Effect of stimulus size on static visual fields in patients with retinitis pigmentosa

Ophthalmology. 2000 Oct;107(10):1950-4. doi: 10.1016/s0161-6420(00)00356-0.


Purpose: To determine the effect of stimulus size on sensitivity of patients with retinitis pigmentosa (RP) as measured by automated static perimetry.

Design: Comparative case series.

Participants: Thirty-nine patients with RP and a control group of 10 healthy volunteers.

Methods: Automated static perimetry (full threshold programs 24-2 or 30-2) was performed twice on one eye of each participant using stimulus sizes III (0.43 degrees diameter) and V (1.72 degrees diameter). Data from the same 50 test locations were used from each field.

Main outcome measures: At each location, for each participant, the size effect was computed as the difference (in decibels) in sensitivities for sizes V and III, and the average sensitivity was computed as the mean of sensitivities for the two sizes.

Results: For both patient and control groups, the size effect was negatively correlated with average sensitivity (r(2) > 0.124; P: < 0.001). The mean size effect was significantly greater for the patient group than for the control group: 8.6 (+/- 3.6) dB versus 5. 4 (+/- 2.2) dB (t = 18.0; P: < 0.001). The percentage of abnormal locations (more than 8 dB below mean normal) tended to be lower for size V than for size III, with a mean of 67% for size V versus 95% for size III. The percentage of absolute defects was also lower for size V than for size III, with a mean of 35% for size V versus 54% for size III.

Conclusions: In damaged regions of the visual fields of patients with RP, increase in stimulus size from III to V can produce abnormally large increases in perimetric sensitivity. Size III may be more useful than size V for detection of field abnormality, whereas size V may be more useful than size III for observing progression of advanced RP.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Humans
  • Retina / physiopathology*
  • Retinitis Pigmentosa / genetics
  • Retinitis Pigmentosa / physiopathology*
  • Sensitivity and Specificity
  • Visual Field Tests / methods*
  • Visual Fields / physiology*