Aris Konstantopoulos

Impact of graft thickness on visual acuity after Descemet's stripping endothelial keratoplasty

Objective To evaluate the relationship, over time, between central graft thickness and visual acuity following Descemets stripping endothelial keratoplasty (DSEK). Methods A retrospective analysis of 70 consecutive cases of DSEK. All donor lenticules were dissected manually. Serial postoperative measurements of central graft and total corneal thicknesses were made using anterior segment optical coherence tomography. Visual acuity, refraction and patient demographics were collected from case notes. The correlation between central graft thickness and visual acuity at serial time points was calculated. Results The median age at surgery was 75 years (lower quartile (LQ) 66, upper quartile (UQ) 83, range 36–90 years). Nineteen eyes were excluded from statistical analysis, leaving 51 eyes of 46 patients remaining. Last follow-up occurred a median of 12 months postoperatively (LQ 6, UQ 23, range 4–38 months). The median preoperative visual acuity was 0.71 logarithm of the minimum angle of resolution (logMAR), improving to 0.34 logMAR postoperatively (p<0.001, n=43). Median graft thickness decreased from 209 μm at day 1 to 142 μm at last follow-up (p<0.001). No statistically significant correlation was found between central total corneal thickness and visual acuity at any time point. Except for a single time point, no statistically significant correlation was found between central graft thickness and visual acuity. Conclusion There is no clear association between central graft, or total corneal, thickness and visual acuity following DSEK.

Assessment of the use of anterior segment optical coherence tomography in microbial keratitis.

PURPOSE To investigate the imaging capabilities of anterior segment optical coherence tomography (AS OCT) in microbial keratitis and to assess whether measurements of the quantitative parameters, infiltrate thickness and corneal thickness, were possible. DESIGN Prospective, noncomparative, observational case series. METHODS The study was conducted at a university hospital clinical setting. Seven patients (eyes) with suspected microbial keratitis underwent standard clinical examination and treatment based on slit-lamp clinical findings. AS OCT scanning was performed on presentation and at two follow-up appointments. All scans were carried out with the scanning beam passing through the center of the infiltration and at a specific meridian. Examination was carried out by the same operator. RESULTS Corneal infiltration was imaged as a hyperreflective area in the corneal stroma on high-resolution AS OCT scans. Retrocorneal pathologic features and anterior chamber inflammatory cells could be imaged. Corneal and infiltrate thickness could be measured with calipers in six cases. In one case, corneal and infiltrate thickness could not be measured because of a thick inflammatory plaque attached to the endothelium. In this case, the width of the plaque was measured on serial scans. CONCLUSIONS AS OCT imaging provides a range of parameters that can be used to assess microbial keratitis and the treatment response objectively.

Evaluation of a Micro-Optical Coherence Tomography for the Corneal Endothelium in an Animal Model

Recent developments in optical coherence tomography (OCT) systems for the cornea have limited resolution or acquisition speed. In this study we aim to evaluate the use of a ‘micro-OCT’ (μOCT ~1 μm axial resolution) compared to existing imaging modalities using animal models of corneal endothelial disease. We used established cryoinjury and bullous keratopathy models in Sprague Dawley rats comparing ex vivo μOCT imaging in normal and diseased eyes to (1) histology; (2) in vivo confocal microscopy (IVCM); and (3) scanning electron microscopy (SEM). Qualitative and quantitative comparisons amongst imaging modalities were performed using mean endothelial cell circularity [(4π × Area)/Perimeter2] with coefficient of variation (COV). We found that μOCT imaging was able to delineate endothelial cells (with nuclei), detect inflammatory cells, and corneal layers with histology-like resolution, comparable to existing imaging modalities. The mean endothelial cell circularity score was 0.88 ± 0.03, 0.87 ± 0.04 and 0.88 ± 0.05 (P = 0.216) for the SEM, IVCM and μOCT respectively, with SEM producing homogenous endothelial cell images (COV = 0.028) compared to the IVCM (0.051) and μOCT (0.062). In summary, our preliminary study suggests that the μOCT may be useful for achieving non-contact, histology-like images of the cornea for endothelial cell evaluation, which requires further development for in vivo imaging.

Deep sclerectomy versus trabeculectomy: a morphological study with anterior segment optical coherence tomography

Purpose To investigate the intraocular pressure (IOP) lowering mechanisms of deep sclerectomy (DS) with anterior segment optical coherence tomography (AS-OCT). Methods In a prospective cross-sectional study, AS-OCT parameters were compared between DS, trabeculectomy and control cases. Association with IOP and success (IOP≤16 mm Hg without medication) was investigated. Results 18 DS (15 patients), 17 trabeculectomy (16 patients) and 15 controls (15 patients) were examined. Successful had a taller intrascleral lake (IL) and thicker conjunctival/Tenons layer (CTL) than non-successful cases (513.3 vs 361.1 µm, p=0.027 and 586.7 vs 251.1 µm, p<0.001, respectively). CTL thickness correlated with IOP (r=−0.6407, p=0.004). CTL thickness was significantly different between controls, DS and trabeculectomy (mean (SD): 203.3 (62.6) vs 418.9 (261.9) vs 604.1 (220.7) µm, p<0.0001). Successful trabeculectomy cases had a taller bleb cavity (BC) than non-successful cases (607.5 vs 176.7 µm, p=0.041). CTL microcysts were detected in 50% of DS and 52.9% of trabeculectomy cases (p=1). Conclusions Trans-conjunctival aqueous percolation was identified as a novel DS drainage route. DS had a fluid reservoir below the scleral flap, the IL, in analogy to the trabeculectomy BC. A postoperative tall IL and a thick CTL were associated with good outcome.

Early wound healing and refractive response of different pocket configurations following presbyopic inlay implantation

Background Presbyopic inlays have mostly been implanted under a corneal flap. Implantation in a pocket has advantages including less postoperative dry eye and neurotrophic effect, and better biomechanical corneal stability. This study investigated the effect of different pocket and flocket dimensions on corneal stability and refractive power after Raindrop™ implantation, and the associated wound healing response. Methodology Ten New Zealand White rabbits had bilateral pocket Raindrop™ implantation. Eyes were allocated to 4 groups: pockets with 4mm, 6mm, and 8mm diameters, and 8mm flocket. They were examined pre-operatively, at day 1, weeks 1, 2, 3 and 4 post-surgery with anterior segment optical coherence tomography, corneal topography and in-vivo confocal microscopy. After euthanasia (week 4), CD11b, heat shock protein (HSP) 47 and fibronectin corneal immunohistochemistry was performed. Results Corneal thickness (mean±SD) increased from 360.0±16.2μm pre-operatively to 383.9±32.5, 409.4±79.3, 393.6±35.2, 396.4±50.7 and 405±20.3μm on day 1, weeks 1,2,3 and 4 respectively (p<0.008, all time-points). Corneal refractive power increased by 11.1±5.5, 7.5±2.5, 7.5±3.1, 7.0±3.6 and 6.3±2.9D (p<0.001). Corneal astigmatism increased from 1.1±0.3D to 2.3±1.6, 1.7±0.7, 1.8±1.0, 1.6±0.9 and 1.6±0.9D respectively (p = 0.033). CT, refractive power change and astigmatism were not different between groups. The 8mm pocket and 8mm flocket groups had the least stromal keratocyte reflectivity. CD11b, fibronectin or HSP47 weren’t detected. Conclusions Anatomical and refractive stability was achieved by 1 week; the outcomes were not affected by pocket or flocket configuration. No scarring or inflammation was identified. The 8mm pocket and flocket showed the least keratocyte activation, suggesting they might be the preferred configuration.

Presoaking with BSS used for thin manually dissected DSEK (TMDSEK): a viable option for thin DSEK

AimTo describe a novel technique for the safe manual dissection of thin donor lenticules in 10 consecutive patients undergoing DSEK surgery.MethodsA key element of our new technique was to presoak the donor cornea in balanced salt solution (BSS) for 30 min before manual dissection. The cornea was placed on an artificial anterior chamber and pressure in the chamber was maintained at 80 mm Hg. The limbus of the donor cornea was incised to the same depth as the central corneal thickness. Lamellar dissection was started with the short side of the Morlet dissector (Duckworth & Kent Ltd) and completed using the lamellar (less sharp) end of the Morlet dissector. Outcomes of 10 consecutive cases of thin manually dissected DSEK (TMDSEK) were prospectively analysed for thickness and visual outcome.ResultsMean graft thicknesses measured less than 100 μm at 1 month post surgery (mean thickness 90.7 μm, range 48–137 μm, SD 29.96 μm). Presoaked donor corneal pachymetry was strongly negatively correlated with graft thickness (correlation r=−0.75, P<0.05).DiscussionOur dissection technique achieves consistently thin endothelial donor corneal grafts that can be safely produced with minimal financial investment and no limitations on surgical time. This technique is likely to be of significant importance for a large proportion of the eye centres where microkeratomes may not be routinely available.

Limitations of Fourier-domain OCT

Limitations of Fourier-domain OCT At the time of writing this letter, the RTVue-100 (Optovue, Inc.) used byWylęgala et al. is the only commercially available Fourier-domain optical coherence tomography (OCT) device that can scan the anterior segment without ‘‘personal’’ modifications. Similar to all commercially available Fourier-domain OCT devices, it uses shorter wavelength light than the Visante-OCT (Carl Zeiss Meditec) (840 nm versus 1310 nm). It scans at a faster rate (26 000 A-scans/s) than time-domain OCT devices (2048 A-scans/s for Visante-OCT). This improves image quality by achieving higher resolution and also reducing motion artifact. We agree with the authors that Fourier-domain OCT can image Bowman layer as a distinct entity in a healthy cornea (Figure 1, A, in article). However, Figures 3, A, and 4, A, suggest that visualization of Bowman layer may be limited in the presence of corneal pathology. The use of short wavelength light may be a contributing factor. Using a modified Fourier-domain OCT, the Cirrus high-definition OCT (Carl Zeiss Meditec), Wong et al. imaged the termination of the Descemet/endothelium layer at the Schwalbe line. As this may potentially be important in analyzing the angle, do the authors have any information regarding the capabilities of the RTVue-100 in imaging this landmark? Wavelength light of 1310 nm has a good depth of penetration, including through nontransparent structures such as limbus and corneal opacity. Figure 6 illustrates the poor penetration of shorter wavelength light. Fourier-domainOCT visualization of theAhmed valve and ocular structures deeper than this is inferior to that with the Visante OCT. Similarly, in Figure 2, the root of the angle is not imaged adequately with the Fourier-domain OCT. We would not necessarily agree with the authors’ statement that ‘‘all angle structures