Oxygen diffusion and edema with modern scleral rigid gas permeable contact lenses

PURPOSE. We defined the theoretical oxygen tension behind modern scleral contact lenses (CLs) made of different rigid gas permeable (RGP) materials, assuming different thickness of the tear layer behind the lens. A second goal was to show clinically the effect of the postlens tear film on corneal swelling. METHODS. We simulated the partial pressure of oxygen across the cornea behind scleral CLs made of different lens materials (oxygen permeability Dk, 75–200 barrer) and different thickness (Tav, 100–300 lm). Postlens tear film thicknesses (Tpost-tear) ranging from 150 to 350 lm were considered. Eight healthy subjects were fitted randomly with a scleral lens with a thin and a thick postlens tear layer in two different sessions for a period of 3 hours under open-eye conditions. RESULTS. The CLs with less than 125 barrer of Dk and a thickness over 200 lm depleted the oxygen availability at the lens–cornea interface below 55 mm Hg for a postlens tear film of 150 lm. For a postlens tear film thickness of 350 lm, no combination of material or lens thickness will meet the criteria of 55 mm Hg. Our clinical measures of corneal edema showed that this was significantly higher (P < 0.001, Wilcoxon signed ranks test) with the thicker compared to the thinner Tpost-tear (mean 6 SD, 1.66 6 1.12 vs. 4.27 6 1.19%). CONCLUSIONS. Scleral RGP CLs must be comprised of at least 125 barrer of oxygen permeability and up to 200 lm thick to avoid hypoxic effects even under open eye conditions. Postlens tear film layer should be below 150 lm to avoid clinically significant edemaSupported by the Ministerio de Educacion y Ciencia (MEC) through Project ENE2011-24761, and by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011. The authors alone are responsible for the content and writing of the paper

Stabilization in early adult-onset myopia with corneal refractive therapy

Purpose: To describe the stabilization of early adult-onset myopia in three university students after initiating orthokeratology treatment with corneal refractive therapy contact lenses. Methods: Three Caucasian early adult-onset progressing myopic subjects (1 male, 2 females) were fitted with corneal refractive therapy lenses to correct myopia between ?1.50 and ?2.50 D of sphere using Paragon CRT (Paragon Vision Sciences, Mesa, AZ)lenses for overnight orthokeratology. The pre-treatment refractive history from 2005 as well as refraction and axial length after treatment onset are reported over a period of 3 years between December 2009 and January 2013 with an additional year of follow-up after treatment discontinuation (January–December 2013). The peripheral refractive patterns and topographic changes are also reported individually. Results: Treatment was successful in all three subjects achieving uncorrected visual acuity of 20/20 or better monocularly. During a period of 3 years of follow-up the subjects did not experience progression in their refractive error, nor in their axial length (measured during the last 2 years of treatment and 1 year after discontinuation). Furthermore, the subjects recovered to their baseline refraction and did not progressed further over the following year after lens wear discontinuation. Conclusions: We cannot attribute a causative effect to the orthokeratology treatment alone as underlying mechanism for myopia stabilization in this 3 patients. However, the present report points to the possibility of stabilization of early adult-onset myopia progression in young adults using corneal refractive therapy treatment.This study has been funded by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of projects PTDC/SAU-BEB/ 098391/2008, PTDC/SAU-BEB/098392/2008 and the Strategic Project PEST-C/FIS/UI607/2011

Performance of three multipurpose disinfecting solutions with a silicone hydrogel contact lens

"Article ID 216932"To evaluate the clinical performance of a silicone hydrogel (Si-Hy) soft contact lens (CL) in combination with three differentmultipurpose disinfecting solutions (MPDSs).Methods.Thiswas a prospective, randomized, single-masked, crossover, and comparative study in which 31 habitual soft CL wearers were randomly assigned to one of the three MPDSs (Synergi, COMPLETE RevitaLens, and OPTI-FREE PureMoist) for 1 month with a 1-week wash-out period between each exposure. All subjects were successfully refitted with a Si-Hy CL (Biofinity). Subjects were then scheduled for follow-up visits after 1 month of lens wear, being evaluated at 2 and 8 hours after lens insertion. Visual Analogue Scales (VAS) were used to gauge comfort rating. Results. The tarsal conjunctiva showed a significantly different degree of lid redness between the MPDSs at the 2-hour visit (P < 0.05, Kruskal- Wallis test), being lower for COMPLETE RevitaLens compared to the other two MPDSs (Mann-Whitney U test). Furthermore, a significantly different degree of lid roughness at the 8-hour visit was seen (P < 0.05, Kruskal-Wallis test), being higher for Synergi (Mann-Whitney U test).Thesubjective comfort was similar with the threeMPDSs. Conclusion. Tarsal conjunctival response should be also considered in the context of the clinical performance of MPDs at the ocular surface.This work has been funded by an unrestricted grant from AMO Germany GmbH and it was also partially supported by Xunta de Galicia, Spain (Predoctoral Grant) and Fundacao para a Ciencia e Tecnologia, Portugal

Prevalence of refractive conditions in the general population attending eye care clinics in the north of Portugal

The purpose of this study was to report the fi rst estimations on the prevalence of refractive conditions in a Portuguese population attending several ophthalmologic and optometric clinics within the same region. Methods: Values of non-cycloplegic subjective refraction from the right eye of 4288 patients (40.08±18.75 years) were analyzed to estimate the prevalence of refractive conditions as a function of age and gender. The prevalence of anisometropia and presbyopic correction as a function of age and gender were also investigated. Results: Mean spherical equivalent refractive error was –0.29±2.01D. 29.8% of the patients had myopia, 45% had emmetropia and 25.2% had hyperopia. Young adults ranging from 20 to 35 years of age presented the highest prevalence of myopia. Conversely, the peak of hyperopic condition was for the oldest population. Anisometropia, defi ned as a difference in spherical equivalent equal or higher than 3D was present in 1.4% of our population. Conclusion: The prevalence of refractive conditions has been established for a large non-randomized sample of the Portuguese population for the fi rst time. Important refractive changes were evidenced in the fi fth decade of life, comprising an increase in the prevalence of hyperopia along with a shift in the amount of astigmatism. Although this study is not representative of the overall Portuguese population, there seem to be evidence that myopia could be increasing among the younger age groups

Light distortion and spherical aberration for the accommodating and nonaccommodating eye

To evaluate how different amounts of induced spherical aberration (SA) affect the light distortion (LD) phenomena, tests were performed using an experimental device to measure the distortion (haloes, glare, and so on) of a point source. To simulate the effect of SA, eight different phase plates between þ0.300 and −0.300 μm of SA for a 5-mm aperture were used in a random and double-masked experimental design. Measurements were performed at a distance of 2 m in a darkened room in 10 eyes of five subjects with a mean age of 26.4 6.1 years and a mean refractive error of −0.50 0.70 D. Data were obtained with natural pupil and after pupil dilatation. The measurements with this experimental system showed a significant increase in all distortion parameters with cycloplegia for the phase plates with the higher positive SA (þ0.300 and þ0.150 μm). The disturbance index increased from 14.86 6.12% to 57.98 36.20% (p < 0.05) with the þ0.300 μm plate. The same effect was observed through at a much lower rate when the eye could accommodate. Plates inducing negative SA did not change the LD compared to the control condition without induction of SA or even decreased the effect of distortion. Pupillary dilation and cyclopegia led to a significant increase in the size of the LD when increasing values of SA were induced. Accommodation and pupillary constriction are capable of compensating the degradation of the optical quality induced.This study was funded by the FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of projects PTDC/SAUBEB/098391/2008, PTDC/SAU-BEB/098392/2008 and the Strategic Project PEST-C/FIS/UI607/2011. The authors thank the assistance of Professor Norberto López-Gil for the loan of the SA plates and the discussion of the results. R.M.A, J. M.G.M., H.F.N., L.R.V., and S.C.P.M have applied for a patent on the experimental device. Other authors declare that they do not have any proprietary or financial interest in any of the materials mentioned in this article

Symptoms and signs in rigid gas permeable lens wearers during adaptation period

Objectives: To evaluate neophyte contact lens wearers’ fitting to rigid gas permeable (RGP) contact lenses in terms of wearing time, tear volume, stability, corneal staining, and subjective ratings, over a 1-month period of time. Methods: Twenty-two young healthy subjects were enrolled for wearing RGP on a daily wear basis. The participants included in this study never wore contact lenses and showed a value under 10 in McMonnies Questionnaire. Contact Lens Dry Eye Questionnaire, Visual Analog Scales, Schirmer test, tear film break-up time (BUT), and corneal staining grading were performed. Follow-up visits were scheduled at 1, 7, 15, and 28 days. Results: Six subjects dropped out due to discomfort from the study before 1 month (27% of discontinuation rate). Successful RGP wearers (16 participants) achieved high levels of subjective vision and reported comfort scores of approximately 9 of 10 between 10 and 15 days. They reported wearing their lenses for an average of 10.1262.43 hr after 1 month of wear. Conversely, unsuccessful wearers discontinued wearing the lenses after the first 10 to 15 days, showing comfort scores and wearing time significantly lower compared with the first day of wear. Schirmer test showed a signifi- cant increase at 10 days (P,0.001), and the BUT trends decreased after the first week of wear in unsuccessful group. Conclusions: Symptomatology related with dryness and discomfort, detected during the first 10 days of the adaptation, may help the clinician to predict those participants who will potentially fail to adapt to RGP lens wear

Strategies to regulate myopia progression with contact lenses: a review

Purpose: Higher myopic refractive errors are associated with serious ocular complications that can put visual function at risk. There is respective interest in slowing and if possible stopping myopia progression before it reaches a level associated with increased risk of secondary pathology. The purpose of this report was to review our understanding of the rationale(s) and success of contact lenses (CLs) used to reduce myopia progression. Methods: A review commenced by searching the PubMed database. The inclusion criteria stipulated publications of clinical trials evaluating the efficacy of CLs in regulating myopia progression based on the primary endpoint of changes in axial length measurements and published in peerreviewed journals. Other publications from conference proceedings or patents were exceptionally considered when no peer-review articles were available. Results: The mechanisms that presently support myopia regulation with CLs are based on the change of relative peripheral defocus and changing the foveal image quality signal to potentially interfere with the accommodative system. Ten clinical trials addressing myopia regulation with CLs were reviewed, including corneal refractive therapy (orthokeratology), peripheral gradient lenses, and bifocal (dual-focus) and multifocal lenses. Conclusions: CLs were reported to be well accepted, consistent, and safe methods to address myopia regulation in children. Corneal refractive therapy (orthokeratology) is so far the method with the largest demonstrated efficacy in myopia regulation across different ethnic groups. However, factors such as patient convenience, the degree of initial myopia, and non-CL treatments may also be considered. The combination of different strategies (i.e., central defocus, peripheral defocus, spectral filters, pharmaceutical delivery, and active lens-borne illumination) in a single device will present further testable hypotheses exploring how different mechanisms can reinforce or compete with each other to improve or reduce myopia regulation with CLs.Supported in part by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of projects PTDC/SAU-BEB/098391/2008, PTDC/SAU-BEB/ 098392/2008, and the Strategic Project PEST-C/FIS/UI607/2011