Posters

Corneal graft central thickness and central thickness of non-transplanted corneas measured by two non-contact devices compared to contact ultrasound device

Poster Details

First Author: S.Stunf SLOVENIA

Co Author(s):    V. Pfeifer              

Abstract Details

Purpose:

The value of central corneal thickness in evaluation of glaucoma patients is debatable but it certainly has the value in evaluation of glaucoma after corneal transplantation. Contact ultrasonic pachymetry is still regarded as the gold-standard; however it requires contact with the cornea, topical anesthesia, and is influenced by operator skills. This study was designed to compare the measures of corneal graft central thickness after penetrating corneal transplantation and the central corneal thickness in non-transplanted corneas obtained by the optical coherence tomography (OCT) or Sirius Scheimpflug imaging system, and compared to ultrasound pachymetry in order to find a suitable noncontact replacement for measurement of corneal graft central thickness.

Setting:

University Eye Hospital Ljubljana.

Methods:

Patients after penetrating keratoplasty underwent full ophthalmological examination and three different methods of corneal pachymetry measurement: ultrasonic pachymetry, high-resolution SD anterior segment OCT (Heidelberg Engineering, Heidelberg, Germany), and Sirius (Costruzione Strumenti Oftalmici, Florence, Italy). The control group consisted of patients with normal (around 550 µm), thin (< 520 µm) and thick (> 580 µm) non-transplanted corneas. The ultrasonic pachymetry was done under topical anesthesia in the center of the cornea, averring 10 measurements. The anterior segment OCT of the cornea was performed at the same time. The center of the cornea was chosen using the concurrent photography of the anterior eye segment, and 10 measures perpendicularly to the cornel surface were performed under 5-times magnification using the integrated software. The Sirius is a combination of rotating Scheimpflug camera and a small-angle Placido disk topographer. The central corneal thickness was taken from the full exam performed at the same time as the other two measurements.

Results:

There were 10 eyes after penetrating keratoplasty and 10 eyes in each of the control subgroups included in the study; average thicknesses measured by ultrasound were 494,3 µm in transplanted corneas, and 503,3 µm in thin , 543,5 µm in normal, 597,5 µm in thick non-transplanted corneas subgroups. Performing the paired T-test between the measures obtained by different devices, we found out that the OCT measurement were not statistically significantly different than the ultrasound measurements for transplanted as well as for thin, normal or thick non-transplanted corneas (p values > 0.05). Comparing the measurements from these two devices to the measurements obtained by Sirius, however all groups but thick non-transplanted corneas showed statistically significant difference. The measures taken by Sirius were bigger for an average of 20 µm. Looking at the transplanted corneas separately, the difference was even bigger, an average of 36,3 µm (the difference range 28 - 50 µm if compared to ultrasound and 30 - 48 µm if compared to OCT).

Conclusions:

The anterior segment SD OCT measures correlated well with the ultrasonic measures in transplanted corneas also in the control groups, while the Sirius measures were more or less inconsistent in all groups and especially so in the transplanted corneas. The best measurement of central corneal thickness can thus be obtained combining the ultrasonic contact and the OCT measurements and the best choice for noncontact measurement of the transplanted corneas as shown here is the anterior segment OCT. FINANCIAL INTEREST: NONE