Different Methods, Similar Outcomes: Case Study
Using toric calculators in the Pentacam AXL Wave for determining the right IOL
| 3 min read
sponsored by OCULUS
With Giacomo Savini, Researcher at the G.B. Bietti Foundation – IRCCS in Rome, Italy
Every eye surgeon aims at the best quality of vision currently attainable for the patient. Therefore, finding the right IOL for the patient is the vital task for any cataract specialist. This case study shows how different methods to calculate the toric IOL power led to similar outcomes, and the right IOL was found for a 59-year-old patient with the use of the Pentacam® AXL Wave.
I had been following up this patient for 20 years. When she was 59 years old, she developed a bilateral cataract. Surgery was performed first in the right eye, which had a moderate amblyopia and revealed about 3 D of corneal astigmatism. A toric monofocal IOL was selected.
The Pentacam AXL Wave provided the following measurements (see Figure 1, Full Sequence Overview):
Refraction: sphere -3.46 D, cylinder +4.40 D @140.4°
K1 = 41.0 D
K2 = 44.2 D
ACD = 3.15 mm
AL = 23.943 mm
The Cataract Pre-OP Display (see Figure 2) showed a difference of 0.4 D between the magnitude of keratometric astigmatism (3.2 D @142°) and the magnitude of total corneal astigmatism, as measured by TCRP over the pupil and within the 3 mm zone (2.8 D @145°). The axis of astigmatism, on the contrary, had a negligible difference.
The low amount of HOA and chord μ would have made it possible to implant a multifocal IOL, but this was discarded due to the amblyopia. Therefore, we selected an SN6ATx toric monofocal IOL (Alcon Labs).
The four available calculators suggested a SN6AT7 IOL, which corrects 4.50 D at the IOL plane and, according to our calculations, 3.22 D at the corneal plane. Based on Barrett, Haigis and Olsen formulas, a 21.5 D power was implanted. The IOL was aligned at 145°, as recommended by all toric calculators, and one month after the surgery, the refraction was plano.
This is a typical case where different approaches for toric calculations lead to the same outcome: Barrett’s toric calculator is based on a predicted total corneal astigmatism (although information from the posterior corneal surface can be used to improve the results), whereas Savini’s and Olsen’s toric calculators are based on the total corneal astigmatism measured by the Pentacam (with no further adjustments).
Pentacam® AXL Wave
The Pentacam® AXL Wave is the first device to combine Scheimpflug tomography with axial length, ocular wavefront, refraction and retroillumination.
The device incorporates intuitive reports based on clinical studies – helping the surgeon to detect abnormalities that may influence the expected outcome, prior to surgery.
The IOL Calculator provides different formulas for virgin and post corneal refractive eyes. Spheric, aspheric, multifocal and toric IOLs are included in the database. The data of the implanted IOL as well as the post-op refraction can be stored with only two clicks.
Toric IOLs can be calculated based on the individual SIA (surgically induced astigmatism) and TCRP. The latter takes the posterior corneal surface into account, improving the accuracy of IOL power calculation (1).
- G Savini, K Naeser, “An analysis of the factors influencing the residual refractive astigmatism after cataract surgery with toric intraocular lenses,” Invest Ophthalmol Vis Sci, 56, 827 (2015). PMID: 25587061.