Ophthalmology & Optometry/determining intermediate rx


from any precription writtin with an add for lets say a progressive lens or even a trifocal, how is the intermediate determined when the lens is made.  is there a specific formula or a general sort of "rule of thumb" as it may.  

please help

Dear Adam  :  

The general rule of thumb is that the intermediate power of a trifocal is generally 50% of the power of the Add, i.e if the power of the bifocal add is 2.50, then the intermediate power is generally 1.25 giving clarity of focus at an intermediate range like, for example, the computer, dashboard, table top, card playing, etc. Having said that, the intermediate can be ground to patients specific visual needs either closer or further away. In these cases the intermediate power may be 40% or 60% of the add power.  hope this helps

Dr. Ken

Ophthalmology & Optometry

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Any and all questions with regard to ocular ailments, eye diseases as cataracts, glaucoma, macular degeneration, diabetic retinopathy, etc , eye and visual sympomatology, eyeglasses, contact lenses, low or subnormal vision, pediatric vision conditions,and special and unique ailments will be discussed.


36 years of clinical experience in opticianry and therapeutic optometry. Still in private practice with special interests in vision conditions, diagnosing and treating ocular ailments, prescibing treatment plans which include medicine, eyeglasses, and contact lenses primarily. Although surgery is not within the realm of my area of expertise, I co-manage many pre and post -op surgical cases which include Lasik and PRK procedures.

New Jersey Society of Optometric Physicians American Optometric Association

B.A.,1968, Hunter College of the City University of New York B.S.,1970, Pennsylvania College of Optometry O.D.,1973, Pennsylvania College of Optometry Therapeutic Pharmaceutical Administration Certification, New Jersey 1992

Awards and Honors
Clinical Efficiency Award, 1973, Pennsylvaania College of Optometry

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