A new procedure for evaluating smoothness of corneal surface following 193-nanometer excimer laser ablation.

BACKGROUND: The routine technique for evaluating the smoothness of an excimer laser keratectomy has been scanning electron microscopy (SEM). However, this method suffers from tissue shrinkage and surface artifacts, and evaluates the surface only in a qualitative manner. In our study, we used a Zygo microscope to quantitatively assess the smoothness of the excimer laser ablated corneas, without complicated tissue processing. METHODS: Five rabbit eyes and five PMMA blocks underwent 193-nanometer excimer laser ablations (5.00-millimeter diameter and 80-micrometer depth). The ablation zones of the corneas were trephined and fixated prior to the measurement. The surface smoothness was measured under the Zygo and characterized by two surface parameters (Ra and RMS). After measurement, the corneal and PMMA samples were processed for SEM. RESULTS: The Ra and RMS (mean +/- SD) for the ablated corneas are 183.33 +/- 20.6 and 240.06 +/- 23.10 nm, respectively; for the PMMA blocks, 79.49 +/- 23.02 and 96.45 +/- 27.16 nm, respectively. There are significant differences of Ra and RMS between the ablated corneas and PMMA blocks (p < .01), indicating the ablated corneal surfaces are rougher than the ablated PMMA surfaces. Qualitatively, SEM correlated well with the results of the Zygo measurements. CONCLUSIONS: We found this technique to be a simple, accurate, and reproducible means of objectively assessing the surface smoothness following excimer laser ablation. Combined use of the Zygo and SEM enables more complete evaluation of the ablated corneal surface.

Collagen shields as a vehicle for collecting and studying migratory cells on human corneas.

Collagen shields have been studied in the enhancement of the initial healing of epithelial defects, as an adjunct in the treatment of dry eye, and as a reservoir and delivery system for topical ocular medications. The authors used collagen shields to collect information on the numbers and types of free cells populating the normal and postoperative ocular surface. In addition, correlative microscopic techniques were used to study details of the mechanisms responsible for the dissolution of the shields when applied to the human eye. Collagen shields were applied as a bandage lens on the eyes of patients who underwent extracapsular cataract extraction (n = 10) or penetrating keratoplasty (n = 10) and on normal volunteers (n = 10). The shields were collected at the 1-day postoperative examination and fixed in aldehyde mixtures. Specimens then were processed for correlative light (LM), transmission (TEM), and scanning (SEM) microscopy. Cell accumulation was shown by SEM on both anterior and posterior shield surfaces. Cell adherence occurred primarily on the posterior shield periphery for approximately 2 mm, with the central zone relatively clean. Both LM and TEM evaluation revealed cell counts ranging from 0.066 cells/10(4) microns2 (standard deviation, +/- 0.256) in healthy eyes compared with shields placed on postoperative eyes (194.25 +/- 7.32 cells/10(4) microns2). Various correlative microscopy techniques revealed that most cells were polymorphonuclear leukocytes with a low number of other hematogenous (lymphocytes and monocytes) and exfoliated epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)