Murray C. Killingsworth

Evolution of geographic atrophy of the retinal pigment epithelium

The aim of this study was to trace the evolution of geographic atrophy (GA) by clinical documentation and by clinico-morphological correlation in representative eyes. Geographic atrophy commonly commenced within a parafoveal band of incipient atrophy of varying width, characterised by semisolid drusen and a microreticular pigment pattern. Progession of atrophy mostly skirted fixation and visual acuity was a poor guide to the functional impact, an estimate of the percentage of fovea involved proving a more useful clinical parameter. The rate of progression slowed once GA had involved all the retina affected by incipient atrophy and the risk of choroidal neovascularization appeared to decline.An earlier histological classification of the evolution of GA is revised according to the ultras- tructural findings. Membranous debris was not previously recognised and its contribution to the findings in incipient atrophy and to dot-like drusen is described.

Senile macular degeneration : The involvement of immunocompetent cells

Senile macular degeneration (SMD) is a leading cause of legal blindness in western countries. The role of immunocompetent cells in the pathogenesis of this disease has not been widely recognised. In this work specimens were studied by electron microscopy to provide ultrastructural details of the role of immunocompetent cells in early, intermediate and late stages of the disease. Additionally, we have analysed the frequency and distribution of inflammatory cellular infiltrates using wax histology. The results illustrate the involvement of macrophage-series cells, fibroblasts, lymphocytes and mast cells in neovascularisation, atrophy of the retinal pigment epithelium and the breakdown of Bruchs membrane. These observations, together with previous clinicopathological studies, have led us to suggest that SMD has a chronic inflammatory component.

Reticular pseudodrusen. A risk factor in age-related maculopathy.

Background: Reticular pseudodrusen refer to a yellow interlacing network 125µm to 250µm wide appearing first in the superior outer macula and then extending circumferentially and beyond. Unlike true drusen, they do not fluoresce on fluorescein or indocyanine green angiography, and are best seen in red-free light or with the He-Ne laser of the scanning laser ophthalmoscope. Methods: One hundred patients have been seen in our retinal practice with this clinical feature in the past 3 years. Results: All had some manifestation of age-related maculopathy (ARM), and 66% had or subsequently developed subretinal new vessels in one or both eyes. The appearance is attributed to changes in the choroid. Conclusions: Reticular pseudodrusen are an easily recognizable clinical sign, and may be an important risk factor for choroidal neovascularization in ARM.

Early drusen formation in the normal and aging eye and their relation to age related maculopathy: a clinicopathological study

AIM To describe the early formation of drusen and their relation to normal aging changes at the macula and to the development of age related maculopathy (ARM). METHOD Histopathological features of 353 eyes without histological evidence of ARM are described and correlated with the clinical appearance. In addition, 45 of these eyes were examined by transmission electron microscopy. RESULTS Drusen were detected histopathologically in 177 (50%) eyes but were seen clinically in only 34% of these. Drusen were mainly small hard drusen with an occasional soft distinct drusen: no soft indistinct drusen were seen. Only those drusen deposits larger than 25–30 μm in diameter were detectable clinically. Preclinical drusen in eyes with only an occasional drusen were seen on electron microscopy as entrapment sites of coated membrane bound bodies which formed adjacent to the inner collagenous zone of Bruch’s membrane. In contrast, preclinical drusen deposits in eyes with many drusen were seen as accumulations of amorphous material which appeared hyalinised by light microscopy. A distinct feature were rows of dense hyalinised microdrusen (1–2 μm in diameter), over which larger globular hyalinised drusen formed. CONCLUSION Histological and ultrastructural examination can recognise and distinguish the earliest drusen formed as a result of normal aging from those associated with ARM. In eyes without diffuse deposits, histologically all drusen were of the hard hyalinised variety or their derivatives; no soft drusen composed of membranous debris were found. These findings support and explain those of other authors who do not consider the presence of a few small hard drusen to be a risk factor for the development of ARM.

Evolution of soft drusen in age-related macular degeneration

The pathways by which soft drusen are formed are illustrated by representative clinical and clinicopathological cases. One type is derived from small hard drusen which first tend to aggregate into clusters and then fuse, forming larger deposits termed hard clusters. Breakdown of the hard drusen results in varying degrees of softening and confluence. These soft clusters may appear in middle age and, like the preceding hard drusen, remain a focal pathology. Soft clusters commonly lead to the atrophic form of age-related macular degeneration. Another type of soft drusen is formed from membranous debris as part of a diffuse disturbance of the retinal pigment epithelium. These membranous soft drusen first appear in the seventh decade and are commonly associated with choroidal neovascularisation.

Conditional Müller Cell Ablation Causes Independent Neuronal and Vascular Pathologies in a Novel Transgenic Model

Müller cells are the major glia of the retina that serve numerous functions essential to retinal homeostasis, yet the contribution of Müller glial dysfunction to retinal diseases remains largely unknown. We have developed a transgenic model using a portion of the regulatory region of the retinaldehyde binding protein 1 gene for conditional Müller cell ablation and the consequences of primary Müller cell dysfunction have been studied in adult mice. We found that selective ablation of Müller cells led to photoreceptor apoptosis, vascular telangiectasis, blood–retinal barrier breakdown and, later, intraretinal neovascularization. These changes were accompanied by impaired retinal function and an imbalance between vascular endothelial growth factor-A (VEGF-A) and pigment epithelium-derived factor. Intravitreal injection of ciliary neurotrophic factor inhibited photoreceptor injury but had no effect on the vasculopathy. Conversely, inhibition of VEGF-A activity attenuated vascular leak but did not protect photoreceptors. Our findings show that Müller glial deficiency may be an important upstream cause of retinal neuronal and vascular pathologies in retinal diseases. Combined neuroprotective and anti-angiogenic therapies may be required to treat Müller cell deficiency in retinal diseases and in other parts of the CNS associated with glial dysfunction.

Evolution of reticular pseudodrusen

Aims To report observations relating to the clinical recognition and possible basis of reticular pseudodrusen (RPD). Methods This retrospective study reports the evolution of RPD in 166 patients who had follow-up of over 1 year using multiple imaging techniques. Mean age when first seen was 73.3 years and the mean period of observation was 4.9 years (range 1–18 years). Associated macular changes were recorded. Results RPD were first identified in the upper fundus as a reticular network, which then became less obvious, developing a diffuse yellowish appearance. RPD also faded around choroidal neovascularisation (CNV). RPD therefore could be transient but the pattern often remained visible outside the macula or nasal to the discs. Manifestations of age-related macular degeneration (AMD) were present in nearly all eyes and there was a particularly high association with CNV (52.1%). In one clinicopathological case abnormal material was found in the subretinal space. Conclusions The prevalence of RPD may be underestimated because their recognition depends upon the imaging method used, the area of fundus examined and the confusion with typical drusen. The pathology of one eye suggests that RPD may correspond to material in the subretinal space.

Morphology of early choroidal neovascularisation in age-related macular degeneration: correlation with activity.

The purpose of this study was to describe the morphology of early choroidal neovascularisation (CNV) and compare the findings in two patients, in the first of whom the vessels appeared inactive and in the second progressive. Changes common to both included a diffuse deposition of membrane coils external to the basement membrane (BsM) of the retinal pigment epithelium (RPE), and macrophages and foreign body giant cells beneath thinned segments of Bruchs membrane (BrM). In the first patient small activated vessels surrounded by enlarged pericytes were found in the choroid beneath these areas and pursued a convoluted course, bulging into or through BrM, but without spreading in the sub-RPE space. This choroidal phase of CNV may be common and unrecognised. In the second patient there was spread of CNV in the sub-RPE space with extravasation of red cells and fibrin. The tips leaking fibrin were covered by a thick BsM-like material and naked endothelial cells were not seen. Pericytes were absent here but were observed at the non-leaking edge. The difference in activity of CNV in the two patients appeared to correlate with the quantity of membranous debris present.

Age-related components of Bruch's membrane in the human eye

Age-related deposits within the inner and outer collagenous zones (ICZ/OCZ) of Bruchs membrane have been studied in normal aged human eyes. Electron microscopic examination of tissue from the macular region of 28 post-mortem eyes has shown that age-related deposits comprise mainly coated membrane-bound (CMB) bodies and their fragments. These bodies appear to be released from the RPE via the basal plasma membrane. Morphometric analysis of the average thickness and distribution of age-related deposits has demonstrated that as the thickness of the deposit increases with age, the major part is contained within the OCZ. The ICZ shows only a minimal increase in thickness during life. These results suggest that in the normal ageing eye the inner layers of Bruchs membrane (RPE basement membrane, ICZ and elastic layer) permit an unimpeded flow of CMB bodies from the RPE through to the OCZ.

Attenuation of Experimental Allergic Encephalomyelitis in Complement Component 6-Deficient Rats Is Associated with Reduced Complement C9 Deposition, P-Selectin Expression, and Cellular Infiltrate in Spinal Cords

The role of Ab deposition and complement activation, especially the membrane attack complex (MAC), in the mediation of injury in experimental allergic encephalomyelitis (EAE) is not resolved. The course of active EAE in normal PVG rats was compared with that in PVG rats deficient in the C6 component of complement (PVG/C6−) that are unable to form MAC. Following immunization with myelin basic protein, PVG/C6− rats developed significantly milder EAE than PVG/C rats. The anti-myelin basic protein response was similar in both strains, as was deposition of C3 in spinal cord. C9 was detected in PVG/C rats but not in PVG/C6−, consistent with their lack of C6 and inability to form MAC. In PVG/C6− rats, the T cell and macrophage infiltrate in the spinal cord was also significantly less than in normal PVG/C rats. There was also reduced expression of P-selectin on endothelial cells, which may have contributed to the reduced cellular infiltrate by limiting migration from the circulation. Assay of cytokine mRNA by RT-PCR in the spinal cords showed no differences in the profile of Th1 or Th2 cytokines between PVG/C and PVG/C6− rats. PVG/C rats also had a greater increase in peripheral blood white blood cell, neutrophil, and basophil counts than was observed in the PVG/C6−. These findings suggest that the MAC may have a role in the pathogenesis of EAE, not only by Ig-activated MAC injury but also via induction of P-selectin on vascular endothelium to promote infiltration of T cells and macrophages into the spinal cord.