Refractive Surprise Post IOL Implantation- How to check what went wrong
- Subhabrata Bhattacharya
- Mar 17, 2020
- 8 min read
Updated: Mar 16
Doctor X was much excited to implant his first presbyopia correction lens, and so was the patient. Together they chose one of the best lenses, that promised to give the opportunity to junk the glasses that the patient hates to wear. With the best optical biometry done with an experienced biometrician, and all necessary tests done to rule out any ocular pathology that may hinder the patient having a sub optimal outcome, nothing but the best outcome was predicted for the patient, not a refractive surprise.
The post operative outcome surprisingly, turned out to be a dampener. The patient landed up with a myopic surprise of a -1.50 D spherical. **The doctor is now in a dilemma, should he go for the second eye targeting a refractive number that would balance the surprise in the first eye ? Or should he first try to find out what went wrong in the first eye, so that he is sure that a mistake, if there at all had been in biometry of first eye, would not be repeated again. Doctor X, decided to go for the second option, deciding to take the pain of investigating what went wrong.
To start with, and within the scope of this write up, there would be four broad aspects worth looking into. First, where is the IOL sitting in the eye or the Effective Lens Position (ELP). Second, was the axial length rightly measured ? Third, Was the right IOL power implanted? and last, the changes in corneal curvature post surgery.
Note, for a thorough examination, a dilated pupil may be necessary to check for any decentration/IOL position in bag, bag distension, retained viscoelastics that could lead to myopic shift, or retinal challenges like post operative macula edema that could lead to a hyperopic shift. In their article, Refractive changes and visual quality in patients with corneal edema after cataract surgery, Ajenjo et al shows a hyperopic shift post significant corneal edema. The authors hypothesize a decrease of corneal power that could be explained by a increase in central corneal thickness and a corresponding lowering of conreal refractive index. However, before dilatation drops are administered, pseudophakic measurement should be done to avoid dilatation drops interfering with corneal readings.
1. ELP - Biometry is not about measuring the right IOL power. It is at best, only half of the story. Even, a right IOL power implanted may give a wrong result if it is not sitting at the right place in the eye. How far an IOL sits from the cornea, is typically called the ELP of the IOL, which has a direct impact on the post operative outcome. So is the IOL implanted sitting at the right place. A pseudophakic anterior chamber depth can provide an idea. Without this information, it may be impossible to understand the right cause of the unexpected outcome. In one such study, and on an average eye, a .1mm of deviation in the ELP was found to impact the final outcome by .19 dioptres for an average Axial Length. Pseudophakic anterior chamber depth, though in some cases is difficult to obtain, may have an answer to the unexpected outcome.
