Mark R Wilkins

Standardized arcuate keratotomy for postkeratoplasty astigmatism

Purpose: To assess the effect of standardized, paired arcuate keratotomy (AK) on the change in astigmatism in postkeratoplasty eyes. Setting: Moorfields Eye Hospital, London, United Kingdom. Methods: A retrospective review was conducted of 20 eyes of 19 patients having the same AK procedure regardless of the magnitude of the preoperative astigmatism. Each eye had a pair of 60‐degree arc length incisions placed in the corneal stroma. The incisions were 600 μm deep and 6.0 mm apart. The preoperative and postoperative refractions and complications were analyzed. Astigmatic change was analyzed without regard to axis, as surgically induced refractive change, and using a modified polar plot of change in astigmatism. Results: The mean cylinder was reduced from −10.99 diopters (D) ± 4.26 (SD) to −3.33 ± 2.18 D. There was no significant change in the mean spherical equivalent. There was a strong correlation between the magnitude of the preoperative cylinder and the magnitude of the change in astigmatism (R2 = 0.76). In 3 eyes, the surgically induced axis of astigmatism was more than 15 degrees from that expected. Conclusions: In postkeratoplasty eyes, the change in the magnitude of astigmatism induced by standardized AK was proportional to the preoperative magnitude of astigmatism. Arcuate nomograms for congenital astigmatism have no role in the management of astigmatism in postkeratoplasty eyes.

Descemet membrane endothelial keratoplasty

Descemet membrane endothelial keratoplasty (DMEK) allows for selective replacement of damaged endothelial cells, using only donor Descemets membrane with endothelium. However, early adoption by corneal surgeons has been limited (illustrated by graft registry reports: 0.7% all corneal transplants in the USA; 0.4% in Australia for 2011) due to challenges in donor preparation and surgical technique. Recently, innovative donor preparation techniques may improve availability of pre-stripped DMEK donors from eye banks. The refinement of donor insertion and manipulation techniques has also improved outcomes and reduced graft detachment rates—still, the most common postoperative complication following DMEK. Randomised studies are needed to compare clinical practices and surgeon preferences, such as intraoperative use of long-acting gas, early versus late intervention of graft detachments and postoperative steroid management. A review of current literature reveals that most publications to date are reports from similar study cohorts by surgeons who pioneered and advocate this technique. Thus, more long-term clinical studies in other tertiary centres are required in order to confirm if the purported advantages of DMEK such as improved visual outcomes and reduced graft rejection are replicable among most corneal surgeons.

Sponge delivery variables and tissue levels of 5-fluorouracil

AIM To study how the delivery of 5-fluorouracil (5-FU) to ocular tissues is affected by altering delivery variables. METHOD Sponge(s) soaked in radiolabelled 5-FU were placed between the conjunctiva and sclera of pig eyes. Application time, sponge size, sponge make (Altomed, Weck, Merocel), and 5-FU concentration were varied. Conjunctival and scleral tissue levels were determined in samples taken from the application site. RESULTS Dose-response curves for scleral and conjunctival 5-FU levels against application time showed increasing tissue levels that reached a plateau after 2–3 minutes. Application beyond 3 minutes did not increase tissue levels. There was no difference in tissue levels between 7×4 and 3.5×2 mm sponges. Altomed sponges produced 5-FU tissue levels that were twice as high as those obtained with Weck-cell (p<0.01) or Merocel (p<0.02) sponges. Changing the 5-FU concentration from 25 mg/ml to 6.25 mg/ml reduced the conjunctival concentration by a factor of 3.5 (p<0.003). CONCLUSION Application time up to 3 minutes, sponge make, and 5-FU concentration can have a large effect on the tissue delivery of 5-FU. Application time beyond 3 minutes, using 3.5×2 mm or 7×4 mm sponges, and replacing sponges every minute did not have a significant effect on tissue levels. This study models the effect that different variables can have on the ocular tissue levels of an antimetabolite applied intraoperatively.

En face optical coherence tomography angiography for corneal neovascularisation

Background/aim Recently, there has been an increasing clinical need for objective evaluation of corneal neovascularisation, a condition which cause significant ocular morbidity. We describe the use of a rapid, non-invasive ‘en face’ optical coherence tomography angiography (OCTA) system for the assessment of corneal neovascularisation. Methods Consecutive patients with abnormal corneal neovascularisation were scanned using a commercially available AngioVue OCTA system (Optovue, Fremont, California, USA) with the split-spectrum amplitude decorrelation angiography algorithm, using an anterior segment lens adapter. Each subject had four scans in each eye by a trained operator and two independent masked assessors analysed all images. Main outcome measures were scan quality (signal strength, image quality), area of neovascularisation and repeatability of corneal vascular grade. Results We performed OCTA in 20 patients (11 men, 9 women, mean age 49.27±17.23 years) with abnormal corneal neovascularisation. The mean area of corneal neovascularisation was 0.57±0.30 mm2 with a mean neovascularisation grade of 3.5±0.2 in the OCTA scans. We found the OCTA to produce good quality images of the corneal vessels (signal strength: 36.95±13.97; image quality score 2.72±1.07) with good repeatability for assessing neovascularisation grade (κ=0.84). Conclusions In this preliminary clinical study, we describe a method for acquiring angiography images with ‘en face’ views, using an OCTA system adapted for the evaluation of corneal neovascularisation. Further studies are required to compare the scans to other invasive angiography techniques for the quantitative evaluation of abnormal corneal vessels.

Understanding and controlling the scarring response: The contribution of histology and microscopy

In response to injury, the body usually initiates a full and swift wound healing response resulting in reconstructed, repaired tissue. In certain instances, due to a variety of factors, this may not happen, an example being chronic granulating venous leg ulcers. At the other extreme, the wound may heal excessively, producing disabling hypertrophic scarring such as can occur following large, deep burn injuries. Our group is interested in the surgical treatment of the eye disease glaucoma. As will be explained, the successful surgical treatment of this disease depends on a reduced scarring response at the end of wound healing. The purpose of this article is to give an overview of our microscopic and histological experimental work which has furthered our understanding of tissue repair, particularly the scarring response and its potential modification for successful glaucoma surgery. Microsc. Res. Tech. 42:317–333, 1998.

Comparison of Early Surgical Experience and Visual Outcomes of DSAEK and DMEK.

Purpose: To compare the outcomes of 2 different endothelial keratoplasty (EK) techniques [Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK)] sequentially learned by a corneal fellow. Methods: This is a retrospective comparative audit of all patients undergoing EK by 1 surgeon (M.G.) during fellowship. Surgical and functional success of both procedures were compared. Surgical success was evaluated by comparing short-term complications, and functional success by comparing visual outcomes in patients with Fuchs endothelial dystrophy (FED). Results: Twenty-six patients were included in the review (DSAEK 12 and DMEK 14). Phacoemulsification was combined with EK in 14 patients (DSAEK 6 and DMEK 8). The average follow-up duration was 3.5 months. Partial detachment requiring rebubbling was slightly more common in the DMEK group (DSAEK 1 and DMEK 5); total detachment requiring repositioning was less in the DMEK group (DSAEK 2 and DMEK 1). Only 1 patient experienced primary graft failure due to complicated graft insertion, and this patient underwent DMEK. Functional analysis included 14 patients with FED (DSAEK 7 patients, preoperative 6/18, postoperative 6/12; DMEK 7 patients, preoperative 6/12, postoperative 6/6). Average visual improvement was greater in the DMEK group (3.3 lines) than in the DSAEK group (1.3 lines; P = 0.047). In DMEK patients, the average postoperative endothelial cell count was 1612 cells per square centimeter. Conclusions: Contrary to common expectation, there were similar rates of surgical success while learning DMEK and DSAEK. Visual improvement in patients with FED undergoing DMEK was significantly better at this early point of comparison.

Spectacle use after routine cataract surgery

Aims: To measure spectacle dependence following bilateral monofocal intraocular lens (IOL) implantation and assess how it is predicted by postoperative refraction. Methods: 300 cataract patients had bilateral phacoemulsification surgery with monofocal IOL implantation. A spherical equivalent of 0 to −0.5 D was targeted. Three months after surgery, patients answered a questionnaire and had a spectacle refraction. Refractions were converted into vector notation. Logistic regression was used to evaluate whether spectacle dependence for near and distance was related to overall refractive error, spherical error, signed spherical error and astigmatic error. Results: 169 patients attended for assessment. 38 wore distance glasses, and 160 wore reading glasses either some or all of the time. The mean right spherical equivalent was −0.03 D, and the mean right cylinder was −0.64 D. Left outcomes were similar. Patients were 34 times more likely to always use distance glasses per dioptre of astigmatic error in the better eye (p<0.003), but there was no significant increase in the likelihood of wearing distance glasses with spherical error (odds ratio = 3.85, p>0.15). Similar effects were seen for both the better and worse eyes. Near-spectacle use was not dependent on astigmatic error (odds ratio = 0.22, p>0.12). It was only related to the signed spherical error in the worse eye with hypermetropic patients 6.74 times more likely to always wear spectacles per dioptre of positive spherical error (p<0.005). Conclusions: Following bilateral monofocal intraocular lens implantation, small levels of overall refractive error, in either eye, particularly astigmatism, predict distance-spectacle dependence, whereas spherical ammetropia in the range of ±1.0 D does not. Hypermetropia in the worse eye, but not astigmatism, predicts reading-spectacle dependence.

Differential precision of corneal Pentacam HR measurements in early and advanced keratoconus

Background/aims Serial Scheimpflug corneal tomography to monitor the progression of keratoconus has become standard practice in most countries where corneal cross-linking is available. The tomographic definitions of progression are, however, poorly defined. The aims of this study were: (a) to estimate the 95% limits of intraobserver and interobserver agreement of corneal shape parameters on Pentacam in patients with keratoconus and (b) to investigate whether these limits of agreement varied according to disease severity. Methods 96 adult patients with keratoconus and no corneal scarring or history of previous surgery were recruited from a corneal clinic in a tertiary ophthalmology hospital. One eye of each subject was scanned twice by each of the two observers with the Pentacam HR. 95% limits of intraobserver and interobserver agreement for K1, K2, Kmax and corneal thickness at the thinnest corneal location (TCT) were calculated. Results Reproducibility of keratometry measures was better for early keratoconus than advanced keratoconus. In patients of Pentacam-derived Krumeich stage 1 or 2, the 95% limits of interobserver agreement for Kmax were from −0.90 to 1.01. In patients of Pentacam-derived Krumeich stage >2, the 95% limits of interobserver agreement for Kmax were from −3.71 to 3.86. Conclusions Keratometric measurements on Pentacam HR are less reproducible in advanced keratoconus than in early keratoconus. In patients of Pentacam-derived Krumeich stage 1 or 2, an increase in K1, K2 or Kmax of more than 1 dioptre is likely to represent the real change in the corneal shape.

Microbial keratitis after corneal laser refractive surgery

Corneal laser refractive surgery is increasingly being performed on patients with the aim of improving unaided vision. Most candidates for surgery have excellent spectacle- or contact lens-corrected vision. Although microbial keratitis following refractive surgery is a rare complication, and usually has a good visual outcome, it can be sight-threatening. The spectrum of pathogens differs to other causes of microbial keratitis, such as contact lens-associated keratitis, and a different management approach is required. Postoperatively, patients are prescribed topical steroids and broad-spectrum topical antibiotics, typically fluoroquinolones. These do not cover unusual organisms, such as fungi, Nocardia, Acanthamoeba and some atypical mycobacteria. In post-laser-assisted in situ keratomileusis microbial keratitis, the lamellar flap should be lifted to acquire samples for specific microbiological examination, including these atypical organisms. Confocal microscopy is a noninvasive test that provides morphological information, and is operator dependent, but may assist in the rapid diagnosis of fungal, Acanthamoeba or Norcardia keratitis. PCR is not in widespread use, but has high sensitivity and specificity, and may facilitate early diagnosis and specific treatment of the causative organism, which is critical in obtaining the best clinical outcome.

In vivo production of interferon beta by human Tenon's fibroblasts; a possible mediator for the development of chronic conjunctival inflammation

Background: Chronic inflammation may develop from failure of the immune system to deactivate itself during resolution of the wound healing response, and is recognised as a major risk factor for trabeculectomy failure. Fibroblast/T cell interactions may contribute to aggressive scarring. Our previous research showed that in vitro human Tenons fibroblast produced interferon β was responsible for preventing T cell apoptosis, suggesting that this interaction could contribute to the development of chronic inflammation. Methods: Immunohistological techniques were used to investigate the in vivo components of this particular fibroblast/T cell interaction in conjunctival biopsies from glaucoma patients undergoing filtration surgery. Results: Fibroblast produced interferon β and T lymphocytes were identified in human conjunctiva. Conclusion: The components of fibroblast mediated prevention of T cell apoptosis were identified in vivo, suggesting that the development of this interaction is possible and that it may contribute to the development of chronic inflammation and excessive scarring.