Ophthalmology & Optometry/Change in Prism Correction


I have had a prism correction in my glasses for over 30 years.  I went to a new optometrist last week.  The exam was the over in record time.  When she got done, I asked her if she caught that I had a prism correction.  She acted surprised and asked to see my glasses.  She spent a lot of time looking at my glasses.  I also had last year's prescription for her.  She never did the test where I lined up horizontal and vertical lines.  (By the way, I have been to probably 5 different optometrists through the years and they all have come up with a need for prism correction).

When I got home and was comparing the prescription, I noticed the following:  Prior prescriptions I had .75 BO in each eye.  For the new prescription I have  1 BI in one eye, 1 BO in other eye.  I'm concerned that because whole exam was at lightening speed and she didn't do the alignment test, that this isn't going to be right.

Does it make sense that the prism would change that much.  Does it make sense that it would go from BI to BO?

In general she seems to have changed the Cylindrical and Axis measurements quite a bit too.  I haven't been noticing any vision problems...so that surprises me.  Here are old and new prescriptions in case that factors into the prism:
OD:  -6.75 sphere, -.75 cyl, 020 axis .75 BO Prism
OS:  -7.0 sphere, -.5 cyl, 020 axis, .75 BO Prism
Add +3.25

OD:  -6.25 sphere, -50 cyl, 45 axis, 1 BI Prism
OS:  -6.75 sphere, -25 cyl, 25 axis, 1 BO Prism
Add:  +3.25

I haven't picked up my new glasses yet, it will be another week.  

Thanks for your help!

You're right, it doesn't make sense at all to have such a large change.  It seems like the doctor didn't put as much time into assessing your vision needs as you have had in the past.

Another, very interesting note, is that horizontal prism is prescribed with the same base direction for each eye. For example, if your eye tend to drift out they will put base IN for each eye. (If you tend to drift in, they will put base OUT for each eye.)  The only time you would do a bi/bo prism is for someone with a visual field defect or stroke, where they may be missing a large area of vision.

Because the eyes work as a team, having different direction in base eye, the prism in the right eye neutralizes the left. You effectively have zero prism in your new glasses.

Also to note, vertical prism (base up / base down) is the opposite of horizontal--vertical prism is always up one eye, down in the other.

I wouldn't even take them home to try, the measurements don't make any sense.  I would schedule a consult / prescription check and have those alignment tests done. At the very least, have them match your old prism.

Hold your doctor to a higher standard. Make him/her work for it.

On another note, I'm not sure where you got your eyes checked, but to some degree, you get what you pay for. If you go to the Sam's Club $39 eye exam, in and out in 10 minutes, you're more likely to have problems because they don't/can't spend as much time with you.  I would always suggest scheduling an exam with a private-owned / private practice optometrist.

Good Luck,

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John M. Dovie, OD, FAAO


As a residency-trained Fellow of the American Academy of Optometry I am able to answer most questions regarding eye and vision health. Anything is welcome, ranging from dry or allergy eyes, bifocal contact lenses, or thoughts on LASIK surgery. As I am not a surgeon, detail-oriented surgical-related questions may be better answered by an ophthalmologist.


Selected to participate in the PCO residency program in Philadelphia at The Eye Institute, where I worked OD and MD specialists gaining invaluable experience in various clinics including glaucoma, cornea and cataract, oculo-plastics, retinal disease, neuro-ophthalmic disease, primary care, emergency medicine, and special populations. Have practiced and trained in numerous settings including hospital, academic, retail and private practice. I earned my Fellowship in the American Academy of Optometry (FAAO). There are currently only about 3000 active fellows worldwide, and there are only about 70 Fellows in the state of Virginia. I currently own and operate my own optometric practice/clinic.

American Academy of Optometry, American Optometric Association (Contact Lens/Cornea Section member since 2001), Southwest Virginia Optometric Association, Virginia Tech Alumni Association

“Nyctalopia as the Presenting Sign of Vitamin A Deficiency: A Late Complication of Gastric Bypass Surgery.” Clinical Case Study Poster presented at The American Academy of Optometry Denver, Colorado, December 2006, co-authored with Bradley Lane, OD.
“The Importance of Considering Paranasal Sinus Mucocele as a Differential Diagnosis in Diplopia.” Clinical Case Study Poster presented at The American Academy of Optometry San Diego, California, December 2005, co-authored with Kelly Malloy, OD, FAAO and Cherie Farkash, OD.
“Acute Onset of Halos and Glare: Bilateral Keratitis—An Atypical Presentation of Amiodarone Keratopathy.” Clinical Case Study Poster presented at The American Academy of Optometry Tampa, Florida December 2004. Also Presented to New Jersey Academy of Optometry, Neptune, New Jersey March 2005.
“The Opportunity for an Optometrist to Save a Life.” Clinical Case Study and Grand Rounds Presentation presented at The Pennsylvania College of Optometry, Philadelphia, Pennsylvania, September 2004.
“Corneal whorls cause wonder.” Clinical Challenges Quiz, co-authored with Andrew Gurwood, OD, FAAO, Review of Optometry. Published 10/15/2006.
“Acute onset of halos and glare: bilateral corneal epithelial edema with cystic eruptions--atypical presentation of amiodarone keratopathy.” Co-authored with Andrew Gurwood, OD, FAAO. Published February, 2006, Optometry.
“Pondering the posterior polka-dots.” Clinical Challenges Quiz, co-authored with Andrew Gurwood, OD, FAAO, Review of Optometry. Published 5/15/2005.
Professional Involvement:
“AION: Amiodarone-Induced or Anterior Ischemic Optic Neuropathy?” Participated as a peer-review referee for Expert Review of Ophthalmology (London, UK); refereed 10/2006.

Bachelor of Science, Cum Laude, Virginia Tech. Bachelor of Science, Pennsylvania College of Optometry. Doctorate (OD), Pennsylvania College of Optometry Residency, Pennsylvania College of Optometry Fellow of the American Academy of Optometry

Awards and Honors
Winner, First Place, "Best Beside Manner" by Our Health Magazine: 2012, 2013, 2014 Winner, First Place, "Best Eye Doctor" by The Roanoke Times: 2013, 2014 Recognized as a Fellow of the American Academy of Optometry, December, 2006 Recipient of the Onofrey G. Rybachok Memorial Scholarship, 2000-2001 Member: The Golden Key International Honor Society Member: The National Biological Honor Society Member: The National Honor Society Eagle Scout awarded 1994

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