Place of astigmatism among refractive errors
The human eye is an optical system that forms an inverted, reduced image on the retina. This principle was formulated as early as 1604 by Johannes Kepler, who also described myopia (nearsightedness) and hyperopia (farsightedness). Astigmatism, along with myopia and hyperopia, is one of the frequent ophthalmological causes of vision deterioration—refractive errors. A systematic doctrine of these anomalies was created in 1864 by Frans Donders.
Differential diagnosis of decreased vision
Patient complaints of decreased visual acuity (amblyopia) require a clear distinction between ophthalmological and neurological pathology.
- Ophthalmological causes: these include refractive errors (including astigmatism) and lesions of the light-conducting media (e.g., the lens). A key sign of astigmatism is that the use of corrective lenses makes it possible to completely normalize visual acuity.
- Neurological causes: if vision does not improve with lenses, and fundus examination (ophthalmoscopy) reveals no changes in the retina and refractive media, the cause should be sought in a lesion of the optic nerve or the optic chiasm (chiasm).
Research methods
To detect astigmatism and assess the degree of visual impairment, a standard algorithm is used:
- Taking the history: assessing the rate of vision decline, identifying its association with somatic, neurological, and mental illnesses.
- Visometry (visual acuity testing): performed sequentially for each eye. Special Snellen charts (with letters, numbers, or figures), based on the principle of the minimum angle of resolution, are used for this.
- Prescribing correction: precise determination of refractive parameters and prescription of lenses is carried out by an ophthalmologist.
For the differential diagnosis of the causes of decreased vision, remember the lens rule: if the lens helps, the problem is refractive (e.g., astigmatism); if not, look for a nerve or chiasm lesion.
Class and exam questions
What is amblyopia in the context of astigmatism?
Amblyopia is a medical term denoting decreased visual acuity that may be the result of uncorrected astigmatism.
How to distinguish astigmatism from an optic nerve lesion?
In astigmatism, vision improves after prescribing appropriate lenses. In optic nerve pathology, lens correction has no effect.
Who first proposed the chart method for determining visual acuity?
The chart method for assessing visual acuity (visometry) was proposed by Snellen in 1882.
What else to study on this topic
- Anatomy and physiology of the visual pathway (lateral geniculate body, optic radiations)
- Topical diagnosis of visual cortex and radiation lesions
- Principles of physiological optics according to Helmholtz
- Myopia and hyperopia as other types of refractive errors
- Differential diagnosis of amblyopia and amaurosis
Master the entire topic in the "Propaedeutics" course
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- Complete study guide on "Astigmatism" and 3,152 more pages of the subject
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Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.