Why some patients land up with unexpected refractive surprise after IOL implantation.
- Subhabrata Bhattacharya
- Dec 28, 2023
- 5 min read
Updated: Mar 21
Recently I was visiting an eye hospital in a Tier II city in India wherein I was referred to a case of unexpected refractive surprise, postoperatively. Though the patient had preoperative .77 diopter of cylinder, a non toric lens was selected as there was no toric model available,. The patient landed with a spherical surprise along with the uncorrected astigmatism/cylinder error. The objective of my article here is to analyze why some patients land up with unexpected spherical surprise when patients have a pre operative astigmatism that is not corrected with either a TORIC or an LRI.
Below is the biometry sheet of the patient. The eye operated is left eye.
According to the biometry sheet above (left eye), if a 20.50 D of IOL is implanted the patient should land up with emmetropia (-.04). Of course there will be some astigmatism left over as no Toric IOL or LRI is planned. But most clinicians would expect almost a zero spherical power with a 20.50 diopter, postoperatively.
However, in reality this is not the case. Most of us fail to realize that the value of -.04 shown against the 20.5 D IOL implanted is not emmetropia, but a spherical equivalent. Or in other words, the expected refraction of -.04 is not a spherical component only, it is a combination of spherical and cylinder power that would be closest to zero. That is, it is only a spherical equivalent.
What is Spherical Equivalent?
