|Year : 2018 | Volume
| Issue : 4 | Page : 216-220
Assessment of corneal thickness in soft contact lens users using anterior segment optical coherence tomography
Nehal A Hasan1, Ahmed H Aldghaimy2, Mohamed A Hamed2, Doaa A Ahmed2
1 Depertment of Ophthalmology, Cairo University, Cairo, Egypt
2 Depertment of Ophthalmology, South Valley University, Qena, Egypt
|Date of Submission||19-Jun-2018|
|Date of Acceptance||04-Sep-2018|
|Date of Web Publication||20-Dec-2018|
Mohamed A Hamed
Department of Ophthalmology, Qena Faculty of Medicine, South Valley University, Qena 83523
Source of Support: None, Conflict of Interest: None
Purpose The aim of this study was to evaluate the effect of soft contact lens (SCL) use on corneal thickness measured by anterior segment optical coherence tomography (AS-OCT).
Patients and methods The epithelial and overall thicknesses of both the central cornea and the nasal and temporal cornea of SCL wearers (25 patients) were obtained by AS-OCT and compared with those of refraction‐matched controls (25 individuals) and patients with emmetropia (25 patients).
Results The mean corneal epithelial thickness in SCL-wearing, spectacle-wearing, and emmetropic groups was 48.13±2.39, 51.92±2.81, and 53.13±2.11 μm, respectively. The corneal epithelium of members of the SCL group was significantly thinner than both the spectacle-wearing and emmetropic groups (P=0.000 and 0.006, respectively). The central corneal thickness in SCL-wearing, spectacle-wearing, and emmetropic groups was 517.67±21.95, 562.53±20.58, and 547.83±26.71 μm, respectively. The corneal thickness of the SCL group was significantly thinner than both the spectacle-wearing and emmetropic groups (P=0.0395 and 0.0255, respectively).
Conclusion Contact lens wear is related to thinning of both corneal thickness and epithelium. AS-OCT is a noninvasive and clinically applicable technique used to assess assessing the involvement of the cornea in contact lens wearers.
Keywords: anterior segment, contact lens, corneal thickness, optical coherence tomography
|How to cite this article:|
Hasan NA, Aldghaimy AH, Hamed MA, Ahmed DA. Assessment of corneal thickness in soft contact lens users using anterior segment optical coherence tomography. Delta J Ophthalmol 2018;19:216-20
|How to cite this URL:|
Hasan NA, Aldghaimy AH, Hamed MA, Ahmed DA. Assessment of corneal thickness in soft contact lens users using anterior segment optical coherence tomography. Delta J Ophthalmol [serial online] 2018 [cited 2019 Sep 18];19:216-20. Available from: http://www.djo.eg.net/text.asp?2018/19/4/216/248088
| Introduction|| |
The interaction between the contact lens (CL) and the ocular surface is a key area of interest for clinical practice. Mechanical forces exerted when the eyelid moves over the CL are transmitted from the anterior to the posterior surface of the lens and subsequently to the cornea and conjunctiva .
Technology has exploited this interaction to improve the biomechanical interaction between the CL and the ocular surface; however, many questions remain on how to cope with these dynamic forces. A slit-lamp biomicroscope is often used for in-vivo visualization of the gross appearance of the cornea. Impression cytology can be used for ex-vivo evaluation of the corneal surface epithelium ,,; however, these techniques limit the capacity to take cross‐sectional thickness measurements of the corneal layers.
Anterior segment optical coherence tomography (AS‐OCT) is being used more widely in clinical studies, for example, to investigate the thickness changes of the total cornea and epithelium .
Using this technology, corneal epithelial involvement in soft contact lens (SCL) wearers has been reported.
The aim of this study was to evaluate the effect of SCL use on corneal thickness measured by AS-OCT.
| Patients and methods|| |
This is a prospective, case–control study. Patients were selected from the Outpatient Clinic of Ophthalmology Department, Qena University Hospital. Patients in the age range between 18 and 40 years of both sexes were included in the study.
The study was approved by the Local Ethical Committee of Qena University and all participants signed a written informed consent to participate in the study.
Participants were divided into three groups:
- Group A: 25 CL wearers for more than 1 year.
- Group B: 25 spectacle wearers.
- Group C: 25 healthy control participants.
- Age range between 18 and 40 years.
- No contraindication for CL wear.
- Patients with symptoms of ocular surface diseases.
- Chronic eye-drop use.
- Patients with any ocular surgery.
All participants underwent an ophthalmic examination including visual acuity, autorefractometry, slit-lamp examination, applanation tonometry, and ophthalmoscopy.
All CL wearers were asked to wear their CLs in the morning and to remove them 1 h before measurements were taken.
Both eyes of all participants were assessed and all measurements were carried out between 9:00 a.m. and 2:00 p.m. Epithelial and overall thicknesses of the cornea were measured by Spectralis OCT (Heidelberg Engineering GmbH, Heidelberg, Germany). Anterior segment lens system images were obtained from the central cornea using the anterior segment 5 Line raster scanning protocol, which scans through five parallel lines all 3.0 mm in length and separated by 250 μm. Corneal images were captured with well-defined anterior and posterior surfaces and images with the least number of motion artifacts were chosen for analysis. The epithelial and overall thicknesses of the cornea were measured using the caliper tools on the OCT device ([Figure 1]).
|Figure 1 Epithelial and overall corneal thicknesses of the central cornea.|
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The qualitative variables were recorded as frequencies and percentages, and were compared using the χ2-test. The quantitative measures were presented as mean±SD and were compared using the Student t-test. Regression analysis was carried out and the correlation between different variables was assessed as indicated. A P value less than 0 · 05 was considered significant. All analyses were carried out using the IBM SPSS Statistics for Windows, Version 20.0 (SPSS; IBM Corp., Armonk, New York, USA).
| Results|| |
The mean corneal epithelial thickness in SCL-wearing, spectacle-wearing, and emmetropic groups was 48.13±2.39, 51.92±2.81, and 53.13±2.11 μm, respectively ([Table 1]). The corneal epithelium of the patients in the SCL group was significantly thinner than both the spectacle-wearing and emmetropic groups (P=0.000 and 0.006, respectively; [Table 2]). The central corneal thickness in SCL-wearing, spectacle-wearing, and emmetropic groups was 517.67±21.95, 562.53±20.58, and 547.83±26.71 μm, respectively ([Table 1]). The corneal thickness of the SCL group was significantly thinner than both the spectacle-wearing and emmetropic groups (P=0.0395 and 0.0255, respectively; [Table 2]).
In addition, the nasal cornea was thicker than the temporal cornea in the three groups ([Table 3]). A moderate negative correlation was found between the thickness of the cornea and duration of CL use ([Table 4]).
|Table 4 Relation between duration of contact lens use and thickness in group A|
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In group A, the correlation between thickness and duration of CL use was examined as shown in Tables 4 and 5. There was a significant negative correlation between the two measurements, suggesting that corneal thickness is related inversely to the duration of CL use.
| Discussion|| |
The current study was designed to investigate the differences in overall and epithelial thickness of the cornea in patients who had worn SCLs for a minimum of 1 year compared with patients who used spectacles for refractive error correction and control participants who had no refractive error.
In this study, we observed a significantly thinner corneal epithelium in the SCL group (48.13±2.38 μm) compared with the emmetropic group (53.13±2.105 μm)
In addition, in the present study, the corneal epithelial thickness and the central corneal thickness did not differ between the spectacle-wearing group, which had a mean spherical equivalent refraction of −2.70±1.63 diopters, and the emmetropic group.
In the current study, patients in the emmetropic group had a mean central corneal epithelial thickness of 53.13±2.11 µm, which is in agreement with the Haque et al.  study, which reported a value of 54± 2 μm. However, in group A, the mean central corneal epithelial thickness was 48.13±2.38 μm, which was slightly lower than that reported by the Haque et al.  study (50±4 μm).
In the present study, the mean central corneal epithelial thickness in group C was 53.13±2.11 µm, which was in agreement with the result of the Hong et al.  study, which was 54.4±1.1 μm. In addition, in group A, the mean central corneal epithelial thickness was 48.13±2.38 μm, which was in agreement with the Hong et al.  study (49.2±1.9 μm).
This study reported slightly lower values than the Feng and Simpson  study in group C, which had a mean central corneal epithelial thickness of 54.7±1.9 μm.
This study was in agreement with the Reinstein et al.  study in the mean central corneal epithelial thickness of group C, which was 53.4±4.6 μm. However, the Reinstein et al.  study used digital ultrasound scanning to measure the epithelial thickness of the cornea.
This study was in agreement with the Eckard et al.  study in the mean central corneal epithelial thickness of group C, which was 54±7 μm. The Eckard et al.  study used a confocal Rostock laser scanning microscope.
The Jalbert et al.  study used a modified optical pachymetry and observed thinner corneal epithelium in CL users (46±4 μm) than in non-CL users (58±9 μm). Similarly, the Pérez et al.  study used a modified optical pachymeter and showed that lens wearers had significantly thinner epithelium (41±8 μm) than controls (48±5 μm), which was lower than the current study.
We found that the corneal epithelial thickness in the SCL group was significantly thinner than in both the spectacle-wearing and emmetropic groups. Our result showed that epithelial thinning in SCL wearers was associated with the CL usage and not with refractive error.
To the best of our knowledge, stromal thinning is a chronic pathophysiologic change that can occur in patients who have worn CLs for more than a year .
In this study, corneal thinning was observed in the CL user group with a mean corneal thickness of 517.67±21.95 μm compared with the spectacle user group (562.53±20.58 μm) and the emmetropic group (547.83±25.71 μm), which is in agreement with the Sanchis et al.  study, who used Orbscan pachymetry to measure the central corneal thickness before (552±7.14 μm) and after CL use (545±8.35 μm) and observed a decline in central corneal thickness after CL use, although their result was higher than that in the present study.
The I Skeleli et al.  study found that corneal thickness in CL wearers (510.57±27.2 μm) was thinner than the normal group (526.43±31.14 μm) and this was in agreement with the present study, with a slightly higher result obtained in our study.
The results of the Ersan et al.  study were not in agreement with those of the present study; they did not observe central corneal thinning in CL users (541.82±33.97 μm) and emmetropes (540.43±38.14 μm). They reported that epithelial thinning occurred without stromal change, which may be because of corneal epithelial metabolic impairment, without impairment in the corneal stroma, in which the metabolism is supported by the aqueous humor and may also be associated with direct dynamic contact between the corneal epithelium and the CL.
In this study, the nasal corneal thickness in group A was 528±22 μm and the temporal corneal thickness was 512±20 μm, whereas in groups B and C, the nasal corneal thickness was 543±45 μm and the temporal corneal thickness was 531±45 μm; this was in agreement with the Yeniad et al.  study, which used corneal topography in the assessment of corneal thickness in CL users and a normal control group and found that the nasal corneal thickness in CL users was 583±40 μm and the temporal corneal thickness in CL users was 515±40 μm, whereas the nasal corneal thickness in controls was 528±60 μm and the temporal corneal thickness in controls was 521±40 μm.
The specific reason for this corneal thinning has not yet been established. Possible explanations for this phenomenon include chronic edema of the corneal stroma and biochemical changes in the corneal stroma composition ,. Structural alterations in stromal keratocytes in response to chronic edema interfere with the synthesis of stromal tissue and result in gradual stromal thinning . Two other factors may also contribute toward this corneal thinning . One of these factors is increased tear osmolality, which has been reported to occur in CL wearers . Chronic exposure to a hyperosmotic tear film has been reported to be capable of inducing generalized corneal thinning . Another possible cause for this phenomenon could be increased apoptosis of keratocytes and epithelial cells in the corneas of CL wearers . Chronic microtrauma and hypoxia induced by CLs, especially wear of poorly fitting CLs, may contribute toward these increased levels .
| Conclusion|| |
In the present study, we showed that the corneal epithelial thickness and central corneal thickness in the SCL group were significantly thinner than in both the spectacle-wearing and emmetropic groups. In addition, the corneal thickness was inversely related to the duration of CL use.
The corneal epithelial thickness and central corneal thickness did not differ between the spectacle-wearing group, with a mean spherical equivalent refraction of −2.70±1.63 diopters, and the emmetropic group.
AS‐OCT is a noninvasive and clinically applicable technique for assessing the involvement of the cornea in CL wearers.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]