Dioptrie Oculaire PDF

## Dioptrique Oculaire ### Dioptre - The surface that separates two media. - Light rays obey the laws of Descartes. ### Natural Light - A superposition of electromagnetic waves with different wavelengths. ### A Ray of Light - A propagation ray of light. - It is a straight line in a transparent...

## Dioptrique Oculaire ### Dioptre - The surface that separates two media. - Light rays obey the laws of Descartes. ### Natural Light - A superposition of electromagnetic waves with different wavelengths. ### A Ray of Light - A propagation ray of light. - It is a straight line in a transparent and isotropic medium. ### Stigmatic Optical System - A point object gives a point image. ### Astigmatic Optical System - A point object gives a blurred image. ### Power of a Dioptre - The power of a dioptre is equal to (n'-n)/h. ### The Image is at Infinity - The object is at infinity. - The image is on the focal plane F2. ### Definitions - **Emmetropic Eye:** An eye with normal optics. The image falls on the retina. - **Ametropic Eye:** An eye with a refractive error. - **Phakic Eye:** An eye with its natural lens. - **Pseudophakic Eye:** An eye with an artificial lens. ### Ametropia - A disturbance of eye refraction. - It's the lack of coincidence between the image plane of an object at infinity and the retina. - **Spherical Ametropia:** The symmetry of revolution is maintained. The diopters are spherical. - **Astigmatism:** The symmetry of revolution is not maintained because the cornea is not perfectly spherical. ### Myopia - **Definition:** Object at infinity forms in front of the retina. - The eye is too strong. - **Etiology:** - **Axial Myopia:** The axial length is too long - **Curvature Myopia:** The curvature of the cornea is too strong. - **Index Myopia:** The index of refraction of the lens is too high. - **Degree of Myopia:** DM = PR/PR. The PR is the most distant point that can be seen clearly. - **Accommodation:** The myopic eye has a shorter accommodation range compared to an emmetropic eye. - **Correction:** The myopia is corrected by wearing concave lenses. - For contact lenses: T = 1/PR. - For spectacles: T = 1/(PR - d). ### Hyperopia - **Definition:** The image of an object at infinity forms behind the retina. - The eye is too weak. - **Etiology:** - **Axial Hyperopia:** The axial length is too short. - **Curvature Hyperopia:** The curvature of the cornea is too weak. - **Index Hyperopia:** The index of refraction of the lens is too low. - **Degree of Hyperopia:** DH = 1/PR. The PR is the most distant point that can be seen clearly. The PR is virtual. - **Accommodation:** The hyperopic eye has a longer accommodation range compared to an emmetropic eye. - **Correction:** The hyperopia is corrected by wearing convex lenses with a power equal to the degree of hyperopia. Contact lenses or refractive surgery can also be used. ### Astigmatism - **Definition:** The eye has different refractive powers in different meridians. - The image of a point is not a point but a line. - **Types:** - **Simple:** One focal point falls on the retina. - **Compound:** Focal points are not both on the retina. - **Myopic:** The focal points are in front of the retina. - **Hyperopic:** The focal points are behind the retina. - **Mixed:** One focal point is in front of the retina, and one is behind. - **Direct:** The horizontal focal point is in front of the vertical focal point. - **Indirect:** The vertical focal point is in front of the horizontal focal point. - **Regular Astigmatism:** The curvature of the cornea varies slowly and regularly with the meridian. The correction is made with cylindrical lenses. - **Simple:** The correction is done with a cylindrical glass. - **Compound:** The correction is done with a spherocylindrical glass. - **Irregular Astigmatism:** The curvature of the cornea is irregular, with no specific pattern. This can occur due to trauma, burns, or congenital abnormalities. The correction is made with contact lenses, and in some cases, corneal transplantation.