Indications of optical coherence tomography in keratoplasties: literature review

Determination of Surgical Strategies for Burn-Induced Conjunctivalized Corneas Using Optical Coherence Tomography

PURPOSE

To evaluate the clinical use of optical coherence tomography (OCT) in optimizing surgical treatment strategies for conjunctivalized corneas secondary to ocular burns.

METHODS

This noncomparative observational study included 25 patients with stable ocular burns and conjunctivalized corneas. OCT was performed on each eye. The thickness of corneal opacity or pseudopterygium and the underlying healthy stroma were measured. Individual surgical strategies were performed based on clinical examination and OCT images.

RESULTS

Three types of conjunctivalized corneas were evaluated, including conjunctival pannus (4 of 25), pseudopterygium (10 of 25), and a white fibrovascular membrane (11 of 25). All 25 patients received a procedure of allograft limbal stem cell transplantation. In addition, with information provided in OCT images, 8 patients had combined lamellar keratoplasties; 3 patients had deep anterior lamellar keratoplasties, and 2 patients received penetrating keratoplasties. The remaining 12 patients received limbal stem cell transplantation alone. All fibrovascular tissues were successfully removed from the cornea in all patients.

CONCLUSIONS

OCT is a valuable method in the evaluation of conjunctivalized corneas. This is helpful in determining the surgical treatments for individual patients, allowing for less corneal graft rejection and making good use of corneal donors.

Accuracy of optical coherence tomography (OCT) in pachymetry for glaucoma patients

Background

Central corneal thickness (CCT) measurement has become an important test in the diagnosis and management of glaucoma. Currently, ultrasound corneal thickness measurement (pachymetry) is the most frequently used clinical technique and the gold standard to assess CCT. Newer instruments are currently available including the optical coherence tomography (OCT) instrument. The aim of the present study was therefore to evaluate the accuracy of the CCT measurements performed by three different observers, both with the OCT and ultrasound pachymetry (USP), in patients suffering from glaucoma.

Methods

Patients who had been previously diagnosed with glaucoma participated in this cross-sectional study. Glaucoma was defined as patients who had at least two repeatable Humphrey visual fields showing glaucoma damage using the software 24–2, and with the optic nerve showing typical glaucoma damage. The patients CCTs were measured with OCT and USP by three different examiners.

Results

Seventy eyes of 35 patients were included. The average age was 74 ± standard deviation (SD) 10.88, the average pachymetry value with OCT was 536 ± 29 μm, and the average pachymetry with USP was 532 ± 32 μm. The differences between OCT and USP were not significant (t-test, p = 0.32). The intraclass correlation coefficients were, for OCT, 0.99 [confidence interval (CI): 0.98–0.996], and for USP, 0.97 (CI: 0.95–0.98).

Conclusions

Agreement among the three observers using OCT or USP for pachymetry measurements was good. OCT might be used as an alternative method for pachymetry in glaucoma patients.

Dependability of posterior-segment spectral domain optical coherence tomography for measuring central corneal thickness

PURPOSE

The aim of this study was to assess the intersession and interobserver reliability of central corneal thickness (CCT) measurements using a posterior-segment spectral domain optical coherence tomography (SD-OCT).

METHODS

Sixty patients were examined with a posterior-segment SD-OCT system (Topcon 3D-OCT). To analyze intersession reproducibility, 1 examiner measured CCT in 60 eyes 2 times 1 week apart, and to study interobserver reproducibility, a second examiner obtained another measurement during the first session. Within-subject reproducibility, coefficient of reproducibility (CR), and intraclass correlation coefficients (ICC) were calculated. Agreement between Topcon 3D OCT and ultrasound pachymetry (USP) was also assessed.

RESULTS

Posterior-segment SD-OCT showed an intersession reproducibility of 12.7 μm (CR = 2.4%) and an excellent ICC (0.96). No systematic difference between sessions was found (average difference, 1.7 μm; P = 0.15). We found no significant bias between observers (mean difference, -1.5 μm; P = 0.29). The interobserver reproducibility was 16.4 μm (CR = 3.1%), and the ICC was 0.94. Topcon 3D OCT CCT values were lower than USP readings (mean difference, 7.6 ± 8.1 μm; 95% confidence interval, 9.9-5.3 μm; P < 0.001).

CONCLUSIONS

With a commercially available retinal SD-OCT system, reliable intersession and interobserver CCT measurements can be feasibly obtained. The criteria for a significant change, which would be the one exceeding the reproducibility, indicate that intersession and interobserver variations in CCT of more than 13 and 16 μm, respectively, may reflect true corneal change with this particular device. These estimates should help investigators and clinicians differentiate actual CCT modification from measurement random error. The slight CCT underestimation with respect to USP is within the range of other OCT devices.