This article was reviewed by David R. Hardten, MD
When it comes to intraocular lenses (IOLs) in patients with severe myopia, phakic IOLs play a real role in treating higher refractive errors.
According to David R. Hardten, MD, associate professor of ophthalmology at the University of Minnesota at Minnetonka, by offering natural lens replacements and phakic IOLs, surgeons who offer LASIK or PRK can expand a practice’s spectrum for refractive patients.
Hardten also noted that phakic IOLs are valuable in younger patients because accommodation is preserved and IOLs can treat high grades of up to about 15 days. In addition, the accuracy achieved with this technology is excellent.
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A disadvantage is that complications can arise, such as B. Angle closure, a crowded angle, reduced endothelial cell count, atonic iris and cataract formation resulting from the implantation of phakic IOLs that are too long or have an enclave that is too narrow.
Therefore, careful preoperative investigations are required to ensure that patients are good candidates for them IOL’s.
In cases where a phakic IOL is being considered, preoperative planning is essential.
Anterior chamber depth (ACD) can be measured using Pentacam (Oculus), Ultrasound Biomicroscopy (UBM), and Optical Coherence Tomography to determine if there is adequate space in the anterior chamber (AC) to accommodate a Verisyse (Johnson & Johnson Vision) or Visian ICL (STAAR Surgical). According to Hardten, 3.04mm is considered borderline ACD.
Hardten described a new technology, ClearScan (ESI, Inc.), which is a probe cover for any UBM instrument that provides distortion-free images, as well as improves the safety of the UBM, improves the safety and accuracy of imaging when measuring ACD and the dimensions of Sulcus to sulcus which are crucial for Visian-phakic IOL implantation.
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The recommended safety parameters when implanting these IOLs are a safety distance of 1.5mm between the mid-peripheral iris at approximately 7mm optic zone or between the tip of an AC implant.
Surgeons should be aware that lens growth occurs with flattening of the ACD at approximately 20 μm per year.
For patients with ACs that are too shallow to accommodate a phakic IOL, Hardten suggested that natural lens replacement might be a better option.
Hardten said he likes using the Pentacam because of the instrument’s software when planning the implantation of both the Visian and Verisyse phakic IOLs.
With the Visian IOL, the iris advances an average of approximately 0.44 mm after implantation, which is similar to the AC requirements for removing a Verisyse implant.
The Verisyse implant is not widely used in the United States, but surgeons should be aware of IOL enclavation.
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“It is important to do peripheral iridotomies; enclavation occurs nasally and temporally. The paracenteses are usually at the 10 and 2 o’clock positions and are aimed at the mid-peripheral iris where enclavation will occur,” he said.
When implanting the Verisyse, it is important to know the patient’s ACD because of the possibility that IOL centering cannot be completed until the ACD returns to normal. He advised to check centration after enclavation with the physiological ACD.
Steps to insert keys
The 6mm Verisyse implant is best placed through a scleral incision due to the astigmatic effect. Hardten demonstrated the implantation procedure, in which he drew a small amount of iris into the implant’s claw and then used forceps to stabilize the implant.
An iris fold is created on the opposite side with an enclavation needle. The implant is rotated slightly posteriorly on the left side to pull the iris up into the claw, which helps hold the implant in place.
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“These implants have been shown to be extremely safe over the long term when enclaved with enough iris, but not so much that the implant is pressed against the iris and natural lens, which can cause posterior synechiae,” he explained.
Laser correction is possible after implantation of a phakic IOL. Because of the large incisions that may have resulted in irregular astigmatism, Hardten prefers to do PRK for improvements. The results are excellent. LASIK could also be performed if preferred by the surgeon.
Hardten reported on a series of 22 eyes followed up for at least 1 month (mean 5 months) after PRK and Verisyse IOL. The mean spherical equivalent at the last visit was +0.12 and the mean astigmatism was 0.25 d.
Uncorrected visual acuity (UCVA) was 20/25 or better in 82% and 20/40 or better in 95%. In eyes where the original best-corrected visual acuity (BCVA) was 20/20, 94% had UCVA of 20/25 or better and 100% had 20/30 or better. No eye lost BCVA.
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All patients implanted with phakic IOLs will develop cataracts, requiring removal of the IOL and subsequent cataract surgery. Hardten said he prefers to do a scleral incision to remove the Verisyse IOL and then a clear corneal incision for cataract removal and new IOL implantation.
He also prefers the use of a capsular tension ring as small areas of zonular dialysis may occur in these cases due to previous iridotomies and AC mobilization.
After the scleral incision is made in the explantation process, a paracentesis is performed as created for the enclavation. The incision is opened the full 6 mm length, adequate viscoelastic injected, and a procedure reverse to that described for implantation performed.
After the incision is closed, standard cataract surgery can be timed through the clear corneal incision.
See also: IOLs with extended depth of field: clarification of current nomenclature
Phakic IOLs are extremely useful in cases of severe myopia and are an excellent addition to a practice’s refractive instrumentation. Improvements are possible with PRK or LASIK.
Those patients will eventually develop cataracts that need to be removed, Hardten summarized.
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David R. Hardten, MD
David R. Hardten, MD has financial interests in Johnson & Johnson and ESI. inc