Dynamic Measures Needed for Quality of Vision

More dynamic approaches beyond visual acuity and contrast sensitivity measurements are needed to more accurately determine quality of vision after cataract surgery, particularly when a presbyopia-correcting IOL has been implanted, according to Nino Hirnschall MD, PhD.

“Visual quality is about much more than visual acuity,” he said. “More dynamic approaches should be used in the future. Ideally, different near real-life situations should be simulated in our testing and the psychological aspect also needs to be taken into account.”

One of the key issues is postoperative refraction measurements—whether auto-refraction, subjective refraction, or derived from wavefront aberrometry—are not as accurate or reproducible as they should be.

Dr Hirnschall cited a study by Norrby (et al.) that showed preoperative estimation of postoperative intraocular lens (IOL) position, postoperative refraction determination, and preoperative axial length (AL) measurement are the largest contributors to error in IOL power calculations (35%, 27%, and 17%, respectively).¹

“That means one-third of the error derives from refraction itself, and the reason is the reproducibility or reliability of our measurements are not very good,” he said.

Postoperative evaluation after cataract surgery should ideally include functional vision testing that simulates real-life experiences and captures dynamic information about a patient’s quality of vision.

“Too often, we perform standardised testing of only a single parameter of vision, such as visual acuity or contrast sensitivity,” he said. “There is no dynamic information—we have letter guessing, and patients have time to guess the right letter. So, this is not a real-life measurement.”

Dr Hirnschall noted functional visual acuity (FVA) measurement is a more effective method to determine postoperative satisfaction in cataract patients. One such method developed in Japan shows different letters in a randomized fashion with different possible contrasts.

“This is a continuous, dynamic measurement method that includes the worst and best visual acuity and the FVA, which is an average visual acuity within a specific time,” he said, adding average response time and blinks are also measured.

Another option is the Salzburg Reading Desk (SRD), a functional testing platform which allows multiple visual acuity, reading speed, and acuity tests on one device. While simulating a natural reading environment, the SRD calculates distance-corrected logMAR and reading speed at various illumination and contrast levels.

It is also important to bear in mind the deviation between forward scatter light and backward scatter light.

“Backward scatter is basically everything we see at the slit lamp, Scheimpflug imaging, and OCT imaging, but this is not really what the patient sees,” Dr Hirnschall said. “Measuring forward light scatter with a straylight meter can be a useful additional tool, as it has a significant impact on positive dysphotopsia. This is not only a problem for multifocal and extended depth of focus (EDOF) IOls but also monofocal lenses.”

Several devices can measure positive dysphotopsias—glare, halos, and starbursts—and are particularly useful for assessing patients implanted with multifocal or EDOF lenses. Negative dysphotopsias are more difficult to quantify, and it is often best to ask the patient to make a drawing of what is obscuring their temporal field of vision.

Finally, Dr Hirnschall said the psychological component should not be overlooked.

“There are a wide variety of resilience tests and personality and lifestyle questionnaires which can help give an idea of how patients might respond to EDOF or multifocal lenses,” he said. “Patient motivation also plays an important role.”

Dr Hirnschall presented at the ESCRS Winter Meeting in Frankfurt.

Nino Hirnschall MD, PhD is a clinician and researcher at the Kepler University Clinic, Linz, Austria. nino.hirnschall@googlemail.com

1. Norrby S. “Sources of error in intraocular lens power calculation,” J Cataract Refract Surg, 2008 Mar; 34(3): 368–376. doi:10.1016/j.jcrs.2007.10.031.