Digital imaging in the contact lens practice

Subjective and objective measures of corneal staining related to multipurpose care systems

An objective, digital-imaging method of measuring corneal staining was evaluated in 24 subjects wearing soft contact lenses. The method was used to compare the clinical performance of common multipurpose care systems (MPS) for soft contact lens care. Subjects used three different MPS, one containing polyquaternium-1 (PQ) and two containing polyhexanide (PX1 and PX2), for 2 weeks in a randomised, single-masked (investigator) crossover study. Corneal staining induced with the three MPS was analysed using an image-processing program (ImageTool, UTHSCSA Version 2, University of Texas, USA). Conjunctival hyperaemia and papillae were also evaluated. The intraclass correlation coefficient was similar with image analysis to that of investigator grading (0.876, 0.879, respectively). Significant differences in staining response were detected using the objective method. There was significantly less staining area with polyquaternium-1 (PQ) than polyhexanide (PQ: 0.12 mm(2), PX2: 0.91 mm(2)). Inferior palpebral papillae were significantly greater with PX2 than with PQ (1.0, 0.7 (0-4), respectively). The technique was shown to be an effective method of evaluating different corneal staining responses. Bilateral corneal staining in three or more quadrants is useful in the diagnosis of MPS-related staining.

Clinical monitoring of ocular physiology using digital image analysis

AIM

To examine the use of image analysis to quantify changes in ocular physiology.

METHOD

A purpose designed computer program was written to objectively quantify bulbar hyperaemia, tarsal redness, corneal staining and tarsal staining. Thresholding, colour extraction and edge detection paradigms were investigated. The repeatability (stability) of each technique to changes in image luminance was assessed. A clinical pictorial grading scale was analysed to examine the repeatability and validity of the chosen image analysis technique.

RESULTS

Edge detection using a 3 x 3 kernel was found to be the most stable to changes in image luminance (2.6% over a +60 to -90% luminance range) and correlated well with the CCLRU scale images of bulbar hyperaemia (r=0.96), corneal staining (r=0.85) and the staining of palpebral roughness (r=0.96). Extraction of the red colour plane demonstrated the best correlation-sensitivity combination for palpebral hyperaemia (r=0.96). Repeatability variability was <0.5%.

CONCLUSIONS

Digital imaging, in conjunction with computerised image analysis, allows objective, clinically valid and repeatable quantification of ocular features. It offers the possibility of improved diagnosis and monitoring of changes in ocular physiology in clinical practice.

The use of digital image capture in contact lens practice

The present decade has seen the introduction of digital imaging systems to a number of medical environments, including contact lens practice. During the past year, the authors have used two anterior segment video-based digital image capture systems. These systems allow instantaneous image capture and have both diagnostic value to practitioners and educational value to patients. This paper discusses and clarifies the terminology that surrounds such systems and looks carefully at the advantages and disadvantages when compared to more traditional 35 mm photography in particular with reference to image colour, resolution and storage. The difference between video digital image capture and the more recently available digital camera image capture is also discussed. The value of digital imaging is shown by a series of images from the authors' archives.