Patients with multifocal intraocular lens implants (M-IOLs) can be divided into two broad categories:
1) True Accommodating IOLs (TA-IOLs) and
2) Pseudo-Accommodating IOLs (PA-IOL)
Crystalens is the principal TA-IOL on the U.S. market. In our practice we use the Grand Seiko Auto-Refractor that measures accommodation objectively while the patient looks at a near target.
When a patient has a Crystalens implant, and you measure the ability to accommodate at near shortly after cataract surgery, it is rare to find more than a diopter of accommodation. This makes it difficult to read without reading glasses, something the patient has to be apprised of prior to consenting to pay the significant amount of money required to obtain Crystalens implant. Surgeons have found that if the patient doesn’t give in to wearing reading glasses right away, some accommodative ability will be restored with the passage of time and effort.
Most patients with cataracts have had bifocal or multifocal glasses for many years prior to receiving their prosthetic lens implant. It should not be surprising therefore that the neural network involved in activating the crystalline lens has been relatively dormant. At a minimum, this network involves the lens, the ciliary ganglion, and at least several cortical areas in the brain. The Crystalens IOL is therefore a neuroprosthetic device, and it is not surprising that the optimal outcome would involve neuro-rehabilitative therapy.
Shortly after Crystalens was introduced, a series of workbooks was put together to help patients exercise their nearpoint of accommodation.
The problem was that most ophthalmic practitioners had little idea of what to do with these workbooks. Practitioners of optometric vision therapy, however, recognize this concept from tracking workbooks such as the Ann Arbor Series known as Michigan Letter Tracking that have been part and parcel of VT programs for 40+ years.
And while letter tracking is helpful with reading from the standpoint of keeping one’s place, the bigger problem faced by most patients with sluggish accommodation is how to re-learn the activation and relaxation of accommodation. Back to the future, again! It’s time to break out the near/far accommodative rock procedures, such as Hart Charts, loose lens rock, and accommodative flippers.
This approach is very consistent with neuro-optometric rehabilitation approaches after the patients brain function has been altered relative to their habitual state. We most commonly think of this after brain injury, when the patient experiences post-trauma vision syndrome and has difficulty with accommodation and convergence.
Patients often re-acquire improved visual-spatial and nearpoint function with the passage of time, but why leave matters to chance or serendipity? It is well-recognized now that a more aggressive rehabilitative approach is in the patient’s best interest. So rather than wait for months or years before guiding the patient, we roll up our sleeves and present the patient with procedures that actively restore visual function by re-training the visual brain.
This is fairly straightforward for the Crystalens as a TA-IOL, and when re-measuring accommodation objectively one can actually see the patient’s accommodative response improve over baseline. But what about the PA-IOLs? We’ll continue with that thought in Part 2.