Russell Lowe

Effect of Hydrogel Lens Wear on Tear Film Stability

Noninvasive break-up time (NIBUT) of the tears was measured in a controlled, randomized, double-masked study to assess: (1) the stability of the prelens tear film during wear of new high and low water content lenses and (2) the stability of the precorneal tear film following lens removal after 1 h of wear. The prelens tear film NIBUT of 6 subjects was found to be relatively constant over a 1-h wearing period, averaging 6.1 ± 1.1 s (mean ± SEM). These values were significantly (Scheffes S test, p<0.05) lower than those recorded for the precorneal tear film before lens insertion (33.5 ± 10.6; mean ± SEM), although 85% of prelens tear film Nl- BUTs were greater than the 3-s average interblink period reported previously for soft lens wearers. After lens removal, precorneal tear film NIBUT was reduced significantly compared to prewear levels (Scheffes S test, p<0.05) for up to 15 min. Application of the monomolecular growth model to the NIBUT recovery data revealed a half-time for recovery of 6.0 min, with recovery 95% complete 25.8 min after lens removal. Lens type was not a significant factor in tear film stability, either during wear or after lens removal. The basis for reduced precorneal tear film NIBUT after lens removal is unknown; however, a disruption of the mucin layer coating the corneal epithelium is the most likely mechanism. Indeed, the technique of measuring precorneal tear film NIBUT after lens removal may be a useful determinant of the extent to which contact lens wear disrupts the precorneal mucin layer, providing an indication of the susceptibility of the cornea to a variety of complications.

in Vivo Dehydration of Disposable (acuvue) Contact Lenses

The in vivo dehydration of the Acuvue disposable contact lens was measured in six subjects using a contact lens refractometer. On average, the lenses dehydrated 6.2 ± 1.9% after 20 min and 10.2 ± 3.9% after 6 h of wear. The magnitude of dehydration is greater than has been reported for other hydrogel lens types of similar water content. This information may assist practitioners in the interpretation of clinical signs pertaining to lens behavior and associated patient symptoms.

Corneal reshaping influences myopic prescription stability (CRIMPS): an analysis of the effect of orthokeratology on childhood myopic refractive stability.

Objective: To determine whether overnight orthokeratology (OK) influences the progression rate of the manifest refractive prescription in myopic children, when compared with an age- and refraction-matched spectacle-wearing control group, over a period up to 8 years. Methods: The right eyes of control (n=30) and OK (n=26) children were compared. Treatment groups were matched for baseline age and refractive error. At baseline, children were younger than 16 years and showed manifest spherical refractive error more than −0.50 diopters. The minimum period of evaluation for each child was 2 years. Changes to manifest refractive prescription were compared between the groups in 2 yearly intervals up to 8 years. Results: On the whole, OK eyes showed a significantly (P<0.05) more stable myopic refractive prescription than control eyes over all of the 2-year treatment intervals. A subpopulation (n=18; 64%) of OK eyes demonstrated an apparent total arrest of manifest myopic refractive change. Symmetry in the vertical meridian of baseline corneal topography was associated with a greater degree of refractive stability in OK eyes. Conclusions: This retrospective study provides evidence that OK can reduce the rate of progression of childhood myopia over the long term. In addition, these findings offer some early insight into a potential indicator that may help predict the extent of refractive stability in individual eyes undergoing OK.

Hydration changes of Acuvue™ disposable contact lenses during disinfection

To model hydrogel lens parameter changes during disinfection, the water content of 24 new Acuvue™ disposable lenses was measured with a contact lens refractometer prior to disinfection and at various intervals during the course of disinfection/neutralisation. The disinfection systems investigated were: a two‐step hydrogen peroxide system (using three alternative disinfection/neutralisation cycles), a one‐step hydrogen peroxide system, a preservative‐based chemical system and heat disinfection. Hydrogen peroxide disinfection resulted in mean endpoint decreases in lens water content ranging from 2.1 per cent to 6.7 per cent, while the other systems resulted in changes of water content of less than 1.0 per cent. This information may assist contact lens practitioners in advising on the appropriate choice of disinfection systems to be used with daily wear of Acuvue™ lenses.

Corneal refractive therapy, uncorrected visual acuity, and "E" values: personal experiences.

Purpose. The author describes selected aspects of his clinical experience in fitting and prescribing orthokeratology lenses to temporarily reduce or eliminate myopia. The precision of videokeratography (VK) data in determining corneal sagittal depth is examined. Treatment outcomes are analyzed after overnight wear of two proprietary corneal remodeling systems. Two case reports describing off-label treatments are presented. Methods. A retrospective analysis was performed of the baseline VK data of 25 consecutive candidates (50 eyes) for corneal remodeling, captured with a Keratron topographer. Sixteen consecutive patients fitted with Paragon corneal refractive therapy (CRT) lenses were compared against an age- and sex-matched group of patients fitted with the Mountford BE lens for 1-day, 1-week, and 1-month uncorrected visual acuity. Results. The mean ± SD of the apical radius (“Ro”) and corneal eccentricity (“E”) values was 0.03 ± 0.01 mm and 0.03 ± 0.01°, respectively, indicating a spread of 24 μm in the sagittal elevation data. Mean target myopia and 1-day uncorrected visual acuity were −1.71 ± 0.71 diopters and 20/20 ± 20/0.86, respectively, for the Paragon CRT lenses and −2.30 ± 0.89 diopters and 20/31 ± 20/20.6, respectively, for the Mountford BE lenses. Conclusions. The Paragon CRT and the Mountford BE lenses delivered impressive reductions in uncorrected visual acuity after the first night of overnight wear. The Paragon CRT lens had the advantage of not requiring a previous overnight lens trial before commencing the treatment program.

Hydration of high-water nonionic soft lenses during hydrogen peroxide disinfection

Abstract With the recent introduction of a number of high-water nonionic (Group II) materials, it is germane to consider the influence of hydrogen peroxide on the stability of these hydrogels using high-water ionic (Group IV) lenses as a basis for comparison. We measured the water content (hydration) of nine Group II lens types and two Group IV lens types during three different protocols using two-step hydrogen peroxide (Omnicare, Allergan)—brief: 20 minute disinfection followed by 10 minute neutralization; overnight: 9 hour disinfection followed by 20 minute neutralization; and extended: 1 week disinfection followed by 20 minute neutralization. The water content of each lens was measured with a refractometer before disinfection, after disinfection, and after neutralization. The Group II lenses showed a consistent decrease in mean percentage water content after disinfection; however, the extent of dehydration was unlikely to pose clinically significant problems. In addition, the Group II lenses exhibited a greater tendency to return to baseline hydration levels following 20 minute neutralization compared to ]0 minute neutralization despite the longer periods in hydrogen peroxide. The Group IV lenses were less stable—hydration changes were of greater magnitude and were less consistent. We concluded that although two-step hydrogen peroxide lens care is acceptable with Group II lenses it may not be appropriate for use with Group IV lenses.

Overnight corneal reshaping for the correction of childhood myopia: a single case study.

In February 2003, a seven-year-old myopic, female patient, GMD, was referred by an optometrist to assess her suitability for overnight corneal reshaping (OCR). The child was described as an avid reader by her parents, who were concerned by a rapid progression in her myopia over the previous two years (Table 1). At presentation, the initial refractive error was OD -2.25 DS, OS -3.00/-0.50 ¥ 180. Data provided by the referring practitioner showed that the mean (spherical equivalent) rate of refractive change over the previous two years had been OD -1.06 DS per year, OS -1.50 DS per year. The child’s father was a moderate myopic astigmat (OD -4.75/-1.00 ¥ 30, OS -4.75/-0.75 ¥ 180) and her mother a mild astigmat (OD -0.25/-0.25 ¥ 180, OS +1.00/1.00 ¥ 165). The child had no significant general medical history. Internal and external ocular examinations were unremarkable, with no contraindication for overnight lens wear. Baseline videokeratography (VK) maps (Keratron topographer, EyeQuip, Ponte Bedra Beach, FL) showed a low degree of with-the-rule corneal astigmatism in each eye (Figure 1). The baseline simulated keratometric values are detailed in Table 2. Mountford BE lenses (Capricornia Contact Lens Pty Ltd, Slacks Creek, QLD, Australia) were fitted using the methodology prescribed in the user handbook with diagnostic lenses to assess the cornealens interaction with fluorescein. The Date Age OD OS

Two different concentrations of Opti-Plus® compared for daily protein cleaning of a disposable contact lens

The aim of this study was to compare the relative safety, efficacy, comfort, and convenience of the daily use of a pancreatin-based, liquid enzyme daily protein remover (DPR) at two different concentrations for protein cleaning of Group IV disposable contact lenses.We enrolled 73 subjects (146 eyes) into a 3-month, randomized, investigator-masked clinical study comparing a test regimen of DPR (Opti-Plus(R) or Supra-Clens(R)) containing four drops per 10 mL of multifunctional solution (Opti-Free(R)) to a control regimen containing only two drops per 10 mL of multifunctional solution.The liquid enzyme regimens provided safe and effective protein cleaning of the Group IV lenses with no additional cleaning benefit observed at the higher concentration. Three convenience parameters (steps required, time required, and dexterity required) had mean improvements for both regimens at Day 90 compared to baseline (Day 0). Thus, subjects perceived the DPR regimen as more convenient than their pre-study regimen, which required weekly use of an enzymatic cleaning tablet. Comfort remained consistent with baseline levels throughout the study regardless of concentration of DPR for 72 of 73 subjects.This study provided evidence that the daily use of a low concentration pancreatin enzymatic solution admixed with multifunctional solution is well tolerated and provides a more convenient method of achieving simultaneous disinfection and protein cleaning during contact lens storage than enzyme tablets.

Is it the modulus or the method that matters

Certainly, this case was an interesting mix of clinical information and no direct correlation could be made with the certainty of testosterone’s role in the elevated intracranial pressure. We agree that Chiari malformations are documented as having the potential to cause obstruction to the point of elevating intracranial pressure. In this case, after consultation with the neurologist, the malformation was deemed to be ‘not a factor’ because it was ‘small’ and therefore, we took that at face value. The dose of testosterone was reduced

Hydrogen peroxide disinfection of hydrogel contact lenses: An overview

Many hydrogen peroxide systems have recently been introduced to the contact lens market. No two systems are identical, and practitioners are confronted with a great deal of information from the various solution companies. When considered en musse, this information is complex and often contradictory. Here, we review the principles of hydrogen peroxide disinfection and neutralization, and critically examine the major differences in the systems with a view to the development of guidelines for the safe and effective use of this disinfecting agent. Attention is drawn to a number of important issues which are yet to be resolved.