EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/176967
September 2013 EW NEWS & OPINION 19 and optical scatter is critical refractive surgery, dry eye syndrome management. A step up from its predecessor, OQAS, it offers faster acquisition and computation, a more compact design with a much smaller footprint and a more elegant display of data. Everything is quickly available on one printout, and the entire workflow is sped up as a result of these improvements. Function Figure 1. The Ocular Scatter Index, measured in 0.5 second intervals through a 7 mm aperture, shows increasing amounts of scatter over time. This is consistent with an unstable tear film and rapid tear break-up. The two dark boxes in the bottom row reflect a blink. Figure 2. The Optical Scatter Index measured at a 4 mm aperture is 2.5, which is consistent with an early lenticular opacity. Note that the predicted vision at 100% and 20% contrast is still reasonably good and the Strehl ratio and MTF cutoff is still in a respectable range. Source (all): Jay Pepose, MD cal scatter.5 The objective scatter index is the only parameter that enables the objective quantification of intraocular scatter light and is useful in a multitude of clinical scenarios, e.g., cataract surgery, The HD Analyzer provides unique information that is otherwise unavailable. When trying to assess a patient's cataract, relying solely on slit lamp microscopy and high contrast vision for disability assessment, many pieces of the puzzle will remain missing. The objective measurement of light scatter can help in the early detection of cataracts and is also useful in cases of identified cataracts where it can help determine the degree of severity and impact on retinal image quality.5–7 Research has shown that the Ocular Scatter Index (OSI) and the derived MTF correlate with visual acuity in patients with all forms of cataract. The OSI correlates closely with the LOCS III grading of cataract, but has the advantage of providing an objective rather than subjective assessment, with less risk of interobserver variability. The various objective metrics produced by the HD Analyzer can be factored in as an adjunct to the patient's symptoms and visual acuity, helping the surgeon decide when to perform cataract surgery, LASIK surgery or enhancement, or consider alternative treatments or observation. In phakic or pseudophakic patients, we can use the technology to help measure the amplitude of accommodation or depth of focus and determine the effect of accommodation on the quality of the retinal image. We have numerous ways of testing for dry eye disease, e.g., tear osmolarity, questionnaire providing an index of symptoms, performing vital dye staining or Schirmer testing, but it is only with a device capable of objectively determining light scatter that we can look at serial measurements of scatter over time; this allows us to essentially see an automated tear break-up time without having to instill fluorescein or other drops into the eye, which could change the entire tear dynamics. Thus, we can get a clearer idea of the patient's tear break-up without perturbing the tear film.8 The device can even be used to test visual quality over time comparing different contact lenses. As dry eye can impact patients' visual outcome, this clear assessment of tear break-up is very significant in our pre-surgical planning. It might prompt the surgeon to treat a patient's dry eye more aggressively before he/she proceeds with surgery. Dry eye could also affect the stability or fidelity of measurements for cataract or refractive surgery, making this assessment even more important. Objective light scatter measurement can also prove useful in less straightforward cases. In our case, the application of the HD Analyzer revealed a marked increase in optical scatter between blinks (Figure 1), consistent with an unstable tear film and low tear break-up time. After instilling a drop of artificial tears to negate the effect of the dry ocular surface, additional measurements with the HD Analyzer revealed an optical scatter index of 2.5, consistent with an early cataract, and other metrics (MTF cutoff, MTF) consistent with reasonably high optical quality (Figure 2). Punctal plugs were placed and additional dry eye treatment was initiated. On repeat measurement a few weeks later, the optical scatter over time showed a decrease in temporal variation, but the overall optical scatter index remained elevated. Quantifying the severity of the patient's cataract according to the objective scatter index and other metrics allowed us to conclude that a LASIK enhancement might produce a short-lived result, as there was already considerable optical scatter. If we were to go ahead with the LASIK enhancement, based only on slit lamp and wavefront analyses, there was a chance that the patient would be dissatisfied with the quality of vision because of a problem that could have been identified with light scatter measurements. From the patient's perspective, undergoing assessment with the HD Analyzer is similar to sitting down in front of an autorefractor, and the near infrared wavelength ensures that patient comfort is not compromised. In our practice, the device is continued on page 20