A comparison of some organizational characteristics of the mouse central retina and the human macula

Mouse models have greatly assisted our understanding of retinal degenerations. However, the mouse retina does not have a macula, leading to the question of whether the mouse is a relevant model for macular degeneration. In the present study, a quantitative comparison between the organization of the central mouse retina and the human macula was made, focusing on some structural characteristics that have been suggested to be important in predisposing the macula to stresses leading to degeneration: photoreceptor density, phagocytic load on the RPE, and the relative thinness of Bruch’s membrane. Light and electron microscopy measurements from retinas of two strains of mice, together with published data on human retinas, were used for calculations and subsequent comparisons. As in the human retina, the central region of the mouse retina possesses a higher photoreceptor cell density and a thinner Bruch’s membrane than in the periphery; however, the magnitudes of these periphery to center gradients are larger in the human. Of potentially greater relevance is the actual photoreceptor cell density, which is much greater in the mouse central retina than in the human macula, underlying a higher phagocytic load for the mouse RPE. Moreover, at eccentricities that correspond to the peripheral half of the human macula, the rod to cone ratio is similar between mouse and human. Hence, with respect to photoreceptor density and phagocytic load of the RPE, the central mouse retina models at least the more peripheral part of the macula, where macular degeneration is often first evident.

[The vitreous and the macula]

The macula is a site where various vitreoretinal disorders occur. In 1983 we started to observe the retinal surface of postmortem eyes with a scanning electron microscope (SEM). We investigated the anatomy of the vitreous in postmortem eyes by slit lamp biomicroscopy. The novel anatomy of the premacular vitreous led us to conduct a clinical study of vitreomacular interface diseases. In 1997, time domain optical coherence tomography(OCT) became available which facilitated visualization of the vitreoretinal interface. Swept source OCT which was introduced in 2012 can depict liquefied lacunae in the vitreous. It enabled us to elucidate the mechanism of vitreoretinal diseases. I. SEM revealed the remnants of vitreous cortex at fovea with high incidence (44%), which suggests strong vitreoretinal attachment at the fovea and vitreous cortex origin of the epiretinal membrane. II. We studied the anatomy of the vitreous in postmortem eyes. The vitreous of bisected eye balls was stained by fluorescein and immersed in water and observed by slit-lamp biomicroscopy. We discovered a "posterior precortical vitreous pocket (PPVP)" in adult eyes without posterior vitreous detachment (PVD). III. We performed clinical study in various vitreoretinal diseases based on the novel vitreous anatomy and explained their mechanism. 1. In diabetic retinopathy, ring shaped fibrovascular tissue surrounding the macula is formed along the outer margin of the PPVP. Although PVD progresses outside the PPVP, its posterior wall remains attached to the retina, which causes macular traction or cystoid macular edema. 2. In eyes with idiopathic epimacular membrane (IEM), detached vitreous cortex had an oval defect corresponding to the IEM. Posterior wall of the PPVP that is premacular vitreous cortex appeared to be the framework of IEM. 3. During vitrectomy for macular hole, premacular round defect appears when PVD is created. The residual cortex on the macula is fibrous membrane with elasticity. The tangential contraction of premacular cortex may generate anterior traction to the fovea, which leads to macular hole. IV. Using time domain OCT, we demonstrated the evolution of macular hole, myopic foveoschisis and lamellar macular hole. After 2007, we investigated age related changes of vitreoretinal interface by spectral domain OCT V. We demonstrated whole structure of the PPVP using swept source OCT. PPVP is a boat shaped premacular liquefied space which has a connecting channel to Cloquet's canal. PPVP develops during childhood. Visualization of vitreous structure proved that our previous assumptions are reasonable. Although the physiological function of the PPVP is unclear, we speculate that the aqueous flows into the PPVP though Cloquet's canal and the connecting channel.

Vestibular dysfunction, altered macular structure and trait localization in A/J inbred mice

A/J mice develop progressive hearing loss that begins before 1 month of age and is attributed to cochlear hair cell degeneration. Screening tests indicated that this strain also develops early onset vestibular dysfunction and has otoconial deficits. The purpose of this study was to characterize the vestibular dysfunction and macular structural pathology over the lifespan of A/J mice. Vestibular function was measured using linear vestibular evoked potentials (VsEPs). Macular structural pathology was evaluated using light microscopy, scanning electron microscopy, transmission electron microscopy, confocal microscopy and Western blotting. Individually, vestibular functional deficits in mice ranged from mild to profound. On average, A/J mice had significantly reduced vestibular sensitivity (elevated VsEP response thresholds and smaller amplitudes), whereas VsEP onset latency was prolonged compared to age-matched controls (C57BL/6). A limited age-related vestibular functional loss was also present. Structural analysis identified marked age-independent otoconial abnormalities in concert with some stereociliary bundle defects. Macular epithelia were incompletely covered by otoconial membranes with significantly reduced opacity and often contained abnormally large or giant otoconia as well as normal-appearing otoconia. Elevated expression of key otoconins (i.e., otoconin 90, otolin and keratin sulfate proteoglycan) ruled out the possibility of reduced levels contributing to otoconial dysgenesis. The phenotype of A/J was partially replicated in a consomic mouse strain (C57BL/6J-Chr 17(A/J)/NaJ), thus indicating that Chr 17(A/J) contained a trait locus for a new gene variant responsible to some extent for the A/J vestibular phenotype. Quantitative trait locus analysis identified additional epistatic influences associated with chromosomes 1, 4, 9 and X. Results indicate that the A/J phenotype represents a complex trait, and the A/J mouse strain presents a new model for the study of mechanisms underlying otoconial formation and maintenance.

[Efficacy of topical ketorolac for improving visual function after photocoagulation in diabetic patients with focal macular edema]

BACKGROUND

Photocoagulation reduces the incidence of visual loss in diabetic patients with focal macular edema, but it can induce it for Efficacy of topical ketorolac for improving visual function after photocoagulation in diabetic patients with focal macular edema 6 weeks after treatment and produces visual improvement in some cases. Topical ketorolac may reduce the inflammation caused by photocoagulation and improve visual outcome.

PURPOSE

To determine the efficacy of topical ketorolac for improving visual function after photocoagulation in diabetic patients with focal macular edema.

METHODS

An experimental, comparative, prospective, longitudinal study in diabetic patients with focal macular edema was conducted. Eyes were randomized into two groups of topical treatment for 3 weeks after photocoagulation (A: ketorolac, B: placebo). Best corrected visual acuity before and after treatment was compared in each group (paired t test), and the proportion of eyes with visual improvement was compared between groups (χ(2)). The evaluation was repeated after stratifying for initial visual acuity (≥ 0.5, < 0.5).

RESULTS

There were 105 eyes included. In group A (n= 46) mean visual acuity changed from 0.50 to 0.58 (p= 0.003), and from 0.55 to 0.55 in group B (n= 59, p= 0.83); mean percent change was 22.3% in group A and 3.5% in group B (p= 0.03). Visual improvement was identified in 25 eyes from group A (54.3%) and 19 from group B (32.2%, p= 0.019, RR 1.65); the difference only persisted when initial visual acuity was ≥ 0.5 (10 [40%], group A, 5 [14.7%], group B, p= 0.02, RR 2.72).

CONCLUSION

Topical ketorolac was more effective than placebo to improve best corrected visual acuity in diabetic patients with focal macular edema.

[Macular morphology and peripapillary retinal nerve fiber layer thickness in children with regressed retinopathy of prematurity]

PURPOSE

morphobiometric evaluation of macula and peripapillary retinal nerve fiber layer thickness with the use of high-resolution optical coherence tomography in children with a history of regressed retinopathy or prematurity.

MATERIALS AND METHODS

18 patients at the age of 8 to 14 years with a history of spontaneously regressed retinopathy of prematurity were studied prospectively. For statistical purposes a control group of 21 matched subjects at the age of 8 to 15 years was used. Ophthalmic examination and optical coherence tomography were performed in each patient. Peripapillary nerve fibre layer thickness, foveal and parafoveal thickness ratio, total macular volume and subfoveal choroidal thickness were measured in both groups.

RESULTS

in the optical coherence tomography, the foveal thickness in children with retinopathy of prematurity was significantly higher [269.5 μm (232-321)] compared to the controls [224.5 μm (207-267)]. The macular volume in the study group was also higher (8.68 mm³). The subfoveal choroidal thickness was reduced in study group [321 μm (112-365)] compared to the control group [337 μm (294-358)]. There was no statistical significant difference in total peripapillary nerve fibre layer thickness between the two groups.

CONCLUSION

The morphobiometric macular changes in eyes with a history of regressed retinopathy of prematurity are possibly related to the developmental abnormalities, which retinopathy of prematurity is due to the presence of the abnormal foveal structure across all retinal layers.

Disparity between foveal thickness and macular volume in diabetic macular edema

BACKGROUND

Optical coherence tomography (OCT) quantifies changes of foveal thickness and macular volume after photocoagulation in diabetic macular edema. Macular volume evaluates the whole macula, but it may underestimate changes in foveal thickness induced by photocoagulation. We undertook this study to evaluate the concordance between macular volume and foveal thickness for identifying clinically significant changes of retinal thickness after photocoagulation for diabetic macular edema.

METHODS

We carried out an observational, retrospective, longitudinal, analytical study. Center point thickness (CPT), central subfield mean thickness (CSMT) and macular volume were measured with OCT before photocoagulation and 3 weeks after in diabetic patients with focal macular edema (January 2006--January 2010). Concordance among variables to detect clinically significant changes (CPT >17%, CSMT >11%, macular volume >3%) was identified using the kappa test.

RESULTS

Sixty eight eyes were included; 47 eyes had nonproliferative retinopathy (69.1%). CPT increased significantly in 14.7% of the sample; CSMT in 8.8%, and macular volume in 11.8%. CPT decreased significantly in 4.4%, CSMT in 8.8%, and macular volume in 42.6%. Concordance was regular for CPT and CSMT increased (57%). Concordance was good for CPT and CSMT decreased (64%). Concordance was regular for CSMT and macular volume decreased in eyes with center involvement (43%). The remaining concordances were poor.

DISCUSSION

Two independent events happen after focal photocoagulation: involution of the original thickening and increase in CPT. In order to detect both events, evaluation of either foveal thickness alone or macular volume alone is insufficient.

CONCLUSION

Identifying the efficacy and safety of treatments for diabetic macular edema requires simultaneous measurement of CPT and macular volume.

Villous processes from the inner segments of cones in the human macula lutea

The cones of the human macula lutea were examined by scanning electron microscopy. It was found that each inner segment had about 15 thread-like processes which projected from the cell surface. They were arranged in a longitudinal straight line along the photoreceptor, and were directed away from or towards the fovea contralis. The villous processes may be analogous with the lateral fins of the inner segments of certain vertebrates. They may perhaps bridge the space between neighbouring photoreceptors and may establish contact and interaction between them.

Comparison of morphology of human macular and peripheral Bruch's membrane in older eyes

Deposits in macular human Bruch's membrane (BrM) increase with age and have been postulated to be associated with age-related maculopathy. We used two ultrastructural methods to compare these deposits by electron microscopy in macular and peripheral BrM of eight eyes from donors 63-86 years of age. Quick-freeze/deep-etch (QFDE) was used to prepare replicas that showed the ultrastructure of deposits, and osmium-tannic acid-paraphenylenediamine (OTAP) was used to preserve small extracellular lipid particles. We found that an accumulation of lipoprotein-like particles (LLPs) occurred in the peripheral BrM just as it does in the macular region, but with perhaps a somewhat slower time course. The "lipid wall," reported in macular BrM, was also found occasionally in the peripheral regions. The same processes that lead to age-related accumulation of LLPs in macular BrM appear to also occur in the peripheral regions.

Operative Zielvorgabe in der Makulaforamenchirurgie

We compared the ultrastructure of the inner limiting membrane (ILM) and epiretinal tissue in closed and non-closed, idiopathic macular holes (MH). Peeling of ILM and epimacular tissue during vitrectomy was successfully performed on 77 eyes with stage III MH and on 19 eyes with stage IV MH. In 16 additional eyes with non-closed MH, we performed a second vitrectomy with extended ILM removal. The specimens were processed for transmission electron microscopy. Fibrocellular proliferation at the vitreal side of the ILM was found in 57% of MH that were closed by one operation, and in 100% of non-closed MH. Mono- and multilayered cellular membranes as well as native vitreous collagen at the ILM were significantly more frequent in eyes with stage IV MH than in eyes with stage III MH. In non-closed MH, cellular proliferation was mostly seen as irregular cell accumulation, and masses of newly formed collagen were found. Since ILM remnants and collagen represent a stimulus for the early formation of tangential traction preventing successful MH closure, it appears mandatory to create a complete vitreoretinal separation and to remove the ILM and collagen thoroughly during MH surgery.

Age-related changes in human macular Bruch's membrane as seen by quick-freeze/deep-etch

Lipid-containing inclusions have been observed in human Bruch's membrane (BrM) and are postulated to be associated with age-related maculopathy (ARM), a major cause of legal blindness in developed countries. The dehydration associated with specimen preparation for thin-section transmission electron microscopy causes loss of these inclusions. Better preservation of the ultrastructure of the inclusions and tissue is achieved by using a quick-freeze/deep-etch preparation. We use this technique to examine normal human macular BrM in order to characterize the deposition of the lipid-rich inclusions and their age-related accumulation within different layers of the tissue. We find that various inclusions mentioned in other studies can be formed by combinations of three basic structures: lipoprotein-like particles (LLPs), small granules (SGs) and membrane-like structures. These inclusions are associated with collagen and elastic fibrils by fine filaments. In younger eyes, these inclusions are found mostly in the elastic (EL) and outer collageneous layer (OCL) and occupy a small fraction of the interfibrillar spacing. As age increases, LLPs and SGs gradually fill the interfibrillar spacing of the EL and inner collageneous layer (ICL) of the tissue, and later form a new sublayer, the lipid wall, within the boundary region between the basal lamina of retinal pigment epithelium (RPE) and ICL. Because the formation of the lipid wall only occurs after these inclusions fill the ICL, and it seems unlikely that the LLPs can pass through the packed layer, this result suggests a possible RPE origin of the LLPs that make up the lipid wall.

Secreted Proteome Profiling in Human RPE Cell Cultures Derived from Donors with Age Related Macular Degeneration and Age Matched Healthy Donors

Age-related macular degeneration (AMD) is characterized by progressive loss of central vision, which is attributed to abnormal accumulation of macular deposits called "drusen" at the interface between the basal surface of the retinal pigment epithelium (RPE) and Bruch's membrane. In the most severe cases, drusen deposits are accompanied by the growth of new blood vessels that breach the RPE layer and invade photoreceptors. In this study, we hypothesized that RPE secreted proteins are responsible for drusen formation and choroidal neovascularization. We used stable isotope labeling by amino acids in cell culture (SILAC) in combination with LC-MS/MS analysis and ZoomQuant quantification to assess differential protein secretion by RPE cell cultures prepared from human autopsy eyes of AMD donors (diagnosed by histological examinations of the macula and genotyped for the Y402H-complement factor H variant) and age-matched healthy control donors. In general, RPE cells were found to secrete a variety of extracellular matrix proteins, complement factors, and protease inhibitors that have been reported to be major constituents of drusen (hallmark deposits in AMD). Interestingly, RPE cells from AMD donors secreted 2 to 3-fold more galectin 3 binding protein, fibronectin, clusterin, matrix metalloproteinase-2 and pigment epithelium derived factor than RPE cells from age-matched healthy donors. Conversely, secreted protein acidic and rich in cysteine (SPARC) was found to be down regulated by 2-fold in AMD RPE cells versus healthy RPE cells. Ingenuity pathway analysis grouped these differentially secreted proteins into two groups; those involved in tissue development and angiogenesis and those involved in complement regulation and protein aggregation such as clusterin. Overall, these data strongly suggest that RPE cells are involved in the biogenesis of drusen and the pathology of AMD.

Ultrastructure of vitreomacular traction syndrome associated with persistent hyaloid artery

AIM

To demonstrate the ultrastructure of vitreomacular traction associated with persistent hyaloid artery.

METHODS

Pars plana vitrectomy was performed in a 66-year-old man with progressive vitreomacular traction associated with a persistent hyaloid artery. Epimacular tissue was peeled and processed for transmission electron microscopy.

RESULTS

Ultrastructural analysis revealed multiple sheets of cellular and collagenous components. Myofibroblasts and newly formed collagen were the predominant features. Fibrous astrocytes, fibroblasts, macrophages, and basement membrane were also present.

CONCLUSION

The cellular composition of the epimacular tissue and high cellular activity suggest that persistence of the hyaloid artery may contribute to the development of vitreomacular traction.

Decreased thickness and integrity of the macular elastic layer of Bruch's membrane correspond to the distribution of lesions associated with age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness in the elderly. In its severest form, choroidal neovessels breach the macular Bruch's membrane, an extracellular matrix compartment comprised of elastin and collagen laminae, and grow into the retina. We sought to determine whether structural properties of the elastic lamina (EL) correspond to the region of the macula that is predilected toward degeneration in AMD. Morphometric assessment of the macular and extramacular regions of 121 human donor eyes, with and without AMD, revealed a statistically significant difference in both the integrity (P < 0.0001) and thickness (P < 0.0001) of the EL between the macular and extramacular regions in donors of all ages. The EL was three to six times thinner and two to five times less abundant in the macula than in the periphery. The integrity of the macular EL was significantly lower in donors with early-stage AMD (P = 0.028), active choroidal neovascularization (P = 0.020), and disciform scars (P = 0.003), as compared to unaffected, age-matched controls. EL thickness was significantly lower only in individuals with disciform scars (P = 0.008). The largest gaps in macular EL integrity were significantly larger in all categories of AMD (each P < 0.0001), as compared to controls. EL integrity, thickness, and gap length in donors with geographic atrophy did not differ from those of controls. These structural properties of the macular EL correspond spatially to the distribution of macular lesions associated with AMD and may help to explain why the macula is more susceptible to degenerative events that occur in this disease.

Internal limiting membrane: ultrastructural relationships, with clinical implications for macular hole healing

BACKGROUND

Recent data on macular hole formation have changed our understanding of the mechanisms involved. However, the mechanisms of macular hole closure, despite the introduction of internal limiting membrane (ILM) removal, are not fully understood. We reviewed the charts of patients who underwent surgery for macular hole with and without intentional removal of ILM and reviewed the basic science literature on the components and relationships of the ILM-glial cell interface to help interpret our surgical data.

METHODS

We reviewed the records of 205 eyes with a clinical diagnosis of macular hole at a university centre in Montreal between 1998 and 2002. Of these, 117 eyes of 108 patients were included. Vitrectomy with intentional ILM removal was done under indocyanine green (ICG) staining. Macular hole stage and rates of hole closure, failure and reopening were recorded, comparing the eyes with intentional ILM peeling versus no ILM peeling. Anatomic success was defined as a flat/closed configuration. A basic science literature review was done through the PubMed search engine with the key words "internal limiting membrane," "internal limiting lamina," "macular hole," "retinal glial cells" and "retinal Müller cells."

RESULTS

Eighty-four eyes had ICG-guided ILM removal (26 stage 2 macular holes, 45 stage 3 holes and 13 stage 4 holes), and 33 eyes had no ILM removal (10 stage 2 holes and 23 stage 3 holes). Of the 117 eyes 110 (94.0%) were successfully closed. Four (3.6%) of the closed holes reopened (none had ILM peeling), and 7 (6.0%) of the 117 eyes had primary failure. Ten of the 11 eyes that had primary failure or hole reopening were reoperated, and 8 were successfully closed after the second procedure. One patient refused reoperation. Including second procedures, the final anatomic closure rate was 97.4% (114/117).

INTERPRETATION

Intentional ILM peeling is not mandatory for all macular holes to close but does play a role in preventing reopening. Removal of ILM increases the rate of flat/closed hole configuration on reoperation without the need for biologic adjuvants. Review of the basic science evidence helped clarify the possible role of ILM removal.

3D structure of the macula flava in the human vocal fold

OBJECTIVE

To investigate the 3D structure of the macula flava in the human vocal fold.

MATERIAL AND METHODS

The 3D structure of the macula flava in the human vocal fold was investigated by means of scanning electron microscopy using a chemical digestion method (modified sodium hydroxide maceration method) and the results compared with those obtained using light microscopy.

RESULTS

The macula flava of the human vocal fold comprised a dense mass of cells and extracellular matrices. Many cells were stellate in shape and possessed cytoplasmic processes. Extracellular matrices were composed of collagenous, reticular and elastic fibers, and ground substances (hyaluronic acid). Many fibers ran in various directions. The stellate cells were surrounded by these extracellular matrices. Amorphous materials were attached to the surface of the stellate cells. Extracellular matrices in the macula flava extended to those in the lamina propria of the vocal fold mucosa.

CONCLUSION

Anterior and posterior maculae flavae in the human vocal fold mucosa are postulated to be involved in the metabolism of extracellular matrices, which are essential to the viscoelasticity of the lamina propria (the vibrating tissue) of the human adult vocal fold mucosa.

Facilitation of artificial retinal detachment for macular translocation surgery tested in rabbit

PURPOSE

For macular translocation surgery, the native attached retina has to be detached either locally or completely. Although different surgical techniques are used, there is a general search for supporting procedures that facilitate and accelerate the retinal detachment.

METHODS

Pars plana vitrectomies were performed in pigmented rabbits. In all experimental groups, a local retinal detachment was created by infusing the test solution with a thin glass micropipette attached to a glass syringe. In control animals a standard balanced salt solution was used at room temperature, in combination with a standard vitrectomy light source. In two test groups, a calcium- and magnesium-free solution was used for the vitrectomy, under illumination by a standard light source in group I (solution at room temperature) and group II (solution heated up to body temperature). In group III the rabbits were dark-adapted for half an hour, and then, during surgery, a red filter was used in front of the light source (standard balanced salt solution at room temperature). After the rabbits were killed at the end of surgery, the adherence of the retinal pigment epithelium (RPE) to the neural retina in the detachment area was quantified microscopically, and the morphologic integrity of the detached retinal tissue was examined by light and electron microscopy. No electrophysiology was performed.

RESULTS

In all four groups, it was possible to detach the retina. The maximum adherence of the RPE cells to the neural retina was observed in the control group. Virtually no decrease in adherence was found in test group II (36 degrees C solution without calcium and magnesium), whereas a significant decrease was seen in both group I (calcium- and magnesium-free solution at room temperature) and group III (dark adaptation-red light technique; standard balanced salt solution at room temperature). In none of the experimental groups was any obvious damage of the retinal structure observed, even after exposure to the test solutions for 60 minutes.

CONCLUSIONS

Both dark adaptation (red illumination) and the use of a calcium chloride- and magnesium chloride-free solution (at room temperature) can facilitate retinal detachment in macular translocation surgery. Both techniques are proposed as a gentle support for the operation, because they protect an intact RPE cell layer and do not cause retinal damage at the ultrastructural level.

[Ultrastructural analysis of tissue removed during surgery of idiopathic macular holes]

AIM

To analyze the ultrastructural features of epimacular tissue removed during idiopathic macular hole (IMH) surgery and to compare them with those of idiopathic epimacular membranes.

METHODS

Three consecutive patients with unilateral stage 3 IMH underwent pars plana vitrectomy with surgical removal of delicate gelatinous membranous epimacular tissue. One patient was previously treated with laser photocoagulation. The excised material was investigated by means of light and transmission electron microscopy. Results were compared with the findings of the excised material in two idiopathic epimacular membranes.

RESULTS

The excised material included variable proportions of cellular and membranous material. Glial cells (Müller cells, fibrous astrocytes) and fibroblast-like cells dominated in the cellular component both in the specimens from IHM eyes and in the comparative material. Neural elements were revealed in two of three specimens from IMH eyes. Membraneous material was formed by fragments of internal limiting membrane.

CONCLUSIONS

Dominance of the glial cells in the cellular component of epimacular formations may reflect the important role of these cells both in formation and in healing process of IMH. The presence of neural elements in the removed epimacular tissue suggests that, at least in some cases, IMH surgery with peeling of an epimacular membrane can be associated with some injury of the macula.

[Ultrastructural findings of epimacular membrane and detached posterior hyaloid in vitreomacular traction syndrome]

PURPOSE

Vitreomacular traction syndrome is characterized by an incomplete posterior vitreous detachment and by the cortical vitreous remaining attached to the macula. In certain case epimacular membrane is clinically well defined. We studied the electron microscopic features of epiretinal tissue and posterior hyaloid removed from the posterior pole.

MATERIAL AND METHODS

[corrected] Six epimacular membranes were removed during a pars plana vitrectomy, placed in 2.5% glutaraldehyde solution, embedded in Epoxy resin, and examined in a transmission electron microscope. The detached posterior hyaloid was removed and analyzed separately in two cases.

RESULTS

The analysis disclosed five morphologically cell types. Fibrous astrocytes were predominant in five cases. Other cell types were less frequent and were identified as fibroblasts, macrophages and myofibroblasts. In one case epithelial-like cell type was predominant. The stroma was mainly composed of a thin layer of 15-nm diameter collagen evoking a vitreous origin. Internal limiting membrane was present in one case only. Detached posterior hyaloid was constituted by the same cellular constituents on thin layer of vitreous collagen.

DISCUSSION

The cellular proliferation is principally constituted by fibrous astrocyte and occurs on the inner surface of cortical vitreous. Some glial cells seem to present an epithelial differentiation.

CONCLUSION

The attached and detached posterior hyaloid in vitreomacular traction syndrome is the place of glial cells migration and proliferation.

Antioxidant enzymes in the macular retinal pigment epithelium of eyes with neovascular age-related macular degeneration

PURPOSE

To test the hypothesis that neovascular age-related macular degeneration is related to oxidative stress involving the macular retinal pigment epithelium. This study investigated, as a function of age, levels of enzymes that defend tissues against oxidative stress in the macular retinal pigment epithelium of human eyes with this disease.

METHODS

Surgical specimens of macular choroidal neovascular membranes from eyes with age-related macular degeneration and the macular regions of whole donor eyes with neovascular age-related macular degeneration or without evident ocular disease were studied by quantitative electron microscopic immunocytochemistry with colloidal gold-labeled second antibodies. Relative levels in retinal pigment epithelium cell cytoplasm and lysosomes were determined of five enzymes believed to protect cells from oxidative stress, as well as levels of the retinal pigment epithelium marker cytoplasmic retinaldehyde-binding protein, for comparison with the enzymes.

RESULTS

Copper, zinc superoxide dismutase immunoreactivity increased and catalase immunoreactivity decreased with age in cytoplasm and lysosomes from macular retinal pigment epithelium cells of normal eyes and eyes with age-related macular degeneration. Cytoplasmic retinaldehyde-binding protein immunoreactivity showed no significant relationship to age or the presence of neovascular age-related macular degeneration. Glutathione peroxidase immunoreactivity was absent from human retinal pigment epithelium cells. Both heme oxygenase-1 and heme oxygenase-2 had highly significantly greater immunoreactivity in retinal pigment epithelium cell lysosomes than in cytoplasm, differing from the much greater cytoplasmic immunoreactivity of the other proteins studied. This immunoreactivity decreased with age, particularly in the lysosomes of retinal pigment epithelium cells from eyes with neovascular age-related macular degeneration. These decreases were of borderline significance (P = .067 for heme oxygenase-1; P = .12 for heme oxygenase-2) when eyes with age-related macular degeneration were compared with normal eyes by multivariable logistic regression.

CONCLUSIONS

The high heme oxygenase-1 and heme oxygenase-2 lysosomal antigen levels in macular retinal pigment epithelium cells of eyes with neovascular age-related macular degeneration suggest that oxidative stress causes a pathologic upregulation of these enzymes. Increased lysosomal disposal may indicate that the reparative functions of these enzymes are accompanied by deleterious effects, necessitating their rapid removal from the cell. The much higher heme oxygenase-1 and heme oxygenase-2 antigen levels in macular retinal pigment epithelium cells from younger individuals suggest that protective mechanisms against oxidation and, hence, presumably to the development of age-related macular degeneration, decrease with age.

The use of internal limiting membrane maculorrhexis in treatment of idiopathic macular holes

The purpose of this study was to assess surgical results of internal limiting membrane (ILM) maculorrhexis in macular hole surgery. This study is a part of continuing prospective clinical trial of our team of researchers. Thirteen eyes of 13 patients with idiopathic macular hole underwent vitrectomy with the removal of posterior cortical vitreous, peeling of the macular ILM, and intraocular gas tamponade, followed by postoperative face-down positioning. The excised specimens were evaluated with transmission electron microscopy. Complete closure of the hole was observed in all 13 eyes (100% anatomic success rate). Visual improvement of 2 or more lines on ETDRS visual acuity chart was achieved in 11 (85%) of the 13 eyes. Six (54.5%) eyes attained visual acuity of 20/50 or better. Electron microscopy showed ILM in the removed specimens. ILM maculorrhexis is a promising new surgical approach to close idiopathic macular holes but requires further investigation and long-term evaluation.

[A pathohistological study of newly formed subpigment epithelial tissue in patients with senile macular dystrophy]

Efficacy and possibility of direct operations on the macular area of the retina in humid (exudative) maculopathies (senile maculodystrophy) is validated theoretically, morphologically, and clinically. A hypothesis on the mechanism of exudative process development in the macular area in degenerative diseases is formulated on the basis of pathohistological analysis of removed subpigmental material. Indications for such operations are defined.

Photocoagulation of well-defined choroidal neovascularization in age-related macular degeneration: clinicopathologic correlation

PURPOSE

To present the clinicopathologic features of the eyes of a patient with age-related macular degeneration (ARMD): the right eye was treated for well-defined extrafoveal choroidal neovascularization (CNV), and the left eye had an untreated disciform scar.

METHODS

The patient was studied ophthalmoscopically and by fluorescein angiography at the time of presentation and on follow-up examinations up to 54 days after laser treatment, when he died. The posterior portions of both eyes (obtained postmortem), including the macula and optic nerve head, were sectioned serially for light microscopy. Tissue sections from both eyes were removed from glass slides and studied by transmission electron microscopy.

RESULTS

Histopathologic study of the right eye disclosed a thin layer of basal laminar deposit throughout the posterior pole. Two defects in Bruch's membrane without CNV were present within the area of laser photocoagulation located superior to the fovea. No CNV was present in the scar. Eleven areas of early CNV were present in the posterior pole. Histopathologic study of the left eye showed a prominent basal laminar deposit throughout the posterior pole. A 2.6 x 2.7 mm disciform scar was present that was located mostly in the subretinal space. Four sources of CNV were present.

CONCLUSIONS

The clinicopathologic features of a treated eye with well-defined extrafoveal CNV, and the fellow eye with a disciform scar, both associated with ARMD, are presented. Although laser treatment obliterated a choroidal neovascular membrane, 11 additional areas of early, subclinical CNV were present.

Histologic study of a shielded macula

PURPOSE

To illustrate the histologic changes at the macula of an eye shielded from focused light for 76 years. Age-related macular degeneration with a central, subretinal, fibrous scar was present in the fellow eye.

METHODS

Autopsy examination of both eyes of a 91-year-old man was performed. The superior half of the macular area of the shielded eye was studied by light microscopy, and the inferior half was studied by electron microscopy. Serial sections through the macular area of the fellow eye were prepared and studied.

RESULTS

The shielded eye contained basal laminar deposits up to 6.0 microns in thickness and basal linear deposits up to 1.0 micron in thickness in the macular area. The photoreceptor outer and inner segments of the outer nuclear layer were intact. The macular area of the fellow eye contained a two-component, vascularized, disciform scar that measured up to 250 microns in one area, with retinal pigment epithelial tears at the nasal and temporal margins. Extensive photoreceptor layer atrophy was present.

CONCLUSIONS

Such marked asymmetry of macular degeneration in this case may be further evidence of the role of light exposure in the development of age related macular degeneration.

[Microsurgery of the macula lutea]

Modern surgery of the macula exists since 1965, and was initially proposed in membrane removal from patients presenting an idiopathic epiretinal membrane. This first indication authorized the development of macular microsurgical instrumentation and further analysis of membrane fragments. However, the exact pathogenesis of these membranes remains yet unknown. Since 1991 macular surgery was applied in the treatment of macular holes. Results obtained after macular hole surgery confirmed pathogenic hypothesis observed clinically by Gas. Considerable improvement was therefore achieved in anatomical and functional outcome. Chorioretinal adhesion agents were recently proposed to optimize the closure of macular holes. Submacular surgery is the latest technologic achievement under investigation. The ultimate indications are age-related macular degeneration, first cause of blindness in industrialized countries. Retinal transplantation opens new avenues in the treatment of a large number of chorioretinal diseases. The assessment of macular surgery could pave the way in realising such technical advances.

Collagens in the aged human macula

Immunogold cytochemistry was used to investigate the fine structural distribution of collagen types I-VI in Bruch's membrane and choroid of the aged human macula. Macular tissue was obtained from ten eyes, and processed for cryoultramicrotomy and London Resin white embedding. Striated collagen fibrils within the inner and outer collagenous layers were found to contain collagen types I, III and V. In addition, type V collagen was also present in the basement membrane of the choriocapillaris. Gross thickening of the choriocapillaris basement membrane was attributed to the deposition of type IV collagen. However, type IV collagen appeared to be absent from the basement membrane of the retinal pigment epithelium. The interesting location of type VI collagen on the choroidal side of the choriocapillaris suggested that its function is to anchor the choriocapillaris onto the choroid. The collagens studied were absent from fibrous banded material, long-spacing collagen, the elastic layer and amorphous granular material. It was concluded that, of the collagen types studied, only the deposition of type IV collagen contributes to the age-related thickening of Bruch's membrane.

Immunohistochemical light and electron microscopy of basal laminar deposit

The formation of basal laminar deposit (BLD) is one of the histopathologic changes in the aging human macula. BLD is assumed to be an early stage of age-related macular degeneration. The location of BLD, between the RPE plasma membrane and its basement membrane and in the outer collagenous zone of Bruch's membrane, and its ultrastructure suggest that it is composed of excessive amounts of basement membrane material. The main components of basement membranes are type IV collagen, heparan sulfate proteoglycans (HSPG) and laminin. Labeled antibodies against these components can therefore be used for the identification and localization of basement membrane material by means of immunohistochemical techniques. In this study the presence of type IV collagen, laminin and HSPG was determined in aged human maculae by immunohistochemistry and immunoelectron microscopy. Tests for the presence of type VI collagen and fibronectin were also performed. We obtained 76 eyes from 68 human subjects at autopsy or after surgical enucleation for anteriorly located choroidal melanomas. The finely granular component of BLD stained positive with antibodies against type IV collagen, HSPG and laminin, but the long-spacing collagen component of BLD did not. Neither component of BLD was stained with antibodies against type VI collagen or fibronectin. We conclude that BLD consists partly of excess basement membrane material.

Early stages of age-related macular degeneration: an immunofluorescence and electron microscopy study

In subretinal neovascularisation capillaries originating from the choriocapillaris must cross Bruch's membrane to reach the subretinal pigment epithelial space. Thus gaps in Bruch's membrane have to be formed before subretinal neovascularisation. Histological examination of eyes with subretinal neovascularisation or disciform scars has shown macrophages adjacent to thin areas and ruptures in Bruch's membrane. This has been interpreted as phagocytosis of Bruch's membrane. The purpose of this study was to investigate whether immune complex depositions can be detected in maculae with early stages of age-related macular degeneration and to explain the macrophage reaction before the disciform reaction. A series of 20 human maculae were examined by direct immunofluorescence light microscopy to detect the presence of immune complexes with antibodies directed against immunoglobulins, fibrinogen, and complement factors. Transmission electron microscopy on several maculae was performed to identify the macrophages. Macrophages were observed in close relation to the readily recognisable long spacing collagen, which suggested that long spacing collagen was selectively internalised by these cells. Definite immune complex depositions were not found in basal laminar deposits or drusen. Linear deposits of fibrinogen and complement were frequently found in the outer collagenous zone of Bruch's membrane. However, because of the absence of immunoglobulins, it seems unlikely that these non-specific deposits might cause chemoattraction of macrophages and play a role in the initial phase of the development of subretinal neovascularisation and disciform macular degeneration.

Basal laminar deposit in the aging peripheral human retina

A basal laminar deposit (BLD) in the human macula has been described as an early sign of age-related macular degeneration. In some eyes with a BLD in the macula, light microscopic sections of the peripheral retina revealed almost similar deposits between the retinal pigment epithelium and Bruch's membrane. Because the exact pathogenesis of age-related macular degeneration and the origin of the BLD are unknown, we studied the ultrastructure of these peripheral sub-RPE deposits. Parts of the equatorial and peripheral regions of the retina of ten human eyes, with BLD-like deposits between the retinal pigment epithelium and Bruch's membrane, were examined by electron microscopy. In eight of these ten eyes the ultrastructure of these deposits was amorphous and finely granular. Five of the eight deposits also contained small amounts of long-spacing collagen. Ultrastructurally, the deposits were similar to an early type BLD in the macula. In the remaining two eyes, the deposits appeared to consist of flat, elongated drusen. Our findings indicate that a BLD can develop not only in the macula but also in the peripheral region of the retina.

Collagens in the aged human macular sclera

Scleral tissue from the region of the human macula was studied by the immunogold labeling technique (cryoultramicrotomy and LR white resin embedding) in an attempt to identify the fine structural distribution of collagen types I-VI. Labeling of the striated collagen fibrils suggested colocalisation of collagen types I, III and V with type V occurring at the fibril surface. Both types V and VI collagen were localised to filamentous strands in the interfibrillar matrix. Collagen types II and IV were absent from the scleral stroma.

Ultrastructural features of surgically excised subretinal neovascular membranes in the ocular histoplasmosis syndrome

We evaluated the ultrastructural features of seven surgically excised submacular neovascular membranes from seven patients with the ocular histoplasmosis syndrome. Excised neovascular membranes were composed of fibrovascular tissue interposed between Bruch's membrane and the retinal pigment epithelium. Cellular components present in the membranes included, in decreasing order of frequency, retinal pigment epithelium, vascular endothelium, photoreceptor cells, macrophages, erythrocytes, ghost erythrocytes, fibrocytes, myofibroblasts, glial cells, smooth-muscle cells, and lymphocytes. Extracellular constituents of the neovascular membranes included 20 to 25-nm collagen fibrils, fibrin, 10-nm collagen fibrils, and fragments of Bruch's membrane and choroid. Our findings are consistent with the concept that subretinal neovascular membranes in the ocular histoplasmosis syndrome represent a nonspecific healing response to a local stimulus or injury.

Ultrastructural immunocytochemistry of subretinal neovascular membranes in age-related macular degeneration

BACKGROUND

The authors studied various cellular and extracellular matrix components of subretinal neovascular membranes (SRNVM) from patients with age-related macular degeneration (ARMD).

METHODS

Electron microscopic immunocytochemistry was used on the subfoveal neovascular membranes surgically removed from three patients with disciform lesions due to ARMD.

FINDINGS

The SRNVMs always contained large "feeder" vessels along with many new capillaries in different stages of maturation. Capillaries were sparse and embedded in an abundant stroma. The majority of the nonvascular cells were either retinal pigment epithelial (RPE) cells or fibroblast-like cells. The RPE cells formed single or multiple layers on one side of the membranes. The stroma was composed mainly of collagen types I and IV and fibronectin, with small amounts of collagen types III, V, and VI. The absence of Bruch's membrane suggests that a splitting may occur between the RPE cells and Bruch's membrane with the new vessels growing into this cleft. A thickened layer of collagen type IV was often present under the RPE cells. The basement membranes of the newly formed capillaries were morphologically ill-defined, and contained substantial amounts of collagen type IV and fibronectin, but, unlike the basement membranes of normal capillaries, they lacked laminin or heparan sulfate proteoglycan.

CONCLUSION

These results on the ultrastructural components of the SRNVMs may be useful in clarifying the nature of the disciform process in ARMD.

High hyperopia with papillomacular fold

We report a case of evolutive high hyperopia in a child aged 10 years. It is associated with organic amblyopia due to a large papillomacular retinal fold. Ultrasonography and CT scan helped to establish the diagnosis. This is probably a hereditary disease affecting the development of the posterior sclera.

Pericyte coverage of retinal and cerebral capillaries

We performed electron microscopic morphometric analyses on capillaries from macular and peripheral retinas of five adult cynomolgous monkeys and three elderly human subjects. Measurements from the monkey retinal capillaries were compared to those made on capillaries from frontal, temporal, parietal, and occipital cerebral cortex of the same animals. We measured the percent coverage of the endothelial lining of the capillaries by pericyte processes, as well as the ratio of the cytoplasmic areas of pericytes and endothelial cells. In addition, we compared the thickness of the capillary basement membranes in three regions: overlying pericytes; overlying endothelial cells; and interposed between pericytes and endothelial cells. In both monkey and human retinas, pericyte processes covered greater than 85% of the circumference of the capillary endothelial tube, whereas pericyte coverage of monkey cerebral capillaries was highly significantly (P less than 0.001) less than that of capillaries in either the macular or peripheral retina. The ratio of pericyte to endothelial cell cytoplasmic areas also was lower in the monkey cerebral cortex than in the retina, though the statistical significance was less than that of the length measurements. In all tissues measured, both from monkeys and humans, the portions of the capillary basement membranes interposed between pericytes and endothelial cells were highly significantly (P less than 0.0001) thinner than the regions of capillary basement membranes covering pericytes and endothelial cells. Considering functions that have been proposed for pericytes, these measurements suggest that regional control of microcirculatory flow and of blood-tissue barrier integrity, as well as control of endothelial cell proliferation, should be much greater in the retina than in the cerebral cortex. Thinner basement membranes between pericytes and endothelial cells may permit more cell membrane contacts between these cells, thus facilitating such control.

Regional variation within the interphotoreceptor matrix from fovea to the retinal periphery

The interphotoreceptor matrix in the human retina comprises a highly organised extracellular compartment. Using fluorescent labelled peanut agglutinin and the cationic dyes Cupromeronic and Cuprolinic Blue, unique cylindrical domains surrounding cone photoreceptors can be demonstrated. These cone specific domains are relatively insoluble and are closely adherent to cone photoreceptors and to the pigment epithelium, suggesting that these structures may play a role in retinal attachment.

[Dye lasers: experimental histopathologic study of the effects of various wavelengths on the macular region]

Pathological experimental study of dye laser photocoagulation simulating the confluent treatment of subretinal new vessels in the macular area of a Macacas Cynomolgus monkey. 38 days after treatment the lesions become similar on the choriocapillaris and retinal pigment epithelium whatever the wavelength; the choriocapillaris is always occluded and the pigment epithelium destroyed. The internal limiting membrane is ondulated only with yellow and orange colors. These results are compared to those of similar experimental studies.

[Spontaneous rupture of Bruch's membrane and transient macular hemorrhage in patients with myopia]

18 eyes of 14 pathologic myopia patients with lacker cracks have been studied during a mean follow up of 45 months by initial and final clinical and fluoroangiography evaluation. These lacker cracks happen early in the myopia degeneration evolution in young patients. The evolution is marked by transient coinlike macular hemorrhages without CNM detectable. Prognosis for the retention of central vision after macular hemorrhages resolution is good. It mainly depends of lacker cracks initial location if macular quite wrong, if intramacular, quite right. Development of CNM is an infrequent eventuality but must be systematically research by angio-fluorography after spontaneous macular hemorrhage resolution which usually occurs 4 or 6 weeks later.

Lateral cell connections at the inner segment level of human parafoveal photoreceptors

Cytoplasmic processes on macular rod inner segments are described both in torn, fractured, and sectioned human tissue specimens. Longitudinal rows of villi are present along the inner segment's proximal part in fractured and sectioned tissue. Some villi were obviously abutting neighbouring cells. It is concluded that these processes undoubtedly represent a new type of cell extension different from calycal, pigment-epithelial, and Muller basket processes.

Ultrastructural studies of vitreomacular traction syndrome

We performed electron microscopic studies on seven specimens removed from the posterior retina at the time of vitrectomy for vitreomacular traction syndrome. Fibrous astrocytes were the predominant cell type in all cases. Fibrocytes were present in two cases and myofibrocytes were seen in three cases. Additional cellular and extracellular features included fragments of internal limiting membrane in six cases, old collagen in all cases, new collagen in one case, occasional macrophages in four cases, and fibrous astrocytes with myofibroblastic differentiation in one case.

Discontinuities of the external limiting membrane in the fovea centralis of the primate retina

In the center of the fovea centralis of retinas of three cynomolgus monkeys, one baboon and one male human, the external limiting membrane contains circumscribed areas in which zonulae adherentes are lacking between cone inner segments and apices of Müller cells. These discontinuities of the external limiting membrane begin about 300 microns from the foveolar center, involving only a few cones. Towards the center of the fovea the discontinuities become larger.

Aging and human macular pigment density. Appended with translations from the work of Max Schultze and Ewald Hering

The optical density of human macular pigment was measured for 50 observers ranging in age from 10 to 90 years. The psychophysical method required adjusting the radiance of a 1 degree, monochromatic light (400-550 nm) to minimize flicker (15 Hz) when presented in counterphase with a 460 nm standard. This test stimulus was presented superimposed on a broad-band, short-wave background. Macular pigment density was determined by comparing sensitivity under these conditions for the fovea, where macular pigment is maximal, and 5 degrees temporally. This difference spectrum, measured for 12 observers, matched Wyszecki and Stiles's standard density spectrum for macular pigment. To study variation in macular pigment density for a larger group of observers, measurements were made at only selected spectral points (460, 500 and 550 nm). The mean optical density at 460 nm for the complete sample of 50 subjects was 0.39. Substantial individual differences in density were found (ca. 0.10-0.80), but this variation was not systematically related to age.

Basal linear deposit in the human macula

We used electron microscopy and immunohistochemistry to study the macular regions of nine enucleated elderly human eyes and to document the various abnormalities present in the so-called basal linear deposit. These changes include bush-like strands of electron-dense material, which project from the basement membrane of the retinal pigment epithelium, deposition of wide-banded collagen, vesiculoid elements, membrane-bound structures and occasional melanin granules. Fibronectin was also identified in the basal linear deposit and in Bruch's membrane, but mucopolysaccharides could not be demonstrated. The presence of electron-empty space suggests a disturbance in water permeability. Our studies also showed neovascularisation beneath the retinal pigment epithelium in locations where the basal linear deposit was abundant, as well as erosion of Bruch's membrane by macrophages and endothelial cell processes. Our findings suggest that the basal linear deposit is an important precursor of neovascularisation. Possible pathogenetic mechanisms are discussed.

Telodendrial contacts between foveolar cone pedicles in the human retina

The synaptic pedicles of foveolar cones in the human retina contact each other by means of telodendrial processes. Thus direct lateral coupling of photoreceptor terminals exists even in the area of highest acuity function.

Foveomacular vitelliform dystrophy, adult type. A clinicopathologic study including electron microscopic observations

Foveomacular vitelliform dystrophy, adult type (FVDAT), is a dystrophy of the retinal pigment epithelium (RPE) characterized in part by autosomal dominant inheritance, midlife onset, mild visual loss, and various patterns of foveal yellow deposits located at the level of the pigment epithelium. Detailed pathologic studies of two postmortem eyes from a 61-year-old woman with documented FVDAT disclosed striking abnormalities involving mainly the foveal RPE and overlying photoreceptors. By light microscopy, marked focal atrophy of the pigment epithelial cells in the foveolar area was bordered by hypertrophic RPE. Interposed between the atrophic RPE and Bruch's membrane were scattered eosinophilic, fusiform collagenous plaques. The sensory retina overlying the deranged RPE displayed marked atrophy of the outer nuclear layer with loss of photoreceptor inner and outer segments. Pigment-laden macrophages containing periodic acid-Schiff-positive material had migrated into the atrophic, outer sensory retina. Ultraviolet fluorescent microscopy demonstrated massive accumulation of lipofuscin pigment within the macular RPE as well as within macrophages in the atrophic outer retina. By scanning electron microscopy, a confluent area of flattened, atrophic retinal pigment epithelial cells was rimmed by taller, hypertrophic RPE cells. By transmission electron microscopy, the pigment epithelial cells contained myriad lipofuscin granules. Bruch's membrane and the intercapillary pillars were slightly thickened and the choriocapillaris was patent. The possible interrelationships between FVDAT and the other pattern dystrophies of the RPE are discussed.

A clinical, fluorescein angiographic, and electron microscopic correlation of cystoid macular edema

Electron microscopic findings in an eye removed from a woman who had biomicroscopic and angiographic signs of cystoid macular edema occurring in association with a peripheral choroidal melanoma disclosed evidence that the anatomic basis for the biomicroscopic and angiographic changes was the polycystic expansion of the extravascular compartment of the retina by serous exudate and not, as previously reported, edema of the Mueller's cells.

Adult vitelliform macular detachment occurring in patients with basal laminar drusen

We studied 41 young and middle-aged adults who developed innumerable, small, round, uniformly sized, yellow, subretinal nodules that were often arranged in clusters throughout the posterior fundus. Angiographically, they fluoresced discretely during the early arteriovenous phase. In middle or later life 17 of these patients developed visual loss caused by vitelliform retinal detachment in the macula of one or both eyes. Spontaneous resolution of the detachment and retention of good visual acuity occurred frequently. We found evidence indicating that the multiple, small, subretinal nodules are probably focal areas of pigment epithelial attenuation overlying nodular thickenings of the basement membrane of the pigment epithelium. The term basal laminar drusen would distinguish these nodules from those of typical drusen, which are caused by focal detachments of attenuated pigment epithelium and its usually normal-thickness basement membrane from the inner collagenous zone of Bruch's membrane.

Nerve fiber layer of the primate retina: morphometric analysis

The organization of the retinal nerve fiber layer of the cynomolgus monkey was studied by electron microscopy. Nerve fiber size spectra were obtained from measurements of every fiber in enlarged montages of selected bundles. Variation in spectra among nasal, arcuate, and papillomacular bundles was examined, and variation of spectra of a given bundle as it crossed the retina was determined. Among the three types of bundles, the papillomacular contained relatively more small fibers, nasal bundles relatively more large fibers. Systematic variation of fiber spectra was observed as the disc was approached by arcuate and papillomacular but not nasal bundles. Arcuate bundles sampled in the peripapillary area contained relatively more small fibers than when sampled at a greater distance from the disc. In contrast, papillomacular bundles sampled near the disc contained relatively more large fibers than near the fovea.