Cataract surgery is failing to address the astigmatism of most people who undergo the procedure in the United Kingdom, researchers say.
Of those patients receiving standard monofocal intraocular lenses (IOLs), 90% had post-operative astigmatism of at least 0.5D, report Alexander C. Day, from Moorfields Eye Hospital in London, and colleagues in the British Journal of Ophthalmology.
Cataracts impair the vision of about 30% of people in the United Kingdom aged 65 years and over, the researchers found. And patients usually need spectacles if astigmatism greater that 0.50 persists after cataract surgery, they report.
But there is very little epidemiological data on the prevalence and severity of residual astigmatism following cataract surgery.
So the researchers analysed data from the MediSoft Ophthalmology electronic medical record system, a longitudinal database on ophthalmic care for over 1 million patients and 150 ophthalmology clinics around the United Kingdom.
They found 111,591 eyes that had in-the-bag placement of IOLs during surgery in patients who were at least 65 years old and had eligible pre-operative keratometry measures. They excluded patients who had major repeat surgeries, or whose only surgery during the study period was for a second cataract.
That left the researchers with 110,468 eyes in 79,910 patients. Of these, 39,744 had refractive cylinder available for post-operative analysis; 28,845 had both pre- and post-operative cylinder and axis of astigmatism recorded and corneal astigmatism of at least 0.5D; and 19,095 had both post-operative refraction and uncorrected distance visual acuity (UDVA) recorded, and corneal astigmatism of at least 0.5D.
They found that 78% of the study eyes presented at the National Health Service (NHS) for cataract surgery had preoperative corneal astigmatism of at least 0.5D while 42% had at least 1.0D and 11% had at least 2.0D.
The data corresponds to similar studies around the world, the researchers found. Astigmatism of at least 1.0D was found in 36% of eyes with cataract in Germany, 47% in China, and 35% in South Korea.
In this study, on the day of cataract surgery, more than 99% of eyes were implanted with monofocal IOLs and 74% of these surgeries were performed off the steepest meridian. Only 0.1% received a toric lens. Limbal relaxing incisions were done in 0.24% of eyes and opposite clear corneal incisions were made in 0.18%.
Postoperative astigmatism was available for 36% of the eyes that received monofocal IOLs. Of these 90% had at least 0.5D of astigmatism; 58% had at least 1.0D, and 16% had at least 2D. "Our results suggest that astigmatism may worsen (at least in some eyes) following surgery based on shifts away from the origin in power vector analysis," the researchers wrote.
Mild astigmatism, up to 1.5D, can be corrected by operating with the steepest meridian, the researchers reported. But operating with the steepest meridian may be technically difficult and require less comfortable positioning, so many surgeons avoid it.
In this study, surgery off the steepest meridian affected astigmatism negatively, while surgery with the meridian did not.
"Therefore, even in cases of milder astigmatism where operating with the steepest meridian is inconvenient, surgeons should consider corrective methods to improve refractive outcomes after surgery," Day and colleagues wrote.
After surgery, overall UDVA was 20/25 (≤0.10 logMAR) or better in only 26% of eyes. Best-measured distance visual acuity (BDVA) reached this threshold in 51% of eyes. Worse postoperative visual acuity corresponded to worse astigmatism.
The study had some limitations, the researchers acknowledged. In particular, that only 36% of eyes had postoperative refraction measured. To make sure these were representative of the larger sample, the researchers verified that they were similar in average cylinder, incidence of complications, existing co-pathologies and age.
They concluded that residual astigmatism following cataract surgery is significantly impairing the vision of many patients "and therefore, there is a need to improve access to astigmatism-correcting options during cataract surgery."