Subjects Wearing Contact Lenses Research Articles

Tear-film dynamics by combining double-pass images, pupil retro-illumination, and contrast sensitivity.

Tear-film dynamics were analyzed by a synchronizing recording of double-pass (DP) and pupil retro-illumination (RI) images with contrast sensitivity (CS) measurements. Simultaneous DP and RI images were acquired in three subjects wearing contact lenses while keeping the eye open. Changes in contrast sensitivity for an 18 c/deg green grating were also estimated. From the DP retinal images, the effect of the tear film is described through the objective scattering index (OSI). This presented a negative correlation with the increase in CS during tear-film deterioration (as observed by RI imaging). These results show a relationship between visual outcome degradation due to tear-film breakup and the increase in intraocular scattering. This work shows a combined methodology for the evaluation of tear-film dynamics.

The Effects of Soft Contact Lens Wear on Corneal Thickness, Curvature, and Surface Regularity

Contact lenses have various cosmetic and optical advantages over spectacles. However, long term lens use might affect the normal corneal anatomy and physiology in a variety of ways. The aim of this study was to determine the effect of soft contact lens wear on corneal thickness, curvature, and surface regularity.A total of 138 eyes of 69 subjects wearing contact lenses for more than 1 year were evaluated. One eye of each case was randomly selected for the analysis. Nidek Magellan Mapper corneal topography system was used to evaluate the anterior corneal topography. Central corneal thickness (CCT) was measured using Quantel Medical Axis II PR. Corneal topography and CCT measurements on 138 eyes of 69 subjects were performed. The mean age of the cases and controls was 24.76 ± 5.52 25.13±5.49 years respectively. The mean dura­tion of contact lens wear was 4.83±4.19 years. The mean CCT in case and control group was 527.56±37.40 microns and 544.60±26.10 microns respectively. The mean central corneal thickness in the cases was significantly less by about 16.31 μm in comparison to controls (P <0.05, 95% CI of the difference: 9 μm - 24μm). The SRI and SAI indices were significantly greater in contact lens wearers than in the control group (P = 0.00 for both SRI and SAI).Regular corneal pachymetry and topography assessments are mandatory in soft contact lens users as long term lens wear appears to reduce the central corneal thickness and increase the corneal surface irregularity. DOI: http://dx.doi.org/10.3126/jcmc.v4i2.10861 Journal of Chitwan Medical College 2014; 4(2): 35-39

Development of a method to present wide-view visual stimuli in MRI for peripheral visual studies

We developed a novel wide-view visual presentation system for fMRI studies. Computer-generated images were projected onto a hemispheric, translucent screen inside the MRI bore and were then back-projected onto a 52mm diameter screen. To achieve a wide field view, a spherical screen with a curvature radius of 30mm was placed 30mm away from the subjects’ eyes. The subjects wore contact lenses that enabled them to focus on the screen, and the resulting visual field reached 120°. To evaluate the clarity and quality of the MRI images, a signal-to-noise ratio valuation experiment was performed. In addition, we successfully applied this visual presentation system to studies of visual retinotopic mapping and object perception neural function in the peripheral visual field. Our study demonstrated that the system is compatible with the MRI environment. Based on the wide-field mapping results, this system was more effective at mapping a checkerboard stimuli in V1–V3 from the central to peripheral visual fields. In higher-level visual areas, we successfully located several classical category-selective areas, including the face-selective area (FFA), occipital face area (OFA), house-selective area (PPA), transverse occipital sulcus (TOS), lateral occipital complex (LOC) and posterior fusiform area (pFs). In these areas, we found that the response amplitudes exhibited different decreasing trends with increasing eccentricity. In conclusion, we developed a simple, effective method for presenting wide-view visual stimuli within the MRI environment that can be applied to many kinds of fMRI studies of peripheral vision.

Development of a wide‐view visual presentation system for visual retinotopic mapping during functional MRI

To develop and validate the functionality of a novel wide-view visual presentation system with a horizontal and vertical eccentricity angle of 60° for retinotopic mapping by functional MRI (fMRI). The wide-view presentation system consisted of a 52-mm diameter optical fiber, an entrance apparatus and a presentation apparatus. The terminal edge of the optical fiber at the entrance is flat, while the terminal edge on the presentation apparatus is a sphere of 60 mm in diameter. The subjects wore contact lenses with +20, +22, or +25 magnification to focus on the stimulus, and the visual field eccentricity angle could reach 60°. The signal to noise ratio valuation experiment was performed to evaluate the clarity and quality of the MRI picture image. Checkerboard and random dot stimuli were used to prove that this system could be applied to retinotopic mapping by fMRI. The results of the experiment demonstrated that the system is safe in the MRI environment with minimal distortion and can be used for visual retinotopic mapping studies. Wide-field mapping areas (V6, MST) were found in the human visual cortex. Compared with previous studies, the V1 and MT+ surface area approaches but does not fully cover the anatomical area. Nonetheless, the area achieved using the new system is larger than those achievable in previous fMRI studies. We developed a versatile, low-cost system for presenting wide-view visual stimuli in the MRI environment. The fMRI retinotopic mapping results proved the viability of this system.

Effect of 3rd-order aberrations on human vision

To investigate the effect of 3rd-order aberrations on human vision. Grupo de Ciencias de la Visión, University of Murcia, Murcia, Spain. The 3rd-order aberrations coma and trefoil were induced with purpose-designed soft contact lenses, 3 inducing coma (low [0.05 microm], medium [0.13 microm], high [1.03 microm]) and 3 inducing trefoil (low [0.07 microm], medium [0.17 microm], high [0.96 microm]). Monocular high-contrast (HCVA) and low-contrast (LCVA) visual acuities and contrast sensitivity were measured in 11 subjects wearing contact lenses with a 5.0 mm artificial pupil. The reduction in HCVA and LCVA was statistically significant only for the highest coma and trefoil values (P<.0001). For coma, the mean change in HCVA was 0.193 logMAR +/- 0.100 (SD) and in LCVA, 0.386 +/- 0.136 logMAR. For trefoil, it was 0.204 +/- 0.128 logMAR and 0.395 +/- 0.141 logMAR, respectively. No differences were found for the lower degrees (P>.2). Contrast sensitivity was significantly reduced with the highest coma and trefoil values (P<.0001) (mean change 0.390 +/- 0.157 and 0.404 +/- 0.135, respectively). Lower degrees did not cause significant changes in contrast sensitivity (P>.1). The effect of induced coma and trefoil on HCVA, LCVA, and contrast sensitivity was similar at each level of induced aberration (P>.01). Large values of coma and trefoil (approximately 1 mum) significantly reduced visual performance. Only patients with high 3rd-order aberrations, such as those that occur in refractive surgery or in cases of distorted optics, would benefit from this correction.

The effect of artificial tears on visual performance in normal subjects wearing contact lenses.

Disruption of the anterior refracting surface of the eye reduces visual performance. In the case of a contact lens wearer, this surface is the prelens tear film. This study determined whether artificial tears stabilize the tear film in contact lens wearers and maintained optimal visual performance for a prolonged period. Five normal subjects all in good general and ocular health and adapted to contact lens wear were fitted with Acuvue lenses. A temporal, two-alternative, forced-choice paradigm was used to measure contrast sensitivity. The stimuli were vertically oriented sine-wave gratings (between 0.5 and 14 cpd) presented for 16.67 ms. The stimuli were presented at two different times after blink detection: 2 s after blink detection (i.e., before tear layer break-up) or 4 s after tear film break-up. Three conditions were investigated at 4 s after tear layer break-up: (1) without artificial tears added, (2) with Clerz2 (Ciba Vision) instilled, and (3) with Sensitive Eyes (Bausch & Lomb) applied. The artificial tears were instilled at 10-min intervals during the experimental run. High spatial frequency contrast sensitivity was found to be reduced after tear film break-up and was not enhanced by either tear solution. This study indicates that there is no effect of Clerz2 or Sensitive Eyes in maintaining or improving visual performance beyond the normal prelens tear film break-up time in normal subjects wearing Acuvue lenses.

The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity

PurposeTo evaluate the effect of long-term contact lens wear on corneal thickness, curvature, and surface regularity. DesignA prospective, clinic-based, case-control study. ParticipantsA total of 40 eyes of 20 normal subjects and 64 eyes of 35 subjects wearing contact lenses for more than 5 years were evaluated. MethodsThe Orbscan Corneal Topography System was used to evaluate the entire corneal thickness and curvature, anterior curvature and the anterior and posterior elevation topographic patterns in normal eyes and subjects wearing contact lenses on a regular basis for more than 5 years. Indices of TMS-1 Corneal Topography System were used to determine corneal surface regularity in subjects wearing contact lenses and normal eyes. All topographic examinations were performed after contact lenses had been removed for at least 2 weeks. Main outcome measuresThe entire corneal thickness, curvature, surface regularity index (SRI), surface asymmetry index (SAI), potential visual acuity (PVA) and topographic patterns were compared between normal eyes and subjects wearing contact lenses for more than 5 years. ResultsThe 64 eyes of 35 subjects evaluated by the Orbscan instrument had an average of 13.45 ± 6.42 years of contact lens wear. The mean corneal thickness in the center and in eight peripheral areas measured in contact lens wearing subjects was significantly reduced by about 30 to 50 μm compared to normal subjects (P < 0.001 for central and peripheral sites). No correlation was noted between central corneal thickness and degree of myopia in diopters (r = 0.15, 0.10 < P < 0.25). The corneal curvature, maximum keratometry (Max K) and minimum keratometry (Min K) readings, were significantly steeper in eyes wearing contact lenses than normal eyes (P < 0.01 for Max K and Min K measured by both instruments). No difference in the mean corneal astigmatism was noted between groups. The SRI and SAI, but not the PVA index, of the TMS-1 were significantly greater in contact lens wearers than in the control group (P < 0.01 for both SRI and SAI, P = 0.15 for PVA). The color-coded patterns of all curvature and elevation maps made with both instruments showed no significant difference between subjects wearing contact lenses and the control group. There was no significant difference between corneal curvature measurements taken with the Orbscan System or the TMS-1 System in both normal and contact lens groups. ConclusionsLong-term contact lens wear appears to decrease the entire corneal thickness and increase the corneal curvature and surface irregularity.

Histochemical analysis of secretory vesicles in nongoblet conjunctival epithelial cells.

An Alcian-blue/Periodic acid Schiff reagent (AB/PAS) pH dependent staining method was used to identify the mucus content of secretory vesicles of non-goblet epithelial cells of the human conjunctiva. Twenty subjects were selected for biopsy of the midcentral upper tarsal conjunctiva: 10 subjects had no contact lens wearing experience, and 10 subjects wore contact lenses. Human respiratory epithelium was used as a control for the staining procedure. Four-micron paraffin sections of conjunctival and control tissues were stained with Alcian blue at pH 2.5 and 1.0 and counterstained with PAS. Non-goblet epithelial cell secretory vesicles contained neutral mucin, sialmucin, and sulphomucin. This study provides evidence for a 'second' mucus system of the conjunctiva, that this system is in the non-goblet epithelial cells, and that the mucus of this system has sulphomucins, sialomucins and neutral mucins.

Daily contact lens wear. A three year follow-up.

One hundred subjects wearing contact lenses (mainly soft lenses) on a daily basis for non-medical reasons were followed for 3 years. Visual performance was very satisfactory. The lenses were replaced at an average interval of 20.3 months. During the 3 year period 18 patients suffered from eye disease/changes, 17 of which had to be treated by an ophthalmologist: 8 cases of conjunctivitis, 5 cases of virus keratitis, 4 cases of corneal oedema (2 caused by overwear of lens, 1 by a too step fit and 1 by intolerance despite a perfect fit), and 1 case of unacceptable vascular reaction. Some of the infections might not have been related to contact lens wear. All changes healed well with no sequelae. One patient was hospitalized for 2 days. Each incident required 2.8 visits to an ophthalmologist and 7.4 weeks of discountinued lens wear, on the average. Details from patient history and objective findings recorded at the first examination of subjects accepted for lens wear did not seem to correlate well with later eye disease/changes. 11 subjects stopped lens wear. This was in no case mandatory, the most common reason being decreasing motivation. The results appear quite satisfactory.

Tear evaporation from the human eye: The effects of contact lens wear

Tear evaporation rates were measured by resistancehygrometry in a group of five subjects wearing contact lenses of various materials (38 and 70% hydrogel, silicone elastomer, PMMA and modified PMMA). Tear evaporation rates were significantly increased during contact leans wear compared to the evaporation rate from the naked eye. No consistent differences in evaporation rates were attibutable to specific lens materials. It is suggested that the wear of any contact lens disrupts the tear film sufficiently to increase evaporation.