Sensory and sympathetic innervation of the mammalian cornea. A retrograde tracing study

The method of retrograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) was used to study the locations, numbers and somata diameters of corneal afferent and efferent neurons in four different mammalian species. A 2% solution of HRP-WGA was applied to the central cornea of the rat, rabbit, cat and monkey and the animals were perfusion-fixed 48-96 hr later. HRP-WGA-labeled sensory neurons were distributed relatively uniformly throughout the ophthalmic region of the ipsilateral trigeminal ganglion of the rat, cat and monkey. In marked contrast, labeled cells in the rabbit trigeminal ganglion were clustered in a sharply defined longitudinal column located in the midregion of the ophthalmic area. Occasional cells in some cats and monkeys were observed near, and possibly within, the maxillary region of the ganglion. There was no evidence for a dorsoventral somatotopy of corneal afferent neurons in any species. The majority of the labeled afferent somata were small or medium in size, although some larger diameter neurons were also observed. Modest numbers of labeled neurons were observed in the ipsilateral superior cervical ganglion (SCG) of the rabbit and cat; however, only occasional labeled neurons were observed in the SCG of the rat, and none were seen in the monkey. The labeled SCG cells, when present, were concentrated in the rostral half of the ganglion, although many cells in the cat SCG were also found further caudally. No labeled neurons were found in the middle cervical or stellate ganglia of any animal. The results of this study have revealed the existence of subtle interspecies differences in the organization of the mammalian corneal afferent and efferent innervations.     

Sympathetic innervation of the rat's eye and peripheral ganglia: an electron microscopic autoradiographic tracing study

The sympathetic innervation of the rat anterior eye segment and related peripheral ganglia was studied using light and electron microscopic autoradiography after anterograde tracing with ³H-leucine from the superior cervical ganglion. In the trigeminal and pterygopalatine ganglia, unmyelinated nerve fibers were labeled. Some fibers contained accumulations of small vesicles. Close apposition of these labeled sympathetic fibers with other unmyelinated fibers was common, and was also observed at sites where accumulations of vesicles were found. In the iris, ciliary body and trabeculum, numerous fibers and vesicle-containing varicosities were labeled, which all had a similar morphology. No labeling was found in the cornea. Sympathetic fibers traversing the trigeminal and pterygopalatine ganglion closely appose other unmyelinated fibers and contain clusters of vesicles without forming classical synaptic contacts. However, non-synaptic information transfer needs further investigation. The anterior eye segment, except for the cornea, is densely innervated by sympathetic nerve terminals.     

Secretoneurin in the peripheral ocular innervation

PURPOSE: To evaluate whether secretoneurin represents a sensory neuropeptide innervating the anterior segment of the eye. METHODS: The presence and distribution of secretoneurin was investigated in human eyes by radioimmunoassay and immunofluorescence and compared with that of the rat eye. The source of secretoneurin-positive nerves in the eye was established by measuring the concentration in eye tissues, the trigeminal and superior cervical ganglia both in control rats and in rats treated with capsaicin, and by performing immunofluorescence in one rat subjected to sympathectomy. In the rat trigeminal ganglion, the corresponding mRNA was verified by in situ hybridization and the processing of secretogranin II into secretoneurin by gel filtration chromatography. RESULTS: In human eyes, the highest levels of the peptide were found in the choroid. Nerve fibers were visualized in both species in the upper corneal and limbal stroma; in the trabecular meshwork; in the ciliary muscle, the ciliary body stroma, and processes; and in clear association with the dilator muscle, which disappeared after sympathetic denervation in rats; and also innervating the sphincter muscle in the iris and the choroidal stroma and surrounding blood vessels. Significant amounts of secretoneurin were present in the rat trigeminal ganglion and rat eye tissues. Capsaicin pretreatment led to a 57.0% +/- 4.3% and 59.1% +/- 11.9% decrease of the concentration in the trigeminal ganglion and the iris/ciliary body complex, respectively. Despite high levels in the rat superior cervical ganglion, sympathetic denervation failed to lower the concentration in eye tissues. The secretogranin II probe labeled numerous small-sized ganglion cells within the rat trigeminal ganglion, and the precursor of the peptide was found to become completely processed into secretoneurin. CONCLUSIONS: Apart from the sympathetically innervated dilator muscle, there is unequivocal evidence that secretoneurin represents a constituent of capsaicin-sensitive sensory neurons in the rat trigeminal ganglion and of unmyelinated C-fibers in the rat iris/ciliary body complex, which indicates a participation of this peptide in the ocular irritative response, a model for neurogenic inflammation in lower mammals. Because of the association of nerves with blood vessels and potent angiogenic properties, secretoneurin may be involved in neovascularization processes.     

几种新型眼前节影像技术及临床应用

以眼前节光学相干断层扫描（OCT）、Scheimpflug技术、高分辨率磁共振成像及裂隙扫描等为代表的眼前节影像技术提供了房角的各种参数,可测量角膜前后表面的曲率和前房内径,计算出角膜的屈光度,在准分子激光角膜原位磨镶术（LASIK）术后能够测量角膜瓣厚度,甚至可用于调节功能及老视的研究,极大地提高了诊疗水平。就几种新型眼前节影像技术的研究进展及其临床应用进行综述。     

角膜神经调控眼表微环境的研究进展

角膜是眼前段透明的外层结构，由高密度的神经组织支配。在角膜神经支配过程中，三叉神经节起源的角膜神经穿过上皮层和基质层中不同类型的角膜细胞。角膜基质细胞、上皮细胞、免疫细胞等多种细胞和角膜神经之间发生密切的相互作用，共同维持角膜微环境稳态。此外，角膜神经参与许多眼表疾病的发生发展过程。角膜神经释放多种活性肽物质，参与调控角膜感觉、维持上皮完整性和增殖、促进伤口愈合及调控角膜局部炎症和免疫反应等。本文对角膜神经在眼表微环境调控作用的研究进展进行综述，为角膜神经相关疾病的研究及治疗提供新的思路。     

Peripheral neural circuits regulating IOP?

The peripheral nervous system is classically separated into a somatic division containing both afferent and efferent pathways and an autonomic division composed of efferents only. The somatic afferent division is divided in A- and B-neurons. The B-neurons are supposed to be autonomic afferents as part of a reflex system involved in homeostasis. Recent data obtained by neuronal tracing and immunohistochemical experiments concerning the eye related peripheral nervous system endorse the existence of these peripheral reflex systems. Somatic afferents of trigeminal origin synaptically innervate parasympathetic neurons in the pterygopalatine ganglion. This probably represents a pathway mediating autonomically regulated ocular activity in response to sensory stimulation. In addition, it has been hypothesized that trigeminal sensory nerve fibres have an efferent function in response to noxious stimuli e.g. the ocular injury response. Sympathetic nerve fibres originating in the superior cervical ganglion course through the trigeminal and pterygopalatine ganglion without forming direct synaptic contacts. These fibres, however, contain clusters of vesicles suggesting some kind of interneural communication. Parasympathetic nerve fibres of pterygopalatine origin course through the ciliary ganglion. These nerve fibre terminals also contain clusters of vesicles without direct synaptic contacts. Experimental data concerning the distribution of neuropeptides revealed a more detailed knowledge of the anterior eye segment innervation. These experimental data are subject to some debate. The pros and cons of different techniques are discussed. Neural circuits regulating IOP have long been postulated. The possible role of peripheral reflex systems in the regulation of IOP is discussed.     

Immunosuppressive properties of tissues of the ocular anterior segment

To determine whether explants of various tissues comprising the anterior segment of individual normal eyes can display immunosuppressive properties in vitro, explants of iris/ciliary body, cornea, cornea-limbus, sclera and conjunctiva were prepared from single eyes of BALB/c mice and tested for their capacity to suppress alloantigen-driven T cell activation in vitro. Cultured explants of iris and ciliary body, and of cornea, but not sclera or conjunctiva, suppressed T cell activation in vitro. Similarly, the supernatants of cultured iris/ciliary body and cornea explants displayed immunosuppressive properties. Prostaglandins appeared to make a minor contribution to the inhibition observed. The authors conclude that certain tissues within the anterior segment of the eye (iris, ciliary body, cornea) contain cells that secrete immunosuppressive factors, whereas other tissues (conjunctiva, sclera) lack this feature. The secretions of the former tissues undoubtedly contribute to the immunosuppressive features of the microenvironment in the anterior segment of the eye, and help to account for the existence of immune privilege.     

Anterior segment growth and peripheral neural pathways in chick

PURPOSE: To learn if peripheral nerve pathways are necessary for corneal expansion and anterior segment growth under a 12-hr light:dark cycle or for the inhibition of corneal expansion under constant light rearing. METHODS: Recently hatched White Leghorn chicks under anesthesia received unilateral ciliary ganglionectomy (CGx), cranial cervical ganglionectomy (Sx), or section of the ophthalmic nerve (TGx), along with sham-operated and/or never-operated control cohorts. Chicks were reared postoperatively under either a 12-hr light:dark cycle or under constant light. After 2 weeks and with the chicks under anesthesia, corneal radii of curvature and diameters were obtained with a photokeratoscope, refractometry and A-scan ultrasonography were performed, and the axial and equatorial dimensions of enucleated eyes were measured with digital calipers. Corneal areas were calculated from corneal curvatures and diameters. RESULTS: Despite the rich peripheral innervation to the eye, the selective denervations performed here exerted remarkably limited effects on corneal expansion and anterior segment development in chicks reared under either lighting condition. Ophthalmic nerve section did reverse in large part the inhibition of equatorial expansion of the vitreous chamber occurring under constant light rearing. CONCLUSIONS: The ciliary, sympathetic, or ophthalmic peripheral nerve pathways to the eye are not required either for corneal expansion and anterior segment development under a 12-hr light:dark cycle or for the inhibition of corneal expansion under constant light rearing. The ocular sensory innervation may be a means for regulating vitreous cavity shape.     

Neurokinin a is a main constituent of sensory neurons innervating the anterior segment of the eye

PURPOSE: To study the innervation pattern of the anterior segment of the eye by neurokinin (NK)-A-immunoreactive nerves and to determine their sensory origin. METHODS: The presence and distribution of NKA was examined in human eyes by radioimmunoassay and immunofluorescence. The source of nerves was determined by measuring the concentration of NKA in the trigeminal ganglion (TG) in comparison with that of the classic sensory peptides substance P (SP) and calcitonin gene-related peptide (CGRP) and in eye tissues in capsaicin-pretreated rats versus control subjects. The NKA-like immunoreactivities were further characterized by reversed phase HPLC in the rat TG and the human iris-ciliary body complex. The presence of gamma-PPT-A mRNA was studied in the rat TG by in situ hybridization. RESULTS: The levels of NKA in human eye tissues were approximately 10 times higher than those of SP but lower than those of CGRP. Nerve fibers were visualized in the cornea, the trabecular meshwork, the iridial stroma, and, prominently, in the sphincter muscle, the ciliary body stroma and muscle and processes, and the choroidal stroma and surrounding blood vessels. In the rat TG, the concentration of NKA was approximately five times higher than that of SP. Capsaicin led to a >60% decrease of the concentration of the peptide in the rat TG and rat eye tissues except for the retina. NKA-like immunoreactivities were present in a single peak corresponding to synthetic NKA, both in the rat TG and in the human iris-ciliary body complex, and numerous ganglion cells of small size were labeled by a gamma-PPT-A probe in the rat TG. CONCLUSIONS: The present results clearly demonstrate that NKA is a main constituent of sensory neurons innervating the anterior segment of the eye. The presence of the peptide in C fibers in ocular tissues indicates a participation in sensory transmission and an involvement in the irritative response in the eye, a model for neurogenic inflammation in lower mammals.     

Recent advances in ophthalmic anterior segment imaging: a new era for ophthalmic diagnosis?

Anterior segment imaging is a rapidly advancing field of ophthalmology. New imaging modalities, such as rotating Scheimpflug imaging (Pentacam-Scheimpflug) and anterior segment optical coherence tomography (Visante OCT and Slit-Lamp OCT), have recently become commercially available. These new modalities supplement the more established imaging devices of Orbscan scanning slit topography and ultrasound biomicroscopy (UBM). All devices promise quantitative information and qualitative imaging of the cornea and anterior chamber. They provide a quantitative angle estimation by calculating the angle between the iris surface and the posterior corneal surface. Direct angle visualisation is possible with the OCT devices and UBM; they provide images of the scleral spur, ciliary body, ciliary sulcus and even canal of Schlemm in some eyes. Pentacam-Scheimpflug can measure net corneal power, a feature particularly useful for cataract patients having undergone previous corneal surgery. Anterior segment OCT can measure corneal flap depth following LASIK and anterior chamber width prior to phakic intraocular lens implantation. The arrival of the new imaging devices may herald the dawn of a new era for ophthalmic diagnosis, particularly in view of the ease and non-contact nature of examination.     

Sprouting of corneal sensory fibers in rats treated at birth with capsaicin

Normal structure and function of corneal epithelium is known to be related to proper innervation. To investigate possible trophic actions of sensory neurons on corneal epithelium, corneal innervation and various physical parameters were studied in normal rats and in rats treated as neonates with intraperitoneal injections of capsaicin. Corneal lesions were noted in treated rats which varied from multiple punctate areas of corneal opacity to deep stromal opacity with ulceration and neovascularization. These lesions waxed and waned throughout the animal's life. In addition, mechanical threshold of the corneal reflex was higher in capsaicin-treated rats. The tear rate in response to a provocative test was diminished in treated rats, presumably due to reduced afferent trigeminal input to the brain stem; blinking rates were more frequent in these animals. Using fluorescent retrograde tracing techniques, the number of cells innervating the cornea in capsaicin-treated rats was found to be significantly less compared with control animals. Innervation in the cornea (examined using a gold chloride technique) demonstrated a decrease in the number of corneal large axons in treated rats with neurite sprouting of these axons yielding a higher density of nerve fibers compared with controls. Thus, sprouting of residual sensory neurons occurs in response to the partial corneal denervation produced by capsaicin, and this sprouting does not functionally compensate to prevent the development of chronic keratitis.     

应用Sirius眼前节分析系统观察ROP激光术后儿童眼前节结构

目的:应用Sirius眼前节分析系统观察早产儿视网膜病变(ROP)激光光凝术后儿童眼前节各组织发育情况。方法:回顾性病例研究。选取2015-09/2018-04于深圳市眼科医院因ROP已行激光光凝治疗的儿童25例50眼纳入ROP组,同时选取年龄匹配的足月儿童23例46眼为对照组。两组儿童均行最佳矫正视力(BCVA)检查,并采用Sirius眼前节分析系统测量虹膜水平直径(HVID)、角膜最薄点半径、角膜最薄点厚度、角膜最大曲率半径、角膜最大曲率、中央角膜厚度(CCT)、角膜容积(CV)、前房深度(ACD)、前房容积、前房房角。结果:ROP组儿童HVID、角膜最薄点厚度、ACD、前房容积均明显小于对照组(均P<0.05),CV、前房房角均小于对照组,但两组间无差异(均P>0.05)。对照组儿童BCVA明显优于ROP组(0.07±0.10 vs 0.24±0.25,P<0.05)。结论:ROP激光光凝术后儿童眼前节组织的形态结构发生改变,角膜形态较陡峭,前房深度变浅,房角偏小,最佳矫正视力较差,可能更容易发展为屈光不正及青光眼等。     

Calcitonin gene-related peptide immunoreactive nerve fibers in the rat conjunctiva

Calcitonin gene-related peptide (CGRP) immunoreactive nerve fibers were studied in the rat conjunctiva by using indirect immunohistochemistry. Their origin was evaluated in a series of experiments where the animals were denervated by electrocoagulating the two first branches of the trigeminal nerve or by surgically extirpating the superior cervical ganglion. The CGRP-immunoreactive nerve fibers were seen mainly as thin varicose fibers in the epithelium and in the stroma. Many of the stromal fibers showed no apparent destination. However, CGRP-immunoreactive fibers were commonly found in association with stromal blood vessels, the smooth muscle of Müller, and the meibomian glands. Approximately 40% of the ganglion cells in the trigeminal ganglion were immunoreactive to CGRP. In the superior cervical ganglion, a few CGRP-immunoreactive fibers were seen although the ganglion cells were negative. After trigeminal denervation, all the epithelial and most of the stromal CGRP-immunoreactive nerve fibers disappeared. Sympathectomy had no effect on the presence of the CGRP-immunoreactive fibers. These observations indicate that most of the CGRP-immunoreactive nerve fibers in the rat conjunctiva are sensory nerves originating in the trigeminal ganglion. A few of the demonstrated fibers are, however, resistant to the sensory denervation and may be parasympathetic in their origin.     

Acute effects of H-7 on ciliary epithelium and corneal endothelium in monkey eyes

PURPOSE: Topical or intracameral administration of H-7 doubles outflow facility and reduces intraocular pressure in cynomolgus monkeys, by relaxing and expanding the trabecular meshwork (TM) and Schlemm's canal (SC). Since H-7 may have anti-glaucoma potential, we determined its effects on the corneal endothelium and ciliary epithelium for safety considerations. METHODS: Following topical H-7, aqueous humor flow (AHF), corneal endothelial transfer coefficient (k(a)) and anterior chamber (AC) entry of i.v. fluorescein were measured by fluorophotometry; AC aqueous protein concentration ([Protein](AC)) was determined by Lowry assay; and corneal thickness and endothelial cell density and morphology were measured by ultrasonic pachymetry and specular microscopy respectively. Following intracameral H-7, specular and/or light and electron microscopy of the corneal endothelium or ciliary epithelium were performed. RESULTS: Following unilateral topical H-7: (1) AHF and k(a) were essentially unchanged at 0.5--3.0, 3.5--6.0, and 0.5--6.0 hr, with an insignificant increase from 0.5--1.5 hr; (2) [Protein]( AC) was insignificantly increased at 1-1.5 hr but had returned to baseline by 2.5 hr; (3) entry of i.v. fluorescein into aqueous or cornea was modestly and transiently increased; (4) the central cornea thickened significantly at 1--2.5 hr, gradually returning to baseline 2.5 hr after H-7, while peripheral corneal thickness was less affected; (5) corneal endothelial cell borders became indistinct by 1 hr, but cell morphology was recovering by 3--5 hr and had completely returned to normal by 24 hr; (6) corneal endothelial cell density was unchanged at 5--24 hr. Following intracameral H-7, no significant changes were observed in corneal endothelial cell density or morphology by specular microscopy, nor in corneal endothelial or ciliary epithelial morphology by light and electron microscopy. CONCLUSIONS: A facility-effective intracameral dose of H-7 had no discernible structural effect on the corneal endothelium or ciliary epithelium. It is not yet clear whether carefully chosen topical doses of H-7 or analogues can enhance outflow facility without meaningfully affecting the cornea and ciliary processes.     

Presence of Langerhans cells in the central cornea linked to the development of ocular herpes in mice.

Recurrences of herpetic stromal keratitis are believed to be initiated by reactivation of herpes simplex virus infection, probably in the trigeminal ganglion. Genetic features of the virus and the host as well as the immune status of the host influence the outcome of infection. Following infection on the snout with HSV-1, mice with normal corneas usually develop mild anterior segment disease. We studied the induction of herpetic infection in mice that had abnormal corneas, containing center due to trauma or a spontaneous dystrophy. The corneal abnormality led to more frequent herpetic stromal keratitis and more severe anterior chamber reaction. In addition, we found that snout-infected mice with dystrophic corneas had an increased risk of dying from viral infection. Our data suggest that not only the strain of virus and the genetic background of the mouse, but also the state of the cornea itself, can contribute to susceptibility to ocular herpes infection.     

Specificity of a neuronotrophic factor from rabbit corneal epithelial cultures

Previous studies have demonstrated that of the three major cell types of rabbit cornea, only epithelial cells released a neuronotrophic factor that is active in both promoting survival and inducing neurite outgrowth of dissociated trigeminal neurons. In this study, the specificity of neuronotrophic factor production by selected epithelial cell types and the responsiveness of neurons from several different tissues to this trophic factor were determined. Cell cultures of various epithelia and dissociated neurons from several ganglia of neonatal and adult rabbits were utilized. In comparison with adult corneal epithelium, adult bulbar conjunctiva released a similar amount of trophic factor. Neonatal corneal epithelium released five times more, but adult retinal pigment epithelium and neonatal skin epithelium yielded less than a third and one-sixth respectively, and three cell lines (adult skin, kidney and neonatal lens epithelia) released only negligible amounts. Compared with its effect on neonatal trigeminal neurons, the trophic factor from adult corneal epithelium was similarly active on neonatal dorsal root neurons, but only half as effective on adult trigeminal neurons and less than one-tenth as effective on neonatal superior cervical neurons. The effect of nerve growth factor (from mouse submaxillary gland) on these neurons was tested for comparison. The results indicated that of the tissues studied, neuronotrophic factor was released in abundance only from corneal and conjunctival epithelia, and was active predominantly on trigeminal and dorsal root neurons (sensory neurons). This is consistent with the concept that the developmentally regulated release of trophic factor by target cells may be an underlying mechanism for neurogenesis and nerve regeneration.     

Pancreatic polypeptide-like immunoreactive nerves in the guinea pig eye

The indirect immunofluorescence technique with antisera either to avian pancreatic polypeptide or to bovine pancreatic polypeptide stains nerve fibers in the guinea pig eye. In all regions of the uvea, immunoreactive fibers are present around large blood vessels; an association of immunoreactive nerve fibers to melanocytes is seen. Immunoreactive nerves are found throughout the choroid, including the choriocapillaris. In the ciliary body, they are seen in individual ciliary processes. The iris dilator muscle and, to a lesser degree, its sphincter are innervated. The chamber angle of the anterior segment contains immunoreactive nerve fibers, but convincing innervation to the cornea is lacking. No retinal cells stain. With some exceptions, the distribution of peripheral nerve fibers parallels that of the adrenergic innervation. Appropriate controls are negative.     

Distribution of fibronectin in human and rabbit corneas

In order to study the possible role of fibronectin (FN) in corneal wound healing and the relationship between FN and sensory innervation, FN was demonstrated immunohistochemically in both normal and sensorily denervated rabbit corneas and in normal or tissue-cultured human corneas. The distribution of FN was the same in the groups examined: a thin subepithelial band of FN-like immunoreactivity was seen at the level of epithelial basement membrane and at the stromal side of Descemet's membrane. Epithelial abrasions were also performed in both normal and denervated rabbit corneas. The results were compared with those obtained from organ-cultured human corneas. Following abrasion of the corneal epithelium, FN was detected in the anterior margin of the denuded stroma 18 hr after the operation in the areas where the epithelium had not healed, but not 49 hr after. Sensory denervation did not affect the distribution of FN in normal, denervated or healing rabbit cornea. It is concluded that FN is probably not controlled by sensory innervation.     

Ultrasound biomicroscopy diagnosis of congenital glaucoma

BACKGROUND: In children with congenital glaucoma the assessment of the anterior chamber and the chamber angle might be difficult since scarring and opacities of the cornea are often seen. The purpose of our study was to reveal in vivo--morphology of the anterior segment in patients with congenital glaucoma and opaque cornea. PATIENTS AND METHODS: In 46 eyes of 23 children with different degrees of corneal opacities we performed ultrasoundbiomicroscopy (UBM) of the anterior chamber after having performed a complete ophthalmological examination in general anesthesia. RESULTS: Massive abnormalities of the anterior segment morphology were detected in 5 eyes with completely cloudy cornea. In eyes with partial opacity of the cornea, UBM gave additional information concerning the anterior chamber angle topography, as iris remnants in aniridia, or anterior synechia. CONCLUSION: Especially in cases with extensive corneal opacities the UBM allows us to get morphological and topographic information about the anterior segment and helps to establish an individual strategy for surgical management.     

Korneale Neuroparalyse nach Blockexzision im Bereich des 3- und 9-Uhr-Meridians

PURPOSE: Corneal innervation is mainly supported by the long posterior ciliary nerves. Anatomically, the long ciliary nerves run with the long ciliary arteries at 3 and 9 o'clock. The aim of this retrospective study was to find out if block excision of anterior uveal tumors or epithelial ingrowth located at the 3 or 9 o'clock position of the limbal circumference causes corneal neuroparalysis. PATIENTS AND METHODS: Between 1980 and May 1999, a total of 151 block excisions were performed in our department (92 block excisions because of anterior uveal tumors and 59 because of cystic epithelial ingrowth to the anterior chamber). In 27 patients, anterior uveal tumors or cystic epithelial ingrowth were located at the 3 or 9 o'clock position of the limbal circumference (14 patients with cystic epithelial ingrowth and 13 patients with anterior uveal tumors). Mean age of all patients was 54.4 +/- 15.7 years at the time of surgery. Mean diameter of the block excision was 10.7 +/- 4.5 mm for tumor-patients and 9.0 +/- 1.2 mm for patients with anterior chamber cysts. Mean follow-up time was 93.6 +/- 43 months. RESULTS: Only 1 of 27 patients exhibited a moderate neuroparalytic corneal ulcer during the follow-up time. In the remaining 26 patients, no signs of clinically relevant corneal neuroparalysis such as epithelial disorders or neuroparalytic ulcers were found. CONCLUSION: Block excision of tumors or cystic epithelial ingrowth located at the 3 or 9 o'clock position of the limbal circumference did not lead to severe neuroparalytic disorders of the host cornea. This may be an important factor in postoperative management of patients undergoing block excision and corneoscleral grafting.