Abstract
Purpose
To evaluate the changes in corneal epithelial thickness and corneal anterior and posterior curvatures during the day, and the effect of wearing daily disposable soft contact lenses.
Methods
Thirty-two healthy volunteers were enrolled in a randomized crossover study. At the baseline visit, corneal and epithelial thickness maps (OCT; Optovue, Inc., Fremont, CA, USA) and keratometric measurements (Pentacam, Oculus, GmbH, Germany) were performed in the morning and in the afternoon (8 hours after). Then, each subject was fitted with the following brands of daily disposable contact lenses in random order: Dailies Total 1 (Delefilcon A), Dailies Aqua Comfort (Nelfilcon A), TruEye (Narafilcon A) and Biotrue Oneday (Nesofilcon A) on different days. All fitted lenses had a power of −3.00 diopters (D). Measurements were repeated before putting the contact lens on and after an-eight-hour contact lens wear.
Results
With no lens wear, the anterior topographic indices showed significant steepening [Kflat: p < 0.0001; Ksteep: p < 0.0001 and maximum keratometry value (Kmax): p = 0.04] and the corneal thickness significantly decreased in the central and temporal portion of the cornea in the afternoon. There were no significant changes in the posterior topographical indices and corneal epithelial thickness. With contact lens wear, no significant change occurred in the corneal and epithelial thickness, and the anterior and posterior curvatures during the day (all p values >0.05). There was no statistically significant difference in the epithelial thickness among the groups wearing different contact lens types (p > 0.05).
Conclusions
Anterior corneal topographic indices steepen depending on the natural diurnal variations. Daily wear of soft contact lenses appears to mask this steepening. The corneal epithelial thickness is not affected by daily disposable soft contact lenses.
1
Introduction
Refractive errors may be managed by different means in modern ophthalmology. Currently, soft contact lenses (CLs), which provide different designs, materials, and wear schedule, seem to be very popular among them. Daily disposable contact lenses (DDCLs), designed to be worn once and then replaced with a new pair of lenses on a daily basis, offer a number of advantages compared with conventional daily wear or frequent replacement (weekly/monthly) CLs. The causes of noncompliance among the reusable lens wearers can be listed as follows: lens wearing times, procedures for lens care, lens replacement schedules, and procedures for lens case hygiene [ , ]. The advantages of DDCLs include improved comfort (dryness, redness, tiredness), improved vision quality (less blur), reduced lens deposition, and a lower rate of medical complications due to lack of need to use a lens care system or overnight storage [ ].
CL wear induces some morphologic changes in the cornea. The wear time, lens material, design, and the frequency of use may affect those corneal parameters. However, while interpreting these findings, the diurnal changes on the corneal thickness and curvature as a result of the natural metabolism of the cornea and the tear film layer must be kept in mind [ ].
There are studies evaluating the corneal changes induced by both rigid gas permeable [ ] and soft CL wear [ , ]. Some studies showed that long-term soft CL (SCL) wear reduced oxygen uptake and induced cell death, and thus caused central and peripheral corneal epithelial thinning [ ]. It has been shown that daily wear of different design SCLs may induce anterior corneal steepening or flattening [ , , ]. Studies assessing corneal thickness while wearing SCLs showed some degree of corneal swelling [ , ]. A small number of studies evaluating posterior cornea showed slight steepening in the posterior corneal curvature [ , ].
There is a wide range of techniques available to help measure the corneal changes mentioned above. Non-invasive optical systems based on a rotating Dual-Scheimpflug or a Placido tomography system may help quickly analyse the anterior segment of the eye. The corneal epithelial thickness can be measured using optical coherence tomography (OCT), ultrasonography, and confocal microscopy. Recently, a software algorithm based on a Fourier-domain OCT system that prevents large variability in the point thickness was developed in order to automatically map corneal epithelial thickness [ ]. It measures the average central and peripheral epithelial thickness with a single measurement. After a series of repeated measures with OCT, coherent results were reported in normal subjects, patients with keratoconus, dry eyes, and orthokeratology lens-wearing children [ , ].
Posterior corneal measures and epithelial mapping are very useful in the early detection of keratoconus, and also in the evaluation of patients who are candidates for refractive surgery. Comprehension of the effect of diurnal variations and the influence of CL wear on corneal shape gives precious information in the interpretation of results in research and everyday clinical practice. The purpose of this study was to evaluate the changes in corneal epithelial thickness and corneal anterior, and posterior curvatures induced by wearing four types of daily disposable CLs.
2
Methods
Thirty-two healthy volunteers (11 males and 21 females) who had never worn CLs were enrolled in this crossover study. This prospective randomized study was conducted within the tenets of the Declaration of Helsinki after obtaining approval from the local ethics committee. The subjects were recruited from patients attending the outpatient unit of the cornea department of Marmara University, Istanbul. Written informed consent was obtained from all patients. All subjects in the study were CL-naive healthy subjects with refractive errors. The exclusion criteria included a history of any systemic or ocular disease (refractive disorder was included), which would negatively affect the outcome of the study, a history of ocular surgery, a history of previous CL use, use of any topical or systemic drugs, pregnancy or lactation.
2.1
Contact lenses
Four different types of daily CLs were evaluated: Dailies Total 1 (Alcon Lab. Inc., TX, USA), 1 Day Acuvue TrueEye (JohnsonJohnson Vision Care, NJ, USA), Dailies Aqua Comfort (Alcon Lab. Inc., TX, USA), Biotrue Oneday (Bausch and Lomb, NY, USA). The properties of the lenses are given in Table 1 . Two lenses were made of silicone hydrogel (SiHy) and other two were made of hydrogel (Hy). All subjects were fitted with -3 D lenses.
| Lens Properties | Lens Types | |||
|---|---|---|---|---|
| Lens name | Dailies Total 1 | 1-Day Acuvue TrueEye | Dailies Aqua Comfort | Biotrue Oneday |
| Manufacturer | Alcon Laboratories, Inc. | Johnson δ Johnson Vision Care | Alcon Laboratories, Inc. | Bausch + Lomb |
| Material | Delefilcon A | Narafilcon A | Nelfilcon A | Nesofilcon |
| Power, D | −1.00 to −6.00 | −1.00 to −6.00 | −0.50 to −10.00 | −0.25 to −9.00 |
| Water content, % | 33 (core), >80 (surface) | 46 | 69 | 78 |
| Dk/t value (−3.00 D) | 156 | 118 | 26 | 42 |
| Diameter, mm | 14.1 | 14.2 | 14.0 | 14.2 |
| BCOR, mm | 8.5 | 8.5 and 9.0 | 8.7 | 8.6 |
| Modulus, Mpa | 0.7 (core), 0.025 (surface) | 0.66 | unknown | 0.49 |
| Central thickness at −3.00 D, mm | 0.09 | 0.085 | 0.10 | 0.10 |
2.2
Study procedure
All patients underwent a detailed ophthalmologic examination at their first visit including keratorefractometry (NIDEK ARK-530A, NIDEK Co. Ltd., Gamagori, Japan) measurements, best corrected visual acuity (BCVA), biomicroscopic examination, intraocular pressure measurements, Scheimpflug-based anterior segment mapping (Pentacam, Oculus, GmbH, Germany), and epithelial thickness maps using anterior segment OCT (Optovue, Inc., Fremont, CA, USA). Anterior segment imaging was performed using a rotating Scheimpflug camera, which captures 50 images automatically and measures 25,000 true elevation points. This instrument outputs a ‘quality specification’ for images, which provides the reliability data of the scan (checking for poor alignment, excessive blinking, any missing or invalid data). If the image quality was not acceptable, the measurements were repeated. The keratometric measurements were recorded from the Pentacam map. Each eye was scanned 3 times during a single visit. Both anterior and posterior curvature data were obtained from the Pentacam map.
Baseline measurements were taken at approximately 10:00 AM (to avoid the peak in corneal thickness immediately after waking) and at 18:00 PM, without any CLs being worn in order to record each individual’s natural diurnal variation in corneal epithelial thickness and curvature. All measurements were repeated at 10:00 AM, before lens wear and at 18:00 PM, after 8 hours of lens wear. Each eye of the subjects was fitted with lenses of different brands, which were chosen in a random order. After a period of at least three days of non CL wear, in order to allow the cornea to restore its normal state, the other two brands that were not used on the first day were fitted to each eye and the same procedure was followed. All measurements and examinations were performed by the same physician (DDY).
2.3
Epithelial thickness map
OCT epithelial thickness mapping and pachymetry software were obtained using the RTVue Fourier-domain OCT system with a corneal adaptor module (L-Cam lens). The scan pattern (6.0 mm scan diameter, 8 radials, 1024 axial scans each, repeated 5 times) was centred on the coaxially fixating corneal light reflex identified by the central bright reflection. The epithelial thickness map was processed by an automatic algorithm and divided into 2-mm, 5-mm, and 6-mm diameter circular areas according to the centre of the cornea. The paracentral and peripheral zones were also divided into 8 sectors ( Fig. 1 ). The minimum and maximum values were also measured and noted.
2.4
Statistical analysis
Statistical analysis was performed by using the SPSS statistical software package (SPSS version 20.0, SPSS, Inc., Chicago, IL). The Kolmogorov-Smirnov test was applied to determine the normality of data distribution. All descriptive data are presented as mean, standard deviation (SD), median and 95% confidence interval (CI) values. Parametric tests and non-parametric tests were applied depending on the distribution of the data. The paired sample and the Wilcoxon signed-rank tests were used to check within-group differences. The Kruskal-Wallis test was performed for multiple comparisons. Analysis of variance (ANOVA) was used to evaluate the significance between differences among groups. The statistical significance value was set at p = 0.05
3
Results
The mean age of patients was 23.5 ± 7.0 (range, 18 to 14 years. With regard to the diurnal changes, the anterior topographic indices significantly steepened (Kflat: p < 0.0001; Ksteep: p < 0.0001; Kmax: p = 0.04), whereas posterior topographic indices remained unchanged (p > 0.05) ( Table 2 ). The mean diurnal change in corneal thickness showed significant thinning in the central corneal region (−5.5 ± 18.7 μm, p = 0.034) and the temporal corneal region (−7.1 ± 18.5 μm, p = 0.04). There was no significant thinning in the nasal corneal region (−6.4 ± 18.4 μm, p = 0.08) ( Table 3 ). Considering the corneal epithelium, which was divided into five different zones (central, nasal, temporal, inferior, and superior), no significant thinning was observed in any of the five zones between the morning and the afternoon measurements ( Table 3 ).
| Scheimpflug-based Device Anterior and Posterior Curvatures (D) | ||||
|---|---|---|---|---|
| Morning | Afternoon | |||
| Anterior Curvature Mean ± SD Median (CI) | Kflat | 41.9 ± 1.1 42.2 (41.5 to 42.5) | 42.6 ± 1.3 42.95 (41.6 to 43.6) | p < 0.0001 * |
| Ksteep | 42.6 ± 1.2 42.65 (42.0 to 43.2) | 43.5 ± 1.3 43.7 (42.7 to 44.3) | p < 0.0001 * | |
| Kmax | 44.2 ± 1.5 44.45 (43.5 to 45.1) | 44.5 ± 1.0 44.6 (44.2 to 45.2) | p = 0.04 * | |
| Posterior Curvature Mean ± SD Median (CI) | Kflat | −6.2 ± 0.2 −6.2(−6.3 to −6.0) | −6.1 ± 0.2 −6.2(−6.3 to −5.9) | p = 0.07† |
| Ksteep | −6.5 ± 0.2 −6.50(−6.6 to −6.4) | −6.4 ± 0.2 −6.5(−6.6 to −6.4) | p = 0.16† | |
| Kmax | −6.3 ± 0.2 −6.3(−6.5 to −6.2) | −6.3 ± 0.2 −6.3(−6.5 to −6.2) | p=0.06 † | |
| Anterior Segment OCT (μm) | ||||
|---|---|---|---|---|
| Morning | Afternoon | |||
| Pachymetry Mean ± SD Median (CI) | Central | 549.2 ± 30.5 553.5 (544.9 to 556.4) | 542.7 ± 31.8 533.5 (531.2 to 554.2) | p = 0.034 * |
| Temporal | 556.4 ± 31.9 548.0 (538.2 to 560.2) | 549.3 ± 32.3 541.0 (537.2 to 560.7) | p = 0.034 * | |
| Nasal | 571.8 ± 33.2 561.0 (559.8 to 583.8) | 566.3 ± 34.5 557.0 (553.8 to 578.7) | p = 0.08 * | |
| Epithelial Thickness Mean ± SD Median (CI) | Central | 54.3 ± 3.4 54.0 (52.7 to 55.1) | 53.9 ± 3.2 54.0 (52.7 to 55.1) | p > 0.05† |
| Temporal | 53.0 ± 3.6 53.0 (51.3 to 53.5) | 52.4 ± 3.0 53.0 (51.3 to 53.5) | p > 0.05 * | |
| Nasal | 53.6 ± 3.6 54.0 (52.1 to 54.3) | 53.3 ± 3.0 54.0 (52.1 to 54.3) | p > 0.05 * | |
| Superior | 52.2 ± 3.1 53.0 (51.1 to 53.3) | 51.9 ± 3.0 53.0 (50.8 to 53.1) | p > 0.05† | |
| Inferior | 55.1 ± 3.4 56.0 (53.6 to 56.6) | 54.7 ± 4.2 55.0 (53.2 to 56.2) | p > 0.05 * | |
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