Wearing Rigid Gas Permeable Contact Lenses Research Articles

Physiological Changes in the Cornea When Wearing Rigid Gas Permeable Contact Lenses

Rigid gas permeable (RGP) contact lenses are made of materials with excellent oxygen permeability and wettability, so they not only improve oxygen permeability compared to existing lenses, but also provide correction of refractive errors and improved vision in irregular corneas such as keratoconus. However, the hard material of the lens along with hypoxia and hypercapnia of the cornea caused by wearing RGP contact lenses cause various physiological changes in the cornea. Physiological changes in the cornea that may occur when wearing RGP contact lenses include mucin balls, decreased corneal epithelial thickness and increased size, decreased epithelial barrier function, corneal erosion and staining, decreased keratocyte density, decreased corneal sensitivity, and stromal opacities, contact lens‐induced peripheral ulcers, endothelial blebs, increased endothelial polymegethism, and changes in corneal shape. It is necessary to know the performance of the RGP contact lenses being prescribed, be aware of the physiological changes in the cornea caused by wearing RGP contact lenses, and provide the correct lens prescription along with appropriate education to the patient.

Visual rehabilitation using mini-scleral contact lenses after penetrating keratoplasty.

To report the visual rehabilitation outcomes and complications of patients fitted with mini-scleral rigid gas-permeable (RGP) contact lenses (mini-SCLs) after penetrating keratoplasty. We retrospectively reviewed 27 eyes (21 patients) that were fitted with mini-SCLs between October 2013 and December 2014. We analyzed demographic data, previous corneal disorders, visual outcomes, interval from keratoplasty to contact lens fitting, topographic and specular microscope data, fitted contact lens parameters, and complications. The patients were divided into two groups according to the elapsed time since surgery: Group A, grafts with <10 years (n=14 eyes); and Group B, grafts with ≥10 years (n=13 eyes). Lens use was discontinued in four eyes, and microbial keratitis developed in one eye during follow-up. No corneal graft rejection was observed. The mean interval between grafting and initial contact lens fitting was 10.6 ± 7.3 years (range: 1-29 years). The most frequent reason for keratoplasty was keratoconus (22 eyes, 81.4%). The mean contact lens-corrected visual acuity (CLCVA) was 0.09 ± 0.12 logMar (range: 0.50-0.00 logMar). The average topographic astigmatism, mean steepest keratometry (Kmax), and average cellularity on specular microscopy were 6.19 ± 3.49 diopters (D), 58.4 ± 7.8 D, and 1,231 ± 723 cells/mm2, respectively. Mini-SCL use allowed successful visual rehabilitation after corneal keratoplasty, particularly in patients who required corrective lenses for low visual acuity and were unable to wear RGP contact lenses. Our results indicate that mini-scleral lenses may be an option for the treatment of corneal irregularities, such as those associated with keratoplasty.

Effects of rigid contact lenses on optical coherence tomographic parameters in eyes with keratoconus

BackgroundThe aim was to evaluate the effect of irregular astigmatism on the retinal nerve fibre layer (RNFL), macular thickness and ganglion cell analysis obtained by spectral domain optical coherence tomography (OCT) in eyes with keratoconus.MethodsFifty‐two eyes of 31 patients (20 females) with keratoconus that required correction of irregular astigmatism with rigid gas‐permeable (RGP) contact lenses were included to this study. The average, superior, nasal, inferior, temporal and 12 clock hour sector's RNFL, ganglion cell and macular thickness analyses before and 30-minutes after RGP contact lens (Rose K2 ‐Menicon Z material, David Thomas Contact Lenses Ltd, Northampton, United Kingdom) wear were performed to all patients with Cirrus HD spectral domain optical coherence tomography.ResultsThe average thickness of the retinal nerve fibre layer, the thickness at the nasal quadrants and 1‐2‐3‐4 o'clock hour sectors and mean signal strength were increased significantly by RGP contact lens wearing independent of the stage of keratoconus. Central sub‐field thickness increased after correction with RGP contact lens (p = 0.037). After wearing RGP contact lenses, changes on ganglion cell analysis were not significant (all p values ≥ 0.111).ConclusionsOCT is a widely used device for retinal nerve fibre layer and macular thickness evaluation in patients with glaucoma and macular diseases. The study demonstrates that OCT parameters such as retinal nerve fibre layer, central sub‐field thickness and mean signal strength are affected by irregular astigmatism. Correction of irregular astigmatism with RGP contact lenses should be recommended before analysing keratoconic eyes to obtain optimum results on OCT measurements.

Bevel toric multicurve rigid gas-permeable lens for keratoconus

To evaluate the efficacy and safety of Twinbel bevel toric, a newly designed rigid gas-permeable (RGP) lens with a toric bevel curvature, for keratoconus. A retrospective analysis of nine eyes of patients with keratoconus who had been wearing RGP contact lenses and were switched to Twinbel bevel toric at Yamaguchi University Hospital. Visual acuity and contrast sensitivity were measured under photopic conditions. Complaint symptoms were recorded as primary outcome measures at follow-up visits. Efficacy and safety were evaluated at 12weeks after the switch to Twinbel bevel toric or later. Five eyes (55.6%) showed an improvement in visual acuity with Twinbel bevel toric compared with the previous lens, whereas four eyes (44.4%) maintained the same visual acuity as before. The mean best corrected visual acuity±SD with Twinbel bevel toric was 0.01±0.40 logMAR, significantly better (P=0.044, paired Student's t test) than that (0.23±0.51 logMAR) with the previous lens. Contrast sensitivity and subjective complaint scores did not differ significantly between Twinbel bevel toric and the previous lens. No serious complications of Twinbel bevel toric wear were observed. Fitting of Twinbel bevel toric improved visual acuity in eyes affected by keratoconus, thus providing a viable alternative for management of such eyes.

The Effect of Contact Lens Wear on the Ocular Surface Changes in Keratoconus

To investigate the effects of contact lens wear or the keratoconic shape itself on the changes in the ocular surface in keratoconus. Forty-two patients (84 eyes) were enrolled in this study and divided into four groups. Group 1 comprised 22 eyes with keratoconus that had been wearing rigid gas-permeable (RGP) contact lenses for an average of 5.54 +/- 2.11 years. Group 2 comprised 24 myopic eyes that had been wearing RGP contact lenses for 6.42 +/- 1.79 years. Group 3 comprised 20 eyes with keratoconus without any contact lens wear. Group 4 comprised 18 healthy eyes that were used as controls. The ocular surface changes were evaluated by determining the tear film breakup time and performing conjunctival impression cytology. The goblet cell densities, nucleus-to-cytoplasm ratio, and epithelial cell morphology in the four groups were compared with optical microscopy in the high-power field. The tear film breakup times in groups 1 and 2 were significantly lower than those in groups 3 and 4. The goblet cell densities were 5.49 +/- 1.75 and 5.82 +/- 1.63 in groups 1 and 2, respectively, which were significantly lower (P < 0.05) than the 8.79 +/- 1.42 and 10.24 +/- 2.10 in groups 3 and 4, respectively. There were no statistically significant differences in the goblet cell densities, nucleus-to-cytoplasm ratios, and epithelial cell morphologies between groups 1 and 2 and groups 3 and 4. The ocular surface changes in keratoconus may be directly related to contact lens wear and not to the keratoconic shape itself.

Use of a run-in period to decrease loss to follow-up in the contact lens and myopia progression (CLAMP) study

Rigid gas permeable (RGP) contact lenses are initially less comfortable to wear than spectacles. In previous studies evaluating the use of RGP contact lenses to control myopia, more subjects randomly assigned to wear RGP contact lenses have been lost to follow-up than spectacle wearers. Previous rigid contact lens myopia control studies have lost 44% and 47% of the rigid contact lens wearers. This unequal loss to follow-up may compromise the results of the study, so we conducted a run-in period prior to randomized treatment-group assignment to ensure that all participants could adapt to RGP contact lens wear. We enrolled 147 children ages 8–11 years with myopia in the run-in period. Of the 147 subjects, 116 (78.9%) were able to wear RGP contact lenses for at least 40 hours per week and reported that they were “usually comfortable” or “always comfortable.” After 3 years, no subjects were lost to follow-up. The run-in period greatly reduced the loss to follow-up suffered by previous RGP contact lens myopia progression studies and may help provide more definitive answers regarding myopia control with RGP contact lenses.

On-eye measurement of optical performance of rigid gas permeable contact lenses based on ocular and corneal aberrometry.

Our aim was to obtain a complete description of the interactions of rigid gas permeable (RGP) contact lenses with the optics of normal eyes. We measured total and anterior-surface aberrations in four subjects, who were all long-term RGP contact lens wearers. The anterior-surface wave aberration was obtained from videokeratographic elevation maps, and ocular wave aberration was measured with a laser ray-tracing technique. Measurements were performed with and without their own spherical contact lenses. With this methodology, we evaluated the optical performance with RGP lenses compared with the natural optics. We estimated the contribution of the anterior surface of the contact lens, the internal ocular optics, flexure, and the tear lens aberrations to the optical performance of eyes wearing RGP contact lenses. We found that in three of four subjects, the contact lens significantly improved the natural optics of the eye. For the subject with higher dominance of corneal aberrations, root mean square (second-order and higher) decreased from 1.36 microm to 0.46 microm. Third- and higher-order aberrations decreased from 0.77 microm to 0.39 microm. The internal optics and lens flexure imposed limits on aberration compensation. Spherical RGP contact lenses did not produce spherical aberration potentially due to a compensatory role of the tear lens. Aberration measurements are useful to understand the fitting of contact lenses and the interaction with tear, cornea, and internal optics of the eye. Aberrometry can help to choose the best standard RGP lens parameters to improve the optics of individual eyes.

The critical Dk/L to avoid oedema for daily wear RGP contact lenses

Background: A study was conducted to investigate the critical Dk/L required to avoid open‐eye oedema with rigid gas‐permeable (RGP) contact lenses.Methods: RGP contact lenses in matched designs were fabricated from three materials of nominal Dk of 12, 30 and 45 times 10−11 (cm2.mlO2)/(s.ml.mmHg), with a centre thickness of 0.15 mm. A randomised, double‐masked study design was used. Over two lens‐wearing sessions one week apart, nine young adult subjects wore one lens made of each of the three materials for four hours. In one session the non‐lens‐wearing eye served as a control. Corneal thickness was measured using an ultrasonic pachometer before and after lens wear and the extent of corneal oedema calculated.Results: Lenses with a Dk/L of 8 times 10−9 (cm.mlO2)/(s.ml.mmHg) induced statistically significant levels of corneal oedema (1.8 ± 1.5 per cent) after four hours of open‐eye wear. No corneal oedema was detected with lenses above this critical Dk/L value. No evidence could be found to support the concept of ‘osmotic’ corneal oedema induced by reflex lacrimation in unadapted subjects.Conclusion: RGP lenses with a Dk/L of 20 times 10−9 (cm.mlO2)/(s.ml.mmHg) or greater worn for daily wear are unlikely to induce corneal oedema in the majority of patients.

Corneal Pannus Associated With Contact Lens Wear

To determine whether contact lens, related corneal pannus regressed when eyes were refitted with rigid gas-permeable contact lenses and to investigate the role of hypoxia as the putative origin of this complication. Twenty-three eyes of 14 patients with corneal pannus were identified retrospectively from a referral practice population and were separated into two subgroups. One subgroup accepted refitting with rigid gas-permeable contact lenses or discontinued contact lens wear, and the other elected to continue wearing hydrogel or polymethylmethacrylate contact lenses. The response of pannus was observed by slit-lamp biomicroscopy and photographs and was compared between the two subgroups. One eye of each of six patients identified with bilateral corneal pannus secondary to daily wear of hydrogel contact lenses was selected at random. Duplicates of the hydrogel contact lenses worn by these eyes were obtained, and their peripheral oxygen transmissibility (Dk/Lp) values were compared with those of a control group of hydrogel contact lenses identical to those worn by another group of patients, matched by age, gender, and laterality to the study group, but who did not have corneal vascularization. Vascularization regressed in 14 eyes of nine patients refitted with rigid gas-permeable contact lenses and also in both eyes of one patient who discontinued contact lens wear. All seven eyes of five patients who declined refitting showed persistence or increase of pannus. The mean Dk/Lp of the hydrogel contact lenses for six eyes with pannus was 3.8 X 10(-9) cm ml O2/s ml mm Hg; mean Dk/Lp was 8.6 X 10(-9) cm ml O2/s ml mm Hg for the lens of the control eyes. This difference was found to be statistically significant (P = .028). Peripheral, contact lens-induced hypoxia is a risk factor for corneal pannus, and conversion from hydrogel or polymethylmethacrylate contact lenses to daily wear rigid gas-permeable contact lenses in these eyes successfully reversed this complication.

REGULAR REPLACEMENT OF EXTENDED WEAR RIGID GAS PERMEABLE CONTACT LENSES

PURPOSE While the benefits of planned replacement of soft contact lenses have been investigated, the question of whether there are any clinical benefits to planned replacement of rigid gas permeable (RGP) lenses does not appear to have been addressed experimentally. We aimed to determine the benefits of regular replacement of extended wear RGP contact lenses. METHODS We conducted a prospective, single-center, controlled, double-masked study of 39 RGP lens wearers. The subjects were divided into two groups and wore extended wear Quantum 2 lenses (Dk = 120) for 12 months. Subjects in Group I replaced lenses every 3 months, whereas those in Group II were not scheduled to replace their lenses. The integrity of the lenses and the ocular responses to lens wear were monitored in both groups every three months. RESULTS Compared to lenses worn by subjects in Group I, lenses worn by Group II subjects showed significantly more mucous coating, lens binding, and corneal staining over time (P < 0.05; ANCOVA). There was no difference in microcystic or tarsal conjunctiva response, lens comfort, refractive change, or visual acuity between the two groups. CONCLUSIONS We advocate that to maintain optimal lens integrity and ocular health, RGP lenses used for extended wear should be replaced every 3 to 6 months.