Thanks
Thanks
Last edited by raben4; 07-24-2017 at 06:47 AM.
Without knowing if the powers are - or + you can't answer them.
Sorry, Missing during copy. Will update tonight
Is this for a test? If so, are #1 & #3 multiple choice? (For real prescriptive applications we're lacking way too much information.)
#2 Looks like a trick question..."Notes: slab off left eye" is incorrect. A slab off wouldn't go on the left eye, but a reverse slab-off would.
Calculate "Power on the 90" for each lens. In this case, since the cylinder axis OU is 090, there's no cylinder power to add to the sphere powers. F(90) OD: +0.75; F(90) OS: +3.50. The difference in Power is +2.75. Prentice Rule calculates for us that there is +0.275D of vertical imbalance per mm down from the OC. Reading level of 10mm=2.75D of total vertical imbalance--to be offset by a [Base Up] slab off on the lens of "most minus/least plus:" in this case the OD.
Last edited by Hayde; 07-21-2017 at 11:37 AM. Reason: forgot to denote Base! Thanks Robert!
1. Toric or bitoric contact lens for the least possible minification and best peripheral vision. See below for lens type if eyeglasses. Lenses should be antireflective coated.
2. 2.75 prism diopters base down. As Hayde said, a custom slab is base up on the most minus or least plus eye, so in this case it will have to be a molded reverse slab. If they only come in 0.50D increments, round down.
3. Round frame with zero decentration, shortest possible vertex distance, zero values for wrap and pantoscopic tilt, vertical OC level with center pupil, for the best possible weight and thickness reduction, and visual acuity. Modern lens fabrication methods may allow for more latitude with the wrap and panto values. The word 'suitable' in the question allows for some flexibility with decentration and lens shape. Lens material and design depends on factors not provided, but concerns are safety, chromatic aberration, and marginal astigmatism.
Hope this helps,
Robert Martellaro
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
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