Damage To Cornea Research Articles

Tear ascorbic acid levels and the total antioxidant status in contact lens wearers: A pilot study

Aims:The tear ascorbate owing to its high concentration, functions as an effective antioxidant against the oxidative damage of cornea. Contact lens wearers (CLW) are prone to oxidative stress due to the lens-induced hypoxic conditions. A pilot study was done to compare the tear ascorbic acid level and the total antioxidant capacity give as in normal and CLW.Materials and Methods:In this study 21 CLW (Mean age 23 ± 3 years; M-2, F-19), who were daily wear users, with duration of wear not more than four years, along with age-matched 28 controls (Mean age 28 ± 3; M-15, F-13) were recruited in the study for collection of reflex tears using Schirmer's strip. Ascorbic acid in tears was determined using high-performance liquid chromatography (HPLC), total antioxidant capacity (TAC) and total protein assay by spectrophotometric analysis.Results:CLW showed no significant change in the tear ascorbic acid levels (0.4 ± 0.26 mM) compared to the control subjects (0.61 ± 0.59 mM). The amount of ascorbic acid in tears did not correlate with the TAC or the total protein of the tears. The mean TAC in CLW was 0.69 ± 0.16 mM, with a total protein of 1.35 ± 0.46 mg/ml while in controls it was 0.7 ± 0.18 mM and 1.21 ± 0.47 mg/ml respectively.Conclusions:Soft contact lens wear did not show any significant change in tear ascorbic acid, TAC and total protein levels compared to controls.

Long-term eye movement recordings with a scleral search coil-eyelid protection device

The search coil technique is regarded as the gold standard in eye movement recordings. The manufacturers of scleral search coils (SSC) do not recommend using them longer than 30 minutes. The temporal limitations result from potential cornea damage and from irritations of the lid margins and palpebral conjunctiva which subjects perceive as unpleasant. Here we introduce a new coil-eyelid protection device (CEPD) which allows recording intervals up to 2 hours with considerably reduced discomfort. Ophthalmic examinations and saccade recordings were used for comparison with the conventional SSC recording technique. In three experiments subjects were examined using SSCs with a commercially available cornea bandage lens on top of the search coil up to 120 minutes recording time. Ophthalmic testing revealed no apparent harmful effects on eyes or lid surface. Saccade parameters (main sequence) remained unchanged comparing SSC and CEPD recordings. Subjects rated less discomfort by using the CEPD. For the first time we show that SSC recordings can be extended over about 120min without hazard to the eye, when using an eyelid protection lens. This advanced method allows new applications like eye movement recordings during sleep (rapid eye movements) or perceptional or motor learning tasks, e.g. saccade adaptation paradigms.

Long-term eye movement recordings with a scleral search coil-eyelid protection device allows new applications

The search coil technique is regarded as the gold standard in eye movement recordings. The manufacturers of scleral search coils (SSC) do not recommend using them longer than 30 min. The temporal limitations result from potential cornea damage and from irritations of the lid margins and palpebral conjunctiva which subjects perceive as unpleasant. Here we introduce a new coil-eyelid protection device (CEPD) which allows recording intervals up to 2 h with considerably reduced discomfort. Ophthalmic examinations and saccade recordings were used for comparison with the conventional SSC recording technique. In three experiments subjects were examined using SSCs with a commercially available cornea bandage lens on top of the search coil up to 120 min recording time. Ophthalmic testing revealed no apparent harmful effects on eyes or lid surface. Saccade parameters (main sequence) remained unchanged comparing SSC and CEPD recordings. Subjects rated less discomfort by using the CEPD. For the first time we show that SSC recordings can be extended over about 120 min without hazard to the eye, when using an eyelid protection lens. This advanced method allows new applications like eye movement recordings during sleep (rapid eye movements) or perceptional or motor learning tasks, e.g. saccade adaptation paradigms.

Proteinases of the cornea and preocular tear film

Maintenance and repair of corneal stromal extracellular matrix (ECM) requires a tightly coordinated balance of ECM synthesis, degradation and remodeling in which proteolytic enzymes (proteinases) perform important functions. There are natural proteinase inhibitors present in preocular tear film (PTF) and cornea simultaneously with proteinases that prevent excessive degradation of normal healthy tissue. Disorders occur when there is an imbalance between proteinases and proteinase inhibitors in favor of the proteinases, causing pathologic degradation of stromal collagen and proteoglycans in the cornea. Two matrix metalloproteinases (MMPs), MMP-2 and MMP-9, are of major importance in terms of remodeling and degradation of the corneal stromal collagen. Immunohistochemical studies have shown different origins of MMP-2 and -9. MMP-2 is synthesized by corneal keratocytes and performs a surveillance function in the normal cornea, becoming locally activated to degrade collagen molecules that occasionally become damaged. Alternatively, MMP-9 may be produced by epithelial cells and polymorphonuclear neutrophils following corneal wounding. Because the cornea is in close contact with the preocular tear film (PTF), proteinases have been evaluated in the PTF. In damaged corneas, total proteolytic activity in the tear fluid was found to be significantly increased compared to normal eyes and contralateral eyes. Studies analyzing the proteolytic activity in serial PTF samples during corneal healing led to the following conclusions: ulcerative keratitis in animals is associated with initially high levels of tear film proteolytic activity, which decrease as ulcers heal; proteinase levels in melting ulcers remain elevated leading to rapid progression of the ulcers. The success of medical and surgical treatment of the corneal ulcers is reflected by the proteolytic activity in tears. In animals, successful treatment leads to a rapid reduction in tear film proteolytic activity that corresponds with the improvement in the clinical signs of corneal ulceration. The in vitro effects of various compounds on proteolytic activity in the tear fluid of animals with ulcerative keratitis have been evaluated and their important inhibitory effects have been confirmed. Because these various compounds utilize different mechanisms to inhibit various families of proteinases, a combination of these proteinase inhibitors may be beneficial.

Partial enrichment of a population of human limbal epithelial cells with putative stem cell properties based on collagen type IV adhesiveness

The concept that corneal epithelium stem cells reside in limbus has been recognized for more than a decade, but isolation of these stem cells has not been accomplished. This study was an initial attempt to isolate a population of human limbal epithelial cells enriched for certain putative stem cell properties based on their phenotype. Epithelial cells harvested from fresh human limbal rings and their primary cultures were allowed to adhere to collagen IV-coated dishes for 20 min and 2 hr, sequentially. The rapidly adherent cells (RAC), slowly adherent cells and non-adherent cells were evaluated for certain stem cell properties: (a) BrdU-label retention, (b) expression of basal cell (integrin β1, p63, ABCG2) and differentiation (involucrin, keratin 12) markers, and (c) colony forming efficiency (CFE) and growth capacity on a 3T3 fibroblast feeder layer. Among unfractionated cells and the three selected populations, the RAC, accounting for about 10% of whole population, were enriched 5-fold in BrdU label-retaining cells, displayed the highest number of integrin β1 and p63 positive and involucrin negative cells, expressed high levels of ΔNp63 and ABCG2 mRNA, and lacked involucrin and K12 expression, and possessed the greatest CFE and growth capacity. These findings demonstrated for the first time that human limbal epithelial cells with stem cell properties can be partially enriched by their adhesiveness to collagen IV. The RAC population enriched for certain putative stem cell properties may prove useful in the future for transplantation to diseased and damaged corneas with limbal stem cell deficiency.

Treatment with meliacine, a plant derived antiviral, prevents the development of herpetic stromal keratitis in mice

Herpetic stromal keratitis is caused by ocular infection with herpes simplex virus type 1 (HSV-1) and constitutes a leading cause of human blindness. The effect of meliacine, an antiviral compound isolated from leaves of Melia azedarach L. that inhibits HSV-1 replication in vitro, was examined on experimental corneal HSV-1 inoculation in Balb/c mice. Mice were inoculated with HSV-1 strain KOS at their corneas after abrasion. Meliacine was administered topically 3 times a day for 4 days beginning 1 day before inoculation. Infected animals treated or not with meliacine were observed carefully for the development of stromal keratitis and the clinical scoring was done 14 days post-infection. Histological examination of corneas and viral isolation from eyes from HSV-1 infected mice treated or not with meliacine were also carried out. It was found that the treatment of HSV-1-induced ocular disease in Balb/c mice with meliacine reduced significantly the development of clinical disease, as well as the histological damage in corneas. The viral titers detected in eyes of infected and treated mice were 2-orders-of-magnitude lower than those corresponding to HSV-1 infected control animals. Mock-infected and treated mice did not reveal any corneal alteration due to the administration of the compound. Meliacine was found to exert a strong antiviral action on HSV-1-induced ocular disease in mice with no evidence of toxic effects.

Mathematical modeling of the damage threshold of cornea tissues by short IR laser pulses

A series of experimental data on threshold energy levels of cornea damage by IR radiation pulses with duration shorter than 1 μs is generalized. Mathematical modeling of the radiation energy thresholds is based on the concept of the removal of a surface layer of the cornea tissue without a phase transition as a result of the work of pressure forces.

Mid‐Infrared laser ablation of the cornea: A comparative study

The ablation thresholds and patterns of collateral damage in cornea produced by Er:YAG (2.94 microns) and Er:YSGG (2.79 microns) lasers were measured. Two different pulse durations, 200 microseconds (normal spiking mode) and 100 ns (Q-switched mode), were used at both wavelengths. In the normal spiking mode, damage zones of 16 +/- 2 microns and 39 +/- 7 microns and ablation thresholds of 250 +/- 20 mJ/cm2 and 420 +/- 35 mJ/cm2 were measured at 2.94 microns and 2.79 microns, respectively. In the Q-switched mode, damage zones of 4 +/- 2 microns and ablation thresholds of 150 +/- 10 mJ/cm2 were found irrespective of the laser used. The similarity between the results using the Er:YAG and Er:YSGG lasers in the Q-switched mode suggest that either laser can be used with equal effectiveness for corneal trephination.

Biopharmaceutical test of ocular irritation in the mouse

A simple and accurate test for ocular irritation in mice has been developed in which the subjective evaluation of intolerance is supplemented by an objective measurement, based on the change in corneal permeability following ocular damage. An episcopic microscope is used to detect, under blue light, the amount of fluorescein that diffuses across the inflamed or damaged cornea. The fluorescence emitted by this fluorochrome is quantified by a photomultiplier. The degree of ocular damage is expressed as a fluorescence index which can be subjected to statistical analysis. In a first stage of this study a series of surfactants has been examined and classified on the basis of their fluorescence index. The classification thus obtained is in agreement with those previously reported in the literature for assessment of ocular irritation by other methods.

Rabbit Cornea Damage Induced by Alloxan

The application of alloxan solution to the rabbit cornea induces a profound damage to the stroma and endothelium of areas previously deprived of epithelium. A heavy oedema and opacification of the stroma appears in the course of the first day after application: later on, vascularization of the stroma occurs. All the steps of this process were followed experimentally by means of the silver staining methods of Jabonero and McGovern, routine histological staining, and supravital staining with methylene blue.