Prescribing for Presbyopia
Dominant or Nondominant, That Is the Question
BY THOMAS G. QUINN, OD, MS, FAAO
Fitting guides for virtually all soft multifocal contact lenses ask that the dominant eye be identified either prior to initial lens selection or for troubleshooting. Though we talk about identifying the dominant eye, what we generally are most interested in with multifocal fitting is recognizing which is the nondominant eye.
The nondominant eye is the eye that will best accept some degree of blur in the distance. This is important to know when prescribing soft multifocals, particularly when fitting higher adds. More advanced presbyopes often require increased distance plus power or a higher add in one eye to achieve adequate near vision.
Sighting Versus Sensory Dominance
Although many fitters employ some variation of the “extended arms technique” to determine eye dominance, this may not be the best approach. This technique assesses what is referred to as sighting dominance—a measure of how a person’s system is “wired,” such as being right or left handed. Multiple studies have found that sighting dominance has a minimal effect on success with monovision (Shor et al, 1987; Erickson and McGill, 1992).
It has been suggested that sensory dominance may be a better measure (Robboy et al, 1990). This was supported early on by work indicating that binocular summation was influenced by the strength of ocular dominance (Collins and Goode, 1994; Handa et al, 2005). A recent study suggests that this is due to the impact that sensory dominance has on contrast sensitivity and, subsequently, binocular contrast summation (Zheleznyak et al, 2015).
Assessing Sensory Dominance
Sensory dominance can be assessed by simply holding a plus power lens (usually a +1.50D or +2.00D) over one eye and then the other under binocular conditions. During this procedure, ask patients to observe an acuity chart, or some other detailed object, in the distance. Whichever eye is most bothered by the addition of the plus is the dominant eye. More importantly, as discussed above, we’ve identified the nondominant eye; i.e., the eye that most easily accepts plus and its associated distance blur.
For the “plus to blur” sensory method to work reliably, it is important that each eye be corrected with the best distance correction. If the prescription is off so that distance vision is compromised in one eye, it may alter the test findings.
The Phoropter Technique
I’ve found that an ideal way to assess sensory dominance is with the phoropter. Perform the evaluation at the end of a detailed refraction because best-corrected vision will be in place for each eye, which will avoid the potential pitfall described earlier. When using a standard phoropter, have both eyes unoccluded and employ the retinoscopy lens in front of one eye, then the other. It’s quick, easy, and accurate, with no need to mess with loose trial lenses or flippers. CLS
For references, please visit www.clspectrum.com/references and click on document #240.
Dr. Quinn is in group practice in Athens, Ohio. He is an advisor to the GP Lens Institute and an area manager for Vision Source. He is an advisor or consultant to Alcon and B+L, has received research funding from Alcon, AMO, Allergan, and B+L, and has received lecture or authorship honoraria from Alcon, B+L, CooperVision, GPLI, SynergEyes, and STAPLE program. You can reach him at email@example.com.