Small eyes and big ones have special considerations. Cataract surgery in either very short or very long eyes presents specific, unique situations.
Challenges in short eyes include performing IOL calculations and the possible limitations of available IOL powers. A thorough preoperative assessment helps the surgeon be prepared for what he or she will encounter in any given patient.
Small or short eyes have a shorter axial length and a shallower anterior chamber. A smaller corneal diameter can make the effective lens position harder to calculate. In some of these patients, even a maximum power IOL, i.e., 40.00 D, might not fully correct the refractive error. Correcting the power with one lens is preferred, but piggybacking two IOLs may be necessary. IOLs with flexible haptics are a good choice in these patients, as they allow placement in a small bag. It may be a challenge to match the right design, however, with a very high power.
Small errors in axial length measurements in short eyes will have a bigger impact and, therefore, a larger refractive shift than in normal eyes. The Hoffer Q calculation formula is more accurate in short eyes, according to Aristodemou and colleagues.
In terms of the preoperative examination, any endothelial weakness should be noted. These patients have a greater chance of cell loss during phacoemulsification. Eyes with extremely short axial lengths (less than 20 mm) and small white-to-white measurements (less than 11 mm) may also be at higher risk for suprachoroidal hemorrhage, according to the literature. The standard phaco probe can induce more astigmatism in smaller eyes, and a shallow anterior chamber makes creating a capsulorrhexis more difficult. Coexisting pathology may require partial pars plana anterior vitrectomy to deepen the chamber
During surgery, care must be taken to protect the corneal endothelium. There is limited amount of room to maneuver in a small eye, and the phaco probe will be closer to cornea.
Long eyes, those greater than 26 mm, have their own set of special considerations. A peripheral retinal exam is necessary to detect pathology, and a surgeon may consult with a retina specialist depending on any findings. The risk of retinal detachments or tears after cataract surgery is higher in myopic patients. Reverse pupillary block or lens/iris diaphragm retropulsion syndrome can occur.
One of the difficulties with preoperative calculations in highly myopic patients is the determination of axial length. As axial length increases, measurements may become less reliable. IOL power formulas can resulting in hyperopic surprises, therefore the axial length needs to be adjusted. The Wang-Koch axial length adjustment can be used with traditional formulas. The Barrett Universal II formula has also been shown to be accurate in predicting IOL power in long eyes.
Aristodemou P, et al. World J Ophthalmol. 2014;doi:10.5318/wjo.v4.i4.140.
Hoffman RS, et al. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2015.10.008.
Wang L, et al. J Cataract Refract Surg. 2011;doi:10.1016/j.jcrs.2011.05.042.