Dr. Marfurt is a Professor of Anatomy and Cell Biology and Associate Director for Research at the Indiana University School of Medicine - Northwest. Dr. Marfurt brings world-class experience and expertise in the areas of comparative corneal neuroanatomy and neurophysiology, corneal wound healing, and ocular surface disease.
Hyperosmolar Tears Induce Functional and Structural Alterations of Corneal Nerves: Electrophysiological and Anatomical Evidence Toward Neurotoxicity.
Invest Ophthalmol Vis Sci. 2015 Dec;56(13):8125-40
Authors: Hirata H, Mizerska K, Marfurt CF, Rosenblatt MI
PURPOSE: In an effort to elucidate possible neural mechanisms underlying diminished tearing in dry eye disease, this study sought to determine if hyperosmolar tears, a ubiquitous sign of dry eye disease, produce functional changes in corneal nerve responses to drying of the cornea and if these changes correlate with alterations in corneal nerve morphology.
METHODS: In vivo extracellular electrophysiological recordings were performed in rat trigeminal ganglion neurons that innervated the cornea before, and up to 3 hours after, the ocular application of continuous hyperosmolar tears or artificial tears. In corollary experiments, immunohistochemical staining was performed to compare corneal nerve morphology in control and in eyes treated with hyperosmolar solutions.
RESULTS: Our previous studies identified a population of corneal afferents, dry-sensitive neurons that are strongly excited by corneal dessication ("dry response"), a response thought to trigger the lacrimation reflex. In the present study, we found that the dry responses of corneal dry-sensitive neurons were depressed or even completely abolished by hyperosmolar tears in a time- (30 minutes to 3 hours) and dose (450- to 1000-mOsm solutions)-dependent manner. Furthermore, eyes treated with hyperosmolar tears for 3 hours contained large numbers of morphologically abnormal (granular, fragmented, or prominently beaded) subbasal nerves that appeared to be undergoing degeneration.
CONCLUSIONS: These results demonstrate that tear hyperosmolarity, considered to be a "core" mechanism of dry eye disease, significantly decreases physiological sensitivity and morphologic integrity of the corneal nerves important in tear production. These alterations might contribute to the diminished tearing seen clinically in dry eye patients.
PMID: 26720465 [PubMed - indexed for MEDLINE]
Loss of corneal sensory nerve fibers in SIV-infected macaques: an alternate approach to investigate HIV-induced PNS damage.
Am J Pathol. 2014 Jun;184(6):1652-9
Authors: Dorsey JL, Mangus LM, Oakley JD, Beck SE, Kelly KM, Queen SE, Metcalf Pate KA, Adams RJ, Marfurt CF, Mankowski JL
Peripheral neuropathy is the most frequent neurological complication of HIV infection, affecting more than one-third of infected patients, including patients treated with antiretroviral therapy. Although emerging noninvasive techniques for corneal nerve assessments are increasingly being used to diagnose and monitor peripheral neuropathies, corneal nerve alterations have not been characterized in HIV. Here, to determine whether SIV infection leads to corneal nerve fiber loss, we immunostained corneas for the nerve fiber marker βIII tubulin. We developed and applied both manual and automated methods to measure nerves in the corneal subbasal plexus. These counting methods independently indicated significantly lower subbasal corneal nerve fiber density among SIV-infected animals that rapidly progressed to AIDS compared with slow progressors. Concomitant with decreased corneal nerve fiber density, rapid progressors had increased levels of SIV RNA and CD68-positive macrophages and expression of glial fibrillary acidic protein by glial satellite cells in the trigeminal ganglia, the location of the neuronal cell bodies of corneal sensory nerve fibers. In addition, corneal nerve fiber density was directly correlated with epidermal nerve fiber length. These findings indicate that corneal nerve assessment has great potential to diagnose and monitor HIV-induced peripheral neuropathy and to set the stage for introducing noninvasive techniques to measure corneal nerve fiber density in HIV clinical settings.
PMID: 24828391 [PubMed - indexed for MEDLINE]
Anatomy of the human corneal innervation.
Exp Eye Res. 2010 Apr;90(4):478-92
Authors: Marfurt CF, Cox J, Deek S, Dvorscak L
The anatomy of the human corneal innervation has been the subject of much investigation; however, a comprehensive description remains elusive. The purpose of the present study was to provide a detailed description of the human corneal innervation using a novel approach involving immunohistochemically stained anterior-cornea whole mounts. Sixteen donor corneas aged 19-78 years were cut with a 6.0 mm trephine into a central plug and two peripheral rims. Each specimen was sectioned serially on a cryostat to produce several 100 microm-thick stromal sections and a 100-140 microm-thick anterior-cornea whole mount that contained the entire corneal epithelium and much of the anterior stroma. The corneal innervation was stained with a primary antibody against beta neurotubulin and subjected to rigorous quantitative and qualitative analyses. The results showed that a mean of 71.3 +/- 14.3, uniformly spaced, main stromal nerve bundles entered the cornea at the corneoscleral limbus. The bundles averaged 20.3 +/- 7.0 microm in diameter, were separated by a mean spacing of 0.49 +/- 0.40 mm, and entered the cornea at a mean distance of 293 +/- 106 microm from the ocular surface. Each stromal bundle gave rise through repetitive branching to a moderately dense midstromal plexus and a dense subepithelial plexus (SEP). The SEP was comprised of modest numbers of straight and curvilinear nerves, most of which penetrated Bowman's membrane to supply the corneal epithelium, and a more abundant and anatomically complex population of tortuous, highly anastomotic nerves that remained largely confined in their distribution to the SEP. SEP density and anatomical complexity varied considerably among corneas and was less dense and patchier in the central cornea. A mean of 204 +/- 58.5 stromal nerves penetrated Bowman's membrane to supply the central 10 mm of corneal epithelium (2.60 nerves/mm(2)). The density of Bowman's membrane penetrations was greater peripherally than centrally. After entering the epithelium, stromal nerves branched into groups of up to twenty subbasal nerve fibers known as epithelial leashes. Leashes in the central and intermediate cornea anastomosed extensively to form a dense, continuous subbasal nerve plexus, while leashes in the peripheral cornea demonstrated fewer anastomoses and were less complex anatomically. Viewed in its entirety, the subbasal nerve plexus formed a gentle, whorl-like assemblage of long curvilinear subbasal fibers, 1.0-8.0 mm in length, that converged on an imaginary seam or gentle spiral (vortex) approximately 2.51 +/- 0.23 mm inferonasal to the corneal apex. Mean subbasal nerve fiber density near the corneal apex was 45.94 +/- 5.20 mm/mm(2) and mean subbasal and interconnecting nerve fiber diameters in the same region were 1.51 +/- 0.74 microm and 0.69 +/- 0.26 microm, respectively. Intraepithelial terminals originated exclusively as branches of subbasal nerves and terminated in all epithelial layers. Nerve terminals in the wing and squamous cell layers were morphologically diverse and ranged in total length from 9 to 780 microm. The suprabasal layers of the central corneal epithelium contained approximately 605.8 terminals/mm(2). The results of this study provide a detailed, comprehensive description of human corneal nerve architecture and density that extends and refines existing accounts. An accurate, detailed model of the normal human corneal innervation may predict or help to understand the consequences of corneal nerve damage during refractive, cataract and other ocular surgeries.
PMID: 20036654 [PubMed - indexed for MEDLINE]