Posters

Nittany Nomogram: a method to predict refractive astigmatism after cataract surgery based on pre-operative biometry

Poster Details

First Author: N.Kansara USA

Co Author(s):    N. Kansara   C. Seeger   J. Quillen   K. Banerjee   I. Scott   S. Pantanelli     

Abstract Details

Purpose:

The Barrett Toric Calculator (BTC) can be used to predict post-operative refractive astigmatism (RA) and to assist in appropriate intraocular lens (IOL) selection. However, the precise method by which the BTC estimates net astigmatism is unknown. The goal of this study was to develop a method of predicting RA after cataract surgery using pre-operative biometry data.

Setting:

A training database was aggregated from the Penn State College of Medicine using eyes that underwent cataract surgery with a B&L enVista monfocal IOL. A testing database was assembled from the Schein Ernst Mishra Eye Center using eyes that underwent cataract surgery with a B&L Akreos AO60 IOL.

Methods:

The training database included eyes that underwent pre-operative optical biometry (IOLMaster 700) and post-operative manifest refraction between 4 and 12 weeks after surgery. A nomogram was developed that predicted RA from pre-operative biometry. The testing database was used to assess the performance of the nomogram and compare it to the BTC’s net astigmatism prediction. Outcome measures included the difference vector (DV) magnitude (the vector difference between actual and predicted RA), proportion of eyes with a DV magnitude <0.5 diopter (D), and proportion of eyes in which the astigmatism class (against-the-rule [ATR], with-the-rule [WTR], or oblique) was predicted correctly.

Results:

The training and testing databases consisted of 230 and 650 eyes, respectively. The mean DVs for all eyes (0.15 D and 0.16 D), ATR anterior corneal astigmatism (ACA) (0.26 and 0.28 D), WTR ACA (0.09 and 0.18 D), and oblique ACA (0.03 and 0.04 D) were similar for the Nittany Nomogram and BTC, respectively. The proportion of eyes that had a DV magnitude < 0.5 D were 52.1% and 52.6% for the Nittany Nomogram and BTC, respectively (p = 0.92). The proportion of eyes for which the two nomograms predicted the astigmatism class correctly was 63.2% and 65.8%, respectively.

Conclusions:

The Nittany Nomogram performs similarly to the BTC with respect to predicting net astigmatism based on pre-operative biometry values. Further validation is needed, especially on eyes with oblique and higher magnitudes of corneal astigmatism.

Financial Disclosure:

None