Milton N. Moraes-Filho

Melanopsin retinal ganglion cells are resistant to neurodegeneration in mitochondrial optic neuropathies

Mitochondrial optic neuropathies, that is, Leber hereditary optic neuropathy and dominant optic atrophy, selectively affect retinal ganglion cells, causing visual loss with relatively preserved pupillary light reflex. The mammalian eye contains a light detection system based on a subset of retinal ganglion cells containing the photopigment melanopsin. These cells give origin to the retinohypothalamic tract and support the non-image-forming visual functions of the eye, which include the photoentrainment of circadian rhythms, light-induced suppression of melatonin secretion and pupillary light reflex. We studied the integrity of the retinohypothalamic tract in five patients with Leber hereditary optic neuropathy, in four with dominant optic atrophy and in nine controls by testing the light-induced suppression of nocturnal melatonin secretion. This response was maintained in optic neuropathy subjects as in controls, indicating that the retinohypothalamic tract is sufficiently preserved to drive light information detected by melanopsin retinal ganglion cells. We then investigated the histology of post-mortem eyes from two patients with Leber hereditary optic neuropathy and one case with dominant optic atrophy, compared with three age-matched controls. On these retinas, melanopsin retinal ganglion cells were characterized by immunohistochemistry and their number and distribution evaluated by a new protocol. In control retinas, we show that melanopsin retinal ganglion cells are lost with age and are more represented in the parafoveal region. In patients, we demonstrate a relative sparing of these cells compared with the massive loss of total retinal ganglion cells, even in the most affected areas of the retina. Our results demonstrate that melanopsin retinal ganglion cells resist neurodegeneration due to mitochondrial dysfunction and maintain non-image-forming functions of the eye in these visually impaired patients. We also show that in normal human retinas, these cells are more concentrated around the fovea and are lost with ageing. The current results provide a plausible explanation for the preservation of pupillary light reaction despite profound visual loss in patients with mitochondrial optic neuropathy, revealing the robustness of melanopsin retinal ganglion cells to a metabolic insult and opening the question of mechanisms that might protect these cells.

Association of Optic Disc Size with Development and Prognosis of Leber’s Hereditary Optic Neuropathy

PURPOSE To study the optic nerve head (ONH) morphology of patients with Lebers hereditary optic neuropathy (LHON) in a large family from Brazil carrying the 11778/ND4 mutation and in a case series of unrelated Italian families bearing different mitochondrial DNA (mtDNA) pathogenic mutations. METHODS Enrolled in the study were 15 LHON-affected patients (LHON-affected) and 45 LHON unaffected mutation carriers (LHON carriers) belonging to the previously reported Brazilian SOA-BR LHON pedigree and 56 LHON-affected and 101 LHON carriers from 45 unrelated LHON Italian pedigrees molecularly defined. The LHON-affected were subgrouped according to the extent of visual recovery. All individuals underwent optic nerve head (ONH) analysis by optical coherence tomography. RESULTS In the Brazilian sample, the mean optic disc area was significantly larger in LHON carriers than in the control group (P=0.002). In the Italian sample, the mean optic disc area and vertical disc diameter were significantly higher in LHON carriers than in both LHON-affected (respectively, P=0.008 and P<0.001) and control subjects (P<0.001 in both cases). The LHON-affected with visual recovery had a significantly larger vertical disc diameter when compared with those without visual recovery (P=0.03). CONCLUSIONS The results, revealing that the ONH size is larger in LHON carriers than in LHON-affected, suggest a protective role for this anatomic trait. Such a hypothesis is reinforced by the observation that, among the LHON-affected, larger discs correlated with visual recovery and better visual outcome. The findings may be relevant for prognosis and provide a mechanism for identifying nuclear-modifying genes implicated in the variability of penetrance in LHON.

Mathematically modeling the involvement of axons in Leber's hereditary optic neuropathy.

PURPOSE Lebers hereditary optic neuropathy (LHON), a mitochondrial disease, has clinical manifestations that reflect the initial preferential involvement of the papillomacular bundle (PMB). The present study seeks to predict the order of axonal loss in LHON optic nerves using the Nerve Fiber Layer Stress Index (NFL-S(I)), which is a novel mathematical model. METHODS Optic nerves were obtained postmortem from four molecularly characterized LHON patients with varying degrees of neurodegenerative changes and three age-matched controls. Tissues were cut in cross-section and stained with p-phenylenediamine to visualize myelin. Light microscopic images were captured in 32 regions of each optic nerve. Control and LHON tissues were evaluated by measuring axonal dimensions to generate an axonal diameter distribution map. LHON tissues were further evaluated by determining regions of total axonal depletion. RESULTS A size gradient was evident in the control optic nerves, with average axonal diameter increasing progressively from the temporal to nasal borders. LHON optic nerves showed an orderly loss of axons, starting inferotemporally, progressing centrally, and sparing the superonasal region until the end. Values generated from the NFL-S(I) equation fit a linear regression curve (R(2) = 0.97; P < 0.001). CONCLUSIONS The quantitative histopathologic data from this study revealed that the PMB is most susceptible in LHON, supporting clinical findings seen early in the course of disease onset. The present study also showed that the subsequent progression of axonal loss within the optic nerve can be predicted precisely with the NFL-S(I) equation. The results presented provided further insight into the pathophysiology of LHON.

Natural History of Conversion of Leber's Hereditary Optic Neuropathy: A Prospective Case Series

PURPOSE To illustrate the natural history of Lebers hereditary optic neuropathy (LHON). DESIGN Prospective observational case series. PARTICIPANTS The Soave-Brazil pedigree of m.11778G>A/ND4 mitochondrial DNA LHON mutation. METHODS A prospectively acquired database of the Soave-Brazil pedigree was reviewed. Data from 285 individuals were included in the database over a 15-year period. The pedigree was reviewed for unaffected mutation carriers who converted to affected status, 6 patients with LHON were identified. The medical records were reviewed 1 year preconversion to 1 year postconversion for visual acuity (logarithm of the minimum angle of resolution [logMAR]), Humphrey Visual Field (HVF) mean deviation (MD), and retinal nerve fiber layer (RNFL) thickness, as measured by Cirrus (Carl Zeiss, Oberkochen, Germany) optic coherence tomography (OCT). The RNFL thickness values were normalized for age. Visual acuity, HVF, and processed RNFL data from each of the 12 eyes were then sorted into 2-month time periods relative to the date of conversion, within which they were averaged. MAIN OUTCOME MEASURES The main outcome measures were visual acuity, HVF MD, and RNFL thickness. RESULTS Decreased visual acuity preceded conversion by up to 2 months and then declined up to 8 months postconversion. Decrease in HVF MD occurred at least 4 months preceding conversion, after which values decreased until plateau at 6 to 8 months. Average RNFL thickness was above normal baseline thickness in all 4 quadrants as measured by OCT at the time of conversion. Increase in RNFL thickness preceded conversion as early as 4 to 6 months, peaked at conversion, and decreased until individual plateaus. The temporal quadrant was first to be involved, then the inferior and superior quadrants, and the nasal quadrant showed the latest and least changes. CONCLUSIONS Subclinical changes preceded the date of conversion and may reflect the complicated nature of identifying the date of conversion in LHON. Early increases in RNFL preceding conversion suggest that structural changes precede clinically significant vision loss. Asynchronous quadrant involvement supports a previously published mathematical model. The natural history of LHON is not a subacute process, as previously believed, but progresses more slowly, taking up to 8 months to plateau.

In vivo, in vitro toxicity and in vitro angiogenic inhibition of sunitinib malate.

Purpose: To evaluate the in vivo and in vitro toxicity of sunitinib malate, a multikinase inhibitor molecule. Design: Experimental, Prospective, Controlled. Methods: Human retinal pigment epithelial (ARPE-19) and human umbilical vein endothelialcells (HUVECS) were used in a culture toxicity test and exposed to different concentrations of sunitinib malate for 18 hours. The HUVECs also were cultured to evaluate the angiogenesis inhibitory effect of sunitinib malate. Fundus photography and angiographic, electrophysiologic, and histopathologic evaluations with light and electron microscopy were performed in two groups of five rabbits each that received different intravitreal concentrations of the drug. Each rabbit received 0.1 ml of sunitinib malate in the right eye (one group with 12.5 mg/ml, the other group with 25 mg/ml); all animals received 0.1 ml of physiologic saline solution in the left eye. After sacrifice, the eyes were enucleated and fixed with modified Karnovsky solution. Results: No toxicity related to sunitinib malate was observed using an in vitro model with the 12.5 and 25 mg/ml solutions in HUVEC and ARPE cell cultures. No toxicity was observed in the in vivo model with 12.5 mg/ml, but light microscopy showed that the 25 mg/ml solution damaged the photoreceptors layer. No functional changes in the electroretinogram were observed in any group. Conclusions: Sunitinib malate 12.5 mg/ml caused no toxicity in in vivo and in vitro models, but the 25 mg/ml concentration caused retinal changes suggesting toxicity in the in vivo model. Further research with the drug is needed in models of ocular neovascularization.

Use of impression cytology for the detection of unsuspected ocular surface squamous neoplasia cells in pterygia

Purpose: To evaluate the agreement between the methodologies of impression cytology (IC) and histopathology regarding epithelial lesions clinically diagnosed as pterygium and also regarding the detection of unsuspected and associated ocular surface squamous neoplasia (OSSN). Methods: Thirty-two Brazilian patients were included and IC was performed on all pterygia before excision. Histopathogical examination was considered the gold standard and was performed by two experienced ocular pathologists in which consensus existed regarding pterygia diagnosis. IC accuracy was assessed by sensitivity and specificity with a 95% confidence interval. Results: From the 32 primary lesions studied, histopathological examination confirmed the diagnosis of pterygium without atypical cells in 19 cases (60%) and showed unsuspected and associated OSSN cells in 13 cases (40%). IC demonstrated one false-negative and one false-positive result for atypia. Statistical analysis showed an estimated sensitivity of 92%, specificity of 94%, positive predictive value of 92%, and negative predictive value of 94%. Conclusion: IC demonstrated high agreement with histopathological analysis in the detection of atypical epithelial cells in unsuspected OSSN in Brazilian pterygia patients.

Development and initial experience with a colored perfluorocarbon liquid for intraocular tamponade in vitreoretinal surgery

Purpose: To present the development and initial experience of a novel colored perfluorocarbon liquid (PFCL) in vitreoretinal surgery. Methods: This was an experimental laboratory study and prospective human interventional study. F6H8 (Fluoron GmbH) was colored by adding 0.3 g/L blue anthraquinone dye. Subsequently, 20% colored F6H8 was prepared by mixing with perfluorooctane or perfluorodecalin (Fluoron GmbH). The novel product is not yet FDA approved for human application. In the laboratory, the colored PFCL was covered with 1) uncolored PFCL, 2) BSS, and 3) silicone oil. Cell toxicity was evaluated in L929 mouse fibroblasts using a growth inhibition assay. Porcine ex vivo eyes were evaluated after vitrectomy followed by intravitreal and subretinal colored PFCL infusion. A pilot, prospective, noncomparative interventional study was conducted in patients with retinal detachment with proliferative vitreoretinopathy (PVR). Results: The density of the colored PFLC mixture was 1.664 g/cm3 for perfluorooctane and 1.802 g/cm3 for perfluorodecalin. There was no relevant cell growth inhibition with any concentration of colored PFCL tested. Experiments in pigs revealed that infusion of the colored PFCL caused neither staining of the internal limiting membrane nor intravitreal residual droplets. In the prospective study, 9 eyes (75%) underwent surgery for rhegmatogenous retinal detachment with at least grade C PVR. The colored PFCL enabled retinal break examination and detection of residual intravitreal droplets in all surgeries. There was no case of separation or leakage of the dye from the PFCL solution that could have caused unwanted staining of the vitreous or epiretinal surface. Conclusion: The colored PFCL enabled intraoperative maneuvers such as endolaser use. In addition, removal of the colored PFCL was easily achieved at the end of surgery.

The Photopic Negative Response: An Objective Measure of Retinal Ganglion Cell Function in Patients With Leber's Hereditary Optic Neuropathy

Purpose The photopic negative response (PhNR) is a slow negative component of a flash photopic full-field ERG that has been shown to be specific for retinal ganglion cell (RGC) activity. Direct evaluation of RGC function is desirable in patients with Lebers hereditary optic neuropathy (LHON) in which the loss of central acuity can make it difficult to monitor patients with standard metrics. The purpose of this study was to evaluate the use of PhNR as an objective noninvasive clinical metric in LHON. Methods Full-field photopic ERG recordings were collected in subjects with the mt.11778G>A/ND4 LHON mutation using a red on blue stimulus. The PhNR was identified using a computer-based automated detection system, and data were manually examined to remove movement artifacts. Results The PhNR amplitude was compared between controls (n = 13), carriers (n = 17), and affected (n = 6). Mean PhNR amplitude decreased significantly across groups (P < 0.0001). Post hoc Tukeys test revealed a significant decrease in PhNR amplitude between carriers and controls (P < 0.05) and between carriers and affected (P < 0.01). Conclusions We are able to demonstrate that the PhNR amplitude is significantly decreased in patients affected by LHON compared to carriers in a well-described pedigree. Surprisingly, there was also a decrease in PhNR in carriers, suggesting potential subclinical RGC dysfunction in some carriers. This is important in patients affected with LHON who typically have a dense central scotoma. The PhNR may be a useful objective outcome measure for future clinical trials.

State of the art in chromovitrectomy

Vitrectomy is a surgery that involves complex and delicate techniques that treat diseases such as macular hole, epiretinal membrane and diabetic macular edema. Chromovitrectomy is one of these techniques and includes the use of coloring agents such as vital dyes or crystals to enhanced visibility of transparent structures during vitrectomy. The aim of this study was to present a modern approach, based on scientific evidence, about the application and indication of vital coloring agents during vitrectomy. The use of such agents has made this surgery more predictable and has increased its post-operative prognosis. Although research on chromovitrectomy is currently expanding there is still not an established gold standard dyeing agent.