Comeal Thickness

Maintenance of comeal transparency requires precise regulation of stromal water content. AQPl is expressed in comeal endothelial cells and AQPS in epithelial cells. Comeal thickness, water permeability, and the response to experimental swelling was studied in wildtype... 

All comeal thicknesses are normalized relative values compared to the week 0 comeal thickness, which was assigned the thickness value of 1... 

Brandt JD, Beiser JA, Kass MA, Gordon MO (2001) Central comeal thickness in the Ocular Hypertension Treatment Study (OHTS). Ophthalmology 108 1779-1788. 

The ophthalmic toxicology of CR in solution up to 10% in PEG300 was studied in rabbits (BaUantyne et al., 1975). With 1% and 2%, effects (excess lacrimation, conjunctival hyperemia, chemosis, and blepharitis) were just detectable to mild and of 24 h or less duration. A Concentration of 10% CR caused a just detectable keratitis of a few days duration, and 5% was the threshold concentration for keratitis. Measurement of the effect of CR (0.05%-10.0%) on comeal thickness in vivo showed peak increases between 1 and 6 h postinstiUation, with remrn to normal values by 2-10 days. Tonometry showed concentration-related peak increases in lOP at 10 min, ranging from 20% to 40% for 0.5%-5.0% CR. Rabbits exposed for 30 min to a CR aerosol at 360 and 571 mg m showed only just detectable excess lacrimation and conjunctival injection of 1 h duration. 

Myers, R.C., Ballantyne, B., Christopher, S.M., and Chun, J.S., Comparative evaluation of several methods and conditions for the in vivo measurement of comeal thickness in rabbits and rats, Toxicol. Methods, 8, 219-231, 1998. 

The effect of solutions of CN in PEG 300 on corneal thickness was investigated in vivo in the rabbit using solutions in the concentration range 0.01-0.75% with measurements being taken before instillation and at 1 and 24 h, and 2,4, 8 and 17 days post-treatment. Corneal thickness was measured by an optical pachymeter attached to a slit-lamp biomicroscope. Increases in corneal thickness were statistically significant for exposures to 0.03% CN and above, and both the magnitude and duration were related to the CN concentration. Times for comeal thickness to return to control values varied between 2 days for 0.02% and 14 days for 0.75%. 

A method was described by Burton et al. (1981) involving the direct application of irritant test substance to the cornea of eyes removed immediately after sacrifice of rabbits and subsequent evaluation of the cornea for swelling, opacity, and fluorescein staining, The eye is mounted on a clamp in a temperature-controlled superfusion chamber with isotonic saline dripped onto the surface of the cornea, After an equilibrium period of 30-45 min, the test material is applied to the surface of the cornea and then washed off. Eyes are inspected macroscopically. Then, with a slit-lamp biomicroscope, the comeal thickness is measured and any fluorescein staining noted. The predictive value of the method has been confirmed in several studies (Commission of the European Communities, 1991 Koeter and Prinsen, 1985 Price and Andrews, 1985 Whittle et al., 1992), By using comeal thickness measurement, fluorescein retention, and comeal opacity as criteria for ocular injury, the suitability of the chicken eye as an enucleated model was confirmed by Prinsen and Kocier (1993) and Prinsen (1996). 

A 68-year-old woman with Parkinsonism took amantadine HCl 100 mg bd for 2 years and developed comeal edema, with central comeal thicknesses of 871 mm in the right eye and 746 mm in the left eye [280 ]. There was bilateral diffuse stromal and epithelial edema with marked folds in Descemet s membrane. The amantadine was withdrawn and topical prednisolone acetate 1 % and sodium chloride eye-drops were given. There was complete resolution within 3 weeks, and the comeal thicknesses resolved (592 mm in the right eye and 567 mm in the left eye). 

A 61-year-old woman with Parkinson s disease was given amantadine, followed over the next 6 years by pramipexole. ropinirole, co-careldopa, and entacapone [282 ]. She subsequently developed severe comeal edema. Amantadine was withdrawn and within 1 trwnth the comeal edema had completely resolved. The comeal thicknesses improved from 810 to 640 pm in the right eye and from 780 to 660 pm in the left eye. 

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