Bicentric grinding, also known as slab-off, is used to correct vertical imbalance. Typically, slab- off can be used to correct vertical imbalance over 1.5 diopters. Bicentric grinding means we are creating two optical centers on a lens. ‘Bi’ meaning two, and ‘centric’ meaning center. Bicentric grinding or slab-off is used to neutralize an unwanted prismatic effect caused by unequal refractive errors. Slab-off can be either conventional or reverse. Conventional slab-off is added to the front surface, lower part of the lens, and reverse slab-off is added to the rear surface, lower part of the lens.
As an optician, you will use a lensometer on a daily basis. In The Masters in Lensometry (Part 1), we discussed the basics, from focusing the eyepiece and calibrating the lensometer, to starting with simple spherical lenses. As stated in the last article, if you are a seasoned optician trying to share your knowledge with others, start with these basics.
There have been several times when working as a scribe, I have seen some very interesting cases. One in particular stands out in my mind. We had a young patient come in for her eye exam; she was about 7 years old. Her mother said she was a good student for the most part, but had some trouble with reading and was in Title 1 reading assistance. She was a very sweet and curious girl who had abundant questions about all the equipment and all the staff. The young girl did not seem to have issues with distance because her mom said she could see signs farther away than mom could, but she was not reading well and was behind in school. After the doctor’s exam, she was prescribed reading glasses. The doctor prescribed a pediatric bifocal so the child would wear them all the time and not have to remember to take them on and off for reading. The girl was excited! She really wanted glasses just like her friends in school, which is actually quite common among the kids in the area.