system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Astigmatism is:
assistant
The correct answer is  Astigmatism It is that condition of refraction wherein a point focus of light cannot be formed' upon the retina. It includes those anomalies in the optical system wherein an appreciable error is caused by the unequal refraction of light in different meridians. Hence it may be an error either of curvature, of centering or of refractive index. There fore this question is controversial as both the options are given. But since the commonest form of astigmatism is due to curvature defect, this will be the answer.