Biometry, or the process of measuring the corneal power and length of the eye, is crucial in determining a successful cataract surgery. Mistakes in either of these measurements could lead to an unpredicted postoperative refractive error.
Besides taking accurate measurements, it is also important to properly screen patients for ocular surface disease (OSD) prior to and post-surgery in order to achieve better outcomes, said Dr. Sabong Srivannaboon, professor emeritus of ophthalmology from Siriraj Hospital, Mahidol University, Thailand.
“One of the major concerns that we might not be aware of is about the surface of the cornea, before we send the patient to do the biometry,” he said during a session on biometry at the 5th meeting of the ASEAN Ophthalmology Society (AOS) on Saturday, March 26, 2022.
When preparing for cataract surgery, in order to achieve the desired postoperative refraction, the required power of the intraocular lens (IOL) implant can be calculated if the corneal refractive power and axial length are known.
But factors that might affect keratometry measurements include OSD and dry eye.
The Prospective Health Assessment of Cataract Patients’ Ocular Surface (PHACO) study showed that cataract patients are commonly affected by OSD. The study, which included 136 patients (272 eyes), was carried out to determine the prevalence of dry eye disease in patients undergoing cataract surgery.
The results showed that about two-thirds of eyes had poor tear break-up time of less than 5 seconds, and half of eyes showed central corneal staining. “So the conclusion of the study is that the incidence of dry eye in a patient who is scheduled to undergo cataract surgery is very high,” he noted.
Impact of OSD on Outcomes
Visually significant OSD would see imprecise keratometry and postoperative adverse outcomes, he cautioned. Preparing the ocular surface before cataract surgery is necessary. Studies have shown that eyelid hygiene before and after cataract surgery reduced adverse outcomes.
Thus, perioperative eyelid hygiene is recommended for patients with meibomian gland dysfunction (MGD) who undergo cataract surgery. He suggested a regimen that would involve a preoperative lid scrub to reduce the bacterial load and MGD.
Using artificial tears before and after the procedure would improve the ocular surface and IOL calculation. “In conclusion, I believe that the OSD is one of the important factors to achieve better outcomes in cataract surgery, not only for the preoperative IOL calculations, but also for the postoperative visual outcomes.”
What Counts in Biometry
The next speaker for the session, Dr. Thanapong Somkijrungroj, a retina, uveitis and cornea specialist from Chulalongkorn University, Thailand, talked about some of the essential points when it comes to biometry.
Precise biometry is, of course, a requisite for the best outcomes in cataract surgeries. In his opinion, optical biometry is preferred over ultrasound, except in mature or very dense cataracts which still require ultrasound biometry.
“Resolution is better in optical biometry, and it has other options that ultrasound biometry cannot do, like posterior cornea measurements,” he said.
Another point he made is that biometry is preferred before pupil dilation, particularly when using an IOL formula that incorporates anterior segment parameters for more precise calculations, as the anterior chamber depth (ACD) increases significantly after dilation.
It is also important to ensure proper IOL formulae selection — especially in post-corneal refractive surgery, he noted. One of his suggestions is to use the Barrett Toric Calculator. Surgeons can access the calculator via the Asia-Pacific Association of Cataract and Refractive Surgeons (APACRS) website. It uses the Universal II formula to predict the required spherical equivalent IOL power. The calculator derives the posterior corneal curvature based on a theoretical model proposed to explain the behavior of the posterior cornea.
Finally, he touched on surgically-induced astigmatism (SIA). The knowledge and application of the SIA are essential for toric IOL implantation. Errors in estimating SIA adversely affect the predictability of toric IOL outcomes. Postoperative SIA depends on the location, incision width and architecture of the wound. Utilizing the centroid value for SIA can result in better outcomes.
Editor’s Note: The 5th AOS Congress was held virtually on March 26-27, 2022. Reporting for this story took place during the event.