EyeWitness

Winter 2017

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Map-Dot-Fingerprint Corneal Dystrophy Notes from Tim 50 Shades of Gray's Contact Lens Anatomy By Tim Koch, FCLSA, COT 4 CLSA EyeWitness Winter 2017 with corneal astigmatism, and front surface toric lenses for patients whose astigmatism was primarily lenticular. Matching surface to surface. I could never really tell whether that made a profound difference or not, but I did that. • I used to choose low water content soft lenses for patients who exhibited dry eye symptoms on the theory that those lenses required less tears. I kept track of which ones were in that category. • Spherical soft lenses with some stiffness (modulus) were fit on those with low amounts of corneal astigmatism in the hope that they would "mask" some of the cylinder. I thought they did deliver some measure of crisper vision. • With GPs, I had to decide at what power level of plus or minus I wanted to lenticulate the lens for reduced mass and greater comfort. Now, the labs decide for us. Would we know how and when, if they didn't? • Some GP materials are just plain heavier than others. Does that influence our choice at all on the huge designs? • Who remembers to calculate the DK/t of a lens as the thickness changes due to power changes? In the center? In the periphery? Do we remember how? Laboratory consultants and soft lens manufacturers know these things. We should know them too. Just to keep them honest. EW H enry Gray authored the famous definitive book on human anatomy. His book is widely regarded as an extremely influential work on the subject, and has continued to be revised and republished from its initial publication in 1858 to the present day. Every physician I know has a copy. Actually, though, he didn't write a book on Contact Lens Anatomy. But maybe this issue of EyeWitness will add to the literature: • Center thickness • Dk/ Dk/t • Optical zone diameter • Osmolarity • Blend curves • Edge profile • Myo-flange • Hyper-flange • Water content • Front Surface Toric/Back Surface Toric/ Bi-Toric • Prism Ballast • Dual slab-off • Wetting angle • Reverse geometry • Truncation • LARS • Translating bifocals • Specific Gravity • Modulus • Asphericity • HVID OMG. When we speak of the anatomy of a lens, we as fitters used to consider most of these lens features when designing (or choosing) the best lens for the patient. We were actually supposed to know all of this stuff. We still should, really. Maybe not all of it. But, a lot of it, yes! For instance: • I used to choose back-surface soft toric lenses for patients Tim Koch, FCLSA, COT, has over 30 years experience in the eyecare industry and is well known as an author, lecturer and specialist in the contact lens field. He has served on the Board of NCLE, on the Board of CLSA and on the Board of Directors of the Contact Lens Manufacturers Association of America.

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