effects side ocular induced-Chemical  • 8 PART  

Clinical significance

Systemic exposure to these compounds mostly occurs in the ­agriculture industry. Suicide attempts using organophosphates are another means of intoxication. Young children may receive accidental systemic exposure to these toxins from lawn and garden applications. Toxicity from organophosphates leads to a build-up of acetylcholine in nerve synapses, which can cause myriad neurological dysfunctions. In humans poisoning with these agents may cause acute excess secretory activity, including involuntary salivation, lacrimation, urination, emesis, defecation, muscle weakness and seizures.

As with muscarinic compounds such as pilocarpine, miosis and accommodative spasm are part of the symptom complex. Ocular bobbing, opsoclonus and upbeat nystagmus have all been reported as transient effects from toxicity due to organophosphates.

Chronic effects from exposure to organophosphates may include eye findings but these are more controversial. In the 1970s, Japanese researchers identified a symptom complex including myopia, visual field defects, difficulty with ocular pursuit movements and pigmentary changes to the retina occurring in people living in agricultural areas that received heavy organophosphate use. They coined the term ‘Saku disease’ after the name of the region in which a high proportion of the affected patients ­resided, and they presumed the cause to be chronic exposure to organophosphates. Other work has suggested subclinical effects from chronic exposure to these compounds, including changes in color vision, contrast sensitivity and pupil contractility. There is a well-accepted non-ocular syndrome of peripheral neuropathy resulting from chronic exposure to certain organophosphates. The mechanism of this distal axonal dysfunction seems to be related not to decreased cholinesterase activity but to phosphorylation of a receptor protein, neurotoxic esterase. In any case, there is no consensus on whether long-term systemic exposure to organophosphates causes any type of chronic eye toxicity.

Recommendations

Patients suspected to have acute organophosphate poisoning need emergent evaluation. Care may be best provided in an ­intensive care setting as seizures and cardiopulmonary arrest are possible. Treatment involves anticholinergic drugs such as atropine and pralidoxime chloride. Ocular symptoms require no special treatment as systemic therapy will reverse the eye findings as well.

References and Further Reading

Dementi B. Ocular effects of organophosphates: a historical perspective of Saku disease. J Appl Toxicol 14(2): 119–129, 1994.

Dick RB, Steenland K, Krieg EF, Hines CJ. Evaluation of acute sensory-motor effects and test sensitivity using termiticide workers exposed to chlorpyrifos. Neurotoxicol Teratol 23(4): 381–393, 2001.

Dyro FM. Organophosphates. The Emedicine from WebMD page. Available at: http://www.emedicine.com/neuro/topic286.htm. Accessed November 25, 2006.

Geller AM, Sutton LD, Marshall RS, et al. Repeated spike exposure to the insecticide chlorpyrifos interferes with the recovery of visual sensitivity in rats. Doc Ophthalmol 110(1): 79–90, 2005.

Hata S, Bernstein E, Davis LE. Atypical ocular bobbing in acute organophosphate­ poisoning. Arch Neurol 43(2): 185–186, 1986.

Ishikawa S. Ophthalmology due to environmental toxic substances ­especially intoxication by organophosphorus pesticides. Nippon Ganka Gakkai Zasshi 100(6): 417–432, 1996.

Jay WM, Marcus RW, Jay MS. Primary position upbeat nystagmus with organophosphate­ poisoning. J Pediatr Ophthalmol Strabismus 19(6): 318–319, 1982.

Liang TW, Balcer LJ, Messe SR, Galetta SL. Supranuclear gaze palsy and opsoclonus after Diazinon poisoning. J Neurol Neurosurg Psychiatry 74(5): 677–679, 2003.

Paraoanu LE, Mocko JB, Becker-Roeck M, et al. Exposure to diazinon alters in vitro retinogenesis: retinospheroid morphology, development of chicken retinal cell types, and gene expression. Toxicol Sci 89(1): 314–324, 2006.

Pullicino P, Aquilina J. Opsoclonus in organophosphate poisoning. Arch Neurol 46(6): 704–705, 1989.

Rosenstock L, Keifer M, Daniell WE, et al. Chronic central nervous system effects of acute organophosphate pesticide intoxication. The Pesticide Health Effects Study Group. Lancet 338(8761): 223–227, 1991.

Class: Hydrocarbons

Generic name: Gasoline.

Synonyms: Petrol, motor fuel, benzene, motor spirits.

Proprietary names/products containing: There are

many brands of gasoline and gasoline/ethanol blends.

Primary use

Primarily used as fuel in internal combustion engines, gasoline is a complex mixture of hundreds of hydrocarbons. The hydrocarbons vary by class (paraffins, olefins, naphthenes and aromatics) and by the number of carbon atoms in the molecule. Gasoline typically contains dozens of additives to enhance performance, cleanliness, etc., including oxidation inhibitors (aromatic amines and hindered phenols), corrosion inhibitors (carboxylic acids and carboxylates), antiknock compounds (tetraethyl lead, ­tetramethyl lead, methylcyclopentadienyl manganese tricarbonyl, and ferrocene), anti-icing additives (surfactants, alcohols, and glycols), dyes and drag reducers (high-molecular-weight ­polymers).

Ocular side effects

Topical ocular exposure

Certain

1.Irritation

a.Hyperemia

b.Burning

c.Lacrimation

Systemic exposure

Possible

1. Visual hallucination (leaded gasoline)

2. Visually evoked potential abnormalities (leaded gasoline)

3. Corneal anesthesia

Clinical significance

Gasoline splashes in the eye are ubiquitous. A data mining from the American Association of Poison Control Centers Toxic Exposure­ Surveillance System database revealed 6119 ocular exposures to gasoline and related hydrocarbons over a recent 5-year period. Of these exposures, only 318 had an outcome severity­ rated as ‘moderate’ (indicating more prolonged symptoms requiring some type of treatment but resulting in no permanent injury) and only five were rated ‘major’ (indicating some type of significant residual disability). The nature of the injuries was not available. There are no recent reports detailing ocular injuries from direct ocular exposure.

Systemic absorption of gasoline by workers in the petroleum industry or by persons seeking psychotropic effects by ‘huffing’ gasoline fumes may cause some visual side effects, including