Neurotrophic keratitis: inflammatory pathogenesis and novel therapies.

PURPOSE OF REVIEW: Neurotrophic keratitis is a rare degenerative disease characterized by decrease or absence of corneal sensation. Neurotrophic keratitis varies from mild forms with mild epitheliopathy to severe manifestations such as corneal ulceration, melting and perforation that can lead to irreversible visual loss. The cause of neurotrophic keratitis comprises a long list of diseases, medications, congenital or genetic conditions as well as trauma. The mechanism of neurotrophic keratitis is complex and multifactorial and its understanding is crucial to better address the treatment strategies. We aimed to review neurotrophic keratitis pathology, mechanisms and management. RECENT FINDINGS: Corneal nerves are critical for the homeostasis of a healthy ocular surface. The lack of nerve-derived neuromediators and corneal-released neuropeptides, neuro-trophins and neurotrophic factors in neurotrophic keratitis leads to a decrease in trophic supply to corneal cells in addition to a decrease in afferent signaling to the brain. This results in pathological tear secretion, decreased blinking rate, corneal healing along with ocular surface and corneal inflammation. Lately, nerve growth factor in special gained emphasis as a treatment strategy targeting the disease mechanism rather than its manifestations. Other therapies, including surgical interventions, are in the pipeline of neurotrophic keratitis management. However, there are still no proper therapeutic guidelines and neurotrophic keratitis treatment remains challenging. SUMMARY: Neurotrophic keratitis may have a devastating outcome and treatment is still challenging. Understanding the disease pathology may assist in the development of new treatment strategies. Prompt disease recognition and immediate intervention are key factors to promote corneal healing and avoid further deterioration.

Ex vivo demonstration of canine corneal pre-Descemet's anatomy using pneumodissection as for the big bubble technique for deep anterior lamellar keratoplasty.

The recent discovery and characterization of pre-Descemet's layer (PDL; also termed the Dua's layer or the Dua-Fine layer) has advanced the understanding of various posterior corneal pathologies and surgeries in human. This study aimed to characterize the ultrastructure of the posterior stroma and interfacial zone of Descemet's membrane (DM) in canine eyes. Eighteen canine corneo-scleral discs were included. Intrastromal air injection resulted in the formation of type 1 big bubble (BB) in 73% (n = 11/15) of corneas, with a mean diameter of 11.0 ± 1.3 mm. No type 2 BB was created. Anterior segment optical coherence tomography, histology and transmission electron microscopy confirmed that the wall of BB was composed of DM, in contact with remaining stroma (canine PDL; cPDL). The cPDL was populated with keratocytes, of varying thickness of 16.2 ± 4.2 µm in close apposition to the DM, and composed of collagen bundles arranged in transverse, longitudinal and oblique directions. The interfacial zone, between DM and cPDL, showed fibril extension in all three directions, predominantly longitudinal. Irregular extensions of DM material into cPDL stroma were observed. No long-spaced collagen was detected. In conclusion, there exists a well-defined cleavage plane between the posterior stroma and cPDL, with similar but not identical characteristics as in humans, that is revealed by pneumodissection. This adds to our understanding of the anatomy of the posterior most canine cornea, which will have significant clinical impact on posterior corneal surgery and understanding of corneal pathology in dogs.

Profiling ocular surface responses to preserved and non-preserved topical glaucoma medications: A 2-year randomized evaluation study.

BACKGROUND: Use of topical glaucoma medications has been reported to cause ocular surface (OS) discomfort and inflammation. This study explores the profile of inflammatory cytokines and OS symptoms induced in response to preserved and non-preserved drops. METHODS: Prospective, randomized evaluation on 36 treatment-naïve patients over 24 months of three differently preserved glaucoma drop preparations: Preservative-free (PF), polyquad (PQ) and benzalkonium chloride (BAK). Study participants were evaluated at baseline and then at 1, 3, 6, 12 and 24 months while on medication. At each visit, participants completed the OS disease index (OSDI) questionnaire, had basal tear sampling and impression cytology (IC) of the conjunctival epithelium. Quantitative polymerase chain reaction was performed to measure the gene expression of inflammatory cytokines [interleukin (IL)-6, IL-8, IL-10, IL-12A, IL-12B, IL-17A, IL-1ß and tumour necrosis factor-α] in the IC samples. Corresponding protein expression of cytokines in tear samples was assessed by the Becton-Dickinson cytometric bead arrays. RESULTS: Compared to PF and PQ groups, mRNA and protein expression of IL-6, IL-8 and IL-1ß increased in samples from the BAK group in a time-dependent fashion, whereas all other cytokines showed a non-significant increase. In the BAK group, there was a strong correlation between OSDI and the levels of IC/IL-1ß (r = .832, R2 = .692 and P = .040); IC/IL-10 (r = .925, R2 = .856 and P = .008) and tear/IL-1ß (r = .899, R2 = .808 and P = .014). CONCLUSIONS: BAK-preserved topical drops stimulate a sterile inflammatory response on the OS within 3 months which is maintained thereafter, whereas PF-drops and PQ-preserved drops showed no significant OS inflammation.

Dynamics of big bubble formation in deep anterior lamellar keratoplasty by the big bubble technique: in vitro studies.

PURPOSE: To examine the movement of air injected in the cornea in simulated deep anterior lamellar keratoplasty (DALK), from the needle tip to the formation of different types of big bubbles (BB) and to ascertain how air travels through the stroma and pre-Descemet's layer [Dua's layer (PDL)] to create a type-1 (air between PDL and deep stroma) and type-2BB (air between PDL and Descemet's membrane). METHODS: Air was injected in 57 sclerocorneal discs and the passage recorded. Leaking points and sites of commencement of type-1 and type-2BB were examined by scanning electron microscopy. Stromal distribution of air pockets was studied by light microscopy. Uninjected corneas served as controls. RESULTS: Injected air followed a consistent pattern, initially as radial tracks to the limbus, then as circumferential bands along the limbus and finally centripetally to create predominantly a type-1BB. Type-2BB started at the periphery, by air emerging through clusters of tiny fenestrations discovered in the periphery of PDL. Fifteen to 20 such clusters were also seen in control samples on either side of the Descemet's attachment. Type-1BB was formed by air emerging through wide spaces between lamellae of deep stroma. Histologically, the circumferential band revealed an aggregation of air pockets in the mid-stroma. CONCLUSION: The consistent pattern of passage of air is indicative of the architecture and microanatomy of the corneal stroma where collagen lamellae are orthogonally arranged centrally and as a circular annulus at the periphery. The novel peripheral fenestrations explain the peripheral commencement of a type-2BB and the escape of air into the anterior chamber during DALK.

Clinical evaluation and characterisation of corneal vascularisation.

BACKGROUND/AIMS: To clinically characterise corneal neovascularisation (CVas) with a view to elaborate clinical presentations and to standardise descriptors for clinical evaluation and research. METHODS: Corneas of 165 patients with CVas due to a variety of corneal pathologies were observed clinically with the slit lamp biomicroscope and photography at different time points over the course of their disease. Parameters assessed included location, depth, length, branching pattern, colour, lipid leakage, nature of blood flow and presence of haemorrhage. A clinical grading of CVas was applied. RESULTS: CVas can arise from the limbus, conjunctiva and iris. CVas preferentially travels along planes created by corneal incisions, suture tracks and lamellar keratoplasty, both deep lamellar and endothelial keratoplasty. CVas also principally follows the depth of pathology. CVas can be classified into active young, active old, mature, partially regressed and regressed. Herpetic infection was the most common cause of lipid keratopathy. Acanthamoeba keratitis induced the least amount of vascularisation. A simple and efficient clinical grading system for ascertaining the severity of CVas was developed and validated. CONCLUSIONS: The various clinical characteristics of CVas described in this study can be used to standardise the nomenclature and description of CVas and clinically grade its severity. As modern, effective methods of treating CVas are being introduced, it is important that there is uniformity in the descriptors used to establish baseline values and evaluate outcomes of treatment. The parameters established in this study can help in this regard.

Fine needle diathermy occlusion of corneal vessels.

AIMS: To evaluate the efficacy of fine needle diathermy (FND) occlusion of corneal vessels in relation to defined clinical indications. METHODS: A retrospective, consecutive case series including all patients treated by FND for occlusion of corneal vessels between 2004 and 2012. Indications were lipid keratopathy, preparation for keratoplasty to reduce risk of rejection and treatment of recalcitrant corneal graft rejection associated with stromal vessels. Our outcome measures were occlusion of corneal vessels with reduced corneal vascularisation, reduction in amount of lipid deposition, and reduction of graft rejection episodes. RESULTS: FND effectively reduced lipid deposition associated with the treated vessels in 14 out of 17 eyes (82.3%). When used to reduce corneal vascularisation before keratoplasty and to reduce intraoperative bleeding, the 1-year survival of the high-risk grafts was (84.6%). FND prevented further rejection episodes in 3 out of 4 corneal grafts. Fourteen eyes required retreatment (2-5 times) of which 9 had lipid keratopathy and 5 were in preparation for corneal grafting. CONCLUSIONS: FND is effective in occluding established corneal vessels. Corneal microperforation is a potentially serious adverse event, but other adverse events, such as striae, whitening and intracorneal haemorrhages are reversible. It should be considered for established corneal vessels, and can be combined with antivascular endothelial growth factors.

The collagen matrix of the human trabecular meshwork is an extension of the novel pre-Descemet's layer (Dua's layer).

BACKGROUND: The trabecular meshwork (TM) located at the angle of the anterior chamber of the eye contributes to aqueous drainage. A novel layer in the posterior part of the human cornea has recently been reported (the pre-Descemet's layer (Dua's layer (PDL)). We examined the peripheral part of this layer in relation to the origin of the TM. METHODS: The PDL and TM of 19 human donor eyes and one exenterated sample were studied. Samples were examined by light and electron microscopy (EM) for tissue architecture and by immunohistology for four matricellular proteins, five collagen types and CD34. RESULTS: EM revealed that beams of collagen emerged from the periphery of PDL on the anterior surface of the Descemet's membrane and divided and subdivided to continue as the beams of the TM. Long-spacing collagen was seen in the PDL and TM. Trabecular cells (CD34-ve) associated with basement membrane were seen in the peripheral part of the PDL and corresponded to the start of the separation of the collagen lamellae of PDL. Collagen VI was present continuously in PDL and extended into the TM. Matricellular proteins were seen predominantly in the TM with only laminin extending into the periphery of PDL. CONCLUSIONS: This study provides an insight into the origins of the collagen core of the TM as an extension of the PDL of the cornea. This finding adds to the knowledge base of the TM and cornea and has the potential to impact future research into the TM and glaucoma.

Human corneal anatomy redefined: a novel pre-Descemet's layer (Dua's layer).

PURPOSE: To define and characterize a novel pre-Descemet's layer in the human cornea. DESIGN: Clinical and experimental study. PARTICIPANTS: We included 31 human donor sclerocorneal discs, including 6 controls (mean age, 77.7 years). METHODS: Air was injected into the stroma of donor whole globes (n = 4) and sclerocorneal discs (n = 21) as in the clinical deep anterior lamellar keratoplasty procedure with the big bubble (BB) technique. The following experiments were performed: (1) creation of BB followed by peeling of the Descemet's membrane (DM); (2) peeling off of the DM followed by creation of the BB, and (3) creation of the BB and continued inflation until the bubble popped to measure the popping pressure. Tissue obtained from these experiments was subjected to histologic examination. MAIN OUTCOME MEASURES: Demonstration of a novel pre-Descemet's layer (Dua's layer) in the human cornea. RESULTS: Three types of BB were obtained. Type-1, is a well-circumscribed, central dome-shaped elevation up to 8.5 mm in diameter (n = 14). Type-2, is a thin-walled, large BB of maximum 10.5 mm diameter, which always started at the periphery, enlarging centrally to form a large BB (n = 5), and a mixed type (n = 3). With type-1 BB, unlike type-2 BB, it was possible to peel off DM completely without deflating the BB, indicating the presence of an additional layer of tissue. A type-1 BB could be created after first peeling off the DM (n = 5), confirming that DM was not essential to create a type-1 BB. The popping pressure was 1.45 bar and 0.6 bar for type-1 BB and type-2 BB, respectively. Histology confirmed that the cleavage occurred beyond the last row of keratocytes. This layer was acellular, measured 10.15 ± 3.6 microns composed of 5 to 8 lamellae of predominantly type-1 collagen bundles arranged in transverse, longitudinal, and oblique directions. CONCLUSIONS: There exists a novel, well-defined, acellular, strong layer in the pre-Descemet's cornea. This separates along the last row of keratocytes in most cases performed with the BB technique. Its recognition will have considerable impact on posterior corneal surgery and the understanding of corneal biomechanics and posterior corneal pathology such as acute hydrops, Descematocele and pre-Descemet's dystrophies. FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any materials discussed in this article.

Profile of sight-threatening infectious keratitis: a prospective study.

PURPOSE: To prospectively study patients presenting with sight-threatening corneal ulcers with a view to identify the predisposing factors, causative organisms, clinical signs and treatment outcomes. METHODS: Prospectively, over 3-year period, all cases with serious infective keratitis presenting to Queens Medical Hospital in Nottingham, UK, were recruited. Detailed information on the aetiology, culture results, signs & symptoms, the treatment given and the patient's response was collected and statistically analysed. RESULTS: One hundred and forty-three eyes of 129 patients were enrolled. Thirty-one patients were managed as out-patients, and 98 were treated as in-patients. The mean duration of admission was 9 ± 13 days but was significantly higher in older patients and in Acanthamoeba keratitis cases. The important risk factors were ocular surface disease (32%), contact lens wear (26%) and previous ocular surgery (20%). Old age, deep infiltration, steroid use and poor initial vision were risk factors for prolonged course of treatment in bacterial keratitis. Corneal scrapings were done in 89% of the cases, but positive results were obtained only in 41.7%. Staphylococcus aureus was the most common isolated bacteria (18.8%). Acanthamoeba and Pseudomonas aeruginosa were the second and third common causative organisms (16.6% and 15%, respectively). Overall, 8.3% needed corneal grafting, which survived in 83.3% and eradicated infection in 100%. CONCLUSION: Microbial keratitis is an important cause of ocular morbidity. Previous ocular disease is an important predisposing factor. Old age, steroid use and poor presenting visual acuity are important prognostic indicators. Corneal grafting is an effective option for managing recalcitrant corneal infections.

The effect of gravitational force on limbal stem cell growth.

AIM: To evaluate the effect of gravity on corneal epithelial cell migration in vitro. METHODS: Fourteen donor peripheral corneoscleral rims were used. Twenty explants were chosen of which 10 were placed vertically and 10 were placed horizontally during culture. Analyses were performed to investigate the effect of gravity on epithelial growth by measuring the extent of epithelial cell growth above and below the horizontal meridian and counting the total number of cells using a haemocytometer. RESULTS: There was no statistically significant difference in cell growth between the explants that were placed horizontally and vertically. However, in the vertical explant group the cells grew preferentially towards the 6 o'clock direction, possibly as a result of gravity. CONCLUSIONS: Gravitational forces may influence cell migration in vitro. This could be of significance in the planning of limbal transplantation, because a superior graft may be more likely to succeed than a gravitationally challenged inferior graft.

Consensus statement on indications for anti-angiogenic therapy in the management of corneal diseases associated with neovascularisation: outcome of an expert roundtable.

The cornea is the clear window at the front of the eye and is the eye's main refractive medium. Its transparency is essential for vision. Corneal neovascularisation is a common clinical problem with serious consequences for vision; it can compromise corneal transparency and plays a major role in corneal graft rejection by breaching corneal immune privilege. In this review, we formulate a consensus on the unmet medical needs in the management of corneal neovascularisation and outline a framework for the clinical research that is needed to identify suitable agents to meet these needs.