UK national survey on personalized customization of A-constant in cataract surgery

Sir,

At a time when cataract surgery is performed on patients with increasingly high expectations, the refractive outcome is no less important than surgical and visual outcome. A-constants provided by the intra-ocular lens manufacturers are to be considered as guides only; individual customization of the A-constant should be calibrated against the post-operative refraction to achieve the best possible refractive outcome because of potential variation in techniques by biometrists and surgeons.

The 2004 Royal college of Ophthalmologists cataract surgery guidelines¹ strongly recommend that each ophthalmic department, and preferably each surgeon, should customize their A-constant through a regular audit system.

This study aims to determine the practice of A-constant customization in the United Kingdom. To the best of our knowledge, this is the first UK national survey investigating the practice of individual personalized A-constant customization among cataract surgeons.

Paper questionnaires were posted to all NHS consultant ophthalmologists in the United Kingdom. Out of 900 questionnaires, 366 were returned and 341 were analysed. Twenty-five were excluded because of non-involvement of cataract surgery by the corresponding consultants.

A total of 278 (81.5%) consultants were aware of the Royal College guidelines on biometry practice in cataract surgery. Departmental A-constant customization was performed in 57.2% of the units (195/341). However, only 31.7% (108/341) admitted to individually personalizing their individual A-constants, of whom 94.4% customized specifically for each lens type. Years qualified as a consultant was found to be significantly associated with customization of A-constants, with the 11–19 years group being most likely to carry out customization (P=0.013, Figure 1). There was no significant difference between teaching and district general hospitals (P=0.877, Figure 2). Only 41.6% (142/341) performed the customization separately for ultrasound and partial coherence laser interferometry (for example, IOL master) techniques. A total of 28.2% (96/341) did not regularly audit their biometry results. The remaining 245 audited their results ranging from monthly to 3-yearly (Figure 3).

Figure 1

Surgeon customization vs years of experience.

Figure 2

Surgeon customization vs hospitals.

Figure 3

The number of departments customizing A-constants has increased from 47% in 2004 (as given in Gale et al.²) to 57.2%, but less than a third of UK cataract surgeons carry out personalized A-constant customization, a practice which can potentially further enhance the accuracy of refractive outcome in cataract surgery.