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SITA-Faster or Standard Algorithm Options for Glaucoma

A large, independent clinical study comparing SITA-Faster and SITA-Standard in normal, glaucoma suspect and manifest glaucoma patients, confirmed a much reduced test time and found highly comparable sensitivity results. However there were some shortcomings.

In light of findings, should you be using SITA-Faster or SITA-Standard algorithms for your glaucoma patients?

As clinicians, we desire clinical techniques that are quick, non-invasive and accurate as part of the glaucoma diagnostic process. Standard automated perimetry, the current clinical standard for assessing sensitivity across the visual field in glaucoma, is a technique that has traditionally fulfilled none of those requirements. It is typically a long test, taking more than five minutes per eye and even longer in patients with glaucomatous field loss. The time required, combined with the fact it requires sitting in an uncomfortable position and is prone to errors and variability, mean that patients notoriously dislike undertaking this test.

Overall, our patients at CFEH have responded favourably to the implementation of SITAFaster in our routine clinical operations

In response to this clinical issue, Carl Zeiss Meditec released the much-anticipated SITA-Faster algorithm in late 2018. Building upon the experiences with the older Standard and Fast algorithms, seven modifications were built into SITA-Faster to significantly reduce the test duration.

The question now is: should clinicians be using SITA-Faster instead of SITAStandard? Aside from the benefits of reduced test time, are there any drawbacks that we need to be aware of when conducting the test?

Researchers at Centre for Eye Health (CFEH) performed a large, independent clinical study comparing SITA-Faster and SITA-Standard in normal, glaucoma suspect and manifest glaucoma patients. While confirming the much reduced test time (>50% in nearly all cases), we also found highly comparable sensitivity results. These two findings bode well for the new algorithm: faster yet yielding effectively the same clinical result.

But what we also found was a propensity for higher rates of unreliability when conducting SITA-Faster compared to SITA-Standard. Around 30% of all SITA-Faster fields were unreliable compared to less than 10% for SITAStandard. Examining the causes of unreliability, we found that SITAFaster produced a uniquely high rate of false positive and seeding point errors. Interestingly, aspects such as fatigue and waning attention towards the end of the test did not appear to play a significant role. This would make sense due to the shorter duration of the test.

In other words, the quicker test has come at a cost of reliability.

RECOMMENDATIONS FOR BEST RESULTS

As clinicians, we require clinical data of high fidelity to make decisions. Otherwise, there would be no point in conducting the test. Therefore, we have provided several clinically-relevant recommendations when using SITA-Faster to overcome these disadvantages:

  1. Warn the patient that the test targets willappear rapidly: they should press as soon asthey feel like they see the target,
  2. Ask patients to pay particular attentionto the first 30 seconds of the test, as thatwill affect the overall reliability of the result, and
  3. If the results are unreliable, repeat thetest on the same day, as the test is quickand unlikely to affect clinic flow (repeating it on another day will trigger the learning effect again).

Overall, our patients at CFEH have responded favourably to the implementation of SITA-Faster in our routine clinical operations. Having a test that takes less than half the time of the standard algorithm means we can frontload visual field results (performing multiple tests at the same visit). Through this, we have been able to reduce the number of false positive results: defects that are seen in the initial result are often not repeatable, and hence non-glaucomatous in nature.

QUESTIONS REMAIN

Several questions remain regarding SITA-Faster though. First, how does it perform at tracking glaucoma progression over time? Current Guided Progression Analysis software combines legacy mixed SITA data with SITA-Faster data, and the implications of this is currently unknown. Its performance has not been extensively investigated in cases with advanced visual field loss, which characteristically have unreliable and poorly repeatable results. Finally, SITA-Faster is available for the 24-2C test grid, incorporating the classic 24-2 with 10 additional ‘central’ points. However, it is not available for the current clinical standard test grid for central visual field assessment, the 10-2, or the grid for peripheral/neurological assessments, the 30-2.

In the meantime, and as we wait for the answers to unfold, if clinicians are after a clinical test that is quick at producing results that are almost indistinguishable from the current clinical standard, SITAFaster is recommended for visual field testing in glaucoma – as long as reliability issues can be mitigated.

Dr Jack Phu is an optometry-trained clinician-scientist. He is an associate lecturer at the UNSW School of Optometry and Vision Science and Head of the glaucoma/neuro-ophthalmology unit at the Centre for Eye Health. His clinical, research and teaching responsibilities are devoted almost exclusively to glaucoma and optic nerve disease. jphu@cfeh.com.au 

Reference 

Phu J, Khuu SK, Agar A, Kalloniatis M. Clinical evaluation of Swedish Interactive Thresholding Algorithm-Faster compared with Swedish Interactive Thresholding Algorithm-Standard in normal subjects, glaucoma suspects, and patients with glaucoma. Am J Ophthalmol 2019;208:251-264.