Introduction to Glaucoma and the Retina Nerve Fiber Layer (RNFL) – Dr. Oli
Introduction to Glaucoma We have spoken about the importance of the way the front of the optic nerve looks like …more >
Cataract surgery has evolved to a point where refractive outcomes are now a major part of the results of surgery. Spherical outcomes are determined largely by the power of the IOL which is determined by several formulas that have evolved over the years. Astigmatic outcomes are dependent on the use of toric IOLs, limbal relaxing incision (LRIdone either with a blade or now the Femtosecond laser), and positioning of the cataract incision. There is also the option of using the Excimer Laser to correct refractive error.
The results below summarize our internal ESI study dealing with our spherical refractive outcomes after cataract surgery.
The study is retrospective without any peer review. We wanted to know about our spherical outcomes in “short” eyes, “normal length” eyes, and “long” eyes. The reason we decided to divide the outcomes into the above three categories has to do with the known fact that present methods of calculating implant powers works best for normal length eyes and less well with the longer or shorter eyes.
Modern formulas, in particular theHolladaysoftware program, have added factors other than axial length and keratometry to achieve better outcomes.Holladaywas most responsible for realizing the importance of postoperative estimated lens position (ELP).
ELP is known to vary with axial length, butHolladayfound that there are other factors such as White-to-White (corneal diameter) that influence ELP as well. Despite the knowledge that these factors are important we have no perfect way of predicting ELP at the present time.
Our study excluded patients with prior refractive procedures, corneal pathology and those who were implanted with toric IOLs.
The Challenge of Benchmarking
There are no absolute comparisons we can use to judge our outcomes. There is always the theoretical “perfect” outcome we would wish for, namely emmetropia with no astigmatism. This of course assumes the patient did not wish to remain slightly myopic.
There are some studies in the literature that have reported retrospective outcomes. Two such recent articles utilized the following benchmarks:
Our study utilized these benchmarks as the standard against which we compared our outcomes.
1. The Group with Axial Length of 23-25 mm (“Normal” Eyes)
A. We achieved an average spherical outcome of 0.2D. The range of spherical refractive error was -1.25D to +0.50D. Two out of thirty-four had greater than +/-0.5D error.
Due to these results, when we see a patient with spherical outcome that deviates by more than a 0.5D we restudy our preoperative data on which we based the IOL power calculation
2. The Group with Axial Length of 25-31 mm (“Long Eyes”)
A. Average spherical outcome was again 0.2D. Range was -1.50 to +0.25D. The majority had minimal myopia.
3. The Group with Axial Length of 20-23 mm (“Short Eyes”)
A. Average postoperative sphere was +0.25D. Due to the small number of patients in this group the outcomes were not statistically significant.
While our study was very encouraging, we are using the information gained to continually improve our results. Our goal is to achieve outcomes within 0.25D of the desired spherical outcome. To pursue this outcome we have invested in technologies such as the iTrace (ray tracing) and OPD to determine the necessary information in the most accurate manner. Additionally we endeavor to keep up with upgrades and developments in the IOLMaster technology and spend considerable resources and time training and educating the clinical staff in the most accurate acquisition of data. Clinically we work hard to detect corneal surface and tear abnormalities and treat what is treatable prior to final IOL power determination.
We appreciate the efforts of our co-managing doctors to accurately determine the refractive outcomes and return them to use in a timely manner. You are all helping us to continue on the path to a more perfect surgery.