Oxygen diffusion and edema with modern scleral rigid gas permeable contact lenses (original) (raw)
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Modeling Corneal Oxygen with Scleral Gas Permeable Lens Wear
Optometry and vision science : official publication of the American Academy of Optometry, 2016
The main goal of this current work is to use an updated calculation paradigm, and updated boundary conditions, to provide theoretical guidelines to assist the clinician whose goal is to improve his or her scleral gas permeable (GP) contact lens wearing patients' anterior corneal oxygen supply. Our model uses a variable value of corneal oxygen consumption developed through Monod equations that disallows negative oxygen tensions within the stroma to predict oxygen tension at the anterior corneal surface of scleral GP contact lens wearing eyes, and to describe oxygen tension and flux profiles, for various boundary conditions, through the lens, tears, and cornea. We use several updated tissue and boundary parameters in our model. Tear exchange with GP scleral lenses is considered nonexistent in this model. The majority of current scleral GP contact lenses should produce some levels of corneal hypoxia under open eye conditions. Only lenses producing the thinnest of tear vaults should...
Eye & contact lens, 2017
The purpose of this study is to determine the peripheral oxygen transmissibility (pDk/t) and respective central oxygen transmissibility (cDk/t) in soft contact lenses (SCLs) which might preclude SCL-driven corneal neovascularization (NV) in healthy myopic SCL users. Twenty subjectively successful SCL-wearing patients who presented with asymptomatic but active peripheral corneal NV (not ghost vessels) were recruited as study patients. Twenty-one patients who did not have NV were similarly recruited as controls. Demographic data were collected. Corneal NV was documented and photographed. Current habitual SCLs were collected and thicknesses measured to allow for the calculation of both pDk/t and cDk/t and estimation of local tear oxygen tensions. No statistical differences between study and control groups in patient age, refraction, or the numbers of years, days per week, or hours per day patients reported SCL wear were identified. Statistically significant differences were found betwe...
The effects of rigid-gas-permeable contact lens wear on tear film of eyes with keratoconus
Aim: This is a comparative retrospective study aimed to determine the effect of contact lens wearing on the tear fi lm of patients with keratoconus. Material and Methods: A total number of 150 were screened and 66.67% (100 patients) were found to fulfi ll the criteria of selection (35.7% males and 64.3% females). The patients were divided into two groups wearing RGP (medium Dk) (50%) and not wearing contact lenses (50%). The tear fi lm quality and quantity were evaluated using tear break-up time (TBUT) and Schirmer test. Results: One hundred patients were included in the study, of which 66% were in the age group of 21 -31 years. Eighty eight percent of the patients wearing contact lenses between 6 months and one year, and 82% of them have moderate keratoconus. Ninety one percent (46% wearing contact lens and 45% not wearing contact lenses) were found with tear break up time less than normal. About 65% (36% wearing contact lenses and 23% not wearing contact lenses) of patients showed abnormal tear volume (6% dry eye and 59% watery eye). Independent sample t-test showed signifi cant differences in TBUT and Schimer test between males and females wearing and not wearing contact lenses (p < 0.05). Conclusion: Tear quality and quantity were abnormal in patients with keratoconus wearing contact lenses than those with keratoconus not wearing contact lenses. Eye care practitioner may benefi t from these fi ndings in the care and management of keratoconus patients. How to cite this article: Fath-Elrahman N, Merghani I, Abdu M, Binnawi KH. The effects of rigid gas-permeable contact lens wear on tear fi lm of eyes with keratoconus. Sudanese J Ophthalmol 2015;7:6-9. Source of Support: Nil. Confl ict of Interest: None declared [Downloaded free from http://www.sjopthal.net on Wednesday, June 17, 2015, IP: 41.209.76.100]
The purpose is to estimate the oxygen diffusion coefficient and the relaxation time of the cornea with respect to the oxygen tension at the cornea-tears interface. Both findings are discussed. From the experimental data provided by Bonanno et al., the oxygen tension measurements in vivo for human cornea-tears-contact lens (CL), the relaxation time of the cornea, and their oxygen diffusion coefficient were obtained by numerical calculation using the Monod-kinetic model. Our results, considering the relaxation time of the cornea, observe a different behavior. At the time less than 8 s, the oxygen diffusivity process is upper-diffusive, and for the relaxation time greater than 8 s, the oxygen diffusivity process is lower-diffusive. Both cases depend on the partial pressure of oxygen at the entrance of the cornea. The oxygen tension distribution in the cornea-tears interface is separated into two different zones: one for conventional hydrogels, which is located between 6 and 75 mmHg, with a relaxation time included between 8 and 19 s, and the other zone for silicone hydrogel CLs, which is located at high oxygen tension, between 95 and 140 mmHg, with a relaxation time in the interval of 1.5-8 s. It is found that in each zone, the diffusion coefficient varies linearly with the oxygen concentration, presenting a discontinuity in the transition of 8 s. This could be interpreted as an aerobic-to-anaerobic transition. We attribute this behavior to the coupling formalism between oxygen diffusion and biochemical reactions to produce adenosine triphosphate.
Rigid gas permeable contact lens and corneal topography
Ophthalmic and Physiological Optics, 2001
We investigated the effect of high Dk daily wear rigid gas permeable contact lenses on corneal topography. Eight young myopic subjects wore hard contact lenses for 21 days. Corneal topography was monitored using the EyeSys system. It was measured every day during the next 21 days after the ®tting. We recorded the corneal radius of curvature at 16 peripheral points approximately 1, 2, 3 and 4 mm along the four principal meridians (nasal, superior, inferior and temporal). Our study showed that daily wear RGP Forum 210 does not produce signi®cant alterations of the corneal curvature as a function of time. q
Investigative ophthalmology & visual science, 2002
To devise a procedure for direct estimation of corneal oxygen consumption in human subjects. Tear oxygen tension (PO2) was measured at the posterior surface of two standard hydrogel contact lenses (38% water, 0.2 and 0.06 mm thick, oxygen transmissibility [Dk/t] = 4.2 and 14 x 10(-9) cm x mL O2/mL x sec x torr) and one newly available hydrogel-silicone polymer lens (Dk/t = 99 x 10(-9)). The oxygen-sensitive dye, Pd-meso-tetra (4-carboxyphenyl) porphine, bound to bovine serum albumin, was incubated with the lenses overnight. The lenses, coated with the protein-dye complex, were placed on four subjects' eyes, and tear PO2 was measured in the open eye and after 5 minutes of eye closure, using a time-domain phosphorescence measurement system. Given the tear PO2, lens Dk/t, and corneal thickness, oxygen consumption (Q(C), in mL O2/cm(3) x sec) could be calculated from established oxygen diffusion models. Protein-dye complex bound to the lens surface enabled reporting of tear PO2 for ...
Journal of Optometry, 2015
Purpose: We present an analysis of the corneal oxygen consumption Q c from non-linear models, using data of oxygen partial pressure or tension (p O2 ) obtained from in vivo estimation previously reported by other authors. 1 Methods: Assuming that the cornea is a single homogeneous layer, the oxygen permeability through the cornea will be the same regardless of the type of lens that is available on it. The obtention of the real value of the maximum oxygen consumption rate Q c,max is very important because this parameter is directly related with the gradient pressure profile into the cornea and moreover, the real corneal oxygen consumption is influenced by both anterior and posterior oxygen fluxes. Results: Our calculations give different values for the maximum oxygen consumption rate Q c,max , when different oxygen pressure values (high and low p O2 ) are considered at the interface cornea-tears film.
Predicting estimates of oxygen transmissibility for scleral lenses
Contact Lens and Anterior Eye, 2012
Background/Purpose: Although scleral contact lenses are prescribed with increasing frequency, little is known about their long-term effects on ocular physiology. The main goal of this paper is to predict values of oxygen transmissibility of scleral lens systems by applying the concept of resistors in series to parameters characteristic of current scleral lenses. A second aim is to find the maximal lens and post-lens tear layer thickness combinations above which hypoxia-induced corneal swelling would be found. Methods: Theoretical calculations were used to predict the oxygen transmissibility of scleral lens systems, considering several material permeabilities (Dks 100-170), varying lens thicknesses (250-500 m), the known tear permeability (Dk of 80) and expected post-lens tear layer thicknesses (100-400 m). The Holden-Mertz Dk/t criteria of 24 Fatt units for the central cornea and the Harvitt-Bonanno criteria of 35 Fatt units for the limbal area were used as reference points. Results: Our calculations of oxygen transmissibility, with varying tear layer and lens thicknesses, ranged from 10 to 36.7 at the scleral lens centers and from 17.4 to 62.6 at the peripheries. Our calculations of maximum central lens thicknesses show a practical range of 250-495 m, in conjunction with a post-lens tear layer thickness of 100-250 m. Conclusion: Our computations show that most modern scleral lenses, with recommended fitting techniques, should lead to some level of hypoxia-induced corneal swelling. Recommendations are made to minimize hypoxia-induced corneal swelling: highest Dk available (>150) lens with a maximal central thickness of 250 m and fitted with a clearance that does not exceed 200 m.
Purpose: To evaluate changes in anterior corneal topography and higher-order aberrations (HOA) after 14-days of rigid gas-permeable (RGP) contact lens (CL) wear in keratoconus subjects comparing two different fitting approaches. Methods: Thirty-one keratoconus subjects (50 eyes) without previous history of CL wear were recruited for the study. Subjects were randomly fitted to either an apical-touch or three-pointtouch fitting approach. The lens' back optic zone radius (BOZR) was 0.4 mm and 0.1 mm flatter than the first definite apical clearance lens, respectively. Differences between the baseline and post-CL wear for steepest, flattest and average corneal power (ACP) readings, central corneal astigmatism (CCA), maximum tangential curvature (KTag), anterior corneal surface asphericity, anterior corneal surface HOA and thinnest corneal thickness measured with Pentacam were compared. Results: A statistically significant flattening was found over time on the flattest and steepest simulated keratometry and ACP in apical-touch group (all p < 0.01). A statistically significant reduction in KTag was found in both groups after contact lens wear (all p < 0.05). Significant reduction was found over time in CCA (p = 0.001) and anterior corneal asphericity in both groups (p < 0.001). Thickness at the thinnest corneal point increased significantly after CL wear (p < 0.0001). Coma-like and total HOA root mean square (RMS) error were significantly reduced following CL wearing in both fitting approaches (all p < 0.05).
Minimum oxygen permeability required for mini-scleral contact lens daily wear
Contact Lens and Anterior Eye, 2019
Purpose: To investigate the total extracted ex vivo cholesterol, daily comfort, and pre-lens tear film stability over a period of 30 days with lotrafilcon B lenses packaged in blister solution containing EOBO (polyoxyethylene-polyoxybutylene) wetting agent, cared for with H2O2 lens care solution containing EOBO (Regimen1) or MPS solution containing EOBO (Regimen2). Method: 122 subjects were randomized to either Regimen1 (n = 59) or Regimen2 (n = 63) in this multi-center, prospective, randomized, observer-masked study. A subset of right lenses were assessed for ex vivo total cholesterol extraction (n = 23 Regimen1; n = 25 Regimen2) at Day30. Overall daily comfort ratings (10-point scale; 1 = poor, 10 = excellent) were collected every day on Day1/6 h to Day30/6 h by answering text messages. Pre-lens tear film stability was determined by time (seconds) to first distortion (TFD) analyzed from 25 seconds by non-invasive keratography break-up time (NIKBUT) (Keratograph5, Oculus, Germany) videos over the right lens at Day1/8 h and Day30/8 h. All data is presented as Mean (SD; 95 % CI). Results: Total ex vivo cholesterol extracted from lenses with Regimen1 was 0.28 g/lens (0.18; 0.20-0.36) and 0.28 g/lens (0.48; 0.08-0.48) for Regimen2. Overall daily comfort for Regimen1 was rated 8.