydrophilic mixtures have been shown to impair color vision in those exposed to paints and lacquers, printers, and workers in microelectronics plants. I81-83 The authors of these studies did not offer any hypothesis for the observed effects. 

Adverse Effects. Sildenafil is well tolerated in patients with normal cardiovascular function. Most of the side effects reported in the clinical trials at a higher rate than placebo are mild and are related to the drug s vasodi-latory effect. They include headache, flushing, and nasal congestion. Other frequent side effects include abnormal vision (impairment of color discrimination) and dyspepsia. The... 

Kishi R, Tozaki S, Gong YY Impairment of neurobehavioral function and color vision loss among workers exposed to low concentration of styrene—a review of literature. Industrial Health 38 120-126, 2000... 

C. Retinal toxicity occurs 9-10 hours after ingestion and includes blurred vision, impaired color perception, constriction of visual fields, and blindness. The pupils are often fixed and dilated. Fundoscopy may reveal retinal artery spasm, disk pallor, and macular edema. Although gradual recovery occurs, many patients are left with permanent visual impairment. 

In a retrospective study of 857 Korean patients who took ethambutol, 89 had impaired vision [65 ]. Ethambutol-induced optic neuropathy was diagnosed in during a mean follow-up period of 13 months. The average dose of ethambutol was 18 mg/kg/ day and the duration of therapy was 9.4 months. Ophthalmic findings included reduced visual acuity (n = 58), abnormal visual fields (n = 58), abnormal color vision (55), optic disc pallor (34), and increased latency on VEP tests (58). Slightly less than one-third of the patients had improved visual function after discontinuing ethambutol. The mean time to recovery was 5.4 months. However, no patient with optic disc pallor at the time of diagnosis had improved visual function. Renal dysfunction and the daily dose of ethambutol, but not the duration of treatment, contributed. The authors estimated the incidence of ethambutol-induced optic neuropathy in Koreans to be under 2%. Thus, visual function after withdrawal of ethambutol is reversible in only a minority of patients and does not occur if optic disc pallor is present. 

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