Intraoperative changes in corneal structure during excimer laser
phototherapeutic keratectomy (PTK) assessed by intraoperative optical
Received: 22 June 2017 / Revised: 21 November 2017 / Accepted: 11 December 2017 / Published online: 4 January 2018
Springer-Verlag GmbH Germany, part of Springer Nature 2018
Purpose Excimer laser phototherapeutic keratectomy (PTK) is a safe treatment for superficial corneal opacities, e.g., in corneal
dystrophies or degenerations. Nevertheless, no standardized treatment protocols are available and intraoperative monitoring was
not possible, so far. Here we evaluate the potential benefits of the intraoperative assessment by microscope-integrated intraop-
erative optical coherence tomography (MI-OCT) of corneal optical properties during PTK.
Methods Retrospective study of eight patients (one male, seven females; age range, 43–80 years, mean = 66.1 years) using an
840-nm microscope-integrated spectral-domain OCT (iOCT; OptoMedical Technologies, Luebeck, Germany adapted to HS Hi-
R Neo 900A, Haag Streit Surgical, Wedel, Germany). Images were acquired before and after corneal abrasion and after PTK. For
PTK, a SCHWIND Amaris 750S excimer laser (SCHWIND eye-tech-solutions GmbH und KO. KG) was used. Parameters
assessed were the central corneal thickness (CCT), changes in central depth-dependent corneal tissue intensity (TI), and corneal
surface roughness (SR) in cross-sectional images of the cornea.
Results Intraoperative monitoring using microscope-integrated OCT was possible in all patients at all time points. TI of the
anterior corneal stroma decreased significantly (p = 0.037) after PTK (T1 = 15.1 ± 3.6, T2 = 15.0 ± 3.84, T3 = 13.7 ± 3.38), but
not after corneal abrasion alone, indicating increased transparency caused by excimer laser PTK. CCT was significantly lower
after corneal abrasion (p = 0.017), but not after PTK (T1 = 630.4 ± 70 μm, T2 = 544.1 ± 59.4 μm, T3 = 558.3 ± 52.5 μm. SR
significantly decreased (p = 0.043) after PTK (T1 = 614.4 ± 37.5 pixels, T2 = 634.4 ± 35.6 pixels, T3 = 611.0 ± 40.3 pixels).
Conclusions Intraoperative OCT allows real-time imaging during PTK and the assessment of corneal optical transparency and its
surface roughness. It has to be clarified in larger studies if these parameters correlate with later postoperative visual outcomes.
Intraoperative optical coherence tomography
Excimer laser phototherapeutic keratectomy (PTK) is an ef-
fective treatment for superficial corneal opacifications due to
scars, corneal dystrophies, or recurrent erosions [1–3].
Generally, PTK is a safe and standardized procedure.
Corneal optical properties are in this context improved by
removing superficial opacities of the anterior corneal stroma
and by smoothening the corneal surface to lower glare or
higher-order aberrations [4, 5].
Optical coherence tomography (OCT) is an important tool
that is widely used for the planning of the PTK by estimating
the depth of the corneal opacities. Additionally, it is one of the
standard imaging procedures for the postoperative treatment
In most cases, the PTK is conducted with an automatically
calculated programme, based on the preoperative calculated
ablation depth and the measured corneal thickness and diam-
eter of the cornea. To date, individual intraoperative changes
* Sebastian Siebelmann
Department of Ophthalmology, University of Cologne, Kerpener
Strasse 62, 50924 Cologne, Germany
Cluster of Excellence: Cellular Stress Responses in
Aging-Associated Diseases, University of Cologne,
Graefe's Archive for Clinical and Experimental Ophthalmology (2018) 256:575–581