Ans. d. Cylindrical lens increases the distoion Distoion occurs when the transverse magnification is not constant but changes as distance from the axis increases within a transverse plane. In pincushion distoion, magnification increases as distance from the axis increases (in the same transverse plane), whereas in barrel distoion, magnification decreases as distance from the axis increases. Distoion is field dependent, pupil independent, and stigmatic. Pincushion distoion occurs in practically all spectacle corrected aphakes and is occasionally seen in high myopes after clear lens extraction.' Aniseikonia Aniseikonia is an ocular condition where there is a significant difference in the perceived size of images. It can occur as an overall difference between the two eyes, or as a difference in a paicular meridian Causes: Aniseikonia can occur naturally or be induced by the correction of a refractive error, usually anisometropia (having significantly different refractive errors between each eye) or antimetropia (being myopic in one eye and hyperopic in the other) Meridional aniseikonia occurs when these refractive differences only occur in one meridian. Refractive surgery can cause aniseikonia in much the same way that it is caused by glasses and contacts. One cause of significant anisometropia and subsequent aniseikonia has been aphakia Symptoms: When this magnification difference becomes excessive the effect can cause diplopia, suppression, disorientation, eyestrain, headache, and dizziness and balance disorders. Treatment: Treatment is done by changing the optical magnification propeies of the auxiliary optics (corrective lenses). The optical magnification propeies of spectacle lenses can be adjusted by changing parameters like the base curve, veex distance, and center thickness. Contact lenses may also provide a better optical magnification to reduce the difference in image size. The difference in magnification can also be eliminated by a combination of contact lenses and glasses (creating a weak telescope system). The optimum design solution will depend on different parameters like cost, cosmetic implications, and if the patient can tolerate wearing a contact lens. When the image disparity is astigmatic (cylindrical) and not uniform, images can appear wider, taller, or diagonally different. When the disparity appears to vary across the visual field (field-dependent aniseikonia), as may be the case with an epiretinal membrane or retinal detachment, the aniseikonia cannot fully be corrected with traditional optical techniques like standard corrective lenses. However, paial correction often improves the patient's vision comfo significantly. Little is known yet about the possibilities of using surgical intervention to correct aniseikonia.