A 3-year prospective study of the clinical performance of daily disposable contact lenses compared with frequent replacement and conventional daily wear contact lenses.

PURPOSE: To determine the clinical performance of daily disposable contact lens wear compared to conventional daily wear contact lenses and frequent replacement contact lenses. METHODS: This 3-year prospective study was conducted in 12 U.S. practices. Of 338 eligible subjects enrolled (126 conventional daily wear, 144 frequent replacement, and 68 daily disposable), 229 subjects disposable group were compared with the conventional daily wear group and two sub-groups of frequent replacement subjects: (a) those with replacement at 2-weak intervals and (b) those with replacement at 1 or 3 months. RESULTS: Comparing the daily disposable and conventional daily wear groups, the daily disposable subjects were more likely to be asymptomatic, reported fewer symptoms of redness, cloudy vision and grittiness/dirty sensation, reported better vision and overall satisfaction, and had fewer lens surface deposits, complications, tarsal abnormalities, and unscheduled visits, while conventional daily wear subjects reported better lens handling. Comparing the daily disposable and frequent replacement (1/3 months) groups, daily disposable subjects reported fewer symptoms of foreign body sensation, redness, cloudy vision and grittiness/dirty sensation, reported better subjective vision, comfort and overall satisfaction, and has fewer lens surface deposits, complications, and tarsal abnormalities, while frequent replacement (1/3 months) subjects reported fewer dryness symptoms and better lens handling. Comparing the daily disposable and frequent replacement (2-weeks) groups, daily disposable subjects reported better subjective vision and overall satisfaction and had fewer lens surface deposits and tarsal abnormalities, while frequent replacement (2-weeks) subjects reported fewer photophobia symptoms. CONCLUSIONS: The results indicate that daily disposable wear may be the most trouble-free way of wearing contact lenses.

A clinical evaluation of frequent replacement contact lenses on patients currently wearing premium reusable daily wear soft contact lenses.

A 3-month clinical investigation was undertaken to evaluate a population of premium reusable daily wear soft contact lens wearers when refitted with soft contact lenses worn on a daily wear schedule and replaced every 2 weeks. In addition to an initial visit, follow-up visits occurred at 2-, 4-, 8-, and 12 weeks. Areas of assessment included vision, lens fitting performance, ocular physiology, subjective comfort and handling responses and lens surface deposits and damage. Of the 51 patients recruited, 50 were successfully trial fit and enrolled. During the course of the investigation, all subjects utilized a multipurpose care regimen without the addition of an enzymatic cleaner. Upon conclusion of the investigation, 75.0 percent of the subjects chose to continue wearing the study lenses on a 2-week frequent replacement basis.

Topographical corneal oedema.

Corneal thickness changes were monitored across the cornea in 10 subjects during 7 days continuous wear of 3 types of hydrogel contact lenses of different back vertex powers. Analysis of topographical corneal thickness changes indicates that the periphery of the cornea swells significantly less than the central cornea. The effect is more dramatic with higher levels of central corneal oedema, and with lenses of higher minus power, in spite of their thicker lens periphery. An anoxic stimulus was also found to produce greater central than peripheral corneal swelling, indicating that tear exchange under the periphery of the contact lens is not a significant factor in limiting peripheral corneal swelling. It was concluded that the topographical swelling profile is not contact lens-related, but reflects a reduced swelling capability of the peripheral cornea, due to physical restraint in the limbal region.

Critical oxygen levels to avoid corneal edema for daily and extended wear contact lenses.

The relationship between corneal edema and hydrogel lens oxygen transmissibility was examined for both daily and extended contact lens wear by measuring the corneal swelling response induced by a variety of contact lenses over a 36-hr wearing period. The relationships derived enable average edema levels that occur with daily and extended wear in a population of normal young adults to be predicted to within +/- 1.0%. The critical lens oxygen transmissibilities required to avoid edema, for the group as a whole, for daily and extended contact lens wear were obtained from the derived curves. It was found under daily wear conditions that lenses having an oxygen transmissibility of at least 24.1 +/- 2.7 X 10(-9) (cm X ml O2)/(sec X ml X mmHg), an Equivalent Oxygen Percentage (EOP) of 9.9%, did not induce corneal edema. This level of oxygen transmissibility can be achieved (1) in standard, low water content, poly-HEMA lenses by using an average lens thickness of 33 microns or less, or (2) in a higher water content material, such as Duragel 75, by using an average thickness of 166 microns or less. The critical hydrogel lens oxygen transmissibility needed to limit overnight corneal edema to 4% (the level experienced without a contact lens in place) was found to be 87.0 +/- 3.3 X 10(-9) (cm X ml O2)/(sec X ml X mmHg)--an EOP of 17.9%. This ideal level of oxygen transmissibility cannot, at present, be provided with hydrogel materials.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cataract surgery on corneal function.

Recent reports suggest that the aphakic eye develops less corneal edema than the phakic eye during hydrogel contact lens wear. Measurements were made of several ocular characteristics that might account for this difference in nine unilateral aphakic subjects. The measurements showed that compared with the phakic eye, the aphakic eye averaged a 15% lower epithelial oxygen uptake rate, 18% fewer endothelial cells, 85% loss of corneal sensitivity, and 8% thinner corneal epithelium. Both eyes of each subject were exposed to a reduced oxygen environment for 2 hr in separate experiments: (1) by wearing a thick hydrogel contact lens and closing the eyes, and (2) by exposing the eye to 100% nitrogen gas. In the gel lens-closed eye experiment the aphakic cornea swelled an average of 7.5%, compared with 11.0% for the phakic cornea. For the nitrogen gas experiment the results were 4.3% and 6.2%, respectively. Eighty-five percent of the edema was in the stromal layer. The lower swelling response for the aphakic eye was significant (p less than 0.01) in both experiments. Corneal swelling after hypoxia is considered to be caused by an increase in corneal osmolarity resulting from an increase in the rate of production of lactic acid. The reduced corneal swelling in the aphakic eye, when compared with the phakic eye, could therefore be the result of either (1) a reduction in the overall metabolic activity of the epithelium, as indicated by the lower epithelial oxygen uptake rate and the thinner corneal epithelium in the aphakic eye, or (2) an increased efflux of lactic acid from the cornea resulting from an increased endothelial permeability to lactate.

Corneal swelling response of the aphakic eye.

Corneal swelling response was measured for 12 unilateral aphakic subjects wearing high-plus hydrogel contact lenses on both eyes. Significantly less corneal edema was measured for aphakic eyes than for phakic eyes after 2, 4, and 6 hr of lens wear. These results indicate that the cornea of the aphakic eye responds differently to a given physiologic challenge than does the cornea of the phakic eye. Previous estimates of oxygen permeability required of contact lens materials for extended wear may be artificially high for aphakic eyes.

Overnight swelling of the living human cornea.

The overnight corneal swelling of nine subjects was measured with an electronic digital pachometer. Corneal thickness measurements were taken just before eye closure and after seven hours of sleep. Post-sleep recovery to original corneal thickness was followed. Results showed overnight corneal swelling to be about 4 1/2% with logarithmic recovery to baseline within the first hour after eye opening. Considerable variability in the magnitude of overnight swelling among human corneas was indicated. A review of current theories on the cause of overnight corneal swelling is also included.

Corneal-thickness response to ultra-thin Bausch & Lomb Soflens (polymacon) contact lenses.

A study was conducted to test the hypothesis that a more favorable corneal-edema response for hard-to-fit patients might be expected from ultra-thin Bausch & Lomb Soflens (polymacon) contact lenses than from standard-thickness lenses because of the additional oxygen reportedly available to the cornea. Corneal edema was monitored by measuring changes in corneal thickness over 6 hr of lens wear with an electronic pachometry assembly. Statistical analysis showed significantly less edema for a group of hard-to-fit patients wearing ultra-thin lenses than for a group of successful patients fitted with standard-thickness lenses.