Advanced diagnostic, surgical planning tool plays role in patient care

Take home

George O. Waring IV, MD, FACS, discusses how the ability to evaluate quality of vision by assessing forward light scatter of the dysfunctional lens, measure depth-of-focus, guide in centration, and functionally evaluate unstable tear film to diagnose dysfunctional tear syndrome have made an advanced diagnostic/surgical planning device invaluable in practice.

By George O. Waring IV, MD, FACS, Special to Ophthalmology Times

Charleston, SC-Snellen acuity-described in the mid-1800s by Herman Snellen-is considered the gold standard for quantifying a patient’s vision. Things have changed since then.

Now, along with visual acuity, ophthalmologists can objectively analyze and improve patients’ quality of vision. Optical aberrations, contrast sensitivity, ocular surface quality, and other formerly subjective assessments can now be objectively quantified, allowing ophthalmologists to identify and address the root cause of patients’ visual dysfunction.

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One of the most important determinations is whether a patient seeking surgical vision correction is best served by a corneal- or lens-based procedure. I combine clinical examinations with objective data analysis from an advanced diagnostic/surgical-planning instrument (AcuTarget HD, AcuFocus) to find the best solution for the individual patient. The ability to evaluate quality of vision by assessing forward light scatter of the dysfunctional lens, measure depth-of-focus, guide in centration, and functionally evaluate unstable tear film to diagnose dysfunctional tear syndrome have made this tool invaluable in treatment planning in my practice.

Ocular light scatter

Objective quantification of subjective visual complaints has been of enormous benefit. The instrument essentially sends a low-energy laser beam into the eye and then evaluates the relative intensity of the beam through a double-pass analysis. An Ocular Scatter Index (OSI) is created which quantitatively describes the amount of scattered light and the point spread function demonstrates qualitatively the pattern of light scatter distribution. While physicians could previously detect the occurrence of early senile lens changes with careful slit lamp examination-and perhaps contrast sensitivity measurements that may not be widely used in clinical practice-these changes were often overlooked.

Dysfunctional tear syndrome can result in irritation, light-sensitivity, and poor visual quality. Awareness of dry eye and ocular surface diseases has intensified over the past couple of years as it directly relates to patient satisfaction following surgery. Being able to generate a series of OSI indices in succession over a 20-second scan period allows ophthalmologists to evaluate-frame by frame-whether image quality becomes distorted in between blinks and if it is restored with a blink.

This helps attribute the scatter to evaporative dry eye. If image quality quickly deteriorates and then restores with every blink, ophthalmologists can easily and objectively see the functional aspect of dry eye, and explain it to patients. Furthermore, this gives the practitioner an objective baseline measurement from which to compare serial exams once ocular surface optimization regimens are established.

Alternatively, if a patient and the OSI shows minimal light scatter and an excellent point spread function pattern with subjective visual complaints, a more extensive retinal evaluation may be warranted as these findings suggest a non-optical etiology of visual disturbance.

I use the device for all my patients with dry eye, as it establishes baseline measurements and allows us to see progress with treatment. For complex patients, where their diagnosis or complaints are not very straightforward, it is possible to determine if there is a tear film etiology or other subtle optical aberrations resulting in suboptimal image quality.

Growing presbyopic population

The general aging of the population means that more and more of patients are complaining about the loss of near vision without the aid of spectacles. Being able to measure and document depth of focus is unique and demonstrates for the patient the actual loss of amplitude of accommodation due to presbyopia, as well as what has been regained via treatment, depending on the modality.

Pseudoaccommodation is complex and historically has only been evaluated via subjective patient comments. Ophthalmologists can now evaluate-pre- and postoperatively-the improvement in the defocus curve from various presbyopia-correcting procedures as well as use the point-spread function across a defocus range to visually educate patients.

Determining optimal placement of presbyopia-correcting technologies, like corneal inlays and IOLs, is gaining rapid interest worldwide. By accurately capturing the 1st Purkinje image and pupil center in a patient fixated coaxially sighted manner, clinicians now have a diagnostic device that objectively maps out desired position for centration of refractive treatments.

Determining best course of treatment

When a patient presents for a surgical vision correction consultation, the decision needs to be made on whether to perform a cornea- or lens-based procedure. If the patient has, for example, a clear lens on exam and they have a minimal ocular scatter index with a high quality point spread function, then they would be better served with a corneal-based procedure.

If, however, they have lens opacification on clinical exam, clinicians can image this and look at the densitometry and objectively measure their quality of vision. If some moderate ocular scatter index is seen, a point spread function consistent ocular scatter, and a dilated scheimpflug image and lens densitometry consistent with dysfunctional lens syndrome, this patient would benefit more from a dysfunctional lens replacement.

This is the key. It is about understanding, objectively evaluating, and optimizing image quality and functional vision. If LASIK is performed on a patient with lens opacities, the patient will have a suboptimal outcome and will likely present in the future with visual complaints and then undergo a lens based procedure, perhaps with more limited options.

Despite the fact that 20/20 is a benchmark standard for perfect vision, there is excellent quality 20/20 vision and poor quality 20/20 vision. Advanced diagnostics allow clinicians to objectively measure the quality and functional aspects of patients’ vision. These metrics not only enable ophthalmologists to make proper diagnoses and determine the best treatment, they are also indispensible tools for patient education.

George O. Waring IV, MD, FACS, is assistant professor of ophthalmology, director of Refractive Surgery at Medical University of South Carolina (MUSC), Storm Eye Institute, and serves as medical director at Magill Vision Center. Dr. Waring also serves as adjunct assistant professor of bioengineering at the College of Engineering and Science at Clemson University. He can be reached via e-mail at georgewaringiv@gmail.com.