Patient data

A total of 16 eyes of 14 patients (6 female), with a mean age of 33.8 ± 12.1 years (range, 19–72 years), underwent manual mid-stromal dissection (Table 1) and had a mean follow-up of 6.6 ± 2.4 years (range, 1.6–9.4 years). All treated eyes had documented evidence of keratoconus progression in the year prior to surgery (defined as ≥1.0 Diopters (D) change in maximum keratometry [Kmax] values (measured by Scheimpflug-based corneal tomography [5])) with or without a history of subjective decline in visual acuity and were included in this analysis. Eyes with concomitant ocular disease not related to keratoconus and eyes with previous episodes of hydrops were excluded from treatment. All patients signed an institutional review board-approved informed consent form prior to surgery. The study was conducted according to the tenets of the Declaration of Helsinki [6].

Table 1 Demographics and preoperative baseline characteristics Full size table

Surgical technique

Manual mid-stromal dissection was derived from a technique previously described by Melles et al. to create a lamellar dissection plane in deep anterior lamellar keratoplasty (DALK) [7]. For stabilization of keratoconic corneas, a manual mid-stromal dissection plane was created at approximately 50–70% corneal depth (to avoid perforation in the anterior chamber) instead of the 90–95% depth of dissection commonly used in DALK (Fig. 1).

Fig. 1 Clinical images of an eye before and up to 9.5 years after manual dissection. Topographic maps, slit-lamp images and Scheimpflug images (segment: 91°- 271°) of Case no. 1 preoperatively (top row a), at 6 months (second row b) and at 9.5 years (third row c) after manual mid-stromal dissection. Note a mild increase in K-readings and the demarcation line at the level of the mid-stromal dissection (arrows). m = months; y = year(s) Full size image

Surgery was performed under local anesthesia (retrobulbar, 4 mL 1% ropivacaine hydrochloride with 1 mL 150 IU Hyason) with the patient positioned in anti-Trendelenburg position and a Honan’s balloon applied for 10 min. A side port was created at either the 3- or 9-o’clock limbus to completely fill the anterior chamber with air. Then, a 5-mm frown-shaped scleral incision was created at 12 o’clock, 1–2 mm from the limbus and tunneled into the superior cornea. Subsequently, guided by the air-endothelium interface, manual lamellar dissection was performed with a dissection spatula (Melles spatula set; DORC International BV, Zuidland, The Netherlands) at 50–75% stromal depth creating a circumferential mid-stromal pocket from limbus to limbus. Finally, the air was removed from the anterior chamber and the eye was pressurized with a balanced salt solution.

Postoperative topical treatment included chloramphenicol 0.5% for 2 weeks; ketorolac tromethamine 0.4% and dexamethasone 0.1% for 4 weeks; switched to fluorometholone 0.1% at 1 month postoperatively, which was subsequently tapered and stopped over months.

Data collection

All eyes were examined at standardized time-intervals before and after surgery: 1 day, 1 week, 1, 3, 6 and 12 months and every 6 months thereafter. Data regarding the first two postoperative years and the latest follow-up visit were included in this analysis. Slit-lamp biomicroscopy, Scheimpflug-based corneal tomography (Pentacam HR; Oculus, Wetzlar, Germany) and endothelial cell density (ECD) measurements were recorded and best-spectacle corrected visual acuity (BSCVA) and best-contact lens corrected visual acuity (BCLVA) were measured.

Regarding Scheimpflug-based corneal tomography, only images of sufficient quality were used for evaluation. BCVA was measured using a Snellen letter chart. The endothelium was photographed and evaluated in vivo using a Topcon SP3000p non-contact autofocus specular microscope (Topcon Medical Europe BV, Capelle a/d IJssel, The Netherlands). Images of the central corneal window were analyzed and manually corrected; up to three measurements of endothelial cell density were averaged (if the central endothelium could not be visualized, paracentral images were used for analysis).

Statistical analysis

All analyses were performed using Excel Software for Windows. Progression of Kmax was defined as an increase in Kmax of ≥1.0 D throughout the follow-up period. Changes in thinnest point thickness (TPT) of less than 5% were considered stable. BCVA was defined as stable for changes ≤1 Snellen lines, and as improving or deteriorating for changes ≥2 Snellen lines. Independent paired Student’s t-test was performed to assess significant differences between preoperative and consecutive postoperative follow-up measurements. Statistical analysis could not be adjusted for inclusion of fellow eyes due to the small cohort size. Additional statistical analysis, excluding fellow eyes, however, yielded equal results. A P-value below an alpha of 0.05 was considered to be statistically significant. Reported data were expressed as mean ± standard deviation (SD) for continuous variables or percentages.