Posters

Accuracy of biometric formulae in hypermetropic patients undergoing cataract surgery

Poster Details

First Author: M.Mustafa UK

Co Author(s):    A. Khan   H. Bennett   M. Wright              

Abstract Details

Purpose:

Cataract surgery guidelines from Royal College of Ophthalmologists (RCOphth) suggest that 85% of post-operative refractions should be within +/-1D of the predicted outcome and 55% within +/-0.5D. These formulae are known to be less accurate at extremes of axial length. RCOphth guidelines suggest that Hoffer Q and Haigis are more accurate in patients with axial lengths of less than 22mm. In our experience we found significant myopic refractive surprises in patients with axial length of less than 22mm undergoing cataract surgery when Hoffer Q was used. This prompted an audit of refractive outcomes in this group of patients.

Setting:

We identified patients whose axial lengths were less than 22mm by performing a retrospective case note based study of all patients who had an intra ocular lens (IOL) of 28D or greater implanted over a 9 month period. This was done at the Princess Alexandra Eye Pavilion, Edinburgh.

Methods:

All patients had pre-operative measurements made using the IOL master and, where necessary ultrasound axial length measurement. Using existing measurements (axial length, keratometry, anterior chamber depth) we calculated predicted post-operative refractive outcome (spherical equivalent (SE)) for SRK/T, Hoffer Q, Haigis and Holladay for each eye and IOL used. The actual post-operative SE was calculated from data on the post-operative refraction form. The mean biometric error and mean absolute error for each formula was then calculated. Additionally, we performed a survey of Scottish ophthalmologists to document current biometric formula preference in patients with axial length of less than 22mm.

Results:

170 patients were identified, 35 patients excluded. Lenses used were Sensar AR40 (83%) and Alcon SN60 (17%). Mean biometry error: SRK/T +0.19D, Hoffer Q -0.58D, Holladay -0.18D, Haigis +0.02D. Proportion of patients within +/-1D of predicted: SRK/T 79.3%, Hoffer Q 63.0%, Holladay 70.4%, Haigis 71.9%. All formulae became less accurate and more variable as the axial length decreased. 2- Way ANOVA analysis revealed significant difference between each formulae (P<0.05). Survey: 28 respondents. 65% generally use Hoffer Q. 18% use a combination of Hoffer Q and SRK/T, 14% use SRK/T and 3% use a combination of Hoffer Q and Haigis.

Conclusions:

Analysis of our results show Haigis has the lowest mean biometric error, whereas SRK/T had the highest proportion of patients achieving results within +/- 1D of predicted outcome and lowest mean absolute error (0.72). We found Hoffer Q was significantly the least accurate of all the four formulae in this group of patients. Predicting refractive outcome in patients undergoing cataract surgery who are significantly hypermetropic remains a challenge. Our results suggest greater biometric accuracy in small eyes when SRK/T or Haigis is used. Our survey shows that most ophthalmologists in Scotland use Hoffer Q for calculating predicted post-operative outcome.

Financial Disclosure:

NONE