Objective: To determine
whether increased long-term variability (LTV) in glaucoma suspect patients with
normal visual fields (VF) precedes the appearance of repeatable glaucomatous VF
defects.
Methods: We analyzed three
consecutive normal VFs from 10 subjects who subsequently converted and had two
or more consecutive abnormal VFs.
Location-specific LTV maps were constructed from raw threshold values of
the three normal VFs, and standardized using a normative LTV database. We then determined if average quadrant
standardized-LTV was predictive of the quadrants that later became
defective. Subjective clinical
evaluation (masked to LTV analysis results) and objective Glaucoma Change
Probability analysis were independently used to rank the relative severity of
the quadrant defects and nasal steps in the abnormal fields.
Results: Strong agreement
was found between average standardized pre-conversion quadrant LTV and
post-conversion clinical subjective ranking of severity (p=0.002) as well as
objective ranking by GCP (p=0.02).
A trend towards prediction of nasal step asymmetry was also observed,
but did not reach statistical significance.
Conclusions: The location with increased LTV in normal VFs was
found to be predictive of the quadrant subsequently emerging as most defective.