Optimal time following fluorescein instillation to evaluate rigid gas permeable contact lens fit

• Fluorescein aids the determination of GP lens fit in the primary position of gaze.
• However the optimal time to assess the fluorescein pattern has not been determined.
• Persistence of fluorescein under aligned, steep & flat lenses degrades from ∼45 s.
• However, expected fitting patterns seen 30–180 s subjectively & 15–105 s objectively.
• This highlights most appropriate time window to evaluate GPs in clinical practice.

PurposeTo examine the optimum time at which fluorescein patterns of gas permeable lenses (GPs) should be evaluated.MethodsAligned, 0.2 mm steep and 0.2 mm flat GPs were fitted to 17 patients (aged 20.6 ± 1.1 years, 10 male). Fluorescein was applied to their upper temporal bulbar conjunctiva with a moistened fluorescein strip. Digital slit lamp images (CSO, Italy) at 10× magnification of the fluorescein pattern viewed with blue light through a yellow filter were captured every 15 s. Fluorescein intensity in central, mid peripheral and edge regions of the superior, inferior, temporal and nasal quadrants of the lens were graded subjectively using a +2 to −2 scale and using ImageJ software on the simultaneously captured images.ResultsSubjectively graded and objectively image analysed fluorescein intensity changed with time (p < 0.001), lens region (centre, mid-periphery and edge: p < 0.05) and there was interaction between lens region with lens fit (p < 0.001). For edge band width, there was a significant effect of time (F = 118.503, p < 0.001) and lens fit (F = 5.1249, p = 0.012). The expected alignment, flat and steep fitting patterns could be seen from approximately after 30 to 180 s subjectively and 15 to 105 s in captured images.ConclusionAlthough the stability of fluorescein intensity can start to decline in as little as 45 s post fluorescein instillation, the diagnostic pattern of alignment, steep or flat fit is seen in each meridian by subjective observation from about 30 s to 3 min indicating this is the most appropriate time window to evaluate GP lenses in clinical practice.