by P. Doug Becherer, OD
Sagittal depth, as it relates to soft contact lenses, has been discussed in the past and I believe will be discussed more in the future. We know there are three anatomical features that contribute to the sagittal depth of the eye and those anatomical features are central corneal curvature, corneal diameter, and corneal eccentricity.
The corneal anatomic feature that has the greatest impact on sagittal depth is corneal diameter, also known as horizontal visible iris diameter (HVID). The corneal feature with the next greatest impact on sagittal depth is eccentricity. Eccentricity is a value that depicts the rate at which is the cornea flattens from center to periphery. The third anatomical feature that impacts sagittal depth is corneal curvature, as measured via keratometry readings.
Knowing that these anatomical features impact the sagittal depth of the eye, I realized, we as practitioners, needed an efficient and easy way to design a custom soft contact lens utilizing that information. Therefore, I developed the SpecialEyes Arc Length Calculator, which is based on the concept of simply needing 2 measurements to yield a custom soft contact lens design that utilizes a sagittal depth fitting philosophy. Using the patient’s corneal diameter (HVID) and corneal curvature measurements (K readings), the calculator will mathematically design, via a proprietary algorithm, contact lenses that match the arc length of the patient’s cornea. This software allows a highly successful custom soft contact lens design for simple to very complicated corneal shapes and prescriptions. You simply insert your patient’s spectacle prescription, central K readings, and an accurate HVID and click calculate. The calculator will produce a contact lens design based on your patient’s corneal arc length.
The SpecialEyes Arc Length Calculator is available on the SpecialEyes website. For more information or assistance with the calculator call 866-404-1060 or submit an online request and one of the SpecialEyes representatives will be glad to assist you.
P. Douglas Becherer, O.D., F.A.A.O.
Dr. Becherer is in private practice in Belleville, IL and is a consulting optometrist to SpecialEyes. He is past chair of the AOA Contact Lens and Cornea Section, Past President of the Heart of America Contact Lens Society, Adjunct Assistant Professor of UMSL, and Adjunct faculty at SCO & ICO.
Young, G. et al. (2002). Clinical evaluation of factors influencing toric soft contact lens fit. Optom Vis Sci: 79:11-19, 2.
Andre, M. et al. (2001). A new approach to fitting soft contact lenses. EyeWitness, 2nd Quarter