In vivo studies on the effect of UV-radiation on the eye lens in animals

Ultraviolet light is a non-ionizing radiation that induces photochemical reactions in the tissue. Its spectral A and B ranges are partially absorbed by the cornea and/or lens thus causing damage on the cellular, cell physiological and molecular level. UV-A does not seem to damage the cornea permanently and its effects in the lens have a very prolonged latency period. Typical reactions of the cornea are oedema, punctate keratitis (photoelectric keratitis) and neovascularization. In the lens all reactions that could be evidenced, were located in the epithelium and in the outer cortical fiber cells.In vivo UV-A induces swelling and slight vacuolation of the anterior suture system, but apart from these transient effects, only very limited permanent damage could be demonstrated. UV-B induces the formation of an anterior subcapsular cataract, starting also with vacuolation of the suture system. These morphological characteristics can be visualized at the slitlamp microscope. Histologically, sutural irregularities (UV-A) and epithelial hyperplasia with capsular multiplication (UV-B) as well as desintegration of the anterior suture system could be observed. Patho-physiologically, a reduction of lens fresh weight (UV-B) as well as changes of the equilibrium of reduced and oxidized glutathione (GSH/GSSG) could be demonstrated. On the protein-biochemical level, changes in the ratio of water-soluble versus water-insoluble protein could be evidenced, as well as effects on specific crystallin fractions, namelyα-crystallin. In addition, the appearance of a newly synthetized 31 kDa protein could be demonstrated in UV-B irradiated mice.     

Spectral transmission of the optical media of the human eye with respect to keratitis and cataract formation

The spectral transmissions of cornea, aqueous humour, lens and vitreous humour of human eyes were measured in the range from 250 nm to 800 nm in 1 nm steps using a high resolution double monochromator. Cornea and lens are good cut off filters; 1% transmission was measured in various cornea samples between 291 and 298 nm, and in different lenses between 389 and 414 nm. Aqueous humour and vitreous humour showed high transparency (80%) at >320 nm. The wavelength range of keratitis effective irradiance was found to be completely within the wavelength range of absorption of the cornea, that of cataract effective irradiance was found to be at the short wavelength end partly outside the wavelength range of absorption of the lens. It may therefore be supposed that the action spectrum of cataract obtained by animal experiments is applicable to the human eye only with certain reservations.     

The effects of sub-solar levels of UV-A and UV-B on rabbit corneal and lens epithelial cells

The purpose of this work was to establish whether exposing cultured rabbit corneal and lens epithelial cells to ultraviolet radiation equivalent to several hours under the sun would damage the cells. Confluent rabbit corneal epithelial cells were irradiated with broadband UV-A or UV-B, and confluent lens epithelial cells were irradiated with broadband UV-A. The maximum dose of UV-A was 6.3 J cm(-2) and that of UV-B was 0.60 J cm(-2). Damage to corneal epithelial cell was studied using the terminal deoxynucleotidyl transferase mediated dUTP-X nick end labeling (TUNEL) assay and damage to lens epithelial cell was studied using the single cell gel electrophoresis (comet) assay and trypan blue exclusion assay. Lipid peroxidation was assayed using the thiobarbituric acid reaction. Both UV-B and UV-A induced cell death in corneal epithelial cells with different latent periods. UV-A damage included cell death, decreased viability and increased lipid peroxidation of lens epithelial cell. In addition, UV irradiation of the corneal and lens epithelial cells decreased the activity of catalase to thirty to fifty percent of its original value, while the activities of glutathione peroxidase and superoxide dismutase did not decrease within experimental error. Thus, even sub-solar UV radiation can cause irreversible damage to corneal and lens epithelial cells.     

Posterior cataract induction by UV-B radiation in albino mice

UV-B radiation (290-320 nm) was very effective at inducing posterior cortical cataracts in mice similar to those seen in the human senile lens. UV-A radiation, in contrast, was at most weakly cataractogenic. The posterior opacities induced by UV-B began to appear 5-6 months after daily exposure to 8 X 10-6 W cm-2 for 12 hr per day or 10-4 W cm-2 for 1 hr per day. Progression was more rapid following the more intense exposure rate. The cataracts developed without any apparent damage to the cornea. A hypothesis of how damage sustained by the epithelium results in posterior opacities is presented.     

Ultraviolet-a light and riboflavin therapy for acanthamoeba keratitis: a case report

Purpose

To report ultraviolet-A (UV-A) light treatment in a patient with Acanthamoeba keratitis (AK).

Methods

Interventional case report. A standard protocol for ultraviolet corneal therapy, with a power emission of 3 mW/cm² and a wavelength of 370 nm, was used. The protocol included an 8-nm bandwidth at a 54-mm distance measured with a collimation system of diodes as well as a protective shield of riboflavin in a case of documented AK.

Results

A 54-year-old female patient with AK, showing no therapeutic response to a wide variety of topical antimicrobial agents and with a visual acuity of 20/400, was treated with UV-A therapy. The patient displayed a favourable response in the first 24 h after treatment, with improvement of symptoms, visual acuity (to 20/200) and biomicroscopy cornea with haze degree I. By the third week post-treatment, the patient was symptom-free. Her visual acuity was 20/30, and the affected cornea was clear. Five months after treatment, there had been no recurrence, and her vision was 20/20.

Conclusions

Treatment with UV-A light was an effective therapy in this case of AK.Key words: Acanthamoeba keratitis, Ultraviolet light, Riboflavin     

Cataract classification

Opacifications of the eye lens — generally defined as cataracts — develop in various different parts of the lens. Therefore, one has to differentiate the types of opacities. For epidemiological studies it is prerequisite to classify the cataracts according to their localization within the lens as well as to the size and intensity of the opacified area. Two approaches have been used in the past: 1) subjective methods of lens observation (based on slit lamp microscopy) and 2) objective methods with measurements of lens transparency or lens opacity respectively based on slit image documentation according to the Scheimpflug principle combined with the retroillumination technique. With ageing, the light transparency of the lens is subjected to considerable changes. Even without the formation of an opacity the transmission of the wavelengths in the UV-B/UV-A and the visible range is diminished. The single lens layers are affected by this phenomenon to different degrees. These changes which might also indicate an early stage of cataract formation cannot be discerned by subjective methods. The densitometric image analysis of Scheimpflug slit images, however, allows the exact measurement of the light scatter in the single lens layers and enables the early recognition of disturbances in transparency which is of crucial importance particularly in cataract epidemiology. In view of our present knowledge the evaluation of risk factors which might be of importance in multifactorial cataract processes will hardly be possible by carrying out prevalence and/or incidence studies involving a single examination of the population. In this case follow-up studies (cohort studies) with repeated examinations are prerequisite. The objective methods for classification alone are able to ensure the necessary reproducibility and the possibility to measure transparency changes in the lensbefore visible (and therefore subjectively recognizable) opacifications occured. The methodical procedure with respect to an epidemiological study on the involvement of UV-B radiation in the processes of cataract formation in man requires the application of objective methods for cataract classification.     

A safer alternative approach to penetrating keratoplasty in opaque corneas

Background:This video demonstrates a useful technique of keratoplasty which can be routinely undertaken by all surgeons when imaging modalities such as anterior segment optical coherence tomography are not available and prior patient history is not forthcoming.Purpose:To demonstrate a technique of lamellar separation and layer by layer removal of host cornea when dealing with keratoplasty in perforated corneal ulcers, adherent leucomas, dense corneal opacities, which obscure visualization of the iris and anterior chamber details.Synopsis:In this video, we demonstrate penetrating keratoplasty in a failed opacified graft with iridocorneal adhesions, with no visualization of anterior chamber details. Lamellar dissection of the host cornea is done starting at its periphery and moving centrally, with gentle peeling of the superficial layers, the epithelium and bulk of stroma, following which, the deeper portion of the cornea is dissected and separated from underlying adherent iris tissue. Layer by layer separation allows better visualization through the remaining thin layers of the cornea. This permits fine dissection and layered removal of the cornea, thereby avoiding injury to iris and lens. Debulking of the host cornea decreases the force that is needed to be applied to separate adherent iris tissue from the host cornea, and reduces the chances of sudden entry into the anterior chamber and subsequent damage to the iris or lens. This also reduces the chance of iris tears, iridodialysis and bleeding from the iris and helps maintain iris integrity, which is essential intraoperatively for protection of lens and anterior chamber formation, and to avoid glare and photophobia postoperatively. Preventing iris damage also reduces the chances of formation of peripheral anterior synechiae (PAS), which can predispose to graft rejection, graft failure and secondary glaucoma.Highlights:Layer by layer corneal separation beginning inside the graft host junction, careful separation of iridocorneal adhesions and PAS is a helpful technique to optimally preserve the anterior segment anatomy during difficult cases of penetrating keratoplasty.Online Video Link: https://youtu.be/ZmQQhuOnAh4     

Ultraviolet B-induced corneal and lens damage in guinea pigs on low-ascorbic acid diet

To evaluate ocular morphological response to ultraviolet B (UV-B) exposure in guinea pigs fed with normal and low-ascorbic acid (ASA) diets, 24 guinea pigs were randomly divided into UVR (normal diet + UV-B), LVC (low-ASA diet + UV-B) and CTL (normal diet, without UV-B) groups. The irradiated animals were exposed to 8.2 J/cm(2) of UV-B over 29 weeks. Changes in the cornea and lens were examined using a Scheimpflug camera, specular microscope and histological studies. ASA contents in the plasma, aqueous humor and lens sections were measured by high-performance liquid chromatography. The results showed low contents of ASA in the plasma, aqueous humor and lens sections in LVC. Both irradiated groups displayed corneal epithelial edema, neovascularization in stroma, increase in corneal thickness, decrease in endothelial density, and lens epithelial damage. No significant morphological differences in cornea and lens were found between guinea pigs fed with low-ASA or normal diet.     

The optical properties of the anterior segment of the eye: implications for cortical cataract.

Epidemiological studies have correlated cortical cataract with exposure to light and have suggested that this is due primarily to relatively short wavelengths of ultraviolet radiation (UV-B). In addition, some cellular and animal models also implicate UV-B. In order to evaluate the likely role of different wavelengths of light in the etiology of cortical cataracts, the optical characteristics of several animal models were ascertained and compared to the primate. This study shows that the mouse model absorbs UV-B almost exclusively whereas other animal models such as the rabbit and the guinea pig also contain chromophores that absorb UV-A. The absorptive characteristics of the human lens varies drastically with age. The young lens absorbs primarily UV-A, whereas with age, there are increases in absorptions at 320 nm and out to wavelengths as long as 550 nm. By sectioning human lenses it was found that these changes in absorption properties increased toward the central and the nuclear regions.These absorptive characteristics were then compared to the amount of light reaching the surface of the lens. It was found that UV-B is a minor component of total energy reaching the surface of the human lens and old human lens proteins absorb 2 orders of magnitude more UV-A and visible light than UV-B. It is concluded that it is premature to exclude UV-A or even visible light in the etiology of human cortical cataracts.     

The challenges of the corneal graft

Indications for post-graft contact lens fitting are primarily therapeutic (healing/suture problems, leaking wound, graft dehiscence) or optical (high/irregular astigmatism, anisometropia, poor vision with spectacles, lens worn on fellow eye). In therapeutic application, 'soft' lenses of varying thickness and water content are generally indicated and for relatively short-term use. For optical management, rigid gas permeable corneal lenses are the mainstay although scleral lenses may be required in certain situations such as the highly irregular cornea where retention of smaller devices is problematic . There are numerous variations from the normal when considering contact lenses for the grafted cornea including physiological/metabolic (thickness variations, reduction in sensitivity, endothelial changes) and topographical (astigmatism, profile, position of graft). For example, in a patient with reduced corneal sensitivity where keratitis is a potential problem, optimising corneal oxygenation and reducing lens wear is recommended. Topographic peculiarities of the cornea can make the fitting of contact lenses a challenge – in extreme cases at best a compromise with the likelihood of limited wearing time and comfort, at worst potentially dangerous with the risk of corneal trauma and graft rejection. Liaison with the corneal surgeon in improving corneal topography by suture manipulation is essential.The practitioner must have access to a wide range of contact lens options and be mindful of lens dimensions and geometry and also material characteristics – this will give the optimal chance of success in dealing with the challenges posed.     

Ultraviolet radiation transmittance of the mouse eye and its individual media components

Recently, the mouse has become the preferred animal model in ophthalmic research. Therefore, there is a need for enhanced understanding of the mouse eye to validate its use in different experimental setting. The purpose of this study was to determine the ocular transmittance of the whole mouse eye, the cornea and the crystalline lens, particularly in the ultraviolet radiation (UVR) wavebands. This was carried out using a non-cuvette based fiber optic spectrometer system and the resulting transmittance curves were compared with published cone spectral response curves and mouse ocular transmittance data. First, transmittance curves of the whole mouse eye were measured by removing a small disc of sclera from the posterior pole to provide an anterior to posterior optical path. No statistical difference was found between left and right eye in each of the four mice sampled, therefore, all eight eyes were included in the final statistical analysis. The average of five test measurements from each left and right eye for the four test mice showed a transmittance cut off at approximately 310 nm. Secondly, the cornea with a scleral rim was excised and transmittance curves obtained for all eight eyes. This data showed an average transmittance cut off at 280 nm for the cornea. Similarly measured data for the excised crystalline lens showed UVR transmittance down to 310 nm. The good correlation between total ocular UVR transmittance and the sum of the individually measured components (i.e. the cornea and the crystalline lens) supported the validity of our method and its findings. This experiment demonstrated that the mouse cornea transmits more UV-B (280-315 nm) than the rabbit and the human corneal transmittance. The mouse crystalline lens on the other hand showed a cut off in the UV-B at 310 nm, which is at a much lower UV-B wavelength than the approximate UV-A (315-400 nm) cut off for the human crystalline lens at around 390 nm. The increased transmittance of UVR in the mouse eye serves its vision, since the mouse has a cone photopigment peaking at approximately 350 nm. Due to the above stated differences between the mouse and the human it is concluded that the mouse is not an ideal model for the human eye in experiments involving UVR.     

Effects of UV-A radiation on lens epithelial NaK-ATPase in organ culture.

PURPOSE: To investigate the mechanisms involved in the damage caused by UV-A irradiation at 365 nm on the eye lens. METHODS: Bovine lenses obtained from animals 1 to 5 years of age were placed in specially designed organ culture chambers for preincubation. Twenty-four hours later, the lenses were irradiated by 33 J/cm2 UV-A at 365 nm. During irradiation, the lenses were oriented in the culture so that the anterior surface faced the incident UV-A radiation source. After irradiation, lens optical quality was monitored throughout the 8 days of the culture period, and lens samples were taken for analysis of NaK-ATPase activity. RESULTS: Lens optics and NaK-ATPase activity were affected by irradiation of 33 J/cm2. The effects on lens epithelial NaK-ATPase activity were stronger at the equators than at the center. The damage to the activity at the center was reversible, as the lens optically recovered from the LW-A damage. CONCLUSIONS: Lens NaK-ATPase activity can recover from damage caused by UV-A at 365 nm. When the lenses received irradiation of 33 J/cm2, NaK-ATPase activity recovered from the damage during the culture period only at the center and not at the equators of the epithelium.     

Langerhans cell alterations in the guinea pig cornea

Langerhans cells (LC) are found in virtually all epithelial surfaces, but are rare or absent in the central cornea. LC migration into the cornea can be induced by several different stimuli. The authors studied LC in guinea pig corneal epithelium after: (1) suture placement; (2) suture removal; (3) UV-A irradiation; and (4) UV-C irradiation. Corneal LC markedly increased after suture placement during a 35-day observation period, and decreased by one-half during a 21-day observation period when sutures were removed. Suture-induced corneal LC decreased after UV-A irradiation, but increased after UV-C irradiation. These results demonstrate that ocular LC can be altered by nonimmunologic perturbations of the cornea.     

Lens epithelial cell death secondary to acanthamoeba keratitis: absence of capsular bag opacification six years after cataract surgery

Purpose

To show the evolution of anterior chamber structures 6 years after cataract surgery in a case with Acanthamoeba keratitis (AK).

Methods

A 37-year-old woman with AK receiving long-term treatment with chlorhexidine, propamidine isethionate and steroids developed a white cataract and iris atrophy. Penetrating keratoplasty and cataract surgery were performed with subsequent intraocular pressure elevation requiring Molteno shunt implantation. Two years after the last surgery, endothelial decompensation developed and another penetrating keratoplasty was performed. Intraoperatively, the anterior and posterior capsules were completely transparent.

Results

Six years after cataract surgery, the intraocular lens was centered with clear anterior and posterior capsules without lens epithelial cells proliferation. No Soemmering''s ring formation or posterior capsule opacification was found. Also, no zonular damage or pseudophacodonesis was observed.

Conclusions

This case suggests that AK infection and AK treatment not only cause white progressive cataract but also lens epithelial cell death. The capsules may be completely clear 6 years after cataract surgery, with a good quality of vision regardless of intraocular lens material or design.Key words: Acanthamoeba keratitis, Lens epithelial cells, Penetrating keratoplasty, Glaucoma, Cataract, Iris atrophy     

Concise review of progress in the management of perforating injury (author's transl)]

Improvement in the management of perforating injuries has become possible since the successful control of infection. However, the decisive step ahead was accurate suturing. The use of finer needles and of thinner, standardised suture material enabled accurate adaption of the margins and closer suturing. The anterior chamber could now be filled with air, thus preventing contact between iris and cornea. Development of new instruments enabled simultaneous management of haemorrhages and of injuries of the lens and vitreous body. Prolapse of iris without essential damage to the iris could be reduced either by limbal puncture or by intensive rinsing with fluid, proceeding from the edges of the wound. Parallel to the successful management of lens injuries a more radical form of vitreous surgery developed without significantly increasing surgical trauma. In Birmingham, during 1950--1958 45% of the patients with perforating injury of the anterior segment--including injury of the lens or iris--achieved a visual acuity of 6/12 or better. During 1971--1974 the corresponding percentage was 62% at the same clinic.     

A review of the evidence that ultraviolet irradiation is a risk factor in cataractogenesis

There are two approaches to the question of whether solar radiation contributes to human cataract. The first, epidemiological studies, investigates correlations between man's environmental UV dose and cataract frequency. The second, animal models, investigates the effects of varying UV strengths and spectra on lens opacificationin vivo orin vitro. While the latter approach typically provides for direct evidence, the data must still be extrapolated to human lenses. Results of physiological studies suggest that UV photons interact with proteins of the epithelial cell membranes, in particular tryptophan residues, transport ATPases and cytoskeletal proteins. One hypothesis is that damage to ion pumps and channels accumulates over the years as repair processes incompletely restore membrane function. Peroxidative damage is likely in view of the formation of UV-induced lipid peroxides in the lens epithelial membranes. Loss of homeostatic control of ions, particularly Ca⁺, leads to crystallin disorder in small regions of the underlying fiber cells. In our diabetic cataract studies, intracellular Ca⁺⁺ electrodes detected large shifts in intracellular Ca⁺⁺ before bulk-lens changes were apparent. Similar occurrences likely characterize UV cataract. Our lab is one of few studying lens physiology and how it is altered following transient exposures to UV-B and UV-A, both of which pass through the cornea. Some changes include: loss of epithelial cell GSH; elevated Ca⁺⁺; loss of membrane voltage; impaired transport of Na⁺; increased permeability to ions and water; inhibition of critical enzymes; and a decrease in the rate of membrane synthesis.     

Bee sting of the cornea - a case report]

BACKGROUND: Bee stings of the cornea are very rare, though its response can range from minimal inflammation to severe damage like lens dislocation, cataract formation, iris atrophy, ophthalmoplegia and optic neuropathy. We report on a patient with typical, severe findings. PATIENT: A 42-year-old patient presented with an acute, corneal bee sting of the left eye, after he was stung only a few hours ago. The patient suffered from pain, blurred vision and epiphora. The left eye showed edema of the upper and lower eyelid, conjunctival hyperemia, chemosis, striate keratitis, a purulent infiltration of the cornea above the limbus at the 7 o'clock meridian and a massive hypopyon. Further examinations showed regular ophthalmological findings. Vision acuity was 1,0/0,4. Under therapy inflammation decreased quickly. One week after we could lokalize the stinger in the depth of the corneal infiltration and it was removed surgically. After one month the eye only showed a minimal infiltration of the cornea with fine neovascularisations. Visual acuity was 0,8. CONCLUSION: Clinical reactions to bee stings of the cornea are caused by toxical and immunological effects of different components of the bee venom. These toxical and/or inflammatory reactions can lead to severe intraocular damage. Treatment of choice is the systemic and local application of steroids and antibiotics as well as local therapy with antihistamins.     

Amniotic membrane covering promotes healing of cornea epithelium and improves visual acuity afterdebridement for fungal keratitis

AIM:To investigate the effect of amniotic membrane covering (AMC) on the healing of cornea epithelium and visual acuity for fungal keratitis after debridement.METHODS:Twenty fungal keratitis patients were divided into two groups randomly, the AMC group and the control group, ten patients each group. Both debridement of the infected cornea tissue and standard anti-fungus drugs treatments were given to every patients, monolayer amniotic membrane were sutured to the surface of the entire cornea and bulbar conjunctiva with 10-0 nylon suture for patients in the AMC group. The diameter of the ulcer was determined with slit lamp microscope and the depth of the infiltration was determined with anterior segment optical coherence tomography. Uncorrected visual acuity (UCVA) was tested before surgery and three month after healing of the epithelial layer. The healing time of the cornea epithelium, visual acuity (VA) was compared between the two groups using t-test.RESULTS:There was no statistical difference of the diameter of the ulcer, depth of the infiltration, height of the hypopyon and VA between the two groups before surgery (P＞0.05). The average healing time of the AMC group was 6.89±2.98d, which was statistically shorter than that of the control group (10.23±2.78d) (P＜0.05). The average UCVA of the AMC group was 0.138±0.083, which was statistically better than that of the control group (0.053±0.068) (P＜0.05).CONCLUSION:AMC surgery could promote healing of cornea epithelium after debridement for fungal keratitis and lead to better VA outcome.     

Inhibitory effects of ovomacroglobulin on bacterial keratitis in rabbits

We studied the inhibitory effects of chicken egg-white ovomacroglobulin (ovoM) on keratitis induced by 56000-Da protease (56 KP) of Serratia marcescens and by elastase (PE) and alkaline protease (PAP) of Pseudomonas aeruginosa. The effects of ovoM on the serratial and pseudomonal keratitis in rabbits were also elucidated. In one model, four drops of 56 KP, PE, or PAP (1 mg/ml) were applied to wounded corneas of eight eyes. Thereafter, 80 l ovoM (10 mg/ml) was dropped into four eyes and 0.01 M phosphate-buffed 0.15 M saline (pH 7.4) into the other eyes as a control. The other in vivo test system involved intrastromal injection of S. marcescens or P. aeruginosa, by which each sample (10⁵–10⁷ colony-forming units) mixed with ovoM was injected into one cornea and the other cornea received organisms without ovoM. OvoM completely inhibited the activity of these bacterial proteases in vitro and reduced corneal destruction in experimental keratitis in rabbits. In addition, greatly accelerated wound healing was observed.Part of this work was presented at the 1989 meeting of the Association for Research in Vision and Ophthalmology in Sarasota, Florida Offprint requests to: H. Maeda     

角膜板栗刺异物伤15例的临床观察

目的：探讨目前角膜板栗刺异物伤有效治疗方法及影响病情进展的因素。方法：回顾性分析2014－07／2015－10武汉市同济医院眼科病房收治的角膜板栗刺异物伤患者15例15眼的临床资料,入院时未并发真菌性角膜炎的患者在剔除角膜板栗刺异物的同时均积极给予以那他霉素为主的抗真菌治疗,而对入院时已并发真菌性角膜炎的患者予以氟康唑溶液前房冲洗和角膜基质层注药,必要时予以羊膜移植术或角膜移植术,总结上述治疗方法的有效性及影响病情进展的因素。结果：入院时未并发角膜溃疡病例11例,入院时平均病程为1～7（2．42±2．15）d,入院时已并发真菌性角膜溃疡病例4例,入院时病程为3～30（18．25±4．35）d。其中并发角膜溃疡病例板栗刺数量平均为4．5根,并均有板栗刺穿透角膜进入前房;未发生角膜溃疡病例板栗刺数量平均为3．5根,而只有28．5％病例有板栗刺穿透角膜进入前房。经抗真菌治疗和相应手术治疗后,所有病例均被判定为治疗有效。结论：影响角膜板栗刺异物伤病情进展的因素可能有板栗刺的数量、板栗刺是否穿透角膜进入前房、就诊时病程的长短、是否积极进行抗真菌治疗等。对已并发真菌性角膜炎的病例积极予以抗真菌药物能有效控制真菌性角膜炎的进展,为进一步行羊膜移植或角膜移植术创造有利条件。