Epidemiology of dry eye disease in Africa: The sparse information, gaps and opportunities.

Dry eye disease (DED) is an increasingly significant clinical problem in developing countries and/or emerging economies. Existing studies on DED conducted in these areas have largely reported on associations between DED and infectious disease (trachoma) and malnutrition (hypovitaminosis A), but current trends of industrialization, urbanization, and modernization in these areas could result in a shift to other forms of DED. Herein, we review the epidemiology of DED in these geographic areas, highlighting potential causes and risk factors of DED while presenting information on diagnostic tools and algorithms and insight into some treatment modalities of DED that could prove useful to clinicians and investigators in these regions.

CD8⁺ cells regulate the T helper-17 response in an experimental murine model of Sjögren syndrome.

This study investigated the regulatory function of CD8⁺ cells in T helper-17 (Th17) cell-mediated corneal epithelial barrier disruption that develops in a murine desiccating stress (DS) model that resembles Sjögren syndrome. CD8⁺ cell depletion promoted generation of interleukin-17A (IL-17A)-producing CD4⁺ T cells via activation of dendritic cells in both the ocular surface and draining cervical lymph nodes in C57BL/6 mice subjected to DS. T-cell-deficient nude recipient mice receiving adoptively transferred CD4⁺ T cells from CD8⁺ cell-depleted donors exposed to DS displayed increased CD4⁺ T-cell infiltration and elevated IL-17A and CC-chemokine attractant ligand 20 levels in the ocular surface, which was associated with greater corneal barrier disruption. Enhanced DS-specific corneal barrier disruption in CD8-depleted donor mice correlated with a Th17-mediated expression of matrix metalloproteinases (MMP-3 and MMP-9) in the recipient corneal epithelium. Co-transfer of CD8⁺CD103⁺ regulatory T cells did not affect the ability of DS-specific pathogenic CD4⁺ T cells to infiltrate and cause ocular surface disease in the nude recipients, showing that CD8⁺ cells regulate the efferent arm of DS-induced immune response. In summary, CD8⁺ regulatory cells suppress generation of a pathogenic Th17 response that has a pivotal role in DS-induced disruption of corneal barrier function.

Autoimmunity at the ocular surface: pathogenesis and regulation.

A healthy ocular surface environment is essential to preserve visual function, and as such the eye has evolved a complex network of mechanisms to maintain homeostasis. Fundamental to the health of the ocular surface is the immune system, designed to respond rapidly to environmental and microbial insults, whereas maintaining tolerance to self-antigens and commensal microbes. To this end, activation of the innate and adaptive immune response is tightly regulated to limit bystander tissue damage. However, aberrant activation of the immune system can result in autoimmunity to self-antigens localized to the ocular surface and associated tissues. Environmental, microbial and endogenous stress, antigen localization, and genetic factors provide the triggers underlying the immunological events that shape the outcome of the diverse spectrum of autoimmune-based ocular surface disorders.

IL-17 disrupts corneal barrier following desiccating stress.

T helper (Th)-17 is a recently identified subtype of Th response that has been implicated in host defense and autoimmunity. We investigated whether there is evidence for a Th-17 response in human and experimental murine dry eye (DE). Gene expression in the human DE conjunctiva showed increased levels of the Th-17 inducers, interleukin (IL)-23, IL-17A, and interferon-gamma (IFN-gamma). In the murine model, we found that desiccating stress increased matrix metalloproteinase-9, Th-17-associated genes (IL-6, IL-23, transforming growth factor-beta1 and -2, IL-23R, IL-17R, IL-17A, retinoid-related orphan receptor-gammat, and CC chemokine attractant ligand-20) and IFN-gamma in cornea and conjunctiva. Furthermore, we found a significantly increased concentration of IL-17 in tears and number of IL-17-producing cells on the ocular surface. Antibody neutralization of IL-17 ameliorated experimental DE-induced corneal epithelial barrier dysfunction and decreased the expression of matrix metalloproteinases 3 and 9. Taken together, these findings suggest that IL-17 has a role in corneal epithelial barrier disruption in DE.

Proteomic analysis of human tears: defensin expression after ocular surface surgery.

Human tear protein profiles were monitored by surface enhanced laser desorption/ionization-time-of-flight mass spectrometry ProteinChip technology (SELDI-TOF ProteinChip) and liquid chromatography-mass spectrometry (LC-MS). Tears were collected from 21 patients scheduled for surgery to remove an ocular surface neoplasm prior to surgery (day 0) and on days 1, 3, and 30 postoperatively. Using this proteomic approach, we verified that three human alpha-defensins (HNP-1, HNP-2, and HNP-3) were significantly up-regulated in their expression after surgery and that their levels decreased to approximately normal by day 30 by which time healing was complete. Further confirmation of the identity of the alpha-defensins in human tears was made by LC purification, trypsin digestion, and ESI-MS/MS analysis of their tryptic digests. The concentrations of HNP-1 and HNP-2 were determined and shown to be markedly increased after ocular surface surgery. The results of the study suggest that human alpha-defensins HNP-1, HNP-2, and HNP-3 are up-regulated after surgery, and may in addition to their antimicrobial properties have an important role in wound healing.

Analysis of topical cyclosporine treatment of patients with dry eye syndrome: effect on conjunctival lymphocytes.

OBJECTIVE: To study the effect of topical cyclosporine on lymphocyte activation within the conjunctiva of patients with moderate to severe dry eye syndrome (Sjögren and non-Sjögren). METHODS: Biopsy specimens were obtained at baseline and after 6 months of cyclosporine treatment from eyes of 32 patients with moderate to severe dry eye syndrome; 19 were cyclosporine treated (0.05% cyclosporine, n = 13; 0.1% cyclosporine, n = 6) and 13 were vehicle treated. Within this group there were 12 with Sjögren syndrome and 20 with non-Sjögren syndrome. Biopsy tissue was analyzed using immunohistochemical localization of binding of monoclonal antibodies to lymphocytic markers CD3, CD4, and CD8 as well as lymphocyte activation markers CD11a and HLA-DR. RESULTS: In cyclosporine-treated eyes, biopsy results of conjunctivae showed decreases in the number of cells positive for CD3, CD4, and CD8, while in vehicle-treated eyes, results showed increases in these markers, although these differences were not statistically significant. Following treatment with 0.05% cyclosporine, there was a significant decrease in the number of cells expressing the lymphocyte activation markers CD11a (P<.05) and HLA-DR (P<.05), indicating less activation of lymphocytes as compared with vehicle treatment. Within the Sjögren patient subgroup, those treated with 0.05% cyclosporine also showed a significant decrease in the number of cells positive for CD11a (P<.001) as well as CD3 (P<.03), indicating a reduction in number of activated lymphocytes. CONCLUSION: Treatment of dry eye syndrome with topical cyclosporine significantly reduced the numbers of activated lymphocytes within the conjunctiva. Arch Ophthalmol. 2000;118:1489-1496

The diagnosis and management of dry eye: a twenty-five-year review.

PURPOSE: To review the advances in the diagnosis, pathogenesis, and management of dry eye disease in the past 25 years. METHODS: Literature review. RESULTS: The preocular tear film is a hydrated mucus gel that contains soluble antimicrobial proteins and growth factors that protect and support the ocular surface. The final common pathway in dry eye is a perturbation of the integrated ocular surface/lacrimal gland reflex unit. Diagnostic tests evaluating tear composition and clearance appear to show stronger correlation with the severity of ocular irritation symptoms and keratoconjunctivitis sicca (KCS) than the conventional Schirmer tests. KCS is a condition of abnormal differentiation and mucus production by the ocular surface epithelium that results in a poorly lubricated, abnormally permeable ocular surface that has increased susceptibility to environmental insults. Chronic subclinical ocular surface inflammation appears to play a key role in the pathogenesis of KCS. New therapeutic strategies are aimed at reducing the ocular surface inflammation of dry eye disease. CONCLUSIONS: There has been a tremendous increase in knowledge regarding dry eye disease in the past 25 years that has resulted in improved diagnostic classification and new targeted therapies.

Effect of anti-infective ophthalmic solutions on corneal cells in vitro.

External ocular infections caused by susceptible strains of bacteria have recently been treated with potent broad-spectrum antimicrobial solutions. This study was conducted to compare the in vitro biologic effects of three anti-infective ophthalmic solutions (Ocuflox, Ciloxan, and Tobramycin) on rabbit corneal epithelial cell cultures. Epithelial cell layers from albino rabbit eyes were isolated and incubated in culture media for 9 days, following which the cultures were rinsed and treated with the anti-infective solutions. Ciloxan and Tobramycin caused extensive ethidium bromide staining of the corneal epithelial cell layer after 5, 10, and 15 minutes, indicating acute cell membrane damage. Ocuflox ophthalmic solution caused less ethidium bromide staining at all evaluated times and, therefore, less cell membrane damage than the comparator solutions.

Distribution of cyclosporin A in ocular tissues after topical administration to albino rabbits and beagle dogs.

PURPOSE: To determine the ocular pharmacokinetics of cyclosporin A after topical ophthalmic administration. METHODS: Radiolabled cyclosporin A in either a castor oil-in-water emulsion or a corn oil ointment was applied to the eyes of beagle dogs or albino rabbits using the following paradigms: (i) single doses of 0.2% emulsion to rabbits and dogs, (ii) single doses of 0.05%, 0.2%, or 0.4% emulsion to rabbits, (iii) multiple doses of 0.2% emulsion to dogs, (iv) single and multiple doses of 0.2% ointment to rabbits. The distribution of cyclosporin A was determined by measuring the distribution of radioactivity. RESULTS: After a single dose, cyclosporin A was rapidly absorbed into the conjunctiva (Cmax: dogs, 1490 ng/g; rabbits, 1340 ng/g) and cornea (Cmax: dogs, 311 ng/g; rabbits, 955 ng/g). High concentrations (>300 ng/g) could be detected in the cornea up to 96 hours post-dose. Lower concentrations were found in the intraocular tissues, and systemic absorption was minimal. After multiple doses, there was some accumulation in the cornea, lens, lacrimal gland, and iris-cilliary body, but limited accumulation in the conjunctiva and sclera. Ocular tissue concentrations of cyclosporin A increased with increasing dose concentration; proportionally in lacrimal gland and intraocular tissues; less than proportionally in conjunctiva and cornea. The pharmacokinetic profile of the cyclosporin A corn oil ointment was similar to that of the emulsion. CONCLUSIONS: Topical ophthalmic cyclosporin A penetrated into extraocular tissues at concentrations adequate for local immunomodulation while penetration into intraocular tissues was much less and absorption into the blood was minimal.

Correlation of tear fluorescein clearance and Schirmer test scores with ocular irritation symptoms.

OBJECTIVE: To correlate and compare the Schirmer 1 test and a new method of measuring tear fluorescein clearance with the CytoFluor II fluorometer with the severity of ocular irritation symptoms, clinical signs of meibomian gland disease, corneal fluorescein staining scores, and corneal and conjunctival sensitivity. DESIGN: Case-control study. PARTICIPANTS: Forty patients presenting with a chief complaint of ocular irritation, and 40 asymptomatic control subjects of similar age distribution. INTERVENTION: All subjects completed a symptom questionnaire, a baseline ocular examination, fluorescein clearance test (FCT), and Schirmer 1 test. MAIN OUTCOME MEASURES: The FCT was performed with a CytoFluor II fluorophotometer by measuring the fluorescein concentration in minimally stimulated tear samples collected from the inferior tear meniscus 15 minutes after instillation of 5 microl of 2% sodium fluorescein. Severity of ocular irritation was assessed with a symptom questionnaire. Schirmer 1 test, biomicroscopic meibomian gland evaluation, corneal fluorescein staining score, and corneal and conjunctival sensation scores were assessed with the Cachet-Bonnet anesthesiometer in all subjects. RESULTS: Irritation symptoms correlated with higher log tear fluorescein concentration (symptomatic 3.08 +/- 0.62 units/,microl, normal control 1.89 +/- 0.7 units/microl, P < 0.005) and lower Schirmer 1 test scores (symptomatic 12.6 mm, normal control 22.3 mm, P < 0.005). The FCT showed greater predictive value for identifying ocular irritation than the Schirmer 1 test. A fluorescein concentration of 274 units//microl eliminated 80% of the normal subjects (specificity) and identified 85% of the abnormal subjects (sensitivity). Log of tear fluorescein concentration and the Schirmer 1 test correlated with meibomian gland orifice metaplasia (2.81 +/- 0.78 units/microl and 14.47 +/- 9.53 mm in those with metaplasia vs. 1.83 +/- 0.71 units/microl and 23.14 +/- 7.67 mm in those without metaplasia, P < 0.001) and with the percentage of acinar dropout. Both log of tear fluorescein concentration and the Schirmer 1 test correlated with corneal fluorescein staining (Pearson correlation of 0.394 P < 0.0001 for Schirmer 1 test and 0.312 P < 0.005 for log of tear fluorescein). In addition, log of tear fluorescein and Schirmer 1 test scores correlated with corneal and conjunctival sensation scores (Spearman's rho for corneal sensation: log of tear fluorescein -0.38, P < 0.003, Schirmer 1 test -0.39, P < 0.002, and for conjunctival sensation: log of tear fluorescein -0.391, P < 0.001, Schirmer 1 test -0.23, P < 0.061). CONCLUSIONS: The FCT shows a greater predictive value for ocular irritation than the Schirmer 1 test. It correlates better with age, meibomian gland dysfunction, and decreased corneal and conjunctival sensation. Decreased tear clearance was identified as a risk factor for ocular irritation, even in subjects with normal Schirmer scores. This simple technique may provide new clues into the mechanism and therapy of ocular irritation.

Separation of a midlevel density current from the bottom of a continental slope.

The high-salinity water flowing out of the Mediterranean Sea descends to mid depths in the density-stratified ocean, continues as a narrow jet along the Iberian continental slope, and intermittently detaches large-scale eddies (called "Meddies"). This process is important because it maintains the relatively high mean salinity of a major water mass (the "Mediterranean Intermediate Water") in the North Atlantic. Our simplified model of this jet consists of a moving layer with intermediate density rho2 sandwiched between motionless layers of density rho1 < rho2 and rho3 > rho2. The inshore (anticyclonic) portion of the midlevel jet (in the "rho2-water") rests on an inclined bottom (the continental slope), whereas the (cyclonic) offshore portion rests on the density interface of the stagnant deep (rho3) layer. An inviscid, steady, and finite-amplitude longwave theory is used to show that if the cross-stream topographic slope increases gradually in the downstream direction, then the "rho2-jet" is deflected off the bottom slope and onto the upper density interface of the rho3 layer. The computed magnitude of this separation effect is such as to produce an essentially free jet which is removed from the stabilizing influence of the continental topography. It is therefore conjectured that time-dependent effects (baroclinic instability) will produce further amplification, causing an eddy to detach seaward from the branch of the jet remaining on the slope.

The pathology of dry eye: the interaction between the ocular surface and lacrimal glands.

BACKGROUND: Most dry-eye symptoms result from an abnormal, nonlubricative ocular surface that increases shear forces under the eyelids and diminishes the ability of the ocular surface to respond to environmental challenges. This ocular-surface dysfunction may result from immunocompromise due to systemic autoimmune disease or may occur locally from a decrease in systemic androgen support to the lacrimal gland as seen in aging, most frequently in the menopausal female. HYPOTHESIS: Components of the ocular surface (cornea, conjunctiva, accessory lacrimal glands, and meibomian glands), the main lacrimal gland, and interconnecting innervation act as a functional unit. When one portion is compromised, normal lacrimal support of the ocular surface is impaired. Resulting immune-based inflammation can lead to lacrimal gland and neural dysfunction. This progression yields the OS symptoms associated with dry eye. THERAPY: Restoration of lacrimal function involves resolution of lymphocytic activation and inflammation. This has been demonstrated in the MRL/lpr mouse using systemic androgens or cyclosporine and in the dry-eye dog using topical cyclosporine. The efficacy of cyclosporine may be due to its immunomodulatory and antiinflammatory (phosphatase inhibitory capability) functions on the ocular surface, resulting in a normalization of nerve traffic. CONCLUSION: Although the etiologies of dry eye are varied, common to all ocular-surface disease is an underlying cytokine/receptor-mediated inflammatory process. By treating this process, it may be possible to normalize the ocular surface/lacrimal neural reflex and facilitate ocular surface healing.

The role of apoptosis in the pathogenesis of canine keratoconjunctivitis sicca: the effect of topical Cyclosporin A therapy.

PURPOSE: The exact etiology of dry eye is unknown but is believed to be multifactorial. Apoptosis has been implicated in the pathogenesis of autoimmune diseases such as Sjögren's syndrome (SS). This study attempted to gain a better understanding of the role of apoptosis and its regulation in the patho-physiology of dry eye. The therapeutic effect of immunomodulatory agents such as cyclosporin A (CsA) in the treatment of dry eye, particularly its impact on the level of apoptosis in the target tissues, is also investigated. METHODS: A colony of dogs with spontaneous chronic idiopathic keratoconjunctivitis sicca (KCS) was maintained. Nictitans lacrimal gland (NLG), an accessory lacrimal gland, and conjunctival biopsies of the KCS and normal dogs were obtained before and after 12 weeks of treatment with 0.2% topical CsA ophthalmic emulsion b.i.d. (Allergan, Inc., Irvine, CA, U.S.A.). Tissues were prepared for the terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) apoptosis assay and immunohistochemical analysis for various apoptosis mediators. RESULTS: The TUNEL assay demonstrated that (i) the normal NLG and conjunctival epithelial cells exhibited a limited level of apoptosis; (ii) in KCS dogs, lacrimal acinar and conjunctival epithelial cells underwent an increased apoptosis, whereas the lymphocytes had a significantly lower level of apoptosis compared to those of the normal dogs; (iii) after topical CsA, apoptosis was induced in the lymphocytes and suppressed in the acinar and conjunctival epithelial cells in KCS dogs. Immunohistochemistry revealed that p53, fas, and fasL, but not bcl-2 were highly expressed in the target tissues of KCS dogs. The immunoreactivity of p53 was significantly decreased, whereas the bcl-2 level was increased after CsA administration. CONCLUSIONS: The induction of epithelial cell apoptosis and the suppression of lymphocytic apoptosis in the NLG and ocular-surface tissues, such as conjunctiva of KCS dogs, indicates the important role of this phenomenon in the etiology of dry eye. Topical CsA appears to facilitate lymphocytic apoptosis and suppress epithelial cell apoptosis in the KCS dog. The differential expression of various apoptotic mediators after topical treatment implicates CsA in facilitating the reestablishment of the normal apoptotic balance, suggesting additional mechanisms by which CsA is therapeutic for dry-eye syndrome.

A unified theory of the role of the ocular surface in dry eye.

It is our belief that the pathology of dry eye occurs when systemic androgen levels fall below the threshold necessary for support of secretory function and generation of an anti-inflammatory environment (Fig. 3). When this occurs, both the lacrimal gland and the ocular surface become irritated and inflamed, and they secrete cytokines that interfere with the normal neural connections that drive the tearing reflex. This leaves the lacrimal gland in an isolated condition, perhaps exacerbating atrophic alterations of the glandular tissue. These changes allow for antigen presentation at the surface of the lacrimal acinar cells and increase lymphocytic infiltration of the gland. A similar series of events may be occurring on the ocular surface. From this hypothesis we conclude: 1. The ocular surface, lacrimal gland, and interconnecting innervation act as an integrated servo-mechanism. 2. Once the lacrimal gland loses its androgen support, it is subject to immune/neurally mediated dysfunction. 3. The ocular surface is an appropriate target for dry eye therapeutics.

Apoptosis in the rabbit cornea after photorefractive keratectomy.

PURPOSE: It is well-known that after trauma to the ocular surface such as that seen in refractive surgeries like photorefractive keratectomy (PRK; laser corneal surface ablation), there is a "dropout" of underlying stromal keratocytes. Recently it was proposed by Wilson et al. that this loss of keratocytes may be the result of apoptosis. This process can be initiated by several cellular factors that result in release of endonucleases, DNA segmentation, and eventual cellular destruction. One protein, bcl-2, has been shown to have a profound role in its inhibition. The goal of this study was to evaluate the mechanisms and level of apoptosis in the cornea after PRK. METHODS: Rabbits were anesthetized systemically with ketamine/xylazine. The corneal epithelium was removed by using phototherapeutic keratectomy (PTK, 100 pulses). PRK was then performed (-9.0 D, 5.0 mm optical zone). Rabbits were killed at 4 days and 4 weeks, and the corneas were prepared for light and electron microscopy, as well as for apoptosis evaluation. RESULTS: The apoptosis assay demonstrated that (a) the normal cornea exhibited a limited level of apoptosis, primarily in the superficial epithelium, very little in the basal epithelium, with none in the keratocytes and endothelium; (b) the entire epithelial layer was found to be apoptotic 4 days and 4 weeks after PRK; (c) an elevated level of apoptosis was detected in both keratocytes and endothelial cells after PRK at the same time points. The immunohistochemical staining showed that (a) the normal cornea had a low level of bcl-2 protein, exclusively in the superficial epithelium; (b) bcl-2 was induced in the basal epithelial cells and anterior keratocytes under the wound bed 4 days after PRK and increased 4 weeks after PRK. CONCLUSIONS: These findings suggest that apoptosis plays an important role in the corneal wound-healing process, which appears to be mediated in part by bcl-2. Bcl-2 induction may protect corneal epithelial cells from apoptosis after trauma such as PRK.

Effect of platelet-derived growth factor on rabbit corneal wound healing.

Human recombinant platelet-derived growth factor was evaluated with the use of wound healing models in New Zealand albino rabbits. The efficacy of the platelet-derived growth factor dimers, AA, AB, and BB, was determined in corneal reepithelialization and anterior keratectomy models which examined the healing response in the presence or absence of the basement membrane. All dimers increased the rate of wound healing in both models at 100 microg/ml when compared with control; however, the platelet-derived growth factor-BB isoform showed the most dramatic increase in both studies. The strength of the healing stroma after incision was evaluated by means of a tensile strength model. Histologic evaluation of the stromal wound area after 9 days of healing showed a marked increase in the number of keratocytes within the wound bed of the corneas treated with platelet-derived growth factor-BB when compared with control corneas. In addition, at 9 days, the epithelial plug was still present in the control corneas but had been extruded to the surface by the granulation tissue in the platelet-derived growth factor-BB-treated corneas. These results are indicative of a more advanced stage of healing in treated versus control wounds at 9 days after the operation. A 30% increase in corneal tensile strength versus control was noted after 21 days of healing. Finally, in an in vitro gel contraction assay, platelet-derived growth factor exhibited a dose-dependent effect on the contraction of fibroblasts for doses ranging from 0.01 to 10 ng/ml. These results indicate that platelet-derived growth factor is active in the corneal wound healing process.