Comparison Of Scheimpflug Corneal Tomography And Anterior Segment Optical Coherence Tomography Measurements In Corneal Cystinosis – A Case Series

The gold standard for imaging and measuring corneal crystal deposition in cystinosis is In Vivo Confocal Microscopy (IVCM) though this technique requires contact, is difficult to perform in children and is not available in many clinics. Alternative methods such as Scheimpflug tomography (ST) can provide a pan-corneal image but the backscatter of dense crystals limits this approach. Anterior Segment Optical Coherence Tomography (AS-OCT) can be of added value as it provides images of the whole cornea and appears to be less influenced by scatter. The aim of this paper is to examine and compare the utility of ST and AS-OCT in three patients with cystinosis and to report the first application of AS-OCT densitometry data based on these patients.

The data from three patients with nephropathic cystinosis were analysed. The measurements of the central corneal thickness (CCT) obtained with the Scheimpflug-based imaging technique were compared with those of the infrared reflection-based AS-OCT. In addition, the three patients were assessed using the corneal densitometry analysis add-on to Tomey Casia's standard software.   

The values of CCT fluctuate depending on the measurement method. The CCT measured with ST in the first patient, with a lower corneal cystine crystal score (CCCS), is equal to that measured with AS-OCT. However, in the other two patients, both with a higher CCCS, there is a notable difference between the measurements, with ST pachymetry showing considerably higher CCT values in comparison with AS-OCT measurements. 

Routine CCT measurement in cystinosis patients is beneficial in the evaluation and treatment of the ocular manifestations of cystinosis. The CCT, which is consistently higher in patients with cystinosis, can be measured by ST or AS-OCT. However, ST pachymetry in patients with cystinosis indicates higher CCT values when compared with AS-OCT, due to scattering of the monochromatic light by the corneal crystals. We can thus assume that the ST pachymetry technique has been outmoded by AS-OCT for the measurement of corneal thickness in patients with cystinosis. Due to the greater accuracy, we propose that AS-OCT should be considered a baseline ocular measurement in cystinosis and in the evaluation of disease progression and treatment efficacy.