Refractive Errors PDF

# Refractive Errors ## 1. What are the four main types of refractive errors? - Myopia - Hyperopia - Astigmatism - Presbyopia ## 2. How are light rays usually focused in a normal eye (astigmatism)? They are focused on the retina to form a clear image. ## 3. Define myopia and mention its types? Myo...

# Refractive Errors ## 1. What are the four main types of refractive errors? - Myopia - Hyperopia - Astigmatism - Presbyopia ## 2. How are light rays usually focused in a normal eye (astigmatism)? They are focused on the retina to form a clear image. ## 3. Define myopia and mention its types? Myopia is blurring of distant objects and focusing of light behind the retina. Types of myopia include: - axial - refractive ## 4. What factors contribute to the development of hyperopia? - Abnormal length of the eye axis - Increased curvature of the cornea - Abnormal position of the lens ## 5. What is the difference between regular and irregular astigmatism? - Regular astigmatism occurs when the main axes are perpendicular, and irregular occurs when they are not perpendicular. * Regular astigmatism is associated with myopia, and irregular is associated with hyperopia. ## 6. What is presbyopia and how is it related to aging Presbyopia is a visual impairment associated with aging and occurs as a result of loss of flexibility of the eye lens. ## 7. What are sphero-cylindrical lenses and how do they differ from spherical lenses? - Sphero-cylindrical lenses correct refractive errors associated with astigmatism. - Spherical lenses correct vision in all axes. - Sphero-cylindrical lenses have different focal planes on different axes. ## 8. Explain the equalization method to determine the power of an unknown lens. - The unknown lens is moved until the image appears clearly. - A lens of known power is placed with the unknown lens until the image is equalized. - The lens is measured using a corometer - Multiple lenses are used to determine the power of the lens. ## 9. Explain the transfer process in spherical lenses Cylindrical. - It is the process of changing the curvature of the lens. - It is the process of converting the value of the cylinder and transferring the axis. - It is the modification of the central thickness of the lens. - It is the process of measuring the lens. ## 10. What are toric lenses and in what cases are they used? Toric lenses: - correct refractions resulting from astigmatism - used to correct myopia - used to correct hyperopia - Only used in contact lenses. ## 11. What does health promotion primarily focus on? - Improving health through education and policy changes. - Conducting health assessments. - Providing direct medical care ## 12. What are environmental issues related to? - Economic development - Technological advancements - Concerns that affect health and the natural environment.