Original article
Noncontact corneal pachymetry with slit lamp-adapted optical coherence tomography

https://doi.org/10.1016/S0002-9394(01)01425-8Get rights and content

Abstract

PURPOSE: The purpose of this study was to determine the accuracy, the reproducibility, and the limits of agreement of noncontact central corneal thickness measurement with slit lamp-adapted optical coherence tomography (OCT).

DESIGN: Nonrandomized comparative clinical trial.

METHODS: In a prospective comparative observational study, a total of 108 consecutive patients (108 eyes) with normal corneas (92 eyes) and different corneal alterations (16 eyes) participated. Six sequential measurements of the central corneal thickness with slit lamp-adapted OCT and with ultrasound (US) pachymetry at 1640 ms−1 were performed. The main outcome measures were accuracy, reproducibility assessed with precision and coefficient of variation (CV), and limits of agreement of central corneal thickness measurement.

RESULTS: The mean central corneal thickness values were 541 ± 43 μm (OCT) and 549 ± 44 μm (US) with a mean precision of ± 5.8 μm (CV 1.08%) and of ± 4.0 μm (CV 0.73%), respectively. The method comparison revealed equivalence (± 2SD) in the 5% range with a mean difference between both methods of 7.9 μm (1.45%). The relative error was 8.7 μm (1.6%), which corresponded to limits of agreement (± 2SD) ranging from −9.5 μm to 25.3 μm.

CONCLUSIONS: Central corneal pachymetry with slit lamp-adapted OCT revealed, for clinical purposes, an excellent accuracy and reproducibility with a high degree of agreement compared with US pachymetry. Thus, the presented OCT system seems to be a promising diagnostic modality to objectively measure corneal thickness in a convenient noncontact mode.

Section snippets

Patients and clinical examination

Prospectively, 108 patients (108 eyes) with normal (92 eyes) and pathologically altered corneas (16 eyes) were consecutively studied in a nonrandomized comparative clinical trial as part of their clinical examination in our department. The mean patient age was 66 ± 14 (mean ± SD) years (range, 25–87 years) with a male-female ratio of 55:53. Fifty-eight right and 50 left eyes were studied. A complete ophthalmologic examination was performed on each patient. The patient’s primary corneal

Results

The validation of the polyethylene test block sample thickness with OCT (n = 1.571) resulted in a mean value of 871 ± 6.7 μm (CV 0.77%) and with US (1950 ms−1) of 864 ± 14.3 μm (CV 1.66%), respectively. This confirmed that both instruments used in this study were able to accurately measure the true sample thickness within approximately 20 μm.

The corneal thickness could be reliably measured in all patients with slit lamp-adapted OCT. The mean geometric central corneal thickness values for OCT

Discussion

The representation of the corneal thickness is an important part of the ophthalmologic examination with the greatest demand for accurate thickness measurements in the field of refractive surgery. Ophthalmic biometry should provide rapid, objective, and accurate measurements of ocular dimensions. Optical coherence tomography is a high-resolution technique that can create precise cross-sectional images of the anterior and posterior eye segment.13, 14, 15, 16, 17, 18 The physical basis of imaging

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      This study shows that CCT measurement with OCT is equivalent for non contact corneal thickness measurement system compared to USP. Among the methods for CCT estimation, USP has been the most commonly used in the last decades,1,4–6,9–11 although the necessary instillation of oxybuprocaine 0.4% for the accomplishment of the CCT measurement with USP has been also described previously as inducing changes in pachymetry, it has been shown that the mean of the pre and post anaesthetic CCT measures are not significantly different7,24,25 and CCT returns to baseline within 80 s.24 On the other hand, today, however, many modern optically based pachymetric techniques are commercially available. The main advantage of the new measuring systems is that they avoid contact with the cornea, thus reducing the possibility of bacterial contamination, eye diseases infection, or epithelial damage.

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    The authors have no commercial, proprietary, or financial interest in any research or devices described in the presented study.

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