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Astigmatism is a very common vision condition that causes blurred vision due to the irregular shape of the cornea or the lens inside the eye. People with astigmatism experience headaches, fatigue, eyestrain, and blurred vision at all distances. Most astigmatism cases can be easily diagnosed and corrected. Learn about the causes, symptoms, diagnosis and treatment for astigmatism in this article.

An irregular shaped cornea or lens prevents light from focusing properly on the retina, resulting in blurry vision. Astigmatism occurs when the cornea is shaped more like an oblong football than a spherical baseball, which is the normal shape. A cornea with astigmatism has two curves, one flat curve and one that is steep. Light is thus focused at two points instead of one.

Regular versus irregular astigmatism

In regular astigmatism, the meridians in which the two different curves lie are located 90 degrees apart. In the case of irregular astigmatism, either the two meridians are not perpendicular or there are more than two meridians.

Lenticular astigmatism

Astigmatism caused by an irregularly shaped crystalline lens is called lenticular astigmatism. Usually, astigmatism is hereditary. However, astigmatism may also develop following an eye injury that has caused scarring on the cornea, or certain types of eye surgery. Keratoconus, a relatively rare condition that causes a gradual thinning of the cornea, may cause a large amount of astigmatism.

Astigmatism causes vision to be blurred at both distance and near vision. Mild astigmatism may be asymptomatic and undetected, particularly in children. More severe astigmatism may cause eyestrain, fatigue, or headaches.

Detection and diagnosis

Astigmatism is easily detected through eye examination. A keratometer is usually used to measure the curvature of the cornea. A corneal topographer and a wavefront aberrometer may give much more precise information about astigmatism.

Astigmatism may be corrected with glasses, contact lenses or surgery.

• Glasses are the primary choice for people with small amount of astigmatism. Individuals with high amounts of astigmatism must have their glasses carefully adjusted to their face.

• Contact lenses, such as 'toric contact lenses' can correct small amounts of astigmatism whereas severe astigmatism will be more successfully corrected with rigid astigmatism contact lenses as they maintain their regular shape while on the cornea.

• Surgical vision correction procedure, such as photorefractive keratectomy and laser in situ keratomileusis, can also successfully correct astigmatism.

Conclusion

Astigmatism causes blurred vision that can be compensated with glasses or contact lenses or corrected with surgery. Astigmatism is easily detected through eye examination. A comprehensive eye examination should be scheduled when experiencing blurry vision at all distance, headaches or eyestrain.

Mercury poisoning from fish and dental amalgam fillings are most common. Acute mercury exposure is rare but results in immediate and severe symptoms. Chronic mercury poisoning is quite common and can also lead to serious damages to the health. Learn about the symptoms and treatment of the various forms of mercury poisoning.

Mercury exists in different forms: methylmercury, elemental mercury, organic and inorganic mercury. The effect on health depends on various factors, such as the health and age of the person exposed, the chemical form of mercury, the dose, duration and route of exposure.

Symptoms of methylmercury poisoning includes impairment of the peripheral vision, disturbances in sensations such as paresthesia, itching, burning or pain, lack of coordination of movements, impairment of speech, hearing, walking and muscle weakness. Methylmercury exposure is particularly damaging for the foetus during pregnancy.

Symptoms of elemental mercury poisoning include tremors, emotional changes, neuromuscular changes, headaches, disturbances in sensations, changes in nerve responses, and performance deficits on tests of cognitive function. At higher exposures of elemental mercury there may be kidney effects, respiratory failure and death. Liquid elemental mercury primarily causes health effects when it is inhaled as a vapour.

High exposures to inorganic mercury may result in damage to the gastrointestinal tract, the nervous system, and the kidneys. Organic mercury compounds are absorbed through the gastrointestinal tract. Symptoms of high exposures to inorganic mercury include kin rashes and dermatitis, mood swing, memory loss, mental disturbance and muscle weakness.

In acute exposures, the first step in treatment is removing the mercury source and clothing. The contaminated person should also be thoroughly cleaned. Acute inhalation of mercury vapour may require emergency respiratory support.

Treatment varies with the form of mercury poisoning. Ingestion of an inorganic form of mercury usually begins with the removal of the source. Activated charcoal is used to bind and inactivate the toxin. Acute organic forms are treated with charcoal and a laxative. Ingestion of elemental mercury usually has no effects on gastrointestinal cells and is removed by a laxative. Medical treatment usually involves chelating agents, such as dimercaprol or DMSA, that bind most toxic forms.

In conclusion, symptoms of mercury poisoning are various and the extent of toxic effects depends on several factors. Mercury poisoning is usually difficult to treat and can lead to serious damages to the health and death.