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Ocular Irritation Testing
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
George P. Daston, F. E. Freeberg
The corneal epithelium is a stratified columnar epithelium, typically 5 to 6 cells thick in the rabbit, 7 to 10 in the human. Bowman’s membrane is thick in the human (8 to 12 μm), but much thinner (approximately 2 μm) in rabbits.5 The endothelium is a single layer of low cuboidal cells. Both epithelia form a coherent barrier to diffusion. The corneal stroma, which is by far the thickest part of the cornea, is composed of collagen fibrils which are arranged in a highly regular pattern in order to achieve transparency. The fluid content of the stroma is higher than that of the adjacent sclera,26 and this probably also contributes to its transparency.
Diagnosis and Treatment of Fungal Keratitis
Published in Mahendra Rai, Marcelo Luís Occhiutto, Mycotic Keratitis, 2019
In more than half of the cases (Li et al. 2017), the ulcer healing time was shortened to be less than 7 days. The maximum diameter of the ulcers in 41 of 48 eyes was less than 5 mm. On the contrary, among the 47 patients with healing time greater than 7 days, 31.2% had an ulcer diameter of 5 mm or more. It indicates that the size of corneal ulcer is an important factor related to the healing rate of corneal epithelium. During 3 months of follow-up, no complication was caused by thinning of the corneal stroma, and no infection recurred. About 3/4 of the patients had improved visual acuity in different degrees.
Special Senses
Published in Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard, Toxicologic Pathology, 2018
Kenneth A. Schafer, Oliver C. Turner, Richard A. Altschuler
The corneal stroma of the common laboratory animals is composed of thin collagen fibers arranged in a lattice pattern, along with a few fibroblasts (keratocytes). The stroma is lined internally by Descemet’s membrane, a thin, uniform layer produced by corneal endothelial cells, and terminates peripherally at the pectinate ligament.
Corneal dellen development after strabismus surgery
Published in Strabismus, 2021
Ahmet Kürşad Sakallioğlu, Rüveyde Garip
Ernst Fuchs firstly described dellen in 1911 as a saucer-like excavations at the corneal margin.1 They are caused by localized dryness and occur next to elevated tissues.2 Dellen formation has been reported in the corneal periphery due to a limbic elevation. Especially rectus muscle surgery, with the limbic approach, has been shown as a cause of dellen formation.3 Some of the other various causes are large filtration blebs, pterygium surgery, severe conjunctival chemosis, dermoids, scleritis, episcleritis,4 and silicone oil escape from the vitreous cavity in an aphakic eye to the subconjunctival space.5 However, dellen formation has been reported after elevation of the conjunctiva after the scleral buckle.6 Foreign body sensation, mild discomfort, and redness in the eyes appear as the complaint of patients. In slit-lamp examination, corneal dellen appear as a depressed area with sharply defined edges with a dull center. They are usually transient and smaller than 4 mm. Intact epithelium overlying a thinned area of dehydrated corneal stroma is the characteristic of the lesions. In most cases, corneal dellen heal within 24–48 hours and usually respond well to firm bandage applied to the eye, but the presence of inflammation with tissue loss, scarring, or epithelial break is associated with chronic dellen formation. Overall, corneal dellen usually heal within 10–15 days. Treatment of dellen involves limbal conjunctival elevation reduction and provision of necessary corneal hydration.7
Ocular manifestations in classic homocystinuria
Published in Ophthalmic Genetics, 2021
Patrícia Ioschpe Gus, Karina Carvalho Donis, Diane Marinho, Tiago Franco Martins, Carolina Fischinger Moura de Souza, Rafael Barboza Carloto, Gabriel Leivas, Ida Vanessa Doederlein Schwartz
Biochemical abnormalities of HCU are supposed to cause the clinical features of this disorder, but underlying mechanisms are not fully understood. Ocular diseases are possibly related to the reduced level of cysteine, since the lens zonules have high cysteine content (2,4,5). Raised tHcy concentrations modify sulfhydryl groups on proteins and also interfere with the cross-linking of sulfhydryl groups in proteins such as elastin (2). High myopia might potentially occur due to alterations of the scleral connective tissue, as much as irregular scars, but the latest can also be a result of inadequate suture after lens removal. Keratoconus can be related to abnormal collagen fibers in corneal stroma. Those abnormalities may hypothetically cause the connective tissue structures of the eye less resistant to intra-ocular pressure.
Ocular toxicity due to colours used during holi celebration in India: correlation of clinical findings with the anterior segment OCT
Published in Cutaneous and Ocular Toxicology, 2019
Amar Pujari, Aswini Behera, Ritika Mukhija, Rohan Chawla, Suresh Yadav, Namrata Sharma
Corneal findings included a varying degree of surface epithelial irregularity. The eyes of the patients were stained with 1% fluorescein dye and the extent of the surface epithelial defect was assessed. The epithelial defects were classified into two patterns. In the first type (type I) there was focal punctate epithelial staining in 12 patients (57.14%) (Figure 1(c)) and in the second type (type II), there was diffuse punctate epithelial staining with variable sized central or paracentral frank epithelial defect in nine patients (42.85%) (Figure 1(d,e)). Furthermore, a varying amount of corneal staining by the colour was observed in all the patients, ranging from superficial to the deep stroma and even endothelial staining, which was evident in two cases. Visual acuity in cases of type I corneal involvement varied from 6/6 to 6/9. Whereas, in type II corneal involvement the visual acuity varied from 6/12 to 6/24 (Table 1). Both the types showed focal epithelial discontinuity with underlying stromal staining on ASOCT. However, the depth of injury was limited to corneal epithelium (Figure 2(a)) and the anterior stroma up to 60 microns from the surface (Figure 2(b)). Horizontally, the defective area measured from 150 microns to 500 microns in cases with punctate staining (Figure 2(b)). Although stromal staining was observed clinically, no appreciable changes were noted in the corneal stroma on ASOCT. Similarly, in type II injuries with large areas of surface epithelial defect bare underlying superficial stroma were noted on ASOCT. However, the corneal thickness did not show any significant change (Table 2).