Association Between Season, Temperature and Causative Organism in Microbial Keratitis in the UK.

PURPOSE: Microbial keratitis (MK) is a major cause of corneal blindness worldwide. Variations in season and temperature can affect MK incidence due to specific causative organisms; however, few studies have examined these factors in the UK. METHODS: Retrospective review of all corneal scrapes from patients with MK presenting to Manchester Royal Eye Hospital, UK, between January 2004 and December 2015. Manchester's monthly temperature data were obtained from Met Office UK. Analysis was performed using logistic regression. RESULTS: From 4229 corneal scrapes, 1539 organisms grew (90.6% bacteria, 7.1% fungi, and 2.3% Acanthamoebae sp.). Gram-positive bacteria grew with increasing temperature [odds ratio (OR) 1.62, 95% CI: 1.11-2.39, P = 0.014], and fungi grew with decreasing temperature (OR 0.29, 95% CI: 0.16-0.51, P < 0.001). Moraxella sp. grew with decreasing temperature (OR 0.91, 95% CI: 0.86-0.96, P = 0.001). Compared with winter, overall culture positivity was significantly less likely in summer (OR 0.57, 95% CI: 0.38-0.87, P = 0.008) and spring (OR 0.65, 95% CI: 0.43-0.99, P = 0.045). Gram-negative bacteria were more likely in summer (OR 1.48, 95% CI: 1.06-2.09, P = 0.022) and autumn (OR 1.75, 95% CI: 1.24-2.47, P = 0.001). Candida sp. were less likely in summer (OR 0.25, 95% CI: 0.07-0.82, P = 0.027) and autumn (OR 0.18, 95% CI: 0.05-0.62, P = 0.009), and Acanthamoeba sp. were less likely in summer (OR 0.39, 95% CI: 0.15-0.92, P = 0.037) and spring (OR 0.26, 95% CI: 0.08-0.69, P = 0.011). CONCLUSIONS: Herein we report variation in the incidence of MK-causing organisms by season and temperature; this finding may aid clinicians in predicting possible causative organisms for MK at differing times of the year.

Enlarging the big-bubble during deep anterior lamellar keratoplasty.

PURPOSE: During big-bubble deep anterior lamellar keratoplasty, a bubble that is not large enough can be formed. Further air injection can result in the rupture of the posterior lamella, necessitating conversion to penetrating keratoplasty. We describe some techniques to safely enlarge the big-bubble in such a circumstance. METHODS: In cases in which a white-margin bubble forms that has extended to the trephination margin, the bubble is collapsed and the margins are extended by blunt dissection. For cases of an undersized clear-margin bubble, the bubble is enlarged by gentle injection of a cohesive ophthalmic viscosurgical device into the bubble cavity. RESULTS: Using these techniques, big-bubbles were safely extended beyond the trephination margin for both white- and clear-margin bubbles. CONCLUSIONS: An undersized big-bubble can safely be extended using blunt dissection for white-margin bubbles and ophthalmic viscosurgical device injection for clear-margin bubbles.

Rupture pressure of the posterior lamella obtained during big-bubble deep anterior lamellar keratoplasty.

PURPOSE: To investigate the pressure required to rupture the posterior lamella obtained during the presumed Descemet membrane-baring big-bubble technique of deep anterior lamellar keratoplasty (DALK). METHODS: DALK using the big-bubble technique was carried out on donor corneoscleral discs mounted on an artificial anterior chamber. Once the anterior lamella was removed, the chamber was connected to a mercury manometer. The pressure inside the chamber was increased until rupture occurred or the manometer reached its measurement limit. RESULTS: The deep lamella ruptured at 252 mm Hg in one cornea, at 270 mm Hg in another, and had not ruptured at 300 mm Hg (upper limit of the manometer) in the remaining 18 donor corneas. CONCLUSIONS: The posterior lamella of big-bubble DALK probably confers significant structural integrity on the globe.

Donor preparation using pneumatic dissection in endothelial keratoplasty: DMEK or DSEK?

PURPOSE: To determine if residual stroma remains on the Descemet membrane when pneumatic dissection is used to prepare donor tissue for endothelial keratoplasty. METHODS: Pneumatic dissection using a posterior peripheral needle insertion was carried out on 5 eye bank corneas. Samples were then sent for histological analysis. RESULTS: A thin layer of stroma remained on the Descemet membrane in all the samples. The average central stromal thickness was 12.4 µm (range 6.5-20.0 µm). CONCLUSIONS: Endothelial keratoplasty using pneumatic dissection to prepare donor tissue should be considered a form of Descemet stripping endothelial keratoplasty and not Descemet membrane endothelial keratoplasty. If future studies show excellent visual results using pneumatic dissection for endothelial keratoplasty, then removal of all donor stroma may be unnecessary.

Use of triamcinolone to judge needle depth in big-bubble deep anterior lamellar keratoplasty.

PURPOSE: To report a technique for judging needle depth in the corneal stroma during big-bubble deep anterior lamellar keratoplasty (DALK). METHODS: With the anterior chamber full of air, a dilute suspension of washed triamcinolone crystals is injected to "wash" over the air bubble. Some crystals are trapped between air and endothelium, making the posterior limit of the cornea easier to identify. The needle is then inserted into deep stroma, and big-bubble DALK is performed in the usual manner. RESULTS: This technique was used in 10 keratoconic eyes undergoing big-bubble DALK. No adverse effects of triamcinolone use were found in any eyes. CONCLUSIONS: This technique provides another option for surgeons who wish to accurately judge needle depth during big-bubble DALK.

Riboflavin/UVA collagen cross-linking-induced changes in normal and keratoconus corneal stroma.

PURPOSE: To determine the effect of Ultraviolet-A collagen cross-linking with hypo-osmolar and iso-osmolar riboflavin solutions on stromal collagen ultrastructure in normal and keratoconus ex vivo human corneas. METHODS: Using small-angle X-ray scattering, measurements of collagen D-periodicity, fibril diameter and interfibrillar spacing were made at 1 mm intervals across six normal post-mortem corneas (two above physiological hydration (swollen) and four below (unswollen)) and two post-transplant keratoconus corneal buttons (one swollen; one unswollen), before and after hypo-osmolar cross-linking. The same parameters were measured in three other unswollen normal corneas before and after iso-osmolar cross-linking and in three pairs of swollen normal corneas, in which only the left was cross-linked (with iso-osmolar riboflavin). RESULTS: Hypo-osmolar cross-linking resulted in an increase in corneal hydration in all corneas. In the keratoconus corneas and unswollen normal corneas, this was accompanied by an increase in collagen interfibrillar spacing (p<0.001); an increase in fibril diameter was also seen in two out of four unswollen normal corneas and one unswollen keratoconus cornea (p<0.001). Iso-osmolar cross-linking resulted in a decrease in tissue hydration in the swollen normal corneas only. Although there was no consistent treatment-induced change in hydration in the unswollen normal samples, iso-osmolar cross-linking of these corneas did result in a compaction of collagen fibrils and a reduced fibril diameter (p<0.001); these changes were not seen in the swollen normal corneas. Collagen D-periodicity was not affected by either treatment. CONCLUSION: The observed structural changes following Ultraviolet-A cross-linking with hypo-osmolar or iso-osmolar riboflavin solutions are more likely a consequence of treatment-induced changes in tissue hydration rather than cross-linking.

Residual corneal stroma in big-bubble deep anterior lamellar keratoplasty: a histological study in eye-bank corneas.

AIM: To determine if residual corneal stroma remains on the recipient posterior lamella in big-bubble deep anterior lamellar keratoplasty (DALK). METHODS: Pneumodissection using the big-bubble technique was carried out on eye-bank corneas mounted on an artificial anterior chamber. Samples that had a successful big-bubble formation were sent for histological evaluation to determine if any residual stroma remained on the Descemet membrane (DM). RESULTS: Big-bubble formation was achieved in 32 donor corneas. Two distinct types of big-bubble were seen: the bubble had either a white margin (30 corneas) or a clear margin (two corneas). The posterior lamellae of all the white margin corneas showed residual stroma on DM with a mean central thickness of 7.0 µm (range 2.6-17.4 µm). The clear margin corneas showed no residual stroma on DM. CONCLUSION: It should no longer be assumed that big-bubble DALK, where the bubble has a white margin, routinely bares DM. True baring of DM may only occur with the less commonly seen clear margin bubble.

Eccentric capsulorhexis and postoperative dysphotopsia following phacoemulsification.

We report a case of troublesome visual symptoms or dysphotopsia in a 68-year-old patient after right phacoemulsification and implantation of a 3-piece AcrySof(R) MA60BM acrylic intraocular lens (IOL) (Alcon) in the capsular bag. The patient described multiple horizontal streaks in dim lighting conditions with light sources in the right temporal visual field. The anterior capsulorhexis was eccentric, leaving the nasal optic edge and site of polypropylene haptic insertion uncovered by the semi-opaque anterior capsule and the probable source of the flare images. Miotic therapy was poorly tolerated and IOL exchange declined. The case illustrates the importance of creating a central capsulorhexis smaller than the IOL optic to reduce the risk photic phenomena and edge effect with square-edged IOLs.