The use of computerized videokeratography as an aid in fitting rigid gas permeable contact lenses.

PURPOSE: To assess the efficacy of computerized corneal topography in (1) fitting cosmetic rigid gas permeable contact lenses on normal corneas and (2) patients who have keratoconus. METHODS: In study 1, 26 patients were fitted with cosmetic contact lenses. In 13 patients, the first rigid gas permeable lens was chosen on the basis of corneal topography using the EyeSys videokeratoscope and contact lens software version 2.11w. Thirteen control patients were fitted with rigid gas permeable contact lenses by means of diagnostic contact lenses. The number of parameter changes required in each group to reach the best fit were compared. In study 2, the records of 28 patients (41 eyes) with keratoconus who had been successfully fit with rigid gas permeable lenses were reviewed. Topographic analysis using the EyeSys videokeratoscope was conducted. The following 8 data points were analyzed: maximum dioptric curvature with respect to the central visual axis, the power at the visual axis (VK), the average keratometry readings within the 3-mm zone, the average flat K at 3-mm central and 5-mm paracentral regions, and the K reading at 1.5, 2.0, and 2.5 mm superior to the visual axis. RESULTS: Study 1: In 10 eyes (38%) fitted with cosmetic contact lenses utilizing corneal topography and the EyeSys contact lens program, the first lens chosen by the computer program was correct with no additional changes in lens parameters required. In the other 16 eyes, 21 parameter changes were required. In the control group, 14 eyes (53%) required no additional change in parameters from the original contact lens that was fitted using diagnostic lenses. In the other 12 eyes, 12 parameter changes were required. Study 2: In the keratoconus group, of the 9 measurements analyzed, the final base curve of patients' rigid gas permeable lenses was correlated most closely with the average flat corneal curvature at the 3-mm central zone. CONCLUSION: Study 1: In fitting cosmetic rigid gas permeable contact lenses, the videokeratoscope with the EyeSys software 2.11w contact lens program proved to be inferior to diagnostic lenses in selecting the final correct contact lens parameters. However, it may be useful in selecting an initial diagnostic lens with which to begin rigid gas permeable fitting. Study 2: In patients with irregular corneas such as keratoconus, corneal topography is helpful in determining the initial base curve of the contact lens. In patients with keratoconus, it appears to be the average flat corneal curvature at the 3.0-mm zone.

A comparison of conventional and disposable extended wear contact lenses.

The charts of 126 extended wear contact lens patients (65 disposable and 61 conventional extended wear lens users) were reviewed for subjective and objective contact lens problems. We found that the number of complication events per person per year of lens wear was higher for conventional extended lens wearers than for disposable extended wear patients. There was a trend in both groups toward decreased numbers of complications in the second and third years of lens wear. Within each group, we also examined first time lens wearers and patients with a history of contact lens related complications. Both of these subgroups also fared better with disposable lenses, with fewer complication events per year and fewer complications overall. Of the 20 individual signs and symptoms that were analyzed, 13 occurred more frequently among conventional extended wear lens users; this difference was statistically significant for itching, burning and dryness, poor vision, foreign body sensation, torn and lost lenses, giant papillary conjunctivitis, mucus, and superficial punctate keratopathy. Five signs were more frequent among the disposable extended wear lens users, but the difference was not statistically significant. There were no cases of ulcerative keratitis in either group. The average wearing time was 11.2 +/- 5.9 days for conventional extended wear patients and 6.7 +/- 2.3 days in the disposable group. The difference in wearing time between the two groups may have been a factor in the higher complication rate among conventional extended wear lens patients.

Treatment of giant papillary conjunctivitis with cromolyn sodium.

We evaluated the efficacy of cromolyn sodium in the management of contact lens patients with GPC. Fourteen of 20 patients (70%) with moderate to severe giant papillary conjunctivitis (GPC) were able to continue wearing contact lenses with the use of 4% sodium cromolyn eye drops. These patients had all failed to stay symptom free with our standard method of treatment (i.e., discontinuing contact lens wear for 1-2 weeks; improving lens care; and refitting with different lens designs and/or polymers). This study examined the indications, therapeutic regimen, complications, and patient response to the use of sodium cromolyn in contact lens patients with GPC.

Composition of interstitial waters of marine sediments: temperature of squeezing effect.

Warmeling of samples of marine sediments to room temperatures prior to the extraction of interstitial water accounts for the apparent enrichments of potassium ion (13.3 percent) and chloride ion (1.4 percent) and depletions of magnesium ion (2.5 percent) and calcium ion (4.9 percent). These differences are the result of changes in ion-exchange selectivity as a function of temperature.