Billy X. Pan

Mouse mtDNA mutant model of Leber hereditary optic neuropathy

An animal model of Leber hereditary optic neuropathy (LHON) was produced by introducing the human optic atrophy mtDNA ND6 P25L mutation into the mouse. Mice with this mutation exhibited reduction in retinal function by elecroretinogram (ERG), age-related decline in central smaller caliber optic nerve fibers with sparing of larger peripheral fibers, neuronal accumulation of abnormal mitochondria, axonal swelling, and demyelination. Mitochondrial analysis revealed partial complex I and respiration defects and increased reactive oxygen species (ROS) production, whereas synaptosome analysis revealed decreased complex I activity and increased ROS but no diminution of ATP production. Thus, LHON pathophysiology may result from oxidative stress.

Melanopsin retinal ganglion cell loss in Alzheimer disease

Melanopsin retinal ganglion cells (mRGCs) are photoreceptors driving circadian photoentrainment, and circadian dysfunction characterizes Alzheimer disease (AD). We investigated mRGCs in AD, hypothesizing that they contribute to circadian dysfunction.

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.

Benefit of Measuring Anterior Segment Structures Using an Increased Number of Optical Coherence Tomography Images: The Chinese American Eye Study.

Purpose The purpose of this study was to evaluate the benefit of analyzing an increased number of anterior segment optical coherence tomography (AS-OCT) images on measurement values of various anterior segment parameters. Methods Subjects for this cross-sectional study were recruited from the Chinese American Eye Study (CHES), a population-based study in Los Angeles, CA. Thirty-two AS-OCT images were acquired from one eye each of 83 consecutive subjects. Sixteen parameters were analyzed in each image, including angle opening distance (AOD), angle recess area (ARA), trabecular iris space area (TISA), trabecular iris angle (TIA), scleral spur angle (SSAngle), lens vault (LV), pupillary diameter (PD), anterior chamber depth (ACD), anterior chamber width (ACW), iris area (IA), and anterior chamber area (ACA). Data from 1, 2, 4, 8, 16, or 32 OCT images were averaged across subjects to calculate the range and mean of measurement values for each parameter. Results Anatomical variations were poorly captured with fewer OCT images for AOD, ARA, TISA, SSAngle, IA, and LV. For these parameters, the range and mean of measurement values obtained from one OCT image deviated from 32-image values by up to 43.9% and 13.3% of the 32-image mean, respectively. These deviations decreased when additional OCT images were analyzed. Deviations from 32-image range and mean values were less pronounced regardless of image number for PD, ACD, ACW, and ACA, measuring up to 3.5% and 5.0%, respectively. Conclusions A multi-image approach should be the standard in OCT-based studies of AOD, ARA, TISA, TIA, SSAngle, IA, and LV.

Inner Retinal Optic Neuropathy: Vitreomacular Surgery- Associated Disruption of the Inner Retina

PURPOSE Macular pucker (MP) and macular hole (MH) are vitreomaculopathies treated by vitrectomy and membrane peel. The complication of postoperative central scotoma can be associated with significant reduction in visual acuity (VA). We seek to determine whether retinal nerve fiber layer (RNFL) disruption is the pathophysiologic basis of this defect. Mitigating clinical circumstances also were sought. METHODS Eleven eyes from 10 pseudophakic patients who had undergone vitrectomy with peeling for either MH or MP were studied with clinical measures, including optical coherence tomography (OCT). Membrane specimens were evaluated by immunohistochemistry for neurofilament, a marker for the inner retina. Ten eyes from 10 pseudophakic patients who underwent repeat surgery for persistent or recurrent pathology were evaluated to determine the relationship between the timing of reoperation and clinical outcome. RESULTS Cases with a postoperative central scotoma (N=4) had worse VA (~20/600) compared to those without (N=7, ~20/30, P=0.01). Eyes with a central scotoma had significantly reduced RNFL thickness in the temporal quadrant (53.67 vs. 72.33 μm, P=0.05) by OCT. A central scotoma was associated with more disruption of the inner retina on immunohistochemistry (P=0.03). In patients with persistent or recurrent pathology, waiting six months before reoperation resulted in better functional outcomes (P=0.03). CONCLUSIONS Central scotomata and poor VA were associated with disruption of the RNFL during membrane peeling. Affected patients have RNFL thinning and signs of optic neuropathy, for which we propose the term inner retinal optic neuropathy (IRON). In patients requiring reoperation, waiting six months between surgeries may reduce the risk of IRON.

Reactive Oxygen Species in Mitochondrial Optic Neuropathies: Comment.

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Pregnancy probabilistically augments potential precursors to chronic, immune-mediated or autoimmune lacrimal gland infiltrates

PURPOSE This study asked whether pregnancy, a risk factor for dry eye disease associated with both chronic, immune-mediated- and autoimmune etiologies, augments development of clusters of coordinately functioning cells (CCFC) that may be precursors to pathological lacrimal gland infiltrates. METHODS Lacrimal glands were from six virgin- and six term-pregnant rabbits of the same age and environmental exposure history. Seventy-two immune response-related gene transcripts were assayed by real time RT-PCR. Principal component (PC) analysis identified transcript signatures of CCFC contributing negative (⊖) or positive (⊕) PC loadings and determined gland PC projections, which reflect levels of CCFC development. RESULTS Three CCFC were of interest as potential precursors to pathological infiltrates. CCFC 1⊖ was suggestive of an ectopic lymphoid structure with resting T cells and B cells. CCFC 1⊕ was suggestive of an immune-mediated infiltrate with TH1 cells and mature, cytotoxic B cells. CCFC 2⊖ was suggestive of an ectopic lymphoid structure with activated T cells, mature B cells, germinal center, and plasmacytes. CCFC 4⊖ and CCFC 5⊖ also included plasmacytes. Pregnancy augmented CCFC 1⊖ in some glands; augmented CCFC 1⊕ in others; and augmented CCFC 2⊖, CCFC 4⊖, and CCFC 5⊖ different combinations. CONCLUSIONS Potential precursors of pathological infiltrates form in the lacrimal glands by the time of sexual maturity. Pregnancy augments lacrimal gland plasmacyte populations, and it can augment development of potential precursors to either chronic, immune-mediated infiltrates or autoimmune infiltrates of various phenotypes. Systemic and strictly local, probabilistic phenomena interact with pregnancy to determine which combinatorial phenotypes are favored.

Macular Hole and Macular Pucker Surgery with Special Emphasis on Reoperations

Recent advances in the techniques of vitrectomy with membrane peeling [See chapter V.A.2. Vitreo-maculopathy surgery], at times with chromodissection [See chapter V.A.3. Chromodissection in vitreo-retinal surgery], have greatly improved patient outcomes. There are, however, risks associated with these procedures, and on rare occasions there can be much worse vision following surgery than preoperatively. This chapter will review the current concepts of pathogenesis and surgical management of macular holes and macular pucker. Special emphasis will be placed on failed cases and reoperations.