Final answer:
For high-power corrective bifocal lenses with a working distance closer than standard, segment inset must be customized based on individual measurements, such as inter-pupillary distance at the working distance. Corrective lens power for vision conditions like myopia and hyperopia is computed considering the far or near point, respectively, and the vertex distance.
Step-by-step explanation:
When dealing with high-power distance lenses, and the working distance is closer than the standard 40 cm, special considerations must be taken into account for determining the correct segment inset for bifocal lenses. In these cases, it is beneficial to customize the segment inset to the specific visual needs of the patient. The inter-pupillary distance (IPD) should be measured at the working distance to ensure that the optical centers of the bifocal segments are aligned with the wearer's line of sight when viewing near objects. Bifocal lenses need careful positioning, as an incorrect inset may result in prismatic effects or eyestrain. Therefore, an optometrist or optician should be consulted to compute the correct segment inset based on the individual parameters of the eyeglass wearer, such as the prescription power and the personal working distance.
As this question also includes examples of determination of corrective lens power for both nearsightedness and farsightedness, it is clear that a thorough understanding of ophthalmic optics and vision correction strategies is essential. The power of the spectacle lens is calculated by taking into account the far point in the case of myopia or the near point in the case of hyperopia, adjusted for the vertex distance, which is the distance between the eye and the back surface of the spectacle lens.