Surface changes in the anaesthetic conjunctiva in man, with special reference to the production of mucus from a non-goblet-cell source

Morphologic alterations of the palpebral conjunctival epithelium in a dry eye model

PURPOSE

To investigate the normal palpebral conjunctival histology in C57BL/6 mice and the structural changes that occur in a dry eye model.

METHODS

Twenty-four male and female C57BL/6 mice, 8 untreated and 16 exposed to experimental ocular surface desiccating stress (DS). Ocular dryness was induced by administration of scopolamine hydrobromide (0.5 mg/0.2 mL) four times a day for 5 days (DS5) or 10 days (DS10). Counts and measurements were obtained using anatomical reference points, and goblet cell density was investigated with a variety of stains.

RESULTS

Near the junction between the lid margin and the normal palpebral conjunctiva, the epithelium had an average thickness of 45.6 ± 10.5 μm, 8.8 ± 2.0 cell layers, versus 37.7 ± 5.6 μm, 7.4 ± 1.3 layers in DS10 (P < 0.05). In the goblet cell-populated palpebral region, the normal epithelium was thicker (P < 0.05) than on DS5 and DS10. In the control, 43% of the goblet cells were covered by squamous epithelium compared with 58% (DS5) and 63% (DS10) (P < 0.05). A decreased number of periodic acid-Schiff (PAS)-stained goblet cells and Alcian blue-stained goblet cells were observed in the dry eye. Not all goblet cells were stained with PAS and Alcian blue.

CONCLUSION

The mouse palpebral conjunctival epithelium was structurally similar to the human. After DS, the palpebral conjunctival epithelium decreased in thickness and goblet cell access to the surface seemed to be inhibited by surrounding epithelial cells, potentially slowing down their migration to the surface. Differential staining with PAS and Alcian blue suggests that there may be different subtypes of conjunctival goblet cells.

Assessment of goblet cell orifice distribution across the rabbit bulbar conjunctiva based on numerical density and nearest neighbors analysis

PURPOSE

To assess density and spatial distribution of the goblet cell orifices at the surface of the rabbit bulbar conjunctiva as an indicator of functional activity.

METHODS

Specimens of the superior or inferior bulbar conjunctiva from six healthy young adult (2 kg) pigmented rabbits were obtained using a special preparation technique by which the conjunctiva was carefully stretched out during fixation with buffered glutaraldehyde. The apical surface of the specimens was examined by scanning electron microscopy. From high magnification prints, the areas and dimensions of 32-49 orifices/image were measured. In addition, the centre-to-centre spacing and spatial distribution of the orifices were assessed using a nearest neighbors principle.

RESULTS

The bulbar conjunctival surface is composed of polygonal cells decorated with surface microplicae and in between which are individual goblet cell orifices. The goblet cell orifices are characterized by tending to be oval in shape (long:short dimensions ratio of 1.57 +/- 0.23) and usually having a distinct line of microvilli around the perimeter. The orifices had a wide range of areas (from 13 to 188 μm(2); group mean +/- SD of 54 +/- 36 μm(2)), and distribution of orifice areas was skewed or even bimodal. The overall orifice density was 387 +/- 68/mm(2), with the group-averaged nearest neighbors distance being 34 +/- 3 μm. Comparisons of the measured nearest neighbors distances to that for an optimum spacing based on numerical density reveals the goblet cell orifices to be slightly further apart and that they were not obviously in groups or clustered.

CONCLUSIONS

Goblet cell orifices at the bulbar conjunctival surface, a presumed indicator of functional secretory activity, appear to have reproducible density and a discrete and reasonably predictable spatial distribution.

Goblet cells of the normal human bulbar conjunctiva and their assessment by impression cytology sampling

Goblet cells of the conjunctiva are the main source of mucus for the ocular surface. The objectives of this review are to consider the goblet cells as assessed by various histological, cytological and electron microscopy methods, and to assess the consistency of published reports (over more than 25 years) of goblet cell density (GCD) from impression cytology specimens from nominally healthy human subjects. Reported GCD values have been notably variable, with a range from 24 to 2226 cells/mm² for average values. Data analysis suggests that a high density of goblet cells should be expected for the healthy human conjunctiva, with a tendency toward higher values in samples taken from normally covered locations (inferior and superior bulbar conjunctiva) of the open eye (at 973 +/- 789 cells/ mm²) than in samples taken from exposed (interpalpebral) locations (at 427 +/- 376 cells/mm²). No obvious change in GCD was found with respect to age, perhaps because the variability of the data did not allow detection of any age-related decline in GCD. Analyses of published data from 33 other sources indicated a trend for GCD to be lower than normal across a spectrum of ocular surface diseases.

[In vivo imaging of the conjunctival epithelium using confocal laser scanning microscopy]

BACKGROUND

In various ocular diseases, cytomorphological findings of the ocular surface are an essential component of clinical diagnostics. When evaluating the conjunctival epithelium, minimally invasive acquisition of biomaterial is necessary for lab and technical processing and in vitro histological examination. To examine corneal structures in vivo, confocal laser scanning microscopy is a successful standard method. Our aim was to employ in vivo confocal laser scanning microscopy also for examining the conjunctival epithelium.

MATERIAL AND METHOD

Results were analyzed and compared with cytomorphological findings of impression cytology. Accordingly, the basic features of conjunctival in vivo examination using RLSM were described and defined. In vivo images were analyzed and compared with impression cytological slide preparations (n=110) of 23 healthy test persons. Examination was standardized. Finally, the confocal laser scan images were compared to the impression cytological patterns.

RESULTS

Due to the distribution of reflectors (pixel brightness), diagnostic analysis of important morphological structures (cell nucleus, cytoplasm, nucleus/plasma relation) of the conjunctiva is possible. Secretory cells of the epithelium (goblet cells) can be easily recognized by their size. Highly reflective pixels depict cell walls or wide intercellular spaces with high contrast.

CONCLUSIONS

The in vivo investigation of important anatomical and morphological structures of the conjunctival epithelium is possible using RLSM. The distribution pattern of goblet cell pixel brightness may correlate with various secretion contents or suggest distinct, recognizable, functional conditions (hypo- or hypersecretion).

Cellular inflammatory response induced by sensory denervation of the conjunctiva in monkeys

The inflammatory response induced by sensory denervation of the cornea, neuroparalytic (neurotrophic) keratitis, has been widely reported in the literature. Clinical evidence has shown that the conjunctiva also responds to sensory denervation, but little is known of the cytology of the conjunctival tissue response to denervation. The purpose of this study therefore was to investigate the cytological aspects of tissue response induced in the conjunctiva of monkeys by sensory denervation. Intracranial ophthalmic neurotomy was carried out in three monkeys, maxillary neurotomy in four, combined ophthalmic and maxillary neurotomy in two, and infraorbital nerve transaction in one monkey. These various operations were performed for other experimental purposes, but the conjunctival tissues from the animals were suitable and available to study the cytology of the inflammatory response induced in the tissue following the sensory denervation. The cytological changes were studied using light microscopy. Complete or severe ophthalmic nerve transection induced significant inflammatory responses, which were largely confined to the tarsal region of the conjunctiva. The responses included a substantial increase in the infiltration of the epithelium by polymorphonuclear leucocytes and severe disruption of the epithelium. The number of macrophages in the conjunctiva also increased. The response induced by maxillary denervation, however, was not as pronounced as that induced by sensory denervation. The restriction of the conjunctival tissue response to the tarsal region was considered to be due to the friction between the tarsal conjunctiva (and the hard tarsal plate) and the cornea during blinking. This study shows that sensory denervation of the conjunctiva elicits an inflammatory response characterized by substantial infiltration of the epithelium by neutrophil and macrophage and disorganization of the conjunctival tissue.

Heterogeneity in the ultrastructure of the mucous (goblet) cells of the rabbit palpebral conjunctiva

AIM

The purpose of this study was to assess objectively the ultrastructure of the secretory granules in rabbit conjunctival mucin-producing 'goblet' cells.

METHOD

The upper eyelids from five young adult dioestrous female rabbits were dissected out, stretched onto a cardboard support and prepared for transmission electron microscopy by repeated application of an isotonic two per cent glutaraldehyde fixative at room temperature. Post-fixation treatment included osmium tetroxide and staining with uranyl acetate and lead citrate. Low magnification micrographs were taken of the goblet cells of the conjunctiva, printed at a magnification of approximately 6,000 and the number, size and features of the secretory granules assessed.

RESULTS

Across the entire palpebral conjunctiva of all five rabbits, the majority of mucous cells displayed a goblet shape and the secretory granules were uniformly pale in staining. The average width of the goblet cells was 10.8 +/- 1.1 microm and the diameter of the secretory granules was 0.82 +/- 0.16 microm. However, in localised regions across the palpebral conjunctiva of two of the rabbits, some goblet cells were different in that the secretory granules had either a denser-staining core, in which some of the granules were densely staining (while others were pale) or most of the granules were densely staining. These mucous cells had an average diameter of 10.3 +/- 1.7 microm and the granule diameters averaged 0.88 +/- 0.01 microm. For these abnormal goblet cells, inflammatory cells were found in their immediate vicinity. Occasionally, goblet cells were seen to be in the process of degranulation with associated apparent cell necrosis and the mucin granule diameter was close to 1 microm.

CONCLUSIONS

The ultrastructure of the mucin-containing secretory granules of the conjunctival mucous cells is not necessarily homogeneous in character and further attention needs to be given to the effects of localised inflammation in the tissue and to possible hormonal influences.

Relationship between goblet cell density and tear function tests

AIM

The objective of this study was to find a relationship between goblet cell density (GCD) and other diagnostic tests of dry eye in a group of normal healthy Chinese subjects. The capability of using GCD as a tear function test was assessed.

METHOD

A total of 42 optometry students with no contact lens wear history were recruited. Subjects were required to fill in a dry eye questionnaire. The non-invasive tear break-up time (NITBUT) of each subject was measured, followed by phenol red thread test (PRTT) and tear break-up time (TBUT) tests. Conjunctival epithelial cells from the inferior nasal bulbar conjunctiva were harvested by the impression cytology technique. The specimens collected were labelled and stained with PAS (Periodic Acid Schiff)-haematoxylin. The goblet cells and the conjunctival epithelial cells were counted under a light microscope of 100x magnification. Spearman's rho (rho) correlation test was used to analyse the relationship between GCD and the other tear function tests.

RESULTS

With a probability level of 0.0051 (corrected for a cumulative familywise error rate of p = 0.05), GCD was found to have no correlation with NITBUT (rho = -0.193, p = 0.222), McMonnies Dry Eye Scores (MCDES) (rho = -0.052, p = 0.742), PRTT (rho = - 0.188, p = 0.234) and TBUT (rho = 0.246, p = 0.117).

CONCLUSION

There was no correlation between GCD and MCDES, NITBUT, PRTT and TBUT. The GCD alone is not a useful diagnostic test for tear film instability in normal eyes although it is a good indicator in the diagnosis of ocular surface diseases.

Corneal protection by the ocular mucin secretagogue 15(S)-HETE in a rabbit model of desiccation-induced corneal defect

The mucin secretagogue 15(S)-HETE was found to stimulate glycoprotein secretion in human ocular tissue at submicromolar concentrations in the present studies. Therefore, the ability of topically applied 15(S)-HETE to preserve corneal integrity was investigated in a rabbit model of desiccation-induced corneal defect. Desiccation-induced corneal injury was elicited in anesthetized rabbits by maintaining one eye open with a speculum. Corneal staining and corneal thickness changes were determined immediately following desiccation. 15(S)-HETE dose-dependently reduced corneal damage (ED50 = 120 nM) during a two-hour desiccation. Corneal staining was unchanged relative to control using a 1 microM dose of 15(S)-HETE. Through four hours of desiccation, 15(S)-HETE (500 nM) decreased corneal staining by 71% and completely prevented corneal thinning. 15(S)-HETE (1 microM) was significantly more efficacious than an artificial tear product over the 4-hour desiccation period. There was no evidence of tachyphylaxis following repeated topical ocular dosing of 15(S)-HETE. These studies demonstrate that 15(S)-HETE stimulates ocular mucin secretion in vitro and effectively protects the cornea in a rabbit model of desiccation-induced injury. The results suggest that the ocular mucin secretagogue 15(S)-HETE may have therapeutic utility in dry eye patients, alleviating corneal injury and restoring corneal integrity.

Ultrastructural evidence of mucus in human conjunctival epithelial cultures

PURPOSE

To demonstrate by ultrastructural techniques that human conjunctival epithelium cells in vitro can produce mucin-like secretion.

METHODS

Primary cultures of human conjunctival epithelial cells were grown in different culture media. Cultures were allowed to grow and were processed after 5 days and 1, 2, 3, 4, or 5 weeks for transmission and scanning electron microscopy, according to the method of Nichols et al. modified in our laboratory.

RESULTS

Marked differences were seen between primary cultures grown with or without hydrocortisone. A thick tannic acid-stained layer was observed when hydrocortisone was present in the culture medium; however, that layer was virtually absent in cultures grown with hydrocortisone-free media. Scanning electron microscopy revealed a dense deposit showing a network-like structure. Moreover, the age of the cultures clearly influenced the thickness of the tannic acid-stained deposit, which thickened as the cultures aged.

CONCLUSIONS

These results strongly suggest that the layer growing in the presence of hydrocortisone is mucus. The fact that this material became more abundant as the cultures aged indicates that mucus is actively produced and secreted by conjunctival epithelial cells in vitro. This study might contribute to the knowledge of mucus-deficient pathologies of the ocular surface.

Scanning electron microscopy study of the tarsal and orbital conjunctival surfaces compared to peripheral corneal epithelium in pigmented rabbits

The mammalian palpebral conjunctiva has not been systematically evaluated by scanning electron microscopy (SEM). The upper eyelid of female grey rabbits (2 kg) was fixed in its extended conformation at 15.00 h; some corneas were prepared with the same fixative protocol. The corneal epithelium, within 1 mm of the limbus, is a mosaic of small-to-large (average cell area of 693 m2) squamous cells with light, medium or dark appearance due to different densities of cell surface microplicae. The tarsal conjunctiva was a 1.5 to 3 mm wide mosaic of small (average cell area of 86 microm2) non-desquamating polygonal cells having distinctive light and dark appearances due surface microplicae. The orbital portion of the palpebral conjunctiva is also composed of small (average cell area of 87 microm2) non-desquamating polygonal cells but with a uniform medium-grey appearance due to a relatively consistent density of surface microvilli. Several types of intercellular pore-like openings were also present across the palpebral surface but not the corneal epithelial surface. Very small type 1 pores (1.5 to 5 microm diameter) were present at a density of 480 to 760 / mm2 for the tarsal and 80-160 / mm2 for orbital conjunctiva. Slightly larger (2.5 to 18 microm diameter) type 2 pores with distinct borders were present at 120-200 / mm2 across the orbital conjunctiva. Very large (10-109 microm diameter) type 3 (Henle) pores were present at 40 to 280/mm2 especially at the tarsal/orbital transition zone. Type 4 pores (goblet cell orifices) were oval with a peripheral ring of microvilli and were present at 40 to 160/mm2 for tarsal and 800 to 1600/mm2 for orbital conjunctiva. The rabbit palpebral conjunctival surface is thus distinctly different from the peripheral corneal epithelium across which it slides following eyelid closure.

Mucin-like glycoprotein secretion is mediated by cyclic-AMP and protein kinase C signal transduction pathways in rat corneal epithelium

Ocular surface mucin is secreted from both goblet cells in the conjunctival epithelium and corneal epithelial cells. To clarify its mechanism of secretion in corneal epithelial cells, a rat cornea organ culture system was used to evaluate the second messenger roles of cyclic-AMP (cAMP), cyclic-GMP (cGMP) and protein kinase C (PKC) in modulating mucin-like glycoprotein secretion. Rat cornea sections (3 mm diameter) were cultured in TC-199 medium, and radiolabeled with sodium sulfate for 18 hr. After washing, the corneas were treated with various second messenger modulating agents for 30 min. The culture media were reacted with Dolichos biflorus (DBA)-lectin, and mucin-like glycoprotein was isolated. Then the radioactivity of DBA-binding mucin-like glycoprotein was isolated. Then the radioactivity of DBA-binding mucin-like glycoprotein was measured. There was a time-dependent increase in mucin-like glycoprotein was measured. There was a time-dependent increase in mucin-like glycoprotein secretion, whereas after corneal epithelial debridement the secretion was markedly inhibited by 81%. Mucin-like glycoprotein secretion was stimulated in a dose-dependent manner following elevation of cAMP levels by exposure to either forskolin, dibutyryl cAMP or 3-isobutyl-1-methylxanthine. Concomitant exposure to the cAMP dependent protein kinase inhibitor, KT5720 completely inhibited their stimulatory effects. Neither exposure to dibutyryl cGMP nor nitroprusside affected mucin-like glycoprotein secretion. Stimulation by PKC, phorbol 12, 13-dibutyrate (PDBu) also increased mucin-like glycoprotein secretion in a dose-dependent fashion. The PKC inhibitor, calphostin C completely inhibited the stimulation by PDBu of mucine-like glycoprotein secretion. These results demonstrate that corneal epithelial cells secrete mucin-like glycoprotein, which is mediated by cAMP and PKC signal transduction pathways.

Ocular mucins: Purification, metabolism and functions

Mucins are present at the ocular surface in both secreted and membrane-bound forms. Mucins are produced in partby the conjunctial goblet cells, and are complemented by non-globet secretions. This review focuses on secreted ocular mucins. They are present in the tear film, probably both in gel and soluble form, and play a role in lubrication and ocular defense. It is apparent that mucins are highly adapted to their functions. State of the art techniques for mucin purification and analysis are presented. Density gradient centrifugation, gel filtration, ion-exchange chromatography and agarose gel electrophoresis are discussed, together with methods of oliogosaccharide analysis. Reagents for the detection of mucin are considered in conjunction with these methods, which we have employed in the analysis of human and canine ocular mucins. The general structure of mucins is reviewed. The biosyntheas and glycosylation of ocular mucins are not yet fully understood, and are discussed in relation to currently established concepts. The impaact of disease on the nature and secretion of mucins is considered, as well as the physiological and pathological significance of mucus degradation.

Simultaneous evaluation of tear turnover and corneal epithelial permeability by fluorophotometry in normal subjects and patients with keratoconjunctivitis sicca (KCS)

PURPOSE

To simultaneously determine the tear turn over rate (TT) and corneal epithelial permeability (Pdc) in normal subjects and patients with KCS by a single-drop fluorophotometric technique using disodium fluorescein (DSF) or carboxyfluorescein (CF).

METHODS

DSF was instilled in one eye chosen at random and CF in the fellow eye of 13 normal subjects and in 13 patients with KCS. TT and Pdc were determined using a single-drop technique on a Fluorotron Master.

RESULTS

In normals and KCS subjects, TT was found to be independent of age and sex and essentially identical for DSF and CF. TT was approximately 42% lower in KCS subjects than normals (Table). TT was independent of Schirmer's I and Pdc. [table: see text] Pdc values were similar for DSF and CF in normals and increased with age. In KCS subjects, Pdc was 3-4 times higher compared to normal subjects (p < 0.01) and was directly correlated with the severity of corneal punctate staining. Pdc was independent of TT.

CONCLUSION

Patients with KCS are more susceptible to the therapeutic and toxic effects of topical medications and preservatives due to increased corneal epithelial permeability. With the decreased TT in KCS patients, there is also slower elimination of substances from the tear film. This, combined with the increase in epithelial permeability, puts the KCS eye doubly at risk for the toxic effects of topically applied substances.

The ocular surface in keratoconjunctivitis sicca

The ocular surface is altered in kerato-conjunctivitis sicca, a disorder of aqueous tear production. Many of the factors leading to these surface changes are now more clearly understood and are discussed in this paper.

Lectin-cytochemical study on epithelial mucus glycoprotein of conjunctiva and pterygium

The epithelium of pterygium and conjunctiva was studied with reference to cytochemical reactivity to six fluorescein-labeled lectins that recognize a certain carbohydrate residue(s) of cellular membrane-bound or secretory glycoprotein: Ulex europaeus agglutinin-1 (UEA-1, specific for fucose); Dolichos biflorus agglutinin (DBA, specific for N-acetylgalactosamine); peanut agglutinin (PNA, specific for galactose-beta 1-3N-acetylgalactosamine): wheat germ agglutinin (WGA, specific for N-acetylglucosamine and N-acetylneuraminic acid); Concanavalia ensiformis (Con A, specific for mannose); Ricinus communis agglutinin-1 (RCA-1, specific for galactose). Non-goblet epithelial cells of pterygium were labeled with UEA-1, DBA and PNA, while those of conjunctiva were not. Distribution density of goblet cells was larger in pterygium than in conjunctiva, but there was no distinct difference in lectin reactivity between the two tissues, with marked label with WGA, PNA and RCA-1. Con A did not bind to either pterygium or conjunctiva. The observations suggest the presence of anomalous mucus glycoproteins secreted from pterygium.

Eyelid secretions and the prevention and production of disease

Tears are necessary for the continued health of the ocular surface. Normal constituents include water, mucin, and lipids, electrolytes, non-electrolytes, and proteins. Lacrimal secretion is under cholinergic control and modulated by sympathetic adrenergic, peptidergic (VIP) and humoral influences; the meibomian glands are innervated, but the goblet cells are not. Retinoids are important for ocular health and prealbumin may be a carrier for vitamin A in the tears to supply corneal epithelium with its requirements. Changes in tear constituents may cause certain ocular disorders. In dry eyes increased osmolarity is thought to cause surface ocular damage but the presence of granulocytes and inflammatory mediators such as prostaglandins and super-oxide may contribute to inflammatory events in this and other external diseases.

Scanning electron microscopy of conjunctival surfaces in patients with ocular cicatricial pemphigoid

The conjunctival surfaces of ten patients with active, ocular cicatricial pemphigoid, three patients with drug-controlled ocular cicatricial pemphigoid, and six patients with normal conjunctivas were studied using scanning electron microscopy. A homogeneous granular sheet of amorphous mucin-like material was observed covering extensive areas of the conjunctiva in eight of ten patients with active ocular cicatricial pemphigoid. This sheet of amorphous material was absent on drug-controlled ocular cicatricial pemphigoid and normal conjunctival specimens. Our study demonstrates that patients with active ocular cicatricial pemphigoid possess ocular surface mucus that appears thicker and more continuous than normal ocular mucus when observed with scanning electron microscopy. This observation is in agreement with clinical observations of thick mucus strands in the inferior fornix of patients with active ocular cicatricial pemphigoid.

Wettability of the corneal surface: a reappraisal

Previous attempts by others to measure the wettability of the corneal epithelium concluded that the surface was strongly hydrophobic, but used methods which seem likely to damage the epithelial cell surface. These experimental techniques were repeated and the effects on the surface analysed by scanning electron microscopy. It is concluded that such methods cannot establish either the hydrophobicity or hydrophilicity of the cornea.

Cicatricial pemphigoid

Images

On the nature and the role of the subsurface vesicles in the outer epithelial cells of the conjunctiva

The layer of the tear film in contact with the conjunctiva is mucus. This mucus comes from two sources, the conjunctival goblet cells and the subsurface vesicles. These vesicles are found just below the surface of the conjunctival cells. They contain long chain mucus glycoprotein molecules that are joined to the vesicle membrane. The vesicles fuse with the surface membrane of the conjunctival cells and expose their mucus glycoprotein chains to the overlying mucus. Chemical and physical bonds between the two types of mucus help to bind the mucus layer to the conjunctiva. The vesicle membrane becomes incorporated in the cell membrane and supplies the membranes for the microvilli that cover the exposed surface.

Application of lectins for detection of goblet cell carbohydrates of the human conjunctiva

Paraffin-embedded and frozen biopsies from the human conjunctival epithelium were examined by fluorescence microscopy after labeling with eight fluorescein-conjugated lectins: wheat germ agglutinin; soybean agglutinin; peanut agglutinin; Ricinus communis agglutinin-1; Limulus polyphemus agglutinin; Ulex europaeus agglutinin-1; Dolichos biflorus agglutinin; concanavalin A. The lectins were used as specific molecular probes to detect carbohydrate composition of glycoproteins secreted from the conjunctival goblet cells. The labeling pattern of goblet cells and conjunctival epithelial surfaces with various lectins suggested that N-acetyl-glucosamine, galactose, N-acetyl-galactosamine and sialic acid are contained in goblet cells and contribute to the formation of tear mucus glycoprotein. Fucose and mannose, which are present in the tear mucus, were not detectable in goblet cells.