Macular membranes

Wisniewska, A. and Subczynski, W.K., Accumulation of macular xanthophylls in unsaturated membrane domains. Free Radio. Biol. Med., 40, 1820, 2006. 

Early macular changes are often called age-related macu-lopathy and are characterized by large drusen and pigmentary abnormalities in the macula.20 Age-related maculopathy accounts for 85% to 90% of all age-related macular changes. Ten to fifteen percent of these patients will develop advanced atrophy and/or develop abnormal blood vessels in and under the retina called choroidal neovascular membranes. Patients are then classified as having AMD.23... 

Drusen ablation may help patients with multiple large drusen in both eyes that have not progressed to neovascular macular degeneration. These laser treatments may lead to resolution of the drusen and improved visual acuity. However, it is not clear if progression to choroidal neovascular membranes and neovascular macular degeneration is reduced.23 There is a possibility that the laser treatments may induce choroidal neovascularization and retinal atrophy.22... 

Bone, R. A. and J. T. Landrum (1984). Macular pigment in Henle fiber membranes a model for Haidinger s brushes. Vision Research 24 103-108. 

Carotenoids are also present in animals, including humans, where they are selectively absorbed from diet (Furr and Clark 1997). Because of their hydrophobic nature, carotenoids are located either in the lipid bilayer portion of membranes or form complexes with specific proteins, usually associated with membranes. In animals and humans, dietary carotenoids are transported in blood plasma as complexes with lipoproteins (Krinsky et al. 1958, Tso 1981) and accumulate in various organs and tissues (Parker 1989, Kaplan et al. 1990, Tanumihardjo et al. 1990, Schmitz et al. 1991, Khachik et al. 1998, Hata et al. 2000). The highest concentration of carotenoids can be found in the eye retina of primates. In the retina of the human eye, where two dipolar carotenoids, lutein and zeaxan-thin, selectively accumulate from blood plasma, this concentration can reach as high as 0.1-1.0mM (Snodderly et al. 1984, Landrum et al. 1999). It has been shown that in the retina, carotenoids are associated with lipid bilayer membranes (Sommerburg et al. 1999, Rapp et al. 2000) although, some macular carotenoids may be connected to specific membrane-bound proteins (Bernstein et al. 1997, Bhosale et al. 2004). 

Recently, due to increased interest in membrane raft domains, extensive attention has been paid to the cholesterol-dependent liquid-ordered phase in the membrane (Subczynski and Kusumi 2003). The pulse EPR spin-labeling DOT method detected two coexisting phases in the DMPC/cholesterol membranes the liquid-ordered and the liquid-disordered domains above the phase-transition temperature (Subczynski et al. 2007b). However, using the same method for DMPC/lutein (zeaxanthin) membranes, only the liquid-ordered-like phase was detected above the phase-transition temperature (Widomska, Wisniewska, and Subczynski, unpublished data). No significant differences were found in the effects of lutein and zeaxanthin on the lateral organization of lipid bilayer membranes. We can conclude that lutein and zeaxanthin—macular xanthophylls that parallel cholesterol in its function as a regulator of both membrane fluidity and hydrophobicity—cannot parallel the ability of cholesterol to induce liquid-ordered-disordered phase separation. 

Wisniewska, A. and W. K. Subczynski. 2006b. Distribution of macular xanthophylls between domains in model of photoreceptor outer segment membranes. Free Radic. Biol. Med. 4 1257-1265. 

A number of speculations can arise from the photo-physical data presented earlier. The major carotenoids that protect the macular are the XANs, ZEA, and LUT, yet, at least in the model membranes studies, these are rather poor 02 quenchers (compared, e.g., with P-CAR and LYC). However, free... 

Hageman, GS, Luthert, PJ, Chong, NHV, Johnson, LV, Anderson, DH, and Mullins, RF, 2001. An integrated hypothesis that considers drusen as biomarkers of immune-mediated processes at the RPE-Bruch s membrane interface in aging and age-related macular degeneration. Prog Retin Eye Res 20, 705-732. 

Hahn, P, Milam, AH, and Dunaief, JL, 2003. Maculas affected by age-related macular degeneration contain increased chelatable iron in the retinal pigment epithelium and Bruch s membrane. Arch Ophthalmol 121, 1099-1105. 

The retina is the most metabolically active tissue in the body and so is very vulnerable to the microvascular changes which occur in diabetes. Diabetes affects the eyes in a number of ways the most common is diabetic retinopathy, which involves increased thickness of the retinal basement membrane and increased permeability of its blood vessels. The severity of the retinopathy is related to the age of the patient, duration of the diabetic state and extent of glycaemic control. Later changes in the eye include macular oedema and retinal ischaemia, which threaten the sight of the patient. All these deleterious changes are minimized if blood glucose is tightly controlled. 

Choroidal neovascularization associated with age-related macular degeneration is difficult to treat with conventional laser procedures because normal retinal tissues can be destroyed, which results in loss of central vision. Photodynamic therapy offers the opportimity to selectively eradicate neovascular membranes while producing minimal damage to normal retinal and choroidal tissues. 

SJS and TEN are systemic disorders typically presenting with constitutional signs, including fever, malaise, headache, loss of appetite, nausea, and vomiting.The skin is involved with inflammatory vesiculobullous lesions, frequently accompanied by hemorrhage and necrosis. In contrast, EMM usually presents with a diffuse erythematous papular and macular eruption that evolves into characteristic target or bull s-eye lesions with an erythematous center surroimded by a zone of normal skin and then by an erythematous ring. The soles of the feet and the palms of the hands often are affected in EMM. Mucous membranes of the nose and mouth are the most commonly affected, and conjunctival involvement is common in both EMM and SJS/TEN.At least two mucous membranes surfeces are involved in SJS and TEN. 

Silicone oil injection has been used to treat retinal detachment. Six patients who had had previous silicone oil injection had the oil extracted, partial introduction of perfluorocarbon liquids, extraction of epiretinal membranes, endodiathermy, retinotomy, retinectomy, complete filling of the intraocular cavity with perfluorocarbon, endophotocoagulation, and silicone oil injection (10). All maintained the reattached retina. One developed a macular epiretinal membrane. Another developed a macular epiretinal membrane with subfoveal perfluorocarbon and a relapse of the retinal re-detachment when the silicone oil was extracted and it had to be re-introduced. Four of the patients developed different degrees of cataracts the other two were aphakic. 

Clinically, bluish-red, well-demarcated, macular, papular, or urticarial lesions, as well as the classical iris or target lesions , sometimes with central vesicles, bullae, or purpura, are distributed preferentially over the distal extremities, especially over the dorsa of the hands and extensor aspects of the forearms. Lesions tend to spread peripherally and may involve the palms and trunk as well as the mucous membranes of the mouth and genitalia. Central healing and overlapping lesions often lead to arciform, annular and gyrate patterns. Lesions appear over the course of a week or 10 days and resolve over the next 2 weeks. 

---