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ORIGINAL ARTICLE
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Evaluation of corneal biomechanical properties in spherical and toric soft contact lens wear


 Dr. D. Y. Patil Institute of Optometry and Visual Sciences, Pune, Maharashtra, India

Date of Submission15-Jun-2020
Date of Decision16-Dec-2020
Date of Acceptance29-Dec-2020

Correspondence Address:
Neeta Mishra,
Dr. D. Y. Patil Institute of Optometry and Visual Sciences, Pimpri, Pune, Maharashtra
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjdrdypu.mjdrdypu_339_20

  Abstract 


Purpose: Corneal hysteresis (CH) and corneal resistance factor was found to be less for patient wearing toric contact lens as compared to soft spherical CH was calculated as the difference in air pressures between force-in applanation (P1) and force-out applanation (P2), or (P1–P2). Materials and Methods: This was the prospective study, 40 eyes of 22 patients with mean age of 22.09 ± 4.05 years. Eleven eyes were fitted with soft toric contact lens and 29 eyes were fitted with soft spherical contact lens. Dry eye, keratoconic or any systemic pathology were excluded. Soft toric and soft spherical contact lenses (Comfilcon A, Coopervision, and Southampton, UK) were fitted. The Ocular response Analyzer (Reichert Ophthalmic Instruments, Depew, New York, USA) was used to measure CH before and after 3 months using soft toric and soft spherical contact lenses. Descriptive statistics were used to analyze the demographic data. Paired t-test was employed for analyzing the difference between the base line value of CH with soft toric and soft spherical contact lens wearers after 3 months. Independent t-test was used to find the association between CH and gender. Results: CH was found to be lesser after 3 months of soft toric contact lens wear, as compared with soft spherical contact lenses. Mean increase of CH was found to range from 10.44 ± 0.96to 10.80 ± 0.96 mmHg (P = 0.000). Conclusion: In this study, there was a decrease in CH after using soft toric contact lenses and increase after using soft spherical contact lenses for 3 months. The increased CH with soft spherical contact lens was reversible in nature. However, CH may differ between lens type and modality of wear which can lead to long-term changes in the corneal biomechanical properties.

Keywords: Central corneal thickness, corneal hysteresis, keratometry



How to cite this URL:
Mishra N, Tandale M, Madan V, Chotaliya R, Bajare U. Evaluation of corneal biomechanical properties in spherical and toric soft contact lens wear. Med J DY Patil Vidyapeeth [Epub ahead of print] [cited 2021 Dec 6]. Available from: https://www.mjdrdypv.org/preprintarticle.asp?id=321293




  Introduction Top


Cornea is a transparent optical surface of the eye which accounts two-third of the eye's refractive power;[1] however, it is considered as a soft tissue whose biochemical and physical property is depended on the component present in the cornea. It is viscoelastic in nature Corneal biomechanics is a branch of science that deals with the deformation and equilibrium of corneal tissue under the application of any force.[2] Corneal hysteresis (CH) represents the biomechanical property of cornea which assess the cornea's ability to absorb and dissipate energy.[3] There is a recent trend to evaluate corneal biomechanics including CH in different corneal conditions such as refractive surgery, ocular disease (glaucoma, keratoconus).[2]

Biomechanical properties provide a valuable information about the risk, progression and the effectiveness of various therapy given to glaucoma patients where decreased in CH indicate worsening glaucoma and faster visual field progression.[4] Study proved that CH in high myopic patients are lower compared to normal subjects.[5] It will be worth to investigate the changes of CH with contact lens wear.

Conkaya et al. reported that myopic subjects wearing contact lenses have higher CH than noncontact lens wearers.[6] Tyagi et al. reported that soft toric contact lenses can lead to changes in corneal shape and thickness after fitting two types of soft spherical (hydrogel and silicone hydrogel) and two types of toric soft (hydrogel and silicone hydrogel) contact lenses.[7] It has been observed that long term use of soft contact lens can lead to changes in the viscoelastic properties of the cornea.[8] Moghadam et al. has stated that CH and corneal resistance factor decreased significantly 1 month after fitting toric soft contact lens while Central corneal thickness and keratometry mean did not change significantly.[9]

Thus, existing literature on CH are quiet limited and fails to establish a proper correlation of CH between soft spherical and soft toric contact lens. We have tried to however establish the difference in CH between soft spherical and soft toric contact lenses.


  Materials and Methods Top


Approval was taken prior to the study from Institutional Review Board and university ethical committee ref no DYP/EC/449/2019. Informed consent was signed by all the subjects who were included in the study.[10] It was a prospective observational study done at a tertiary eye care center. Forty eyes of 22 subjects were included, aged between 18 and 40 years, astigmatism ranged between min 0.75 to min 2 Diopters and spherical power ranged from 0.25 to 10 diopters (myopic and hypermetropic). Patients having a history of systemic and ocular disease or any pathological condition, Dry eye and Irregular astigmatism were excluded from the study.

Clinical procedure

All the patients underwent a complete ophthalmological examination. Ocular response analyzer (reichert ophthalmic instruments [ORA], Depew, New York, USA) was performed which mainly measures corneal biomechanics determines the CH. This instrument is used in glaucoma department to analyze the visual field loss calculating CH for the glaucoma patients. It is a noninvasive device used to measure the biomechanical properties of the cornea. Principle is based on the noncontact tonometry which is mainly used to check intra ocular pressure (IOP) in glaucoma patients. ORA provides the measurements of CH and two different IOP parameters IOP compensated for corneal thickness (IOPcc) and IOP related to Goldman applanation tonometer (IOPg) We used the instrument to calculate CH caused by soft toric and soft spherical contact lens. The calculation was done by calculating the difference in air pressures between force-in applanation, it is the first pressure to ablate the cornea (P1) and force-out applanation. It is the pressure of air recorded when the cornea resumes its shape after P1. The average of P1 and P2 gives IOPcc and IOPg.

Soft spherical and toric contact lenses (Comfilcon A) were fitted to the patients according to their refractive errors. All the patients were advised to use the contact lens for 3 months and to revisit the clinic for follow-up. Patients were asked to restrain themselves from contact lens wear at least for 2 h before they come for follow-up visit. After 3 months, CH was evaluated using ORA.

Data analysis

Data were analyzed using SPSS software (version 17.0, IBM, Chicago, IL, USA). The Shapiro–Wilk test was employed to test normal distribution of the data.

Descriptive statistics were used to analyze the demographic data.

Paired t-test was employed for analyzing the difference between the base line value of CH with soft toric and soft spherical contact lens wearers after 3 months.

Independent t-test was used to find the association between CH and gender and P < 0.05 would be considered as statistically significant.


  Results Top


A total of 40 eyes of 22 patients with mean age of 22.09 ± 4.05 years (range 18–40) where 60% was female and 40% was male subjects were enrolled. Out of 40 eyes, 11 eyes were fitted with soft toric contact lens and 29 eyes were fitted with soft spherical contact lens. Mean value of sphere power was − 1.46 ± 1.12 D (−0.25 to − 4.00 D), cylinder power was − 1.00 ± 0.65 D (−0.50 to − 2.00 D) were found in this present study.

CH was not significantly (P = 0.198) different after 3 months of contact lens wear from the baseline observation [Table 1].
Table 1: Corneal hysteresis after 3 months of contact lens wear from baseline

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There was a significant (P = 0.00) increase in CH after 3 months of spherical contact lens wear [Table 2].
Table 2: Corneal hysteresis after 3 months of spherical contact lens wear

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There was a significant (p=0.004) decrease in corneal hysteresis after three months of soft toric contact lens wear from baseline observation[Table 3].
Table 3: Corneal hysteresis after 3 months of toric contact lens wear

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  Discussion Top


Soft contact lenses are widely prescribed to correct the different refractive conditions as well as the therapeutic conditions of the eye. It was found that soft contact lens causes stromal corneal edema which mainly increases the spacing between collagen fibrils and also affects the biomechanical properties of the cornea.[11]

Xu et al. in 2008 conducted a study on changes in corneal biomechanical properties after Long-Term Soft Contact Lens Wear, where they proved that there was an alteration in CH among the contact lens wears.[8]

Moghadam et al. in 2016 performed a study on corneal biomechanical changes following toric soft contact lens wear where they concluded that CH and corneal resistance factor decreased significantly 1 month after fitting toric soft contact lens,[9] However, this present study showed that there was a significant decrease in CH in soft toric contact lens wear group after 3 months.

This present study also revealed that there was a significant increase in the CH among the soft spherical contact lens wearers after 3 months. However, a study conducted by Tyagi et al. reported that there was subtle flattening in the anterior corneal surface and steepening in the posterior corneal surface 8 h after using toric soft and soft contact lenses. They concluded that posterior curvature was more affected by the soft contact lens, which they attributed to differences in structure and composition of the stroma which can alter the biomechanical properties of the cornea.[7]

However in contrary, Kisser et al. in 2009, have reported that long term usage of soft contact lens may not alter the corneal biomechanical properties.[12]

Xu et al. in 2008 stated that long term use of soft contact lens can lead to changes in the viscoelastic properties of the cornea.[8] Based on the literatures available and the present study results on the effect of contact lens wear on CH are contradictory to each other.


  Conclusion Top


This present study reestablishes the fact that CH may alter with the use of soft toric and soft spherical contact lens and also conclude that influence on CH may differ between soft spherical and soft toric contact lens which mainly results a change in corneal biomechanical properties.

Thus, the present study further emphasizes the need of evaluating long-term changes in the corneal biomechanics and their effect in healthy CL wear with large sample size and for longer duration.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Williams L, Arthur HO, Reyes M, Sulaiman S, Terry R, Sweeney D. Module 1: Anterior Segment of the Eye. 1st ed.. [email protected](https://iacle.org): IACLE Contact Lens Course; 2000.  Back to cited text no. 1
    
2.
Garcia-Porta N, Fernandes P, Queiros A, Salgado-Borges J, Parafita-Mato M, González-Méijome JM. Corneal biomechanical properties in different ocular condition and new measurement techniques. ISRN Ophthalomol 2014;2014:724546.  Back to cited text no. 2
    
3.
Hussnain SA, Teng CC. The role of cornea in glaucoma management: Central corneal thickness and corneal hysteresis. Am Acad Ophthalmol 2017;39:425-30.  Back to cited text no. 3
    
4.
Schultz SK .Corneal hysteresis as a potential glaucoma biomarker. Am Acad Ophthalmol 2017;14:2255-64.  Back to cited text no. 4
    
5.
Shen M, Fan F, Xue A, Wang J, Zhou X, Lu F. Biomechanical properties of the cornea in high myopia. Vision Res 2008;48:2167-71.  Back to cited text no. 5
    
6.
Ali BC, Emrullah B, Faruk O. The effect of contact lens changes in biomechanical properties in myopic patients. Cornea 2012;31:764-9.  Back to cited text no. 6
    
7.
Tyagi G, Collins M, Read S, Davis B. Regional changes in corneal thickness and shape with soft contact lenses. Optom Vis Sci 2010;87:567-75.  Back to cited text no. 7
    
8.
Xu S, Cai C, Wang J, Shen M. Changes in corneal biomechanical properties after long-term soft contact lens wear. Ophthalmol Vis Sci 2008;49:661.  Back to cited text no. 8
    
9.
Radaie-Moghadam S, Hashemi H, Jafarzadehpur E, Yekta AA, Khabazkhoob M. Corneal biomechanical changes following toric soft contact lens wear. J Ophthalmic Vis Res 2016;11:131-5.  Back to cited text no. 9
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10.
Sathi Devi AV. The ocular surface analyser. Journal of Current Glaucoma Practice 2009;3:24-7.  Back to cited text no. 10
    
11.
Farrell RA, Hart RW. On the theory of the spatial organization of macromolecules in connective tissue. Bull Math Biophys 1969;31:727-60.  Back to cited text no. 11
    
12.
Kissner A, Boehm AG, Pillunat LE, Spoerl E. Effect of soft contact lens wear on corneal biomechanical properties. Ophthalmol Vis Sci 2009;50:1753.  Back to cited text no. 12
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

 
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