Localised gamma irradiation and experimental intraocular proliferation

A controlled study was undertaken to assess the effect of gamma irradiation on post-traumatic intraocular cellular proliferation. A standard perforating injury in the posterior segment of the rabbit eye was used to induce intraocular cellular proliferation and vitreo-retinal membrane formation. The site of injury was irradiated with an ophthalmic Cobalt60 applicator which provided a continuous source of gamma rays. Non-irradiated eyes developed traction retinal detachments associated with post-traumatic vitreo-retinal membranes. Irradiated eyes developed attenuated membranes or atrophic retinal scars, with the retina remaining attached. The membranes in non-irradiated eyes were highly cellular with abundant collagen, while irradiated membranes had fewer cells within a sparse collagen matrix. The episcleral fibroblasts, on autoradiographic studies appeared to be the main source of the cells that formed the proliferating tissue in both non-irradiated and irradiated eyes. In irradiated eyes both the inflammatory response and division of fibroblasts were delayed and reduced.

An ultrastructural study of retinal photoreceptor degeneration associated with bronchial carcinoma

We studied both eyes of a 66-year-old man with retinal degeneration and oat cell carcinoma of the bronchus. Retinal degeneration was most marked peripheral to the parafovea where photoreceptor cells and their outer segments were absent. Within the parafovea, photoreceptor cells remained but rod outer segments were absent and cone outer segments were fragmented and disorganized. The retinal pigment epithelium contained many immature melanin granules within melanolysosomes, suggesting abnormal melanin synthesis and resorption. We suggest that a pharmacologically active substance resembling a hormone produced by the tumor increased melanin synthesis in the pigment epithelium and that the increased melanin content in these cells compromised their ability to phagocytose and maintain normal turnover of photoreceptor outer segments. We believe these changes led to photoreceptor outer segment loss and subsequent degeneration of the photoreceptor cells.

Morphologic fluorescein angiographic, and light microscopic features of experimental choroidal neovascularization

We induced choroidal neovascularization in the rhesus monkey by impoverishing the blood supply to the inner retina and producing defects in Bruch's membrane by photocoagulation. Fourteen of 46 eyes undergoing photocoagulation developed neovascular fronds which were identified and categorized by histopathologic examination and fluorescein angiography. All new vessels gained access to the retina through defects in Bruch's membrane at the site of photocoagulation marks. In eight eyes the new vessels remained localized to the immediate vicinity of photocoagulation marks. In four eyes neovascular fronds infiltrated the subretinal space for distances up to 6 disk diameters from the point of entry into the retina. In the two eyes choroidovitreal neovascular complexes developed but rapidly regressed shortly after gaining the vitreous cavity. Fluorescein angiography demonstrated that all neovascular fronds were grossly incompetent to dye but that formed feeding channels had some degree of integrity. Light microscopic studies showed the proliferating networks to be composed of capillaries with well-formed basement membranes and more mature vessels with the basic structure of choroidal arteries and veins.

Evaluation of Microcollimated Pars Plana External Beam Radiation in the Porcine Eye

Purpose: To evaluate the clinical and histological side effects of a prototype stereotactic radiotherapy system delivering microcollimated external beam radiation through pars plana in porcine eyes.

Methods: Five Yucatan mini-swine (10 eyes) were randomized to five treatment groups. Eight eyes were dosed with X-ray radiation on Day 1, and two eyes served as untreated controls. Treated eyes received doses up to 60 Gy to the retina and up to 130 Gy to the sclera using single or overlapping beams. The treatment beams were highly collimated such that the diameter was approximately 2.5 mm on the sclera and 3 mm on the retinal surface. Fundus photography, fluorescein angiography (FA), and spectral domain optical coherence tomography (SD-OCT) were obtained on days 7, 30, 60, and 110. Images were examined by a masked grader and evaluated for abnormalities. Animals were sacrificed on day 111 and gross and histopathological analysis was conducted.

Results: Histological and gross changes to eye structures including conjunctiva and lens were minimal at all doses. Fundus, FA, and SD-OCT of the targeted region failed to disclose any abnormality in the control or 21 Gy treated animals. In the 42 and 60 Gy animals, hypopigmented spots were noted after treatment on clinical exam, and corresponding hyperfluorescent staining was seen in late frames. No evidence of choroidal hypoperfusion was seen. The histological specimens from the 60 Gy animals showed photoreceptor loss and displacement of cone nuclei.

Conclusion: Transcleral stereotactic radiation dosing in porcine eyes can be accomplished with no significant adverse events as doses less than 42 Gy.

Giant retinal tears

A giant retinal tear (GRT) is a full-thickness neurosensory retinal break that extends circumferentially around the retina for three or more clock hours in the presence of a posteriorly detached vitreous. Its incidence in large population-based studies has been estimated as 1.5% of rhegmatogenous retinal detachments, with a significant male preponderance, and bilaterality in 12.8%. Most GRTs are idiopathic, with trauma, hereditary vitreoretinopathies and high myopia each being causative in decreasing frequency. The vast majority of GRTs are currently managed with a pars plana vitrectomy; the use of adjunctive circumferential scleral buckling is debated, but no studies have shown a clear anatomical or visual advantage with its use. Similarly, silicone oil tamponade does not influence long-term outcomes when compared with gas. Primary and final retinal reattachment rates are achieved in 88% and 95% of patients, respectively. Even when the retina remains attached, however, visual recovery may be limited. Furthermore, fellow eyes of patients with a GRT are at higher risk of developing retinal tears and retinal detachment. Prophylactic treatment under these circumstances may be considered but there is no firm evidence of its efficacy at the present time.

Susceptibility of streptozotocin-induced diabetic rat retinal function and ocular blood flow to acute intraocular pressure challenge.

PURPOSE: To consider whether STZ-induced hyperglycemia renders rat retinal function and ocular blood flow more susceptible to acute intraocular pressure (IOP) challenge.

METHODS: Retinal function (electroretinogram, ERG) was measured during acute IOP challenge (10-100 mmHg, 5 mmHg increments, 3 min/step, vitreal cannulation) in adult Long-Evans rats (6-week old, citrate: n=6, STZ: n=10) 4 weeks after citrate buffer or streptozotocin (STZ, 65 mg/kg, blood glucose > 15 mmol/l) injection. At each IOP, dim and bright flash (-4.56, -1.72 log cd.s.m^-2) ERG responses were recorded to measure inner retinal and ON-bipolar cell function, respectively. Ocular blood flow (laser Doppler flowmetry, citrate; n=6, STZ; n=10) was also measured during acute IOP challenge. Retinae were isolated for qPCR analysis of nitric oxide synthase mRNA expression endothelial, eNos; inducible, iNos; neuronal, nNos).

RESULTS: STZ-induced diabetes increased the susceptibility of inner retinal (IOP at 50% response, 60.1, CI: 57.0-62.0 mmHg vs. citrate: 67.5, CI: 62.1-72.4 mmHg) and ON-bipolar cell function (STZ: 60.3, CI: 58.0-62.8 mmHg vs. citrate: 65.1, CI: 58.0-62.78 mmHg) and ocular blood flow (43.9, CI: 40.8-46.8 vs. citrate: 53.4, CI: 50.7-56.1 mmHg) to IOP challenge. Citrate eyes showed elevated eNos mRNA (+49.7%) after IOP stress, an effect not found in STZ-diabetic eyes (-5.7%, P<0.03). No difference was observed for iNos or nNos (P>0.05) following IOP elevation.

CONCLUSIONS: STZ-induced diabetes increased functional susceptibility during acute IOP challenge. This functional vulnerability is associated with a reduced capacity for diabetic eyes to upregulate eNOS expression and to autoregulate blood flow in response to stress.

Relationship between the magnitude of intraocular pressure during an episode of acute elevation and retinal damage four weeks later in rats

Purpose: To determine relationship between the magnitude of intraocular pressure (IOP) during a fixed-duration episode of acute elevation and the loss of retinal function and structure 4 weeks later in rats.

Methods: Unilateral elevation of IOP (105 minutes) was achieved manometrically in adult Brown Norway rats (9 groups; n = 4 to 8 each, 10–100 mm Hg and sham control). Full-field ERGs were recorded simultaneously from treated and control eyes 4 weeks after IOP elevation. Scotopic ERG stimuli were white flashes (26.04 to 2.72 log cd.s.m^-2). Photopic ERGs were recorded (1.22 to 2.72 log cd.s.m22) after 15 min of light adaptation (150 cd/m2). Relative amplitude (treated/control, %) of ERG components versus IOP was described with a cummulative normal function. Retinal ganglion cell (RGC) layer density was determined post mortem by histology.

Results: All ERG components failed to recover completely normal amplitudes by 4 weeks after the insult if IOP was 70 mmHg or greater during the episode. There was no ERG recovery at all if IOP was 100 mmHg. Outer retinal (photoreceptor) function demonstrated the least sensitivity to prior acute IOP elevation. ERG components reflecting inner retinal function were correlated with post mortem RGC layer density.

Conclusions: Retinal function recovers after IOP normalization, such that it requires a level of acute IOP elevation approximately 10 mmHg higher to cause a pattern of permanent dysfunction similar to that observed during the acute event. There is a ‘threshold’ for permanent retinal functional loss in the rat at an IOP between 60 and 70 mmHg if sustained for 105 minutes or more.

Clinical and experimental links between diabetes and glaucoma

Glaucoma is a leading cause of blindness. It is a multifactorial condition, the risk factors for which are increasingly well defined from large-scale epidemiological studies. One risk factor that remains controversial is the presence of diabetes. It has been proposed that diabetic eyes are at greater risk of injury from external stressors, such as elevated intraocular pressure. Alternatively, diabetes may cause ganglion cell loss, which becomes additive to a glaucomatous ganglion cell injury. Several clinical trials have considered whether a link exists between diabetes and glaucoma. In this review, we outline these studies and consider the causes for their lack of concordant findings. We also review the biochemical and cellular similarities between the two conditions. Moreover, we review the available literature that attempts to answer the question of whether the presence of diabetes increases the risk of developing glaucoma. At present, laboratory studies provide robust evidence for an association between diabetes and glaucoma.

Extremely Complex Populations of Small RNAs in the Mouse Retina and RPE/Choroid

Purpose: MicroRNAs (miRNAs) are small non-coding RNAs of ~18-22 nucleotides in length that regulate gene expression. They are widely expressed in the retina, being both required for its normal development and perturbed in disease. The aim of this study was to apply new high-throughput sequencing techniques to more fully characterise the microRNAs and other small RNAs expressed in the retina and retinal pigment epithelium (RPE)/choroid of the mouse.

Methods: Retina and RPE/choroid were dissected from eyes of 3 month-old C57BL/6J mice. Small RNA libraries were prepared and deep sequencing performed on a Genome Analyzer (Illumina). Reads were annotated by alignment to miRBase, other non-coding RNA databases and the mouse genome.

Results: Annotation of 9 million reads to 320 microRNAs in retina and 340 in RPE/choroid provides the most comprehensive profiling of microRNAs to date. Two novel microRNAs were identified in retina. Members of the sensory organ specific miR-183,-182,-96 cluster were amongst the most highly expressed, retina-enriched microRNAs. Remarkably, microRNA 'isomiRs', which vary slightly in length and are differentially detected by Taqman RT-PCR assays, existed for all the microRNAs identified in both tissues. More variation occurred at the 3' ends, including non-templated additions of T and A. Drosha-independent mirtron microRNAs and other small RNAs derived from snoRNAs were also detected.

Conclusions: Deep sequencing has revealed the complexity of small RNA expression in the mouse retina and RPE/choroid. This knowledge will improve the design and interpretation of future functional studies of the role of microRNAs and other small RNAs in retinal disease.

Fundus autofluorescence in patients with retinal pigment epithelial (RPE) tears: an in-vivo evaluation of RPE resurfacing

Aim: Investigate RPE resurfacing by changes in fundus autofluorescence (AF) in patients with retinal pigment epithelial (RPE) tears secondary to age-related macular degeneration (AMD).

Methods: A retrospective case series of patients presenting with RPE tears from 1 March 2008 to 1 April 2011. The pattern and area of AF signal distribution in RPE tears were evaluated. The change in the size of the area of debrided RPE over the follow-up period was used as the main outcome measure. A reduction in this area was termed “RPE resurfacing”, and an enlargement termed “progression of RPE cell loss”.

Results; Thirteen patients (14 eyes) with RPE tears (mean age 82 years) were included in this study. The mean baseline area of reduced AF signal was 4.1 mm2 (range 0.33–14.9, median 0.29). “Resurfacing” of the RPE occurred in ten eyes and “progression of RPE cell loss” in four eyes after a median follow-up of 11.5 months (range, 1–39). The mean area of healing was 2.0 mm2, and progression was 1.78 mm2.

Conclusion: A consistent AF pattern was observed in patients with RPE tears. RPE resurfacing over the area of the RPE tear occurred, to a varying degree, in the majority of the cases.

Treatments for macular oedema following central retinal vein occlusion: systematic review

Objectives: To review systematically the randomised controlled trial (RCT) evidence for treatment of macular oedema due to central retinal vein occlusion (CRVO).

Data sources: MEDLINE, EMBASE, CDSR, DARE, HTA, NHSEED, CENTRAL and meeting abstracts (January 2005 to March 2013).

Study eligibility criteria, participants and interventions: RCTs with at least 12 months of follow-up assessing pharmacological treatments for CRVO were included with no language restrictions.

Study appraisal and synthesis methods: 2 authors screened titles and abstracts and conducted data extracted and Cochrane risk of bias assessment. Meta-analysis was not possible due to lack of comparable studies.

Results: 8 studies (35 articles, 1714 eyes) were included, assessing aflibercept (n=2), triamcinolone (n=2), bevacizumab (n=1), pegaptanib (n=1), dexamethasone (n=1) and ranibizumab (n=1). In general, bevacizumab, ranibizumab, aflibercept and triamcinolone resulted in clinically significant increases in the proportion of participants with an improvement in visual acuity of ≥15 letters, with 40–60% gaining ≥15 letters on active drugs, compared to 12–28% with sham. Results for pegaptanib and dexamethasone were mixed. Steroids were associated with cataract formation and increased intraocular pressure. No overall increase in adverse events was found with bevacizumab, ranibizumab, aflibercept or pegaptanib compared with control. Quality of life was poorly reported. All studies had a low or unclear risk of bias.

Limitations: All studies evaluated a relatively short primary follow-up (1 year or less). Most had an unmasked extension phase. There was no head-to-head evidence. The majority of participants included had non-ischaemic CRVO.

Conclusions and implications of key findings: Bevacizumab, ranibizumab, aflibercept and triamcinolone appear to be effective in treating macular oedema secondary to CRVO. Long-term data on effectiveness and safety are needed. Head-to-head trials and research to identify ‘responders’ is needed to help clinicians make the right choices for their patients. Research aimed to improve sight in people with ischaemic CRVO is required.

Intravitreal Injection of Normal Saline Induces Retinal Degeneration in the C57BL/6J Mouse

Purpose: To investigate the adverse effect of intravitreal injection of normal saline (NS) and phosphate buffered saline (PBS) in mouse eyes.

Methods: NS or PBS was injected intravitreally into C57BL/6J mouse eyes. Retinal lesions were monitored by fundus imaging, spectral-domain optical coherence tomography (SD-OCT), and histological investigations. Retinal immune gene expression was determined by real-time polymerase chain reaction (PCR). The toxic effect of NS and PBS or retinal protein from NS- or PBS-injected eyes on retinal pigment epithelium (RPE) was tested in B6-RPE-07 mouse RPE cell cultures.

Results: Intravitreal injection of NS dose-dependently induced localized retinal lesion in mice. Histological investigations revealed multiple vacuoles in photoreceptor outer segments and RPE cells. The lesions recovered over time and by 3 weeks post injection the majority of lesions vanished in eyes receiving 1 μl NS. Inflammatory genes, including TNF-α, IL-1β, IL-6, iNOS, and VEGF were upregulated in NS injected eyes. Intravitreal injection of PBS did not cause any pathology. The treatment of B6-RPE07 cells with 30% PBS or 30% NS did not affect RPE viability. However, incubation of 1-μg/ml retinal protein from NS-injected eyes, but not PBS-injected eyes induced RPE cell death.

Conclusion: NS is toxic to the C57BL/6J mouse retina and should not be used as a vehicle for intraocular injection. PBS is not toxic to the retina and is a preferred vehicle.

Translational Relevance: NS is not a physiological solution for intraocular injection in the C57BL/6J mice and questions its suitability for intraocular injection in other species, including human.

Traumatic Graft Dehiscence after Penetrating Keratoplasty

Objective: To determine the incidence and to explore the risk factors for traumatic graft dehiscence after penetrating keratoplasty. Design: Retrospective case note review. Participants: Five hundred seventy-two consecutive cases were included. Intervention: All subjects who underwent penetrating keratoplasty in 1 regional center between 1992 and 2004 inclusive. Main Outcome Measures: Cases that experienced postoperative traumatic graft dehiscence were identified. Results from 12 other similar studies were pooled for comparison. Results: Fifteen eyes (2.6%) were treated for traumatic wound dehiscence after penetrating keratoplasty. The most striking feature of this series was the bimodal relationship of age and cause of graft dehiscence, with older patients involved in falls and younger patients in accidental or deliberate trauma. Factors that may influence the risk of traumatic graft dehiscence are discussed, in the light of the present findings and pooled data from previous series. Conclusions: This case series indicates that there is long-term risk of traumatic wound dehiscence after penetrating keratoplasty. Younger patients, especially males, should be made aware that their eye, after keratoplasty, will always be vulnerable to injury. High-risk situations should be avoided if possible. Older patients at particular risk should have adequate risk reduction strategies, social support, and supervision, in particular to minimize the risk of falls. © 2008 American Academy of Ophthalmology.

The incidence and rate of rhegmatogenous retinal detachment seven years after cataract surgery in patients with high myopia

Background: Cataract extraction is the most commonly performed surgery in the National Health Service. Myopia increases the risk of postoperative rhegmatogenous retinal detachment (RRD). The aim of this study was to determine the incidence and rate of RRD seven years after cataract extraction in highly myopic eyes. Methods: Retrospective review was performed of notes of all high myopes (axial length 26.0 mm or more) who underwent cataract extraction during the study period in one centre. Results: 84 eyes met the study criteria. Follow-up time from surgery was 93 to 147 months (median 127 months). The average axial length was 28.72 mm (sd 1.37). Two eyes developed post-operative RRD; the incidence was 2.4% and the rate one RRD per 441.6 person-years. The results of 15 other studies on the incidence of RRD after cataract extraction in high myopia were pooled and combined with our estimate. Conclusion: Both patients in our study who developed RRD had risk factors for this complication as well as high myopia. Risk factors are discussed in the light of our results and the pooled estimate. Our follow-up time is longer than most. Future case series should calculate rates to allow meaningful comparison of case series. © The Ulster Medical Society, 2009.