Nicholas L Occleston

Risk factors for proliferative vitreoretinopathy after primary vitrectomy: a prospective study

AIM To assess clinical variables and vitreous protein as risk factors for the development of postoperative proliferative vitreoretinopathy (PVR). METHODS A prospective study was conducted on 140 patients with a rhegmatogenous retinal detachment in whom a primary vitrectomy was performed. 12 clinical variables were recorded and vitreous samples obtained for measurement of protein concentration. Univariate and multivariate logistic regression analysis was used to determine the risk factors for PVR. RESULTS Complete data were available for 136 of 140 patients. 40 of the 136 patients (29.4%) developed postoperative PVR. Univariate regression revealed that significant (p<0.05) risk factors included aphakia, presence of preoperative PVR, size of detachment, the use of silicone oil, and high vitreous protein level. Multivariate regression analysis revealed only aphakia (odds ratio 2.72), the presence of preoperative PVR (odds ratio 3.01), and high vitreous protein concentration (odds ratio 1.11) to be significant (p<0.05) independent, predictive risk factors for the development of PVR. CONCLUSIONS This study has shown that the significant risk factors for PVR are preoperative PVR, aphakia, and high vitreous protein levels. Two models (clinical factors only and clinical factors and vitreous protein) were constructed to predict the probability of developing postoperative PVR and may be used to identify those at risk for possible intravitreal pharmacological treatment.

Ultrastructural changes during contraction of collagen lattices by ocular fibroblasts

Contraction and scarring of the cornea and conjunctiva following disease or injury are major causes of visual morbidity. The aim of this study was to identify any specific ultrastructural features of ocular fibroblast behavior in different collagen lattices in order to understand some of the mechanisms of cell‐mediated contraction. Normal human Tenons capsule fibroblasts were cultured within both restrained and floating collagen lattices for periods of up to 13 days and then analyzed using transmission electron microscopy. The contractile force of these fibroblasts was also tested using the culture force monitor, an instrument capable of measuring the minute forces exerted by cells within a collagen lattice. The results showed differences in the behavior of fibroblasts cultured in the two gel models. The features seen in restrained gels suggest that fibroblasts were actively migrating across and through the lattice. These migratory features were not seen to the same extent in untethered gels, which lack the inherent tension and support of the tethered model. We hypothesize that contraction of the collagen matrix in tethered lattices is due to cellular migration and that this fact cannot be ascertained from untethered gels. Both lattice models have experimental value, but it is important to appreciate what mechanical signals cells receive from the matrix in order to understand cellular behavior.

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.

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.

Long term growth arrest of human Tenon's fibroblasts following single applications of beta radiation

AIMS/BACKGROUND Antimetabolites are increasingly used to manipulate the healing response after filtration surgery, but problems with thin cystic blebs have been encountered with the liquid agents commonly used such as 5-fluorouracil and mitomycin C. β Radiation appears to be a useful adjuvant treatment for preventing scarring after trabeculectomy, resulting in diffuse rather than cystic bleb formation, but much of the basic cell biology of the ocular fibroblast response to β radiation remains unclear. The effects of β radiation on ocular fibroblast proliferation and cell cycling were investigated to determine the nature and duration of these effects on these cells. METHODS In vitro cell culture techniques were used to investigate fibroblast proliferation. Cell viability was studied using trypan blue dye exclusion. The effect of radiation on cell cycling was investigated using bromodeoxyuridine uptake. p53 expression was demonstrated using immunocytochemistry . RESULTS β Radiation inhibited fibroblast proliferation in a dose dependent manner. Early cell death was not a prominent feature, but irradiated fibroblasts demonstrated a rapid onset and sustained period of growth arrest. p53 expression was found to be increased in irradiated cells. CONCLUSIONS Single doses of β radiation significantly inhibit Tenon’s capsule fibroblast proliferation in vitro over a 28 day period. This inhibition is the result of a rapid onset and sustained period of growth arrest in irradiated cells. Irradiated fibroblasts show an increase in p53 expression, a nuclear phosphoprotein which has been associated with control of the cell cycle. Single applications of β radiation may be an effective treatment for the prevention of bleb failure as a result of prolonged growth arrest of Tenon’s capsule fibroblasts.