Months Of Lens Wear Research Articles

Refractive and Biometric Changes With Silicone Hydrogel Contact Lenses

This study reports data from an 18-month longitudinal study of neophyte contact lens wearers and compares changes in ocular refraction and biometry induced by daily wear and continuous wear of two different silicone hydrogel (SiH) materials. Forty-five subjects were enrolled in the study and randomly assigned to wear one of the two silicone hydrogel materials: Lotrafilcon A or Balafilcon A lenses on either a daily or continuous wear basis. Measurements of objective refraction, axial length, anterior chamber depth, corneal curvature, and the rate of peripheral corneal flattening were performed before and 1, 3, 6, 12, and 18 months after initial fitting. Mean spherical equivalent refractive error increased in the myopic direction in all contact lens groups across time (p < 0.001). Axial length was the main biometric contributor to the development of myopia. After 18 months of lens wear, subjects in the Lotrafilcon A group showed the greater mean increase in myopia (i.e., -0.50 D). The results of this study show that increases in myopia, similar if not higher than those found to occur normally in young adult noncontact lens wearers, still occur with silicone hydrogel contact lens wear. The main biometric contributor to the progression of myopia was an increase in axial length. Differences between our results and those of previous studies with silicone hydrogel contact lenses could be attributed to the differing populations used in which both age and occupation may have played a role.

Overnight Orthokeratology

To determine the refractive and corneal topographic recovery after the use of reverse-geometry contact lenses for overnight orthokeratology. Both eyes of 15 subjects were fitted with reverse-geometry contact lenses that were worn by the subjects for 1 month. Uncorrected visual acuity, refractive correction (sphere and spherical equivalent), corneal curvature, and corneal thickness were measured during this time and for 2 weeks after discontinuation of lens wear. Ten subjects completed the investigation. Uncorrected visual acuity, refractive correction, and corneal curvature had changed significantly (P = 0.01) after 1 month of lens wear. By the end of 1 month, central corneal thickness was significantly thinner than the baseline value (P = 0.01), but it recovered fully after one night of no lens wear. Recovery of corneal curvature was complete 1 week after lens wear was discontinued. Refractive correction and binocular uncorrected visual acuity recovered fully after 2 weeks. Monocular uncorrected visual acuity remained significantly (P = 0.01) different from baseline acuity 2 weeks after lens discontinuation. Full effect of overnight orthokeratology in low myopes is achieved within 1 week of initiating use of reverse-geometry lenses. Recovery after short-term use of reverse-geometry lenses is rapid for corneal thickness and corneal curvature. Refractive correction and binocular uncorrected visual acuity recovered fully after 2 weeks. Monocular uncorrected visual acuity was the slowest to recover and had not achieved full recovery after 2 weeks.

Higher-Order Wavefront Aberrations in Corneal Refractive Therapy

To assess the changes in higher-order (third through sixth) ocular wavefront aberrations produced by Corneal Refractive Therapy (CRT; Paragon Vision Sciences, Mesa, AZ). Eighteen eyes of nine myopic subjects were fit with CRT contact lenses. Baseline subjective spherical refraction ranged from -2.25 to -6.00 D (mean +/- SD, -3.33 +/- 1.26 D), and baseline logarithm of the minimum angle of resolution (logMAR) best-corrected visual acuity was -0.13 +/- 0.06 (20/15 Snellen equivalent). Whole-eye ocular wavefront aberrations were measured using a previously validated Shack-Hartmann aberrometer. Measurements were taken at baseline and 1 month after treatment initiation. Nine measurements per dilated subject were taken and averaged. Zernike coefficients were used to calculate the third-, fourth-, fifth-, and sixth-order root-mean-square values for each eye for both 3- and 6-mm pupil sizes, and aberrations were averaged and compared with prior baseline readings. The mean (+/-SD) myopia reduction was 3.08 +/- 0.93 D, resulting in a subjective refraction of -0.22 +/- 0.38 D after 1 month of lens wear. Both logMAR uncorrected visual acuity (-0.07 +/- 0.18; 20/15- Snellen equivalent) and best-corrected visual acuity (-0.14 +/- 0.09) after CRT wear were not significantly different from baseline logMAR best-corrected visual acuity (paired two-tailed t-test; p = 0.41 and 0.65, respectively). Whole-eye aberrations showed a statistically significant increase in higher-order aberrations for both 3-mm (factor of 2.66; p = 0.01) and 6-mm pupils (factor of 2.50; p = 0.005). Each individual higher-order aberration also increased, ranging from a factor of 2.01 to 3.20 for 3-mm pupil sizes and 2.52 to 2.98 for 6-mm pupil sizes. Spherical-like aberrations (S4 and S6) increased by a factor of 1.79 for 3-mm pupil sizes and 2.42 for 6-mm pupil sizes. The Zernike coefficient most affected by CRT was spherical aberration (Z40), which increased from 0.084 +/- 0.16 to 0.39 +/- 0.16 microm (p = 0.0002) for 6-mm pupils. Use of current CRT lenses for the reduction of myopia increased higher-order wavefront aberrations and spherical aberration (Z40) in particular.

Overnight orthokeratology: visual and corneal changes.

To achieve an optimal fit with reverse geometry Contex OK lenses and to determine a time course for and the stability of visual and corneal changes in achieving maximal refractive, corneal curvature, and corneal thickness changes after overnight wear of OK B and D series lenses. This investigation was conducted under an Food and Drug Administration IDE G000059. Both eyes of 10 subjects were fitted with the lenses, and uncorrected visual acuity, refractive correction, contrast sensitivity, corneal curvature, and corneal thickness were measured at baseline and at 1 day, 1week, 1 month, and 3 months after lenses were worn. Except for baseline, data were collected at four different times during the day, immediately following lens removal and 4, 8, and 12 hours after lens removal. The results from eight subjects showed that uncorrected visual acuity, refractive correction, contrast sensitivity, and corneal curvature all changed significantly (P=0.01) overnight. By the end of 1 week, all corneal and visual changes had reached a maximal level and remained fairly stable during the day. These changes were sustained at 3 months. The epithelial thickness data from four subjects showed that the corneal epithelial thickness was reduced by approximately 19 microm after 3 months of lens wear. Successful fitting of OK B and D series lenses requires a thorough understanding of the lens-cornea relationship. Full effect of overnight orthokeratology is achieved by the end of 1 week. The visual and corneal changes remain stable for all waking hours of the day and allow patients to enjoy excellent device-free vision (20/20).

Confocal microscopic observations of stromal keratocytes during extended contact lens wear

Background: The aim of this study was to monitor changes in keratocyte density during extended contact lens wear and to explore the possible role of hypoxia and oedema in any changes observed. Methods: Twenty‐three neophyte myopic subjects wore a high Dk/t lens (Pure Vision) in one eye and a low Dk/t lens (Acuvue 2) in the other eye on an extended wear basis for six months. Slit‐scanning confocal microscopy and ultrasonic pachometry were performed on both eyes at baseline (before lens wear), after three and six months of lens wear, and one week after cessation of lens wear (the ‘post‐cessation’ visit). Results: No differences were established between die two lenses or between the three study visits for anterior stromal keratocyte density (KD). Posterior stromal KD was similar for the two lenses throughout the study. However, there was an overall drop in posterior KD of 14 per cent in bodl eyes at the six‐month visit, compared to die initial visit. Posterior KD at die six‐mondi visit was no different from diat at die post‐cessation visit. Corneal thickness was similar for die two lenses at die initial and post‐cessation visits, but was diree per cent greater for the eye wearing die Acuvue 2 lens at die six‐month visit. Conclusion: Extended contact lens wear causes a loss of keratocytes; diis loss cannot be attributed to contact lens‐induced hypoxia and/or oedema, or to an artifact of confocal microscopy relating to presence of residual oedema. It is postulated diat lens‐induced keratocyte loss may be related to die physical presence of contact lenses creating some mechanical effect.

ADVERSE EVENTS WITH EXTENDED WEAR OF DISPOSABLE HYDROGELS

Adverse events with extended wear of disposable hydrogels: results for the first 13 months of lens wear. Ophthalmology 1999;106:1671–1680.

Adverse events with extended wear of disposable hydrogels: Results for the first 13 months of lens wear

Objective To determine the type and incidence of adverse events seen in the first 13 months of extended wear from a prospective clinical trial involving the use of disposable hydrogels on a 6-night extended wear and replacement schedule. Design A prospective, noncomparative clinical trial. Participants Three hundred thirty subjects were enrolled in the study from March 1993 to August 1996 and commenced in extended wear. The subjects were new contact lens users with ages ranging from 16 to 39 years and refractive errors from −1.00 to −6.50-diopter (D) sphere with cylindrical component less than 1.0 D. Intervention Disposable hydrogel lenses on a 6-night extended wear and replacement schedule. Main outcome measures To determine the incidence of adverse events in the first 13 months of lens wear with the use of disposable hydrogels on an extended wear schedule. In addition, corneal infiltrative events observed with lens wear were classified based on their presenting signs and symptoms. Results A total of 137 adverse events were seen in 102 subjects in the first 13 months of extended wear. The type of adverse events and the incidence per 100 patients per year of lens wear were as follows: corneal infiltrative events (44.4 events), contact lens papillary conjunctivitis (6.4 events), neovascularization and corneal wrinkling (1.7 events each), corneal striae and superior epithelial arcuate lesions (1.3 events each), and blepharokeratoconjunctivitis (0.4 event). Viral keratoconjunctivitis was also observed (0.8 event). The corneal infiltrative events were further subclassified as follows: contact lens-induced peripheral ulcers (13.6 events), contact lens-induced acute red eyes (12.3 events), infiltrative keratitis (9.7 events), and asymptomatic infiltrative events (8.9 events). There were no events of infectious keratitis. Except for all events of contact lens-induced peripheral ulcers and two isolated events of infiltrative keratitis that resulted in scarring, all of the corneal infiltrative events resolved without sequelae. None of the events caused any loss of best-corrected visual acuity. Conclusions Based on the observations from the first 13 months of extended wear in the trial, the majority of the complications associated with extended wear of disposable hydrogels are corneal infiltrative events. No events of microbial keratitis were seen in the first 13 months of extended wear. None of the events were associated with loss in best-corrected visual acuity. Clearly, frequent and regular disposing of lenses does not eliminate adverse effects, and better materials and designs are required for extended wear to be a successful method.

Conjunctival flora in extended wear of rigid gas permeable contact lenses.

A longitudinal study was performed to examine the effect of rigid gas permeable (RGP) contact lenses (Boston Equalens II and Quantum II) on the conjunctival flora of 45 young healthy subjects. Microbial flora were determined before delivery of lenses. Subjects wore lenses on an extended wear basis, removing them every 7 days for cleaning and disinfection. Cultures were repeated after 2 months of lens wear and the microbial flora were found to be significantly altered compared to the prelens wear results (0.05 greater than p greater than 0.02). Changes to conjunctival flora included an increase in the number of eyes from which potentially pathogenic microorganisms were isolated, an increase in the number of eyes that were culture-negative, and a decrease in the number of eyes harboring only normal conjunctival flora. The increase in potentially pathogenic flora was not specific for Gram-negative bacteria, which are most often associated with infectious keratitis during contact lens wear.

Rigid Gas-Permeable Contact Lenses for Myopia Control: Effects of Discontinuation of Lens Wear

Conventionally fitted Paraperm O2plus contact lenses were worn for 44 months by 23 myopic children, who discontinued lens wear for 2.5 months and then resumed lens wear with Fluoroperm 30 lenses for a period of 8 months. Mean changes in myopia were: (1) an increase of 0.76 D during the initial 44 months of lens wear, (2) a further increase of 0.27 D during the 2.5 months when lenses were not worn, and (3) a decrease of 0.02 D during the 8-month period of Fluoroperm 30 lens wear. These results show that the effect of rigid gas-permeable lenses on myopia progression is diminished if lens wear is discontinued; however, the mean increase in myopia for these children was significantly less than would have been expected if glasses had been worn for the entire 54.5-month period. The results after discontinuation and then resumption of lens wear show that the effect of contact lenses in controlling the progression of myopia could not be accounted for entirely on the basis of corneal flattening as measured by the keratometer, therefore reinforcing the conclusion that corneal flattening due to rigid lens wear takes place primarily at the corneal apex, rather than in the zone of the cornea measured by the keratometer.

Keratoconus: Contact Lens or Keratoplasty?

The success rate of contact lens fitting and rate of progression to keratoplasty were evaluated for 115 consecutive patients with keratoconus. Of 190 nonoperated eyes that needed to be fit, 25 (13%) could not be fit, whereas 165 eyes (87%) could be fit. Most of these eyes had been referred for keratoplasty after previous contact lens fittings had no longer been successful. Of the 165 eyes that could be fit, 51 (31 %) ultimately needed keratoplasty after an average of 38.4 months of lens wear, and 114 eyes (69%) did not require keratoplasty over an average follow-up interval of 63 months of wearing contact lenses. The average initial keratoplasty reading in these two groups was 56.8 and 51.8 diopters (D), respectively. Special design, bispheric lenses were required in 125 of these 165 eyes (76%) and frequent lens changes were necessary. Of 88 postoperative eyes, 53 (60%) wore contact lenses for best vision. Keratoplasty can be delayed or avoided in many keratoconus patients by using contact lenses, especially special design, bispheric lenses. Also, keratoconus eyes often need contact lenses after keratoplasty.

Variations in central corneal thickness during the first year of contact lens wear.

Variations in central corneal thickness during the first year of hard, hydrophilic or silicone lens wear are reported. The mean corneal swelling after 1/2,3 and 6 months was 4.7-3.0% in the first 2 groups (P less than 0.001 - P = 0.005), but only 1.3-0.8% in the latter group (P = 0.011 - 0.050). These differences were statistically significant (P less than 0.001 - P = 0.046) and are ascribed to a higher oxygen tension under the silicone lenses. An over-all reduction of corneal oedema was noted after 1/2 month (P = 0.025). One year after lens fitting a similar and not significant corneal swelling was found in the 3 lens groups. In addition to an initial 'osmotic' adaptation our results indicate that a further corneal adaptation to hard and hydrophilic lenses may take place between 6 and 12 months after lens fitting. Development of lens intolerance was not correlated to the degree of corneal oedema after 1/2 month of lens wear.

Corneal curvature and refractive error changes associated with wearing hydrogel contact lenses.

To determine if there are corneal curvature and refractive error changes associated with hydrogel lens wear, 27 patients wearing F series Bausch & Lomb SOFLENS-TM contact lenses were examined regularly for nine months. During the first month of lens wear, a mean corneal steepening of 0.23 DK plus or minus 0.18 and an increase in with-the-rule toricity were found, which persisted during the following eight months of wear. A mean increase in myopia of 0.35 DS plus or minus .211 DS was found after nine months of lens wear for five randomly selected patients. This amount of change was statistically significant and was highly correlated with the observed corneal steepening. Their lenses were removed after nine months of lens wear. Both corneal changes and the increase in myopia persisted during the 14 days after lens removal. If long term studies with larger samples show similar results, the effect of hydrogel lenses on corneal curvature and refractive error will have to be considered in the decision to fit this type of lens.