The Plus Lens Limbo Stick: How Low Can You Go?

Debates about whether or not to prescribe the full plus lens power found on refraction with young children are as old as the hills. Generally speaking, the higher amount of hyperopia found, and the younger the age at which it is detected, the more aggressive practitioners are in prescribing full plus. Among other clinical pearls, evidenced-based guidelines from the American Optometric Association note that: “In addition to its relationship to the development of strabismus and amblyopia, hyperopia can also affect the development of literacy skills.” Some Optometrists are therefore inclined to prescribe even low plus lens power when a child is at risk academically. On the other hand, pediatric ophthalmologists tend to downplay the need for an isometropic plus lens Rx in the absence of accommodative esotropia, even in the range of +3.00 to +6.00, as long as it is not affecting acuity or stereopsis.

I had an interesting case last week of a seven year-old girl who was referred to me by a reading specialist. Her habitual Rx was OD: +5.50 sph and OS; +6.00 sph, which she had been prescribed at age 18 months. She “lost” her glasses, and had been without them for at least a week. A few years ago she spent the entire summer without them, and after that point her pediatric ophthalmologist reportedly said they were optional. It is not uncommon for children who are over-plussed to look over their glasses as much as they look through them (the photo here is an internet image, and not my patient).

The patient’s entering unaided visual acuity was 20/60 through either eye and with both eyes together. Through her habitual Rx, acuity was reduced to 20/100 through either eye and with both together. Unaided phorias were 4^ esophoria at distance and orthophoria at near. Excellent random dot stereopsis was perceived unaided at near. Unaided NPC was to the nose. Refraction showed that distance acuity improved to 20/25 in either eye through +2.50 sph, though retinoscopy was stable in the right eye and drifted from +2.50 to +4.00 through the left eye. I found the best balance at distance and near objectively and subjectively through +3.50 OU.

It is interesting that when there is little plus found in the system, we tend to “push plus” essentially looking for either latent hyperopia or some functional improvement. Conversely, when there is gobs of plus in the system, we tend to think in the opposite direction which I describe as the “limbo stick” approach of how low we can go before there is any evidence of decrement in findings or performance.

Dr. Joe Miele has talked about the determination of a lens Rx as a negotiation between the clinician and the patient, and that is a very elegant description. In using the range of clarity concept, he illustrated shaving plus in hyperopia depending on what he patient has been habitually using prior to seeing you. In hyperopic anisometropia I have moved in the direction of best binocular balance, which is part of the process of reverse engineering hyperopia. The child in our case above has been progressively self-engineering this process by spending more and more time without her Rx. She has been doing her own version of vision therapy, and classicalists might say that she has a low enough AC/A to get away with accommodating enough to maintain a range of clarity without having to worry about accommodative esotropia.

In any event, getting away from her Rx entirely isn’t anyone’s goal at this juncture. It is more about finding the optimal lens Rx that the patient is comfortable with at distance and near, and that facilitates her being responsive to interventions to improve her reading. That is considerably less than what she has been asked to wear, but considerably more than nothing.

10 thoughts on “The Plus Lens Limbo Stick: How Low Can You Go?

  1. This is always an interesting discussion. Thank you for bringing it up as we all battle with the concepts of over or underplussing our patients. One thing I try to keep in mind is that each patient has resilience, some greater than others. Thus a set amount of over or underplussing doesn’t fit all. First consideration is that the hyperopia(visual tone) may be related to postural tone. Thus if you have a developmentally delayed child who is low tone, you are more likely to find low visual tone(more hyperopia). When the child’s visual demands increase(near tasks), then there is a response of the patient to accommodate at near and the relationship is disrupted. When you Rx full cyclo plus, you now have a visual tone that is active from the plus and low motor tone which creates a mismatch. The patient has to either increase motor tone to match or build in more plus to match the low motor tone. Thus we generally always make sure these patients are in OT and/or provided optometric VT to address low motor tone. The other factor we may need to pay more attention to is the motion of a lens from magnification. Perhaps the reason children don’t adapt to more plus is that the increased motion disrupts the VOR gain, thus patients are uncomfortable, likely related to maladaptation to progressives as well, especially in TBI population. So alot to think about here….how far down the rabbit hole will we go?

  2. I use binocular (dichoptic view) refraction to optimize the optical prescription using primarily a polarized vectographic slide (others options include +0.75 D one eye fog, active shutter glasses with corresponding display and rare/expensive circular polarized LCD display). To further refine, evaluation of clinical performance (cover test at distance and near, stereoacuity, MEM retinoscopy, vergence facility response, fixation disparity/associated phoria at near) and comfort are used to guide any refinements and the magnitude (if any) of added plus at near. Then appropriate follow-up and testing to ensure clear comfortable vision.

    • Thanks for adding that Ronald. All good info, though nothing substitutes for putting the tentative Rx on and asking and/or observing how it looks as well as feels, and/or listening to cadence/confidence in identifying letters. It’s “Back to the Future” for me in some regards.

  3. Some thoughts regarding your post. The first is the impact of any lens prescription on a patient. Ironically, most patients adapt to their glasses whether the Rx is appropriate or not. By creating a dependency on glasses, a patient’s prescription will often dictate future lens changes. In some ways, it is similar to braces in dentistry. The overuse of cycloplegic refraction is a perfect example of this dilemma. Your case reveals how a child can function without full plus without becoming strabismic. The second thought is that it is time to move beyond a total focus on distance acuity. Snellen acuity has dominated eye care for centuries. We need to be focused on near point functioning in our current space world. Lens prescribing will need to include more than an acuity measurement. AND finally, we need to put our glasses in their case and function without them. Obviously, these activities need to be in a safe environment and hopefully OUTDOORS. Just some thoughts to ponder.

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