Loss of visual function may precede retinal layer thinning in glaucoma: Study
USA: True functional change precedes thinning of retinal nerve fiber layer (RNFL) in glaucoma, suggests a recent study in the journal Investigative Ophthalmology & Visual Science.
Previous studies have suggested structural change to be detectable before functional change in glaucoma. However, this may be related to the lower variability and hence narrower limits of structural tests. In this study, Stuart K. Gardiner, Devers Eye Institute, Legacy Research Institute, Portland, Oregon, United States, and colleagues determined whether a time lag exists between the true rates of change in structure and function, regardless of clinical detectability of those changes.
For the purpose, the researchers used structural equation model in order to determine whether the rate of change in function (mean linearized total deviation, AveTDLin) or structure (RNFLT) was predicted by the concurrent or previous rate for the other modality. Rates were calculated over 1135 pairs of consecutive visits from 318 eyes of 164 participants in the Portland Progression Project, with mean 207 days between visits.
Key findings of the study include:
- The rate of change of AveTDLin was predicted by its own rate in the previous time interval, but not by rates of RNFLT change in either the concurrent or previous time interval.
- The rate of RNFLT change was not predicted by concurrent AveTDLin change after adjusting for its own previous rate.
- The rate of AveTDLin change in the previous time interval did significantly improve prediction of the current rate for RNFLT, with P = 0.005, suggesting a time lag of around six months between changes in AveTDLin and RNFLT.
"Although RNFL thinning may be detectable sooner, true functional change appears to predict and precede thinning of the RNFL in glaucoma," concluded the authors.
The study, "Time Lag Between Functional Change and Loss of Retinal Nerve Fiber Layer in Glaucoma," is published in the journal Investigative Ophthalmology & Visual Science.