Advantages of toric scleral lenses.

PURPOSE: The purpose of this study was to investigate whether back surface toric scleral lenses stabilized (i.e., returned to their original position after rotation) and how long the return times were. Return time was studied in relation with actual wearing time and comfort; moreover, the performance of the spherical scleral lens was compared with the toric scleral lens design. METHODS: Toric scleral lenses were rotated clockwise and counterclockwise over 60 degrees. Return times and the actual wearing time were recorded. Results were transformed into nasal and temporal return times for symmetry reasons. The present and former types of correction were compared for comfort (ranging from 0: very poor to 10: excellent) and regular wearing time. All the subjects attended regular follow-up visits. RESULTS: Forty-three subjects (43 lenses) entered the study. All the lenses returned to the original position within a median of 4 seconds after nasal rotation and 6 seconds after temporal rotation. A significant correlation was found between mean return times and actual wearing time (r = 0.63). Significant increases in median comfort (from 6-8) and median wearing time (from 15-16 hours) were demonstrated when the toric scleral lens designs were compared with the former type of correction (both p < 0.001). Median comfort and median wearing time also increased significantly after changing from spherical scleral lenses to the toric design (from 7-8 and from 14-16 hours, both p < 0.001, n = 27 eyes). CONCLUSIONS: Toric scleral lenses returned rapidly to their original position after rotation. The flattest meridian of the toric scleral lenses stabilized symmetrically. Patient interviews demonstrated differences in comfort and wearing time in favor of the toric design.     

Rewetting drops containing surface active agents improve the clinical performance of silicone hydrogel contact lenses.

PURPOSE: The purpose of this study was to investigate the impact of using a rewetting drop (RWD) containing surface active agents (OPTI-FREE RepleniSH; Alcon, Fort Worth, TX) on the clinical performance and protein deposition when using a continuous-wear (CW) silicone hydrogel (SH) contact lens. METHODS: Subjects wore lotrafilcon A SH lenses on a 30-day CW basis for two consecutive 1-month periods while inserting either 0.9% unpreserved unit-dose saline (control) or multidose OPTI-FREE RepleniSH (test RWD). Subjective comfort and symptoms were assessed after 2 and 4 weeks with each product. After 1 month of wear with each product, lenses were collected and analyzed in the laboratory for total protein, total lysozyme, and percentage of denatured lysozyme. RESULTS: Symptoms of dryness and comfort varied across the day regardless of drop type (p < 0.001) with dryness being maximal on waking, least in the middle of the day, and increased towards the evening. The test RWD provided greater comfort on insertion (p = 0.02), better visual quality (p < 0.01), and less mucous discharge on waking (p = 0.02) than the control product. Lysozyme deposition was significantly reduced after the use of the test RWD as compared to saline (0.73 +/- 0.5 microg/lens vs. 1.14 +/- 0.7 microg/lens; p < 0.001) as was total protein deposition (1.17 +/- 0.7 microg/lens vs. 1.86 +/- 0.8 microg/lens; p < 0.001). Lysozyme denaturation was also reduced with the use of the test RWD compared with the control (76 +/- 10% vs. 85 +/- 7%; p < 0.01). CONCLUSIONS: The use of a RWD containing surface active agents provided greater subjective satisfaction, reduced lysozyme and total protein deposition, and reduced denatured lysozyme than a RWD containing saline alone.     

Influence of wear and overwear on surface properties of etafilcon A contact lenses and adhesion of Pseudomonas aeruginosa

PURPOSE: To determine changes in physicochemical surface properties of contact lenses (CLs) during daily wear and effects of lens wear on adhesion of a Pseudomonas aeruginosa strain from a patient with CL-related keratitis. METHODS: Ten new CL wearers used ionic, etafilcon A lenses with 58% water on both eyes for approximately 10 hours each day during 10 and 50 days. All lenses were treated daily with an appropriate lens care solution. After the CLs were worn for 10 days (first pair of lenses) and 50 days (second pair, representing overwear), hydrophobicity by water contact angles, surface roughness by atomic force microscope, elemental surface composition by x-ray photoelectron spectroscopy (XPS), and adsorbed proteins by SDS-PAGE were determined on one lens. The lens from the contralateral eye was placed in a parallel plate flow chamber for bacterial adhesion after each time interval. RESULTS: Water contact angles on lenses changed from 45 degrees on unused lenses to 61 degrees +/- 25 degrees after 10 days of wear and changed significantly (P < 0.05) to 27 degrees +/- 14 degrees after 50 days of wear. Surface roughness increased significantly (P < 0.05) from 4 +/- 2 nm (unused) to 10 +/- 7 nm after 50 days of wear. These changes were accompanied by adsorption of proteinaceous material, as evidenced by XPS and SDS-PAGE, demonstrating adsorption of lysozyme, tear lipocalin, and a 30-kDa protein. Initial bacterial adhesion to worn CLs was lower than to unworn CLs. Furthermore, detachment of adhering bacteria from worn lenses was easier than from unworn lenses. The changes observed in the physicochemical surface properties of the lenses after the CLs were worn for 50 days were accompanied by reports of discomfort by 6 of the 10 new CL wearers. Multiple regression analysis revealed that the most predictive variables for an effect on initial deposition after 10 days of wear were hydrophobicity, roughness, the presence of nitrogen-rich material, including the presence of a 30-kDa protein, and the presence of oxygen-rich material-that is, the type of oxygen adsorbed (O equal or parallel C or Ocjs0807;C). After 50 days of wear, roughness and the presence of tear lipocalin were most predictive. CONCLUSIONS: This study demonstrates that the physicochemical surface properties changed after wear and overwear, whereas overwear of the lenses decreased initial adhesion of P. aeruginosa #3 under the present experimental conditions.     

Tear mixing under a soft contact lens: effects of lens diameter

PURPOSE: Tear exchange under a soft contact lens is modest, and higher exchange rates may be necessary to reduce extended-wear complications; what is not known is the optimal soft lens design to increase tear mixing. We explored the effect of lens diameter on tear mixing. METHODS: Twenty-three subjects wore four different soft contact lenses with diameters of 12.0, 12.5, 13.0, and 13.5 mm. Tear mixing was quantified by placing fluorescein isothiocyanate-dextran on the posterior lens surface, inserting the lens, and monitoring the changes in fluorescence intensity in the postlens tear film. Tear mixing, expressed as the percentage decrease in fluorescence intensity per blink, was estimated using an exponential model. Lens movement was videotaped and lens comfort was graded on a 50-point scale (50 = excellent comfort). Subjects reporting a comfort level of less than 35 were excluded. RESULTS: The mean +/- SE tear mixing rates were 1.82% +/- 0.17%, 1.61% +/- 0.16%, 1.34% +/- 0.17%, and 1.24% +/- 0.17% per blink for the 12.0-, 12.5-, 13.0-, and 13.5-mm diameter lenses, respectively. By regression analysis we found that, on average, mixing under the 12.0-mm lens was 0.59% per blink greater than with the 13.5-mm lens (P = .0024). Lens diameter was a significant predictor of lens comfort, and adjusting for the effects of comfort weakened the relationship between diameter and tear replenishment rate, although the mean rate under the 12.0-mm lens was still 0.43% per blink greater than with the 13.5-mm lens (P = .0468). CONCLUSIONS: These data suggest that smaller-diameter soft lenses provide substantially better tear mixing than larger lenses; however, even small lenses provide modest tear mixing compared with rigid contact lenses.     

Current perspectives in the management of keratoconus with contact lenses

Our aim is to review current and significant articles on contact lens wear in keratoconus patients. A comprehensive literature search of PubMed was performed for the following topics on contact lens wear in keratoconus patients: (1) characteristics of contact lens wearers, (2) safety and efficacy, (3) complications, (4) fitting techniques, (5) contact lens wear after procedures/surgeries, (6) patient satisfaction. A total of 104 studies were finally selected and reviewed. Gas permeable (GP) lens wear provided significantly better vision than glasses. Special cone design lenses had better patient comfort levels though there was no difference in best corrected visual acuity among the GP lenses. Soft lenses showed good efficacy for the treatment of mild-to-moderate keratoconus with newer designs improving visual performance such as customised hydrogel and novel pinhole lenses. Scleral and hybrid lenses provide good visual acuity and comfort for keratoconic patients previously intolerant to RGP lenses. RGP lens wear post-cross linking (CXL) is relatively well-tolerated. Contact lenses may still be required post intrastromal corneal ring procedures and post keratoplasty. Scheimpflug imaging and anterior segment optical coherent tomography (ASOCT) are useful in contact lens fitting. Computerized contact lens fitting techniques could reduce the chair time of lens fitting as well as improve comfort and visual performance. Contact lenses play an important role in the visual rehabilitation of keratoconus patients. New contact lens designs and materials have significantly expanded the available fitting options for keratoconus patients. Imaging technology can be utilized to guide contact lens fitting.Subject terms: Rehabilitation, Rehabilitation, Implants     

Determinants of the initial comfort of hydrogel contact lenses

A double-masked, randomized study was conducted to determine the effects of power and water content on the initial comfort of hydrogel contact lenses in 10 unadapted subjects. Three lens powers (-0.50, -5.00, and -10.00 D) were used in each of three water contents (38, 55, and 70%). A significant negative correlation (p less than 0.05) was found between lens comfort and lens water content; that is, lower water content lenses of lesser bulk were more comfortable than higher water content lenses. These data will allow practitioners to predict patient awareness to various lens types. When fitting hydrogel lenses to an apprehensive patient who has not worn contact lenses previously, it may be advisable to insert a thin, low water content lens initially, thereby maximizing lens comfort.     

Clinical performance of microchannel contact lenses.

PURPOSE: It has been suggested that microchannels placed on the posterior surface of hydrogel contact lenses increase transverse lens movement and therefore increase tear mixing. Lens designs, which can improve tear exchange without adversely affecting lens performance, may play a significant role in improving the safety of contact lens wear. Our aim was to investigate the effect of posterior lens surface microchannels on contact lens performance. METHODS: A randomized, single masked pilot study was conducted. Fifteen experienced hydrogel lens wearers were randomly assigned to wear a microchannel lens (MC) in one eye and a standard hydrogel lens design (STD) in the fellow eye over a period of 6 hours. A range of objective and subjective clinical performance measures were assessed, including visual acuity, lens movement, comfort and patient preference. RESULTS: There were no significant differences between the MC and STD lenses with respect to vision measures, corneal staining, and bulbar and limbal redness (p > 0.05). The MC lenses produced significantly less conjunctival staining than the STD lenses and showed greater lens movement in primary gaze (p < 0.05). Lens distortion with blinking was evaluated through topographic assessment of the contact lenses on eye, and no significant differences were observed in central distortion levels between the two lens designs (p > 0.05). Subjective evaluation of the lenses with respect to comfort, vision, and overall satisfaction did not vary significantly between the two lens types (p > 0.05). CONCLUSIONS: The results of this study suggest that posterior lens surface microchannels do not adversely affect contact lens performance or subjective lens preference over a short-term wearing period. The MC lenses appear to produce less physiological impact on the conjunctival surface than STD lenses with less conjunctival staining observed with the MC lenses. Clinical investigation of the performance of this type of lens design in a larger group of subjects, over longer wearing periods, is warranted.     

Comparing children's,teenagers' and young adults' subjective responses to myopia control contact lenses

Introduction

Myopia control (MC) studies in children link efficacy with subjective performance. There is little MC research in teenagers and young adults. This study compared subjective experience of MC contact lenses in different age groups.

Methods

Data were retrospectively reviewed from two double-masked, bilateral wear, crossover contact lens clinical trials (myopia −0.75D to −3.50D and <1.00 DC; 9–35 years). Participants wore two novel lenses (MC lenses with relative peripheral plus [+1.50D and +2.50D]) and a single-vision (SV) control lens (Clariti® 1 day) for 1 week each. All lenses were made from Somofilcon A material. Data collected included visual acuity (VA), wearing time, subjective ratings of comfort, distance and near vision clarity and overall vision. Generalised estimating equations with subject random intercepts and identity link functions were used in the analysis.

Results

A total of 31 participants (10 children, 11 teenagers and 10 adults) were included, with no difference between the age groups for VA with the dispensed lenses (p > 0.05). All groups could discriminate between the SV and MC lenses for vision (distance, near and overall) after 1 week (p < 0.05). There was no difference between groups for comfort or distance and near vision. Children rated the overall vision quality higher than teenagers and adults for both SV and MC lenses (p < 0.05), but there was no difference relative to the SV lens between groups (p > 0.50). Daily wear time was lowest for children for all lens types (all p < 0.02). Wear time was positively associated with ratings of overall vision quality for children and young adults (both p < 0.05).

Conclusion

All age groups rated SV lenses higher than MC lenses. Subjective ratings of MC lenses appear similar between age groups relative to SV lenses. Wear time was lowest in children and was correlated with overall vision quality ratings in children and young adults.     

The effect of rigid lens back optic zone radius and diameter changes on comfort

The variation in comfort of 12 adapted rigid lens wearers was evaluated when they were fitted with Boston R?CD tricurve contact lenses of three different total diameters (9.0, 9.5, and 10.0 mm) and three different back optic zone radii (BOZR — 0.2 mm, Optimal BOZR, and BOZR + 0.2 mm). The subjects wore 12 pairs of lenses and each lens pair was worn for 1 hour, during which time the comfort of each lens was rated on an analog scale at 0, 15, 30, 45, and 60 minutes. The large-diameter lens (10 mm) was found to be significantly more comfortable than were the other two lens diameters (p < 0. 02) and the steep-fitted lens was significantly less comfortable than were the optimum and flat-fitted lenses (p < 0.01). When the time ratings were averaged, there was no significant difference in comfort over the 1 hour time interval for either diameter or back optic zone radius trials.     

Investigation of the performance of the Menifocal Z gas-permeable bifocal contact lens during continuous wear.

PURPOSE: The Menifocal Z is an alternating vision, concentric, bifocal gas-permeable (GP) contact lens; center distance is connected to near periphery by a smooth transition zone. The lens is produced using tisilfocon A (Menicon Z material), which is approved for up to 30 days of continuous wear (CW). The aim of this study was to evaluate the clinical performance of the Menifocal Z when worn for up to 30 days of CW for 6 months. METHODS: Thirty-five existing GP lens wearers were enrolled in the study. Subjects were fitted with Menifocal Z lenses and follow-up visits were conducted after 2 weeks of daily wear and 1 day, 1 week, 6 weeks, 3 and 6 months of CW. A range of objective and subjective clinical performance measures were assessed, including distance and near visual acuity, the physiological response to CW, and subjective evaluation of vision and comfort. RESULTS: Twenty-seven subjects (77%) completed the study and eight (23%) discontinued: five (14%) as a result of lens-related problems (four vision, one comfort) and three (9%) as a result of non-lens related reasons. Average CW time achieved by the subjects was 22 +/- 2 days. Mean binocular logarithm of the minimum angle of resolution (logMAR) acuities at 6 months were: high contrast distance 0.03 (20/20-), low contrast distance 0.63 (20/80-), and high contrast near 0.26 (20/25, N4). Adverse responses and lens binding were minimal, and there were no significant increases in corneal staining, corneal vascularization, or superior palpebral conjunctival papillae over time (p > 0.05). Problems with night vision (distance and near) with the lenses were the most common difficulties reported by the subjects. CONCLUSIONS: The Menifocal Z appears to be a promising option for presbyopic vision correction, providing successful correction of distance and near vision in a group of experienced GP lens wearers. The hyper Dk tisilfocon A (Menicon Z) material allowed for safe wear of the lenses on a CW basis.     

Rose-K contact lens for keratoconus

AIM: To report clinical experience and the comparative value of axial and instantaneous topography data in fitting Rose-K design contact lenses in moderate and severe keratoconus. MATERIALS AND METHODS: Thirty-eight eyes (of 23 patients) with keratoconus were fitted with Rose-K design contact lenses and followed up for at least six months or more. Visual acuity with habitual vision correction available was measured. Axial and instantaneous topography maps for each eye were recorded. Contact lens wear comfort was graded on a ten point rating scale every three months. RESULTS: Fourteen (100%) moderate keratoconus eyes (average Sim K 48.61 +/- 1.24D) and 23 of 24 (96%) of severe keratoconus eyes (average Sim K 60.88 +/- 5.31D) were successfully fitted with the Rose-K lenses. Final fit contact lenses in severe keratoconus had statistically significant steeper base curves compared to average axial corneal curvature than in moderate keratoconus eyes. Average simulated corneal curvature on axial maps predicted final fit contact lens base curves significantly better than on instantaneous maps. Thirty-three of the 37 eyes fitted with contact lenses maintained wear comfort over average follow up period of 13 +/- 3.5 months. CONCLUSIONS: Rose-K design rigid contact lenses are successful in visually rehabilitating 100% of moderate and 96% of severe keratoconus eyes. Most patients (90%) maintained contact lens wear comfort. Corneal curvature on axial maps is a better predictive of base curve of final fit contact lens.     

Hydrogel contact lens ageing.

PURPOSE: To determine if hydrogel lens water content decreases over wearing periods of up to four weeks; that is, demonstrate an 'ageing' effect. METHODS: Six subjects (4 males, 2 females; age range: 34.8 +/- 11.0 years) wore each of the following lenses for one month: Acuvue, Frequency 38, Gentle Touch and Proclear. Pre-insertion and post-removal lens water content was measured daily by the subjects using an Atago CL-1 Soft Contact Lens Refractometer for a 28 day period. Post-insertion and pre-removal comfort was recorded over the same period. RESULTS: A significant lens ageing effect was noted whereby the pre-insertion lens water content decreased significantly over the 28 day cycle for all lenses (P < 0.05). The pattern for daily dehydration remained consistent for the 28 day period for the Acuvue lens and the Gentle Touch lens but decreased for the Frequency 38 lens and the Proclear lens. Comfort decreased significantly by the end of the day for three of the four lens types investigated. CONCLUSIONS: It is apparent that the extent of lens dehydration changes over time, and that this pattern of change is different for different lens types. The associated loss of oxygen performance with dehydration is demonstrated. These data will assist practitioners in understanding the clinical effects of soft lens dehydration over time.     

A three-month comparative daily-wear study of two high-water-content soft lenses

Proclear^™ (Omafilcon A) is a novel biomimetic, 59% water content hydrogel lens. The material is termed “biomimetic” because it incorporates synthetic phosphorylcholine (PC), which is the predominant headgroup found on the outer surface of human cell membranes. PC has been shown to be the primary cell component responsible for human cell compatibility. The purpose of the study was to further investigate an earlier finding that Proclear lenses were more comfortable than Acuvue lenses. This was a 100-subject, 3-month, daily-wear study undertaken to assess the comparative clinical performance of Proclear (Biocompatibles) and Acuvue (Vistakon) lenses. The study was conducted at 10 optometric sites in the United States. Before the study, all of the subjects were successful Acuvue wearers. Subjects wore a Proclear lens in one eye and an Acuvue lens in the other eye. The Acuvue lenses were worn on a 14-day replacement schedule, whereas Proclear lenses were only replaced as necessary. The Proclear lenses achieved higher mean comfort scores at each of the follow-up visits, and this difference was significant (p = 0.03). More subjects expressed a preference for the Proclear lens at all visits, and this number was statistically significant at the 1-week, 1-month, and 3-month visits (p < 0.01). The reasons for lens preference tended to be because of comfort. Significant differences were noted in lens fit at all visits. More Proclear lenses showed minimal decentration, postblink movement, and optimal overall fit than did the Acuvue lenses. Significantly greater dehydration was noted with the Acuvue lens compared with Proclear (p < 0.001). The study confirmed that the Proclear lenses were preferred to the Acuvue lenses. Preference was primarily based on subjective comfort.     

Influence of special effect soft lenses on visual function

BACKGROUND: Contact lenses which change the structure and color of the iris are used not only for many therapeutic situations but also for cosmetic reasons. The purpose of this study was to investigate whether such lenses cause impairment of visual functions. MATERIAL AND METHODS: In healthy volunteers with an uncorrected visual acuity of 20/20 a clear soft-fitting lens and a special effect soft contact lens (Crazy lens, Bach Optic, Cologne) were tested in changing sequence. The following parameters were studied: visual acuity, contrast sensitivity (MCT 8000, VisTech Cons., Dayton, Ohio), Goldmann visual field, mesopic vision (Nyktometer, Rodenstock, Munich), and subjective wear comfort on a scale from 1 (excellent) to 10 (poor). Statistical analysis was performed using the Wilcoxon test and the Mann-Whitney U-test. RESULTS: Nine volunteers with a mean age of 29.9 +/- 5.1 years were analyzed. Visual acuity was reduced to 0.9 +/- 0.23 in the Crazy lens group compared to 1.2 +/- 0.13 in the clear lens group. Mesopic vision without glare was reduced from 1:2.5 to 1:7.4. Goldmann visual field displayed a significant constriction of following isopters: III/4, I/4, and I/3. Contrast sensitivity was significantly reduced in a photopic condition with and without glare and in a scotopic condition without glare; there was, however, an increase in contrast sensitivity in a scotopic condition with glare. Furthermore a decrease in wear comfort from 2.8 +/- 1.4 with the clear fitting lens to 5.7 +/- 2.1 with the print-lens was found. CONCLUSION: The tested special-effect contact lenses are associated with a reduction of many visual functions, including visual acuity and contrast sensitivity. This may interfere in some wearers with the ability to drive a car.     

Theoretical performance of progressive addition lenses with poorly measured individual parameters

Purpose

The aim of this paper was to present a theoretical study of how poorly measured individual parameters affect the optical performance of progressive addition lenses (PALs). Modern progressive lenses can be prescribed based on parameters such as vertex distance, pantoscopic and wrap angles. These parameters can be measured from the lens wearer using specific devices; however, not all of them can be measured with the same precision, and the impact of measurement errors on the lens performance is still unknown.

Methods

Data from 1900 patients were used to simulate the performance of four PAL designs with different degrees of complexity: perfect individual design, individual design with induced errors in the individual parameters, optimised design and conventional/basic design. For each patient and design, a quality metric was calculated to describe the optical performance of the lens.

Results

The design having the best performance was the perfect individual design, followed by the individual design with induced errors, the optimised design and finally the conventional/basic design.

Conclusions

Individual designs with measurement errors have better optical performance than lenses with less complexity, such as the optimised or conventional designs. This knowledge is useful for the eye care professional to make informed choices when dispensing these lenses.     

Peripheral defocus does not necessarily affect central refractive development

PURPOSE: Recent experiments in monkeys suggest that deprivation, imposed only in the periphery of the visual field, can induce foveal myopia. This raises the hypothesis that peripheral refractive errors imposed by the spectacle lens correction could influence foveal refractive development also in humans. We have tested this hypothesis in chicks. METHODS: Chicks wore either full field spectacle lenses (+6.9 D/-7 D), or lenses with central holes of 4, 6, or 8mm diameter, for 4 days (n=6 for each group). Refractions were measured in the central visual field, and at -45 degrees (temporal) and +45 degrees (nasal), and axial lengths were measured by A-scan ultrasonography. RESULTS: As previously described, full field lenses were largely compensated within 4 days (refraction changes with positive lenses: +4.69+/-1.73 D, negative lenses: -5.98+/-1.78 D, both p<0.001, Dunnett's test, to untreated controls). With holes in the center of the lenses, the central refraction remained emmetropic and there was not even a trend of a shift in refraction (all groups: p>0.5, Dunnetts test). At +/-45 degrees , the lenses were partially compensated despite the 4/6/8mm central holes; positive lenses: +2.63 / +1.44 / +0.43 D, negative lenses: -2.57 / -1.06 / +0.06 D. CONCLUSIONS: There is extensive local compensation of imposed refractive errors in chickens. For the tested hole sizes, peripherally imposed defocus did not influence central refractive development. To alter central refractive development, the unobstructed part in the central visual field may have to be quite small (hole sizes smaller than 4mm, with the lenses at a vertex distance of 2-3mm).     

Effect of lens base curve on subjective comfort and assessment of fit with silicone hydrogel continuous wear contact lenses.

PURPOSE: To study the effect of base curve on subjective comfort of silicone hydrogel extended wear lenses. METHODS: Ninety-five subjects were first trial fitted with 8.6-mm base curve lotrafilcon A (Focus Night & Day) lenses and then with 8.4-mm lenses only if poor subjective comfort or poor fit was present. Comfort and fit were assessed after 15 min. Subjects with discomfort or signs of poor fit were then trial fitted with 8.4-mm lenses. RESULTS: Of 190 eyes, 74.2% were fitted with 8.6-mm lenses, and 23.7% required 8.4-mm lenses. Two (2.1 %) subjects could not be fitted with either base curve. Mean steep keratometry (K) reading for eyes dispensed with 8.6-mm lenses was 43.88 D and 45.56 D for eyes dispensed in the 8.4-mm lenses (p < 0.001). CONCLUSIONS: A clinically useful criterion showing the need for 8.4-mm lenses was steep K of > or = 45.50 D; 77% of these eyes required the steeper lens for good comfort and fit. Subjective discomfort with 8.6-mm lenses was also a useful signal for the need of a steeper lens; mean comfort scores for those subjects rose from 6.33 with 8.6-mm lenses to 9.44 with the 8.4-mm lenses for eyes requiring the steeper lens (p < 0.001).     

Corneal epithelial thinning profile induced by long-term wear of hydrogel lenses

PURPOSE: To characterize the epithelial thickness profile and study the effects of long-term wear of hydrogel lenses on this profile. METHODS: A cross-sectional study was designed. Epithelial thickness was evaluated in 15 subjects who had worn one of two types of low oxygen transmissibility (Dk) hydrogel contact lenses for an average of 10 years (range, 7-16) and compared with a group of 18 control subjects who had never worn contact lenses. Epithelial thickness was measured at the center and at four mid-peripheral and four peripheral locations in the vertical and horizontal meridians of the cornea using a modified optical pachymeter. RESULTS: Lens wearers had significantly thinner epithelium than controls [analysis of variance (ANOVA), p < 0.001] in the central (41 +/- 7 microm versus 48 +/- 5 microm), mid-peripheral (41 +/- 7 microm versus 48 +/- 7 microm), and peripheral (42 +/- 9 microm versus 48 +/- 6 microm) cornea. The extent of this difference ranged from 8.7% to 18.4% of the total epithelial thickness, was not associated with the duration of wear (ANOVA, p = 0.87, power = 0.05), and was significantly greater for the lower Dk contact lens type (ANOVA, p < 0.001). Topographical position did not have a significant effect on epithelial thickness (ANOVA, p > 0.13, power > 0.22). CONCLUSION: This study establishes that the epithelial thinning associated with hydrogel lens wear is topographically uniform. It also confirms that this effect is inversely related to lens oxygen transmissibility but does not appear to increase with longer duration of wear.     

Intraocular pressure by noncontact tonometry over an amniotic membrane patch in humans

PURPOSE: To determine the reliability of noncontact tonometry (NCT) in measuring intraocular pressure (IOP) over a combination of amniotic membrane (AM) patch and therapeutic soft contact lens (TSCL) in normal human eyes. DESIGN: Experimental study. METHODS: Twenty-five healthy volunteers (twenty males, five females) participated in this study. After topical anesthesia, IOP was measured using noncontact tonometry before and after the application of a single layer of AM to the right eye and a double layer of AM to the left eye. To enable the IOP measurement by NCT, a TSCL was placed over the AM patch. The thickness of a single or a double layer of AM was measured by pachymetry and correlated with the IOP reading. RESULTS: We found no statistical difference between IOPs measured with and without a combination of a single-layer AM/TSCL (P = .734). In contrast, the IOPs measured over a combination of a double-layer AM/TSCL decreased significantly when compared with the control (P < .0001). The average thicknesses of the single and the double layer of AM were 72.4 +/- 15.0 mum and 126.9 +/- 14.6 mum (mean +/- SD), respectively. There was a negative correlation between total AM thickness and IOP change (r = -.481, P = .0008). CONCLUSIONS: We found that it is reliable to measure IOP by NCT through a combination of a single-layer AM/TSCL on normal human eyes. However, IOP measured by NCT over a combination of a double-layer AM/TSCL was inaccurate and tended to be an underestimation.