New trends in quantitative assessment of the corneal barrier function

The Effects of Antiglaucoma Ophthalmic Solutions on the Cornea Revealed by a Corneal Electrical Resistance Device

Purpose: We sought to evaluate the effect of antiglaucoma ophthalmic solutions on the cornea with a corneal resistance device (CRD), and to compare the results with those by fluorescein staining. Methods: In 6 rabbit groups (n = 7 each), right eyes were administered latanoprost ophthalmic solution containing 0.02% benzalkonium chloride (BAK); dorzolamide/timolol (1%/0.5%) containing 0.005% BAK; dorzolamide/timolol without BAK; dorzolamide/timolol+latanoprost with 0.02% BAK; 0.005% BAK; or 0.02% BAK to the conjunctival sac 3 × at 15-min intervals. Left (control) eyes were administered saline. Baseline and post-treatment corneal resistance (CR) were measured. The CR ratio = CR before versus after treatment. We evaluated superficial punctate keratitis by fluorescein staining using area and density (AD) grades. Results: In the dorzolamide/timolol-without BAK group, there were no significant difference in the CR ratio between the control and treatment eyes at any time point. In the 0.005%-BAK group at 30 min and the other 4 groups at all time points, the CR ratio differed significantly between the control and treatment eyes (P < 0.05). AD grades were 0 in all control eyes and the dorzolamide/timolol-without BAK and 0.005% BAK treatment eyes. Conclusions: Nonpreservative ophthalmic solutions (and those with low BAK concentrations) do not significantly affect corneal electrical resistance. Eye drop ingredients other than BAK may be involved in altering corneal electrical resistance. CRDs may detect corneal epithelium changes not revealed by fluorescein staining.

In Vivo Measurement of Human Corneal Impedance Value

PURPOSE

To examine the validity of in vivo electrical corneal resistance (CR) measurements taken by a corneal resistance device (CRD).

METHODS

Eighty-two eyes (mean age ± SD, 50.1 ± 23.3; range, 22-87 years: 50 eyes of 33 males and 32 eyes of 17 females) of patients who had undergone cataract surgery and volunteers at the Kanazawa Medical University Hospital were enrolled. The CR was compared among gender; age; side, that is, left versus right eye; healthy (fluorescein-negative) versus epithelium-injured eyes (fluorescein-positive), corneal radius of curvature; corneal endothelial cell count; and corneal thickness.

RESULTS

The mean ± SD of the CR in the 82 eyes was 273.2 ± 78.2 Ω. By age group, the mean ± SD CR was 283.3 ± 87.4 Ω (30 eyes) in the 20s, 275.0 ± 50.0 Ω (4 eyes) in the 30s, 266.7 ± 70.7 Ω (9 eyes) in the 40s, 257.1 ± 53.5 Ω (7 eyes) in the 50s, 242.9 ± 78.7 Ω (7 eyes) in the 60s, 266.7 ± 84.0 Ω (18 eyes) in the 70s, and 300.0 ± 81.6 Ω (7 eyes) in the 80s, with no significant difference among the groups. By gender, the mean ± SD CR was 270.0 ± 83.0 Ω (50 eyes) in males and 278.0 ± 71.0 Ω (32 eyes) in females. By side, the CR values were 282.9 ± 83.4 Ω (44 eyes) in the right eye, 265.9 ± 71.3 Ω (41 eyes) in the left eye, with no significant difference among the groups. By status, the values were 280.0 ± 70.0 Ω (44 eyes) in healthy eyes and 200.0 ± 144.2 Ω (13 eyes) in injured eyes, with a significant between-group difference (P = 0.009). The mean ± SD corneal thickness (0.56 ± 0.03 mm) in 46 healthy eyes was slightly correlated with the CR.

CONCLUSIONS

The CRD quantitatively measured the CR in healthy eyes. The CR did not differ significantly by age, gender, or left versus right eye. The significant difference in CR between the healthy and injured eyes showed that the measurements have validity.