Prescribing for Astigmatism
Presbyopia + Astigmatism = Contact Lens Success
BY ELAINE CHEN, OD; COLTON HEINRICH, OD; & TIMOTHY B. EDRINGTON, OD, MS, FAAO
Presbyopic patients often discontinue or reduce their contact lens wear due to the dissatisfaction of having to wear glasses in addition to contact lenses for many of their daily tasks. This is especially true now due to a need for clear and comfortable vision at several different working distances. For example, today’s presbyopic patients spend time texting, reading, using the computer, and driving. To meet these demands, the availability of multifocal contact lens options has increased, and today’s multifocal lens designs are vastly better. This enables presbyopic patients who have never worn, or who previously discontinued wear of, contact lenses to enjoy the benefits of wearing GP or soft lenses.
Even though GP multifocals have been a viable option for patients for many years, the quality and reproducibility of GP multifocal lenses have dramatically improved largely due to the use of automated lathes in the manufacturing process. GP multifocal lens design options include aspheric, annular, and segmented designs. GPs can also be used for monovision correction.
They also can be successfully prescribed for patients who have high prescriptions, including large amounts of astigmatism. Refractive astigmatism induced by corneal toricity generally can be corrected with a spherical base curve GP lens design. If a toric GP design is indicated, because of excessive residual cylinder or a highly toric cornea, a multifocal addition can be incorporated.
Corneal physiology concerns have decreased due to the increased oxygen provided by today’s high-Dk GP materials, which also enables us to successfully prescribe larger-overall-diameter lenses. Recently, multifocal scleral GP contact lenses have become available in aspheric and annular designs. GP multifocals generally provide our patients with excellent visual quality.
Soft multifocal contact lenses are our first option if a presbyopic patient has minimal (usually <0.75D) refractive astigmatism. As contact lens technology continues to improve, there has been an increase in available soft lens parameters. However, high cylinder power (> –2.75DC) soft multifocal lens options remain limited in silicone hydrogel lens materials. Custom soft multifocal lenses are available that correct up to –10.00D of cylinder and up to a +4.00D add. However, the visual success of correcting large amounts of cylinder with a soft lens is very dependent on rotational stability. We would suggest using these designs for your presbyopes who have low and moderate astigmatism.
Modified monovision is also a viable option if one eye is unable to appropriately be prescribed a multifocal sphere or toric lens. For example, an astigmatic patient may be prescribed a multifocal spherical lens for one eye and a single-vision toric lens for the other. This modality has advantages over traditional monovision in that it offers patients the ability to achieve a degree of simultaneous vision and binocularity. When a patient has limited success with multifocals, monovision may be the most effective modality to correct the patient’s visual needs.
Specialty lenses often come with fitting guides to achieve success. These guides are very useful in determining an initial lens design and parameters. Also, utilize the expertise of the laboratory consultants throughout the fitting process. As with all vision corrections, it is important to discuss patient vocation and avocational needs and expectations before embarking on lens fitting. CLS
Drs. Elaine Chen and Colton Heinrich are the cornea and contact lens residents at the Southern California College of Optometry (SCCO) at Marshall B. Ketchum University (MBKU). Dr. Edrington is the cornea and contact lens residency coordinator at SCCO. He is also a Fellow of the American Academy of Optometry and a Diplomate in its Cornea, Contact Lenses, and Refractive Technologies Section.