Before referring a patient to our practice for IOL power selection, the referring surgeon (not support staff) should contact Dr. Hill first to discuss the case and surgical objectives.
Challenging Situations
East Valley Ophthalmology sees a wide range of patients for challenging IOL power calculations, referred by ophthalmology colleagues around the world. The most common scenario is prior keratorefractive surgery such as RK, ALK, LASIK, and PRK. Below are situations for which we may not be able to provide the type of service requested by the referring surgeon. If you have any questions, Dr. Hill is always available to discuss them with the referring surgeon.
Prior keratorefractive surgery and…
1. Clear lens extraction, or early cataract with good best corrected distance visual acuity.
- Example: Mrs. Jones has 20/20 best-corrected distance visual acuity. She previously underwent RK and later had LASIK for consecutive hyperopia. She now wishes to have a multifocal correcting IOL and be spectacle independent.
- Problem: IOL power selection in this setting is problematic, as this type of IOL requires exact power selection, which is beyond the resolution of this exercise. Also, keratorefractive surgery typically increases higher-order aberrations and reduces contrast sensitivity. It is well known that diffractive multifocal IOLs significantly reduce contrast sensitivity. The combined effect often results in a greater reduction in contrast sensitivity, especially at night, and an overall worsening of visual quality. Presbyopia correcting IOLs, such as the Crystalens, do not reduce contrast sensitivity but are also problematic, as there can be no guarantee of an exact refractive outcome. With 20/20 best corrected distance visual acuity, this would be an elective procedure with a greatly diminished chance of meeting the patient’s objectives.
2. Monovision.
- Example: Mrs. Smith had myopic LASIK with monovision as the original refractive strategy. Her distance eye is -0.25 D, and the non-dominant near vision eye is -2.50 D. She would like to duplicate this scenario as she comfortably reads at 16 inches.
- Problem: Once again, IOL power selection in this setting is problematic. Successful monovision requires the same level of accuracy as a multifocal IOL. Being within ±0.50 D means that the outcome could be anywhere from -2.00 D (20 inches) to -3.00 D (13 inches). An additional problem here is that when a significantly minus target spherical equivalent is selected, unpleasant overcorrections may occur.
3. Specific hobby, or occupational refractive targets.
- Example: Mr. Jones is a watchmaker and likes a working distance of 11 inches (-3.50 D). He was a high myope before LASIK and wants to maintain this spherical equivalent.
- Problem: This is the same issue as with monovision. There can be no guarantee of an exact refractive outcome, and unpleasant overcorrections occur not infrequently.
4. Highly aberrated corneas.
- Example: Mr. Doe had early-generation LASIK with multiple subsequent enhancements and now has a residual bed of 325 microns. It is not possible to obtain any meaningful corneal power readings by keratometry. Topography gives conflicting values, and the aberration profile is dramatically elevated.
- Problem: Without reliable measurements of central corneal power, there is no way to do this type of calculation. And if the aberration profile precludes meaningful visual quality, some other approach may be required, such as penetrating keratoplasty. If a significant cataract is present, IOL power selection may require an educated guess, often aided by a scleral contact lens, to mitigate higher-order aberrations, adjust the spherical equivalent, and neutralize irregular astigmatism. Such cases generally require that the surgeon and Dr. Hill formulate a plan for IOL power selection together.
There are situations where a multifocal, or presbyopia-correcting IOL can be placed following keratorefractive surgery; however, it is required that the surgeon first discuss this with Dr. Hill before the appointment is scheduled.
- Example: In cases where low amounts of LASIK treatment were undertaken and the 6 mm aperture aberration profile is close to normal, an acceptable result may be achieved. However, there is still the issue of IOL power selection accuracy. A decision can only be made in this setting after measurements have been completed. If the aberration profile is unacceptable, a multifocal IOL would have to be placed as an alternative.
