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Swedish Interactive Threshold Algorithm for central visual field defects unrelated to nerve fiber layer.
Kazunori Hirasawa1, Nobuyuki Shoji2
1Orthoptics and Visual Science, Department of Rehabilitation, School of Allied Health Sciences, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa, 252-0374, Japan. hirasawa@kitasato-u.ac.jp.
Summary
New SITA perimetry algorithms show wider, shallower visual field defects compared to older FT and FP methods. Careful conversion is needed when switching between these standard automated perimetry tests.
Area of Science:
- Ophthalmology
- Visual Science
- Medical Technology
Background:
- Standard automated perimetry (SAP) is crucial for detecting visual field defects.
- Swedish Interactive Threshold Algorithm (SITA) offers faster testing than older algorithms like Full Threshold (FT) and FASTPAC (FP).
- Understanding how SITA alters the appearance of induced visual field defects is essential for accurate diagnosis.
Purpose of the Study:
- To characterize central visual field defects induced by opacity filters using SITA Standard (SS) and SITA-Fast (SF) algorithms.
- To compare these findings with those obtained using FT and FP algorithms.
- To assess differences in test duration, sensitivity, and defect parameters.
Main Methods:
- Thirty healthy participants underwent Humphrey 24-2 visual field testing with FT, FP, SS, and SF algorithms.
- Central visual field defects were simulated using a high-density white opacity filter.
- Key metrics including test duration, fovea threshold, mean sensitivity (MS), mean deviation (MD), pattern standard deviation (PSD), visual field index (VFI), defect size, and depth were analyzed.
Main Results:
- SITA algorithms (SS, SF) demonstrated significantly shorter test durations (21-71% reduction) compared to FT and FP.
- Induced defects appeared wider (approx. 4 points larger) and shallower (127-156 dB shallower) with SITA.
- Global indices showed higher fovea threshold, MS, MD, and VFI, but lower PSD with SITA.
Conclusions:
- Central visual field defects present differently on SITA compared to FT and FP, being wider and shallower.
- Global index values are generally higher with SITA, necessitating caution.
- Clinicians must exercise careful attention when transitioning from FT/FP to SITA to avoid misinterpretation of visual field data.
