In the 1980s and 90s, there were a large number of patients who had radial keratotomy who now have developed visually significant cataracts. It has been found that even those who have mild cataracts can experience significant aberrations sooner than would otherwise be expected. For several reasons, the complications can be difficult for these patients because their IOL implant calculations may not be accurate and the surgery is challenging. This can prolong the post-operative recovery. In addition, the patients are often intolerant of refractive errors.
There has been a number of techniques and formulas used for calculating the IOL power in these patients. The conclusion is that there simply isn't a single method that can consistently yield excellent results. One of the biggest errors is in overestimating the corneal power. This often leads to an implantation that has lower power and post-op hyperopia. A high percentage of these patients have lived with myopia their entire life and this can lead to hyperopia which is especially bothersome and uncomfortable. The remedy to this requires that more myopic results be targeted.
A number of the patients that most eye doctors deal with have no old records and when that is the case they will calculate the corneal power by using a method proposed by Dr. Robert Maloney. This method takes the central corneal power as its measured by topography, and in this way, it doesn't depend on history. This works in combination with the anterior corneal power along with posterior corneal power. When you convert the topography back to the interior and then subtract the posterior corneal power, it allows an eye doctor to reasonably estimate the IOL calculations.
Because most of the patients have irregular corneas, most eye doctors try to avoid multifocal IOLs and use single focus lens implants instead. Aspheric IOLs are often a good choice for these patients because of the corneal aberrations they have. When you implant a negative spherical aberration it can offset the positive spherical aberration. When this is the situation it is my preference to use the Advanced Medical Optics Tecnis IOL because it works well to offset large degrees of corneal positive aberrations. On the other hand, when the degree of irregularity is unknown, then I choose to use the SofPort Advanced Optics by Bausch & Lomb. This is known as the ‘Do No Harm’ IOL.
During surgery, it is common for the RK incisions to be weak and that makes them susceptible to opening. When incisions are made it's necessary to avoid intersecting with the existing RK incisions. If not, it could cause substantial fluid leakage. When a patient has previously had 8 cut RK the corneal incisions can be done in between the existing incisions. It's more difficult for patients that have had 16 cut or more because it's not easy to avoid those incisions unless a scleral tunnel incision is used.
Most eye doctors like to use lower flow along with a lower bottle height and the smaller phaco needle because it's more gentle on corneas that are weakened and it helps to ensure that the inflow of fluid is more than the outflow. It is important to be careful not to open RK incisions during the surgery because it could cause instability of the anterior segments and there is a risk of capsule rupture. To check for leaks at the end, most eye doctors paint the cornea with fluorescein dye as this can be easily sutured before the patient is taken from the operating room.
When these techniques are appropriately applied they can yield a positive result. These patients are not as easy as some others, but the end result can be one they are satisfied with. As these patients are typically demanding, it makes using these techniques imperative.