Impulse activity in corneal sensory nerve fibers after photorefractive keratectomy

PURPOSE: To evaluate the changes in spontaneous and stimulus-evoked nerve impulse activity of corneal polymodal and mechanonociceptor sensory fibers of the cornea after photorefractive keratectomy (PRK). METHODS: A central corneal ablation 6 mm in diameter and 70 microm in depth was performed with an excimer laser in both eyes of three anesthetized cats, after removal of the corneal epithelium. Single nerve fiber activity was recorded in these animals 12 to 48 hours after surgery. Activity in corneal nerve fibers with receptive fields (RFs) within and/or close to the wound, as well as with RFs far from the lesioned area, was studied. Incidence and frequency of spontaneous discharges and nerve impulse firing responses to mechanical (Cochet-Bonet esthesiometer) and chemical (CO(2) gas pulses) stimuli were studied. RESULTS: The incidence of nociceptor fibers exhibiting ongoing activity (15/35 vs. 1/9) and the frequency of their spontaneous firing (0.25 +/- 0.09 impulses [imp]/s versus 0.08 +/- 0.08 imp/s) was higher in fibers with RFs within and/or bordering the wounded area than in those with RFs far away from the wound. Mechanical responsiveness of fibers with RFs within or nearby the ablated area was often reduced. In these fibers, CO(2) pulses evoked a lower-frequency impulse discharge (0.9 +/- 0.2 imp/s inside, 2.3 +/- 0.7 imp/s outside the wound). CO(2)-evoked discharges recorded from fibers innervating the intact wound border were similar to those recorded in corneal fibers of intact cats. CONCLUSIONS: The spontaneous impulse activity and the abnormal responsiveness shown by a part of the corneal nerve fibers innervating the injured cornea are presumably the neurophysiological substrate of the pain sensations experienced by human patients hours after PRK surgery.     

Distribution of Corneal TRPV1 and Its Association With Immune Cells During Homeostasis and Injury

PurposeGiven the role of corneal sensory nerves during epithelial wound repair, we sought to examine the relationship between immune cells and polymodal nociceptors following corneal injury.MethodsYoung C57BL/6J mice received a 2 mm corneal epithelial injury. One week later, corneal wholemounts were immunostained using β-tubulin-488, TRPV1 (transient receptor potential ion channel subfamily V member-1, a nonselective cation channel) and immune cell (MHC-II, CD45 and CD68) antibodies. The sum length of TRPV1⁺ and TRPV1^– nerve fibers, and their spatial association with immune cells, was quantified in intact and injured corneas.ResultsTRPV1⁺ nerves account for ∼40% of the nerve fiber length in the intact corneal epithelium and ∼80% in the stroma. In the superficial epithelial layers, TRPV1⁺ nerve terminal length was similar in injured and intact corneas. In intact corneas, the density (sum length) of basal epithelial TRPV1⁺ and TRPV1⁻ nerve fibers was similar, however, in injured corneas, TRPV1⁺ nerve density was higher compared to TRPV1⁻ nerves. The degree of physical association between TRPV1⁺ nerves and intraepithelial CD45⁺ MHC-II⁺ CD11c⁺ cells was similar in intact and injured corneas. Stromal leukocytes co-expressed TRPV1, which was partially localized to CD68⁺ lysosomes, and this expression pattern was lower in injured corneas.ConclusionsTRPV1⁺ nerves accounted for a higher proportion of corneal nerves after injury, which may provide insights into the pathophysiology of neuropathic pain following corneal trauma. The close interactions of TRPV1⁺ nerves with intraepithelial immune cells and expression of TRPV1 by stromal macrophages provide evidence of neuroimmune interactions in the cornea.     

Comparative effects of the nonsteroidal anti-inflammatory drug nepafenac on corneal sensory nerve fibers responding to chemical irritation

PURPOSE: To compare the corneal analgesic efficacy of the nonsteroidal anti-inflammatory drugs (NSAIDs) nepafenac, diclofenac, and ketorolac, and to evaluate the possibility that their inhibitory effects on corneal polymodal nociceptor fiber activity are partly mediated by a decrease in sodium currents. METHODS: Corneal sensory afferent units were recorded in the anesthetized cat. The response of thin myelinated polymodal nociceptor fibers to mechanical and acidic stimulation (98.5% CO(2)) was recorded before and at various times after topical application of the vehicle or of nepafenac 0.1% (Nevanac; Alcon Laboratories, Ltd., Fort Worth, TX), diclofenac 0.1% (Voltaren; Novartis, Basel, Switzerland), and ketorolac 0.4% (Acular LS; Allergan, Irvine, CA). Voltage-clamp recordings were performed in cultured trigeminal ganglion neurons. RESULTS: Nepafenac, diclofenac, and ketorolac reduced the mean frequency of the impulse response evoked by repeated CO(2) stimuli in polymodal nociceptor fibers. The progressive increase in ongoing activity, observed in vehicle-treated eyes after repeated acidic stimulation was also prevented. Nepafenac exhibited a more rapid and a slightly more pronounced effect on spontaneous and CO(2)-evoked activity than did diclofenac and ketorolac and did not affect the responsiveness of corneal mechanonociceptor or cold receptor fibers. In cultured mice trigeminal ganglion neurons, diclofenac significantly suppressed sodium currents, whereas nepafenac or its metabolite, amfenac, exhibited only minimal inhibitory effects. CONCLUSIONS: The inhibition of polymodal nociceptor activity by nepafenac, a weak inhibitor of cyclooxygenase, is most likely due to its greater lipophilicity compared with diclofenac and ketorolac, leading to a rapid saturation of the corneal epithelium where nociceptor terminals are located. In contrast to diclofenac, nepafenac does not exhibit local anesthetic effects.     

Neural basis of sensation in intact and injured corneas

A renewed interest in the characteristics and neural basis of corneal and conjunctival sensations is developing in recent years due to the high incidence of discomfort and altered sensitivity of the cornea following refractive surgery, use of contact lenses and dry eyes. Corneal nerves are functionally heterogeneous: about 20% respond exclusively to noxious mechanical forces (mechano-nociceptors); 70% are additionally excited by extreme temperatures, exogenous irritant chemicals and endogenous inflammatory mediators (polymodal nociceptors), and 10% are cold-sensitive and increase their discharge with moderate cooling of the cornea (cold receptors). Each of these types of sensory fibres contributes distinctly to corneal sensations. Mechano-nociceptors mediate, sharp acute pain produced by touching of the cornea. Polymodal nociceptors elicit the sustained irritation and pain that accompany corneal wounding; cold receptors evoke cooling sensations. Depending on the relative activation by the stimulus of each subpopulation of corneal sensory fibres, different subqualities of irritation and pain sensations are evoked. Corneal sensations can be explored experimentally in humans with a gas esthesiometer that applies controlled mechanical, chemical and thermal stimuli to the corneal surface. When the cornea is wounded, corneal nerves are excited and eventually severed in a variable degree and local inflammation is produced. Activated corneal nerves release neuropeptides (SP, CGRP) that contribute to the inflammatory reaction (neurogenic inflammation). They also become sensitized by local inflammatory mediators, such as prostaglandins or bradykinin and thus exhibit spontaneous activity, lowered threshold and enhanced responses to new stimuli. This leads to spontaneous pain and hyperalgesia. Nerves destroyed by injury soon start to regenerate and form microneuromas that exhibit abnormal responsiveness and spontaneous discharges, due to an altered expression of ion channel proteins in the soma and in regenerating nerve terminals. Presumably, this altered excitability is the origin of the lowered sensitivity and the spontaneous pain, dry eye sensations and other disaesthesias reported in patients following refractive surgery.     

Comparison of factors that influence the measurement of corneal hysteresis in vivo and in vitro

Purpose: The purpose of this study was to compare measurements of corneal hysteresis (CH) obtained in vivo, with similar measurements from excised human eyes and from excised human corneas mounted in an artificial anterior chamber. Methods: Corneal hysteresis was measured using an ocular response analyser (Reichert Ophthalmic Instruments) from three groups: 53 healthy normal corneas of fifty‐three patients, six excised eyes and 17 excised corneas. Results: In vivo, it was found that CH was independent of gender, age and mean spherical equivalent, but has a significant inverse relationship with intraocular pressure (IOP_cc) (r = 0.53; p < 0.0001). However, there was no correlation between CH and IOP_G (r = 0.10; p = 461). The same inverse relationship with IOP_cc was recorded in intact, excised eyes (r = 0.74; p < 0.0001), with no significant differences between the behaviour each individual eye. Excised corneas also showed an inverse relationship between CH and trans‐corneal pressure (r = 0.72; p < 0.0001), but the measured values of CH were lower than those recorded in vivo and from intact globes. In both excised eyes and excised corneas, we found a significant correlation between CH and central corneal thickness [r = 0.86; p < 0.0001 and r = 0.611; p < 0.0005 (respectively)]. Conclusion: The in vitro results indicate that every normal human eye at physiological hydration shows an identical dependence of CH on IOP_cc, the same dependence as is observed in vivo. This therefore would appear to be an intrinsic response of the tissue to a change in IOP. However, it is possible that the lower values of CH recorded from excised corneas reflect the influence of the artificial chamber replacing the eye globe, so in vivo values of CH may be influenced to some extent by the presence of the other components of the eye.     

Eye dryness sensations after refractive surgery: impaired tear secretion or "phantom" cornea?

The cornea is richly innervated by various functional types of sensory nerve fibers. When stimulated, these fibers evoke conscious sensations of different quality including ocular dryness, discomfort, and pain. Refractive surgery involves a variable degree of damage to corneal nerves. This leads to an altered expression of membrane ion channels at the injured and regenerating nerve fibers, giving rise to aberrant spontaneous and stimulus-evoked nerve impulse firing. It is speculated that these abnormal sensory discharges are read by the brain as ocular surface dryness. This would explain the high incidence of eye dryness sensations after photorefractive surgery, which are experienced by a large number of patients despite the often modest disturbance of tear secretion. Therefore, drugs that reduce abnormal activity in injured nerves may represent a therapeutic alternative for eye dryness sensations after refractive surgery.     

Outcomes of photorefractive keratectomy in patients with posterior corneal steepening

PurposeTo assess post-operative outcomes following photorefractive keratectomy (PRK) in patients with posterior corneal steepening compared to an age, gender and refraction matched control group.MethodsA retrospective matched case-control study that analysed outcomes of PRK in eyes with posterior corneal steepening as shown by the Sirius tomography (Sirius, CSO, Italy), versus normal eyes. Both groups were age, gender and refraction matched. Data collected include: demographic data, pre-operative and post-operative refraction, uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), maximal ablation depth. Inferior–superior ratio, central corneal thickness (CCT), mean posterior keratometry (K), Baiocchi Calossi Versaci index for the front (BCV_f) and back (BCV_b) cornea, the symmetry index of front (SI_f) and back (SI_b) corneal curvature were assessed pre- and postoperatively.ResultsOverall, 89 study eyes and 954 normal myopic eyes were included. Compared to the control group, corneas with posterior steepening demonstrated significantly reduced CDVA (p < 0.0001 and p = 0.007) and lower CCT (p < 0.0001 and p = 0.03), before and following the operation, respectively. Pre-operative BCV_f, BCV_b, SI_f and SI_b were significantly higher in corneas with posterior steepening (p < 0.0001) and remained higher following the surgery except for BCV_f. Ectasia occurred in one eye (1.1%). The safety and efficacy indices at 12 months were comparable for both groups.ConclusionPRK on corneas with posterior steepening results in similar refractive outcomes compared to normal eyes, 1 year following the surgery. Keratectasia is a rare, however a possible complication.Subject terms: Outcomes research, Corneal diseases     

Changing pattern of utilization of human donor cornea in India

Purpose:To review the changing pattern of donor, corneal utilization in an eye bank at a Tertiary Care Center in Northern India by analyzing the trend in the years 2003, 2008, and 2011.Methods:A retrospective review of eye bank records for 3 years (2003, 2008, and 2011) was performed at the National Eye Bank. Details including a clinical grade of donor cornea, indication of corneal transplantation (therapeutic or optical), type of procedure (penetrating or lamellar keratoplasty [LK]), and clinical diagnosis of the graft recipients were recorded. Primary outcome measure was to observe any preference toward LK, judicious usage of donor corneal tissue, and impact of lamellar corneal transplant in the usage of donor corneas. Secondary outcomes included overall utilization rate and change in trend of indication for keratoplasty.Results:A total of 673, 745, and 864 corneas were retrieved in the years 2003, 2008, and 2011, respectively. The percentage of donor corneal utilization increased significantly over time with the rate being 65.08%, 70.06%, and 68.29%, respectively, in the years 2003, 2008, and 2011 (P = 0.014); however, this change was reflected only in the usage of nonoptical grade corneas and not for the optical grade corneas. There was an overall increase in lamellar corneal procedures for any clinical grade of cornea (P = 0.0019); number of Descemet''s stripping automated endothelial keratoplasty (DSAEK) procedures increased significantly (P < 0.001), particularly for pseudophakic corneal edema (PCE) (P = 0.0085) and failed graft (P = 0.002). Significant increase in the utilization of nonoptical grade corneas was observed over the years (P = 0.005), though the utilization did not increase significantly for optical purposes viz., LK (P = 0.08).Conclusions:Utilization rate of donor corneas increased over the years, primarily due to increase in usage of nonoptical grade corneas for therapeutic purposes. There was a procedural shift toward DSAEK for PCE and failed graft. However, an increase in usage of nonoptical grade corneas for LK, a single donor corneal tissue for two recipients, and retrieval or utilization of optical grade cornea was not observed.     

Combined scraping,coagulation, and subconjunctival bevacizumab in corneal transplantation for bullous keratopathy with corneal neovascularization

PurposeThis study investigated clinical outcomes of the combined method of scraping, coagulation, and subconjunctival bevacizumab for the treatment of corneal neovascularization (NV) in penetrating keratoplasty (PKP).MethodsThis study included patients undergoing PKP who were diagnosed with bullous keratopathy with dense subepithelial scarring that was not suitable for Descemet’s stripping automated endothelial keratoplasty. Corneal NV was treated by scraping the corneal epithelium and lightly coagulating the superficial corneal stromal NV combined with subconjunctival bevacizumab injection at the end of surgery. Patients without corneal NV were used as the control group.ResultsThere were six patients with vascularized corneas in the study group and three patients without vascularized corneas in the control group. The original corneal NV in the study group disappeared in all patients after surgery. Three of the six (50%) study patients experienced recurrent corneal NV. One of the three (33%) control patients developed corneal NV. These patients had no corneal NV recurrences over the next 6 months after repeat treatment. In both groups, no graft failure or chronic epithelial defects occurred.ConclusionThe combination of scraping the corneal epithelium, coagulating the superficial corneal stromal NV and the feeding vessels in the sclera after peritomy, and subconjunctival bevacizumab injection is an effective method to treat corneal NV in corneal transplantation for bullous keratopathy.     

Benzalkonium chloride,a common ophthalmic preservative,compromises rat corneal cold sensitive nerve activity

PurposeCorneal nerves comprise the densest sensory network in the body. Dysfunction of the corneal cold sensitive neurons (CSN) is implicated in ophthalmic disorders, including Dry Eye Disease, the most common ocular surface disorder. The preservative Benzalkonium chloride (BAK) and the mydriatic agent Phenylephrine hydrochloride (PHE) are considered to be inactive at the level of the CSNs. The purpose of this study is to test the impacts of continuous exposures to BAK or PHE at their clinically used concentrations on corneal nerve structure and function.MethodsIn vivo extracellular electrophysiology of the rat trigeminal ganglion was used to monitor CSN functional response to stimuli mimicking physiological states and stressors of the cornea. Corneal nerve structure was evaluated by immunostaining.ResultsAmong the tested stimuli, cold probe receptive field stimulation and hyperosmolar stress were the most sensitive methods of detecting activity changes. CSN activity was attenuated after 30 min exposure to either PHE or BAK. After an hour-long washout period, BAK-treated neurons failed to recover activity while PHE-treated neurons showed signs of functional recovery. Intraepithelial nerve density was reduced and nerve fragmentation was increased in BAK-treated corneas, while PHE exposure left corneal nerves structurally intact.ConclusionsOur study suggests that prolonged ocular instillations of BAK or PHE alter CSN activity through two different processes — irreversible neuronal damage in the case of BAK vs. reversible attenuation in the case of PHE.     

Effects of posterior chamber lens implantation on the endothelium of transplanted corneas

AIMS—The morphological changes of the corneal endothelium after posterior chamber lens implantation in the transplanted corneas were investigated.
METHODS—36 patients underwent extracapsular cataract extraction with posterior chamber lens implantation. Among these, penetrating keratoplasty had been performed in 18 patients before cataract surgery. The indications for penetrating keratoplasty in these cases included keratoconus, herpetic keratitis, and macula cornea. 18 cataract patients with normal corneas were also studied as controls. The central corneal endothelium in each subject was examined with a wide field specular microscope at a few days before and 3 months after cataract surgery.
RESULTS—Although the transplanted corneas showed lower endothelial cell densities, marked polymegethism, and pleomorphism in the baseline variables, the endothelial morphological changes in the transplanted corneas after posterior chamber lens implantation were comparable with those in the normal corneas. Also, there was no clinical evidence, especially, of corneal epithelial and/or endothelial rejections and corneal decompensation in all corneas.
CONCLUSION—Even though the transplanted corneas have a lower endothelial cell density and marked polymegethism, it is believed that cataract surgery does not induce corneal decompensation in cases where the peripheral recipient endothelium can be considered to have normal morphology.

     

Neuronal-epithelial cell alignment: A determinant of health and disease status of the cornea

PurposeHow sensory neurons and epithelial cells interact with one another, and whether this association can be considered an indicator of health or disease is yet to be elucidated.MethodsHerein, we used the cornea, Confetti mice, a novel image segmentation algorithm for intraepithelial corneal nerves which was compared to and validated against several other analytical platforms, and three mouse models to delineate this paradigm. For aging, eyes were collected from 2 to 52 week-old normal C57BL/6 mice (n ≥ 4/time-point). For wound-healing and limbal stem cell deficiency, 7 week-old mice received a limbal-sparing or limbal-to-limbal epithelial debridement to their right cornea, respectively. Eyes were collected 2–16 weeks post-injury (n=4/group/time-point), corneas procured, immunolabelled with βIII-tubulin, flat-mounted, imaged by scanning confocal microscopy and analyzed for nerve and epithelial-specific parameters.ResultsOur data indicate that nerve features are dynamic during aging and their curvilinear arrangement align with corneal epithelial migratory tracks. Moderate corneal injury prompted axonal regeneration and recovery of nerve fiber features. Limbal stem cell deficient corneas displayed abnormal nerve morphology, and fibers no longer aligned with corneal epithelial migratory tracks. Mechanistically, we discovered that nerve pattern restoration relies on the number and distribution of stromal-epithelial nerve penetration sites.ConclusionsMicrostructural changes to innervation may explain corneal complications related to aging and/or disease and facilitate development of new assays for diagnosis and/or classification of ocular and systemic diseases.     

Comparison of subconjunctivally injected bevacizumab, ranibizumab, and pegaptanib for inhibition of corneal neovascularization in a rat model

AIM:To compare the efficacies of subconjunctival bevacizumab, ranibizumab, and pegaptanib sodium injections for the inhibition of corneal neovascularization in an experimental rat model. METHODS:Sixteen corneas of 16 rats were chemically cauterized and randomized into four groups:bevacizumab group that treated with 0.05mL/1.25mg bevacizumab, ranibizumab group that treated with 0.05mL/0.5mg ranibizumab, pegaptanib group that treated with 0.05mL/0.15mg pegaptanib sodium, and control group that treated with 0.05mL saline solution. Digital photographs of the corneas were taken and analyzed using an image analysis software program. All corneas were excised and examined histologically on the 15^th day. RESULTS: Each treatment group had significantly less neovascularized corneal areas and fewer blood vessels than the control group (all P<0.05). In addition, bevacizumab group had significantly less neovascularized corneal areas and fewer blood vessels than ranibizumab and pegaptanib groups (both P<0.05). However, there was no significant difference between the ranibizumab and pegaptanib groups regarding percentage of neovascularized corneal areas and number of blood vessels (both P>0.05). CONCLUSION:Subconjunctival bevacizumab, ranibizumab, and pegaptanib sodium were effective with no corneal epitheliopathy for inhibiting corneal neovascularization after corneal burn in rats. Bevacizumab was more effective than ranibizumab and pegaptanib sodium.     

Subconjunctival Injection of Regulatory T Cells Potentiates Corneal Healing Via Orchestrating Inflammation and Tissue Repair After Acute Alkali Burn

PurposeThis study aimed to investigate the therapeutic effects and underlying mechanisms of locally delivered regulatory T cells (Tregs) on acute corneal wound healing after alkali burn.MethodsAfter corneal alkali burn, the mice were injected subconjunctivally with regulatory T cells (Tregs) isolated from syngeneic mice. The wound healing process was monitored by clinical manifestation, flow cytometry, and enzyme-linked immunosorbent assay (ELISA). As amphiregulin (Areg) was significantly upregulated, its reparative function in injured corneas was suggested. The hypothesis was further verified via loss- and gain-of-function experiments by administrating the antibody of Areg (anti-Areg) and recombinant Areg (rmAreg).ResultsSubconjunctivally injected Tregs rapidly migrated to injured corneas. The mice treated with Tregs showed prominently reduced corneal opacity, alleviated edema, and faster re-epithelialization compared with the control group. Mechanistically, Treg treatment led to suppressed infiltration of inflammatory cells, along with improved proliferation and inhibited apoptosis of corneal epithelial cells. Tregs expressed upregulated functional markers, including Areg. Expectantly, the levels of Areg in corneas were dramatically higher in the Treg injection group, in line with better corneal restoration. Additional experiments showed that the administration of anti-Areg blunted the reparative effect of Tregs, while exogenous Areg enhanced it. Treg-treated corneas also exhibited less neovascularization and fibrosis at a later reconstruction stage of corneal repair.ConclusionsThe findings showed that the subconjunctival injection of Tregs effectively promoted corneal wound healing by inhibiting excessive inflammation and enhancing epithelial regeneration, with an indispensable reparative role of Areg. Subsequent complications of corneal vascularization and fibrosis were therefore reduced.     

In vivo effects of fluoroquinolones on rabbit corneas

Purpose: The use of topical fluoroquinolones to treat microbial keratitis is associated with an increased incidence of corneal perforation compared to other standard treatments. This study examined the effects of topical fluoro­quinolones on corneal collagen and keratocytes in intact rabbit corneas and corneas with an epithelial defect. Methods: Studies consisted of one group of intact corneas and one group of corneas where a 6‐mm epithelial defect was created with a surgical scrape. Within each group, eyes were randomly assigned to one of four topical medications (0.3% ciprofloxacin, 0.3% ofloxacin, fortified antibiotics (1.36% tobramycin, 5% cefrazolin) or Tears Naturale (Alcon Laboratories, Frenchs Forest, NSW, Australia). Two drops were instilled hourly for 48 h and then 2‐hourly for an additional 48 h. At 96 h the corneas were removed and processed for light microscopy, immunohistology for collagen IV, V and VI, and apoptosis staining. Results: In intact rabbit corneas there was no demonstrable difference between treatment groups. In corneas with an epithelial defect, both fluoroquinolones delayed epithelial healing when compared to fortified antibiotics or tears. Keratocyte loss was seen in all groups and was greatest in the ofloxacin group. Median stromal thickness with keratocyte loss were: ofloxacin 30%; ciprofloxacin 10%; fortified antibiotics 7.5%; and tears 15% (ofloxacin vs tears, Mann?Whitney = 16.0, P = 0.09). Keratocyte loss did not correlate with the amount of demonstrable apoptosis. Collagens IV, V and VI showed no differences between treatments. Conclusions: These results suggest that ofloxacin is potentially cytotoxic to corneal keratocytes. Such an effect could lead to the observed increased incidence of corneal per­foration in microbial keratitis.     

Transepithelial phototherapeutic keratectomy for post-traumatic recurrent corneal erosions

Purpose:To evaluate the outcomes of transepithelial phototherapeutic keratectomy (transepithelial PTK) for treatment of posttraumatic recurrent corneal erosions.Methods:Twenty-four eyes of 22 patients with posttraumatic recurrent corneal erosions who were treated with transepithelial PTK from April 2018 to July 2020 were included in this retrospective study. The rates of recurrent erosions and complications were evaluated during the follow-up after surgery. Visual acuity and refraction were recorded preoperatively and 1 year after surgery. Total corneal astigmatism, total corneal irregular astigmatism, and total corneal spherical aberrations were recorded using corneal tomography preoperatively and 1 year after surgery.Results:Mean postoperative follow-up was 13 months (range: 12–32 months). None of the patients suffered from any complications or further erosions. Uncorrected distance visual acuity, best-corrected distance visual acuity, spherical equivalent, and cylinder remained stable at 1-year postoperatively compared with the baseline (P = 0.214, P = 0.461, P = 0.084, and P = 0.879, respectively). Moreover, there was no significant difference in total corneal astigmatism, total corneal irregular astigmatism, and total corneal spherical aberrations between baseline and 1-year postoperative visit (P = 0.938, P = 0.136, and P = 0.981, respectively)Conclusion:Transepithelial PTK was an effective treatment for patients with posttraumatic recurrent corneal erosions.     

Attitude,beliefs and awareness towards corneal donation in Saudi Arabia

PurposeCorneal donation has not received adequate attention in Saudi Arabia, and donors are lacking. This study explores the underlying knowledge of, attitude regarding, and practice of corneal donation in Saudi Arabia, which will possibly help in designing healthcare policies and creating a national eye bank.MethodsThis observational cross-sectional study used a self-administered questionnaire and was administered to the residents of Saudi Arabia from August to December 2017. We surveyed 1292 random subjects who agreed to fill out the self-administered questionnaire. The sample included Saudi and non-Saudi residents across adult age groups from medical and non-medical professions.ResultsOf the 1292 respondents, only 4.3% believed that they had sufficient knowledge about corneal donation; 66.3% of the sample had not decided whether to donate their corneas after death; 40.2% stated that they would be more willing to donate if they had sufficient knowledge about corneal donation; and 46.1% of the population did not know where to apply to donate their corneas. Those who believed that they had sufficient information about corneal donation were significantly more likely to donate (p < 0.001) than those who believed they did not have enough information.ConclusionIncreased awareness about corneal donation is required, as a higher level of awareness was associated with a higher willingness to donate corneas. Establishing healthcare policies and creating community campaigns is necessary to increase corneal donation awareness and willingness.     

角膜瞬时受体电位通道蛋白超家族的研究进展

角膜对温度、机械和化学等刺激的感受依赖于各种伤害性感受器。早年,对该过程的认识一度停留于神经生理学层面,即以传递相同信号的神经纤维束来划分。随着近年分子生物学技术和方法的发展,伤害性感受器的分类与功能已精确到细胞感受器水平,即各类通道蛋白。其中,瞬时受体电位(Transient Receptor Potential,TRP)离子通道蛋白超家族占有重要地位。已发现多个TRP家族成员在角膜中表达,并参与了角膜疼痛、神经源性角膜病、上皮损伤修复、免疫炎症反应等过程,部分TRP受体甚至成为潜在的治疗靶点。     

Progress of research on corneal transient receptor potential channel superfamily

Cornea senses thermal, mechanical and chemical stimuli via various nociceptors. In the early years, knowledge of the mechanism of corneal nociception was merely restricted to neurophysiology, which classifies nociceptors according to the clusters of nerve fibers which transmit identical stimulation signals. During the past decade, benefiting from the promptly developing molecular biology and technology, classification of the nociceptors has been modified into the level of cell sensors, among which, transient receptor potential (TRP) channel superfamily weighs the most. Researches have shown that there are a couple of TRP superfamily members expressed in cornea, which play major roles in the process of corneal pain, neurotrophic keratopathy, epithelial wound healing and immuno-inflammation. Some TRPs have even been recognized as targets of management of keratopathy.