sulcus IOL placement in complicated cataract surgery скачать в хорошем качестве

sulcus IOL placement in complicated cataract surgery

Changing from one IOL design to another The A-constant of the IOL reflects many variables such as effective lens position, lens geometry, refractive index and more. If we are planning to implant a particular IOL in the capsular bag but then decide to switch to a different IOL, we may need to adjust the power in order to keep the same refractive outcome. This may be the case if a particular power of a specific IOL is not available or if we decide to switch from one brand to another to better match the patient’s tissue. The difference in A-constant between the two IOL types is the same as the adjustment needed to the IOL power. For example, if we are planning to insert an IOL of power +20 D and A-constant of 119.2 in the capsular bag, but then we decide to switch to a different IOL design with an A-constant of 118.7 while still implanting it in the capsular bag, we need to drop the IOL power by 0.5 D to +19.5 D to have the same refractive outcome as originally planned. The difference of A-constants (119.2 - 118.7 = 0.5) is the same as the difference in the IOL powers (20.0 - 19.5 = 0.5). Sulcus IOL placement In the vast majority of cases, we can implant the desired IOL in the capsular bag as planned. But in some cases, notably with weakness of the capsule, we may desire to place the IOL in the sulcus. The sulcus IOL must be suitable for this position and is typically of the three-piece variety. The entire IOL including the haptics and the optic can be placed in the ciliary sulcus. Alternatively, we can do some type of optic capture through the capsulorrhexis such as keeping the haptics in the sulcus while pushing the optic posteriorly through the capsulorrhexis, or the reverse. When we change the effective lens position of the optic, we need to adjust the IOL power to achieve the intended refractive target. If the optic is in the plane of the sulcus, then its power should be adjusted. However, in cases in which the haptics are in the sulcus but the optic is behind the capsulorrhexis, less adjustment or no adjustment is needed because the effective lens position of the optic is still “in-the-bag.” Haptics in Sulcus / Optic Capture through Capsulorhexis = use in-the-bag power because the optic is still technically behind the anterior capsular rim Haptics sutured to back of iris = use in-the-bag power because the sutures are always a little looser than you think and the optic is more posterior than a true sulcus IOL Haptics and Optic in the Sulcus = calculate sulcus IOL power because the optic is clearly in front of the anterior capsular rim in the sulcus The first step is to make sure that the A-constant of the sulcus IOL model is about the same as the A-constant for the original IOL. If not, the adjustment based on A-constant needs to be made. This will give the appropriate IOL power for in-the-bag placement of the three-piece IOL, but because we will be placing it in the ciliary sulcus, we will need to further adjust this. As the IOL moves more anterior in the eye, a lower power is needed for the same refractive outcome. This means that the sulcus IOL will need to have a power lower than the same IOL placed in the capsular bag. This varies with the power of the original IOL and can be calculated specifically or an approximation can be used. This “Rule of 9s” says that IOL powers can be grouped into groups, split at IOL powers 9, 18 and 27. The IOL power is reduced, respectively, by 0.5 D, 1 D, and 1.5 D, as shown below: 0 to +9: no change in IOL power +9.5 to +18.0: drop IOL power by 0.5 +18.5 to +27.0: drop IOL power by 1.0 over +27.0: drop IOL power by 1.5 Zonular laxity and post-vitrectomy eyes In eyes with suspected zonular laxity such as those with pseudoexfoliation syndrome, the IOL optic may sit further posterior in the eye than expected. With loose zonules, the entire lens and iris diaphragm can be pushed forward, and a relatively shallow anterior chamber can be seen during the preoperative consultation. During cataract surgery when the relatively heavy and thick cataractous lens is replaced by the thin and light IOL, the optic can sit further posterior in the eye than would have been predicted by the preoperative anterior chamber depth. In this case, addition of 0.5 D to the IOL power can help buffer against a post-op hyperopic surprise. In eyes that have previously had a posterior vitrectomy for retinal disease, the lack of an anterior hyaloid face can also cause the IOL optic to sit more posterior after cataract surgery. Again, adding 0.5 D to the IOL power can prove to be of benefit.