Automatic quantitative measurement of ocular hyperemia

Abstract

Evaluation of ocular hyperemia has been an important assessment in research studies of effects of contact lenses, medications, and pollutants on the eye. Hyperemia has been difficult to quantitate objectively. The purpose of this study was to validate a computer based image analysis system to quantitate hyperemia automatically and objectively in pixelated images of the external eye using two measures, the percent of the red color, RR, and the fraction of pixels which are blood vessels, VA. Validation was against an established photographic reference scale of ocular hyperemia and against the clinical pharmacologic effects of 0.5% dapiprazole hydrochloride, known to increase hyperemia, and 2.5% phenylephrine hydrochloride, known to decrease hyperemia. Color transparencies from the reference scale were converted to digital images. Temporal and nasal regions of the external eye were imaged directly to magnetic disk before and after pharmacologic intervention. Custom software automatically excluded unwanted regions, and quantitative image analysis produced RR and VA. RR and VA were each correlated with the reference scale. For each region and for each pharmacologic intervention, the mean RR and the mean VA, respectively, were compared at time zero and at a mean elapsed time of 713 +/- 47 s. RR and VA consistently increased as the hyperemia in the reference scale increased. Pearson correlation coefficients were 0.98 and 0.99, respectively, (p < 0.01). At 713 +/- 47 s after each pharmacologic intervention, RR and VA increased and decreased as expected (p < 0.001). Thus, this study successfully validated the methodology against expert clinical judgment and was able to measure automatically and objectively clinical changes in ocular hyperemia.

Automated hyperemia analysis software: reliability and reproducibility in healthy subjects

“…As previously described by Wolffsohn [12], bulbar hyperemia has been graded by a combination of thresholding [13][14][15][16][17], edge detection [14,18,19], smoothing [13,14,18,20], color extraction [13,15,17,20], morphometry and densitometry [21]. However, these experimental methods were highly complex and have not been routinely used in a clinical setting.…”

“…However, these experimental methods were highly complex and have not been routinely used in a clinical setting. Several reports indicate the possible application of software to automate conjunctival hyperemia evaluation [14,15,18,20]. These methods are not widely used in a clinical setting, probably due to difficulties with accessibility, operation, maintenance, and development costs.…”

How red is a white eye? Clinical grading of normal conjunctival hyperaemia

“…The problem of an ordinal grading scale, producing unequal grading divisions, has also been considered by using digitised morphing of the grading scales, or by removing the subjective input of the observer through image analysis of the image. [34][35][36][37][38][39][40] Although conjunctival hyperaemia is accepted as an important clinical sign of ocular disease or inflammation, and grading scales are frequently used to assess the severity or degree of change in bulbar redness, no previous studies have been presented that consider the normal, unstimulated level of conjunctival hyperaemia.…”

Conjunctival redness

“…15 The increasing availability of video-capture technology which can be interfaced with sophisticated computer-based image analysis systems has led a number of researchers to develop objective techniques for measuring the level of conjunctival redness in response to contact lens wear. [16][17][18][19] Owen et al 18 used such a system to demonstrate that, over a 4-month period, rigid lens wear was associated with an increase in conjunctival redness, whereas soft lens wear was not associated with increased redness. These results do not necessarily conflict with those of McMonnies and Chapman-Davies 7,8 who examined the conjunctivae of adapted lens wearers.…”