Table of Contents  
ORIGINAL ARTICLE
Year : 2013  |  Volume : 6  |  Issue : 3  |  Page : 245-249  

A study of corneal endothelial changes in soft contact lens wearers using non-contact specular microscopy


Department of Ophthalmology, Padmashree Dr D Y Patil Medical College, Hospital and Research Centre, Dr D Y Patil Vidyapeeth, Pune, India

Date of Web Publication5-Jul-2013

Correspondence Address:
Renu M Magdum
F-7, Harsh Vihar, New D P Road, Aundh, Pune, Maharashtra
India
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Source of Support: Indian Council of Medical Research (ICMR) New Delhi (Short Term Studentship Project), Conflict of Interest: None


DOI: 10.4103/0975-2870.114645

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  Abstract 

Aim: To study the corneal endothelial changes after soft contact lens wear, to correlate these changes with the duration of soft contact lens wear, and to study the pattern of use and preferences of contact lens among young adults. Materials and Methods: This observational study was carried out in 100 eyes of 50 soft contact lens users aged between 19 and 27 years. Both eyes of 50 medical students who had never worn contact lenses served as controls. Data from each subject were collected using a structured questionnaire of 24 items that included demographic profile, pattern of contact lens use, symptoms, brand name, number of years worn, and hours of daily wear. These data were analyzed using Chi square for association. Specular microscopy was done using TOPCON SP-3000P. Computerized morphometry was used to evaluate central corneal thickness, size, shape, mean cellular density, hexagonality, coefficient of variation, and polymegathism of the corneal cells . Results: It was found that central corneal thickness was 0.532 ± 0.0309 mm in lens users and 0.514 ± 0.03 mm in controls, cell density was 2570.91 ± 432.06 cells/mm 2 in lens users and 2723.17 ± 327.64 cells/mm 2 in controls, while hexagonality was 54.81 ± 39.72% in lens users and 67.65 ± 36.49% in controls. Conclusion: Despite the known effects of long duration of soft contact lens use on corneal endothelial cell morphology, this study could not draw a significant correlation between them. However, a significant difference was found in the corneal endothelial thickness, cell density, and hexagonality. Among the soft contact lens users, 62% used soft disposable type while 38% used soft extended wear contact lens. Contact lenses were preferred over spectacles for better cosmetic appearance, comfort, and wider visual field.

Keywords: Endothelium, hexagonality, polymegathism, specular microscopy


How to cite this article:
Magdum RM, Mutha N, Maheshgauri R. A study of corneal endothelial changes in soft contact lens wearers using non-contact specular microscopy. Med J DY Patil Univ 2013;6:245-9

How to cite this URL:
Magdum RM, Mutha N, Maheshgauri R. A study of corneal endothelial changes in soft contact lens wearers using non-contact specular microscopy. Med J DY Patil Univ [serial online] 2013 [cited 2019 Jul 23];6:245-9. Available from: http://www.mjdrdypu.org/text.asp?2013/6/3/245/114645


  Introduction Top


Corneal clarity is critical for good vision. The corneal endothelium consists of a single layer of flat hexagonal cells in a mosaic form. It controls corneal hydration and is permeable to oxygen and other nutrients from aqueous humor. Contact lenses are small, thin, plastic disks designed to rest on cornea to correct refractive errors. However, wearing contact lenses involves routinely placing a foreign body on the cornea which may lead to altered anatomy and physiology. Prolonged lens wear may cause corneal hypoxia resulting in fluid accumulation in the stroma. Numerous investigators have demonstrated morphologic changes in the corneal endothelial cells of wearers of many types of contact lenses, i.e. hard, soft, and extended wear soft lenses. [1],[2],[3] Such changes may be indicative of cell stress due to chronic hypoxia, which leads to lactate accumulation, elevated carbon dioxide levels, and pH changes. Pleomorphism may be a sensitive indicator of the health of corneal endothelium [4],[5] and polymegathism may be indicative of altered cell function. Hence, the functional capacity of corneal endothelium may be correlated to its morphologic appearance.

Corneal endothelial morphology can be measured with different instruments, including contact specular microscopes, non-contact specular microscopes, and confocal microscopes. Early versions of specular microscopes were contact types that needed the water immersion objective lens and dipping cone to lie directly on the corneal surface to obtain higher magnification and better resolution. Therefore, patients' tolerance was a problem when taking a measurement. With improvements in technology, modern versions of the wide-field specular microscopes are non-contact; they are more patient friendly and can achieve equally high magnification. Non-contact specular microscope has been widely used in studies of corneal endothelial cell changes after contact lens wear.

The aim of study was to study the corneal endothelial changes after soft contact lens wear, to correlate these changes with the duration of soft contact lens wear, and to study the pattern of use and preferences of contact lens among young adults.


  Materials and Methods Top


This observational study was carried out in 100 eyes of 50 soft contact lens users aged between 19 and 27 years. Both eyes of 50 medical students who had never worn contact lenses served as controls. Rigid gas permeable (RGP) lens users and cases with any corneal disease or endothelial dystrophies were excluded from this study. A detailed history of the duration of contact lens use, type of contact lens, any symptoms of foreign body sensation, photophobia or dryness, and redness of eyes was recorded. Data from each subject were collected using a structured questionnaire of 24 items that included demographic profile, pattern of contact lens use, brand name, number of years worn, and hours of daily wear. These data were analyzed using Chi square for association. Specular microscopy was done using TOPCON SP-3000P [Figure 1]. Computerized morphometry was used to evaluate central corneal thickness (CCT) and size, shape, mean cellular density, hexagonality, coefficient of variation, and polymegathism of the corneal endothelial cells [Figure 2]. Outcome (dependent) variables for this study were corneal endothelial cell density (ECD), coefficient of variation, and percentage of hexagonal cells. These were analyzed separately. The independent variables were age in years, gender, refractive error, contact lens type, and duration of contact lens wear. To compare the parameters describing morphology between the lens wearers and the control groups, the t-test and the Mann-Whitney test were used. To quantify the relationship between morphologic parameters and duration of soft contact lens wear, univariate regression analysis was used. Averages of parameters were used for the analysis.
Figure 1: Specular microscope

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Figure 2: Screen of specular microscope

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  Results Top


Both eyes of 50 medical students with a history of regular long-term soft contact lens use since 1-10 years and equal number of controls with no history of soft contact lens use were included in this study. Out of the 100 medical students, 73 were myopic with mean refractive error of −2.9 ± 1.9 Diopters in the right eye and −3.15 ± 1.9 Diopters in the left eye. Of these, 50 used soft contact lenses and constituted the study group. Of the 50 controls, 23 used spectacles for correcting myopia and 27 were emmetropes. Duration of soft contact lens wear varied between 1 and 10 years. All were regular users with mean daily wear of 9.24 ± 2.69 h. None of the users wore soft contact lenses overnight. Among the soft contact lens users, 62% used soft disposable type contact lens, while 38% used soft extended type contact lens.

Among the contact lens users, the common complaints included occasional redness, itching, and dryness of eyes, especially on prolonged wear. Out of the 50 lens users, 21 complained of dry eyes, 18 for red eyes, 23 had watering after long hours of wear, 25 felt discomfort, while 14 experienced infections and frequent deposits related to contact lens wear. None of these were having acute infection or deposits at the time of evaluation.

Regression Model of Central Corneal Thickness

CCT in lens users varied from 0.469 to 0.623 mm, with a mean of 0.532 ± 0.0309 mm.

[Figure 3] and [Figure 4] show the univariate scatter plots of CCT versus the duration of lens wear in years and hours per day, respectively.
Figure 3: Central corneal thickness as per duration in years

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Figure 4: Central corneal thickness as per duration in hours per day

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CCT in controls varied from 0.422 to 0.576 mm, with a mean of 0.514 ± 0.03 mm. Duration of soft contact lens use less than 3 years had mean thickness of 0.532 ± 0.0279 mm and those with longer duration of wear had the mean of 0.532 ± 0.0325 mm.

Soft disposable type of contact lenses had mean CCT of 0.535 ± 0.0325 mm and that for daily wear contact lenses was 0.528 ± 0.0281 mm thickness.

Regression Model of Endothelial Cell Density

In contact lens wearers, ECD varied from 1786 to 4217 cells/mm 2 , with a mean of 2570.91 ± 432.06 cells/mm 2 , while in controls it varied from 2041 to 3865 cells/mm 2 , with a mean of 2723.17 ± 327.64 cells/mm 2 .

[Figure 5] and [Figure 6] show the univariate scatter plots of ECD versus the duration of lens wear in years and hours per day, respectively. Duration of soft contact lens use less than 3 years had mean cell density of 2677.53 ± 561.81 cells/mm 2 and those with longer duration of wear had the mean cell density of 2520.74 ± 349.001 cells/mm 2 .
Figure 5: Endothelial cell density as per duration of lens wear in years

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Figure 6: ECD as per duration of hours per day

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Mean ECD in soft disposable type of contact lens users was 2598.77 ± 459.045 cells/mm 2 and in soft extended wear contact lens users was 2525.45 ± 385.542 cells/mm 2 .

Regression Model of Percentage of Hexagonality of the Endothelial Cells

Hexagonality of endothelial cells in contact lens users varied from 0 to 100%, with a mean of 54.81 ± 39.72%. Hexagonality in controls also varied from 0 to 100%, with a mean of 67.65 ± 36.49%.

[Figure 7] and [Figure 8] show the univariate scatter plots of endothelial cell hexagonality (HEX) versus the duration of lens wear in years and hours per day, respectively.
Figure 7: Hexagonality as per duration of lens wear per year

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Figure 8: Hexagonality as per duration of lens wear in hours per day

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Duration of soft contact lens use less than 3 years had mean hexagonality of 42.81 ± 41.76% and those with longer duration of wear had the mean hexagonality of 60.46 ± 37.73%.

Mean hexagonality in soft disposable type of contact lens users was 53.37 ± 39.36%, while in soft extended wear contact lens users it was 57.16 ± 40.72%.


  Discussion Top


In this study, soft contact lens wearing group of duration 1-10 years and an equal number of control group subjects were investigated in order to determine the morphologic changes in the corneal endothelium due to soft contact lens wear, and these changes were correlated to the duration of soft contact lens wear. Parameters studied were CCT, ECD, and cellular hexagonality.

In our study, we found that the mean CCT of the lens wearing group was more than that of the control group. If contact lens wearers and controls were grouped together, very highly significant (<0.0001) correlation was found between the CCT changes and lens use. This finding does not agree with the findings of clinical examination as none of the patients complained of intermittent blurring of vision which is the presenting symptom of corneal edema.

Various similar studies have reported increased thickness of central cornea following daily soft contact lens wear. [6],[7],[8] However, Holden and Mertz, in their study of critical oxygen levels needed to avoid corneal edema in daily and extended wear contact lens users, concluded that daily lens wear did not induce increased thickness of cornea. [9] Carlson and co-workers also found no difference in the CCT between contact lens wearers and controls. [10] Similar results have been obtained in some other studies as well. [10],[11]

A possible explanation for the varying results in our study could be that the lens wearing group was examined for their corneas within 5 min of lens removal in contrast to other studies which gave an overnight gap. [7],[12],[13],[14] Also, all the corneas were examined in the afternoon between 4 PM and 6 PM after several hours of lens wear.

The second morphologic parameter taken into account was the ECD. The mean cell density was found to be less in the soft lens wearing group than seen in the control group. If contact lens wearers and controls were grouped together, highly significant (<0.01) correlation was found between the variation in ECD and lens use.

This hypothesis is supported by studies stating small decrease in ECD in long-term soft contact lens wear. [15] MacRae and associates used the term "contact lens-induced endotheliopathy," because these changes may represent pathologic processes that may result in premature cell death and reduced ECD. [16] In 2002, a study observed very low mean cell density only in contact lens wearers, [6] and a decade back, Lee et al. [17] also found a significant decrease in cell density among soft lens wearers. These findings disagree with those of earlier studies, in which no effect was found of long-term soft contact lens wear on the ECD. [7],[14]

The third parameter recorded was the endothelial cellular hexagonality. In our study, the mean hexagonality was found to be less in the soft lens wearing group than seen in the control group. If contact lens wearers and controls were grouped together, significant (<0.05) correlation was found between the variation in hexagonality and lens use.

This study supports the hypothesis that the numbers of hexagonal cells are generally reduced to about 50-60% of the endothelial mosaic and they also tend to deviate from the normal hexagonal pattern. Endothelium of eyes exposed to soft lens wear is often characterized by irregular-shaped cells. The findings in this study correspond with the earlier findings reported by other groups [15],[6],[10],[11],[13] which also state that percentage of hexagonal cells in the center in contact lens wearers is reduced as compared to the controls.

The second objective of our study was to study the effect of duration of contact lens wear on corneal endothelium. When these parameters were compared using regression analysis with the duration of lens wear in years and hours per day separately, we saw that no significant correlation was found. This finding is similar to the investigations of Carlson and co-workers. [10]

However, Lee et al. [17] carried out a comparative study of corneal endothelial changes induced by different durations of soft contact lens wear. They found that all soft contact lens subgroups had a significantly greater coefficient of variation in cell size than non-contact lens users. The proportion of hexagonal cells and the mean corneal endothelial density in those using lenses for more than 6 years were significantly lower than in the control group. The different result we obtained could be because the duration of soft lens wear in our study group was not more than 10 years. Another explanation could be the technical and methodological errors. The value of the clinical non-contact specular microscope used in this study may be limited by the extremely small field of view of the image obtained. Secondly, only one photograph was taken.

Our third objective in this study was to study the pattern and preferences of soft lens use. Maximum of the lens users in this study wore the monthly disposable type of soft lens. While all used it for daytime daily wear, none of them wore lenses during sleep. However, there was a considerable proportion that used the extended wear type which was yearly disposable. 97% of the lens users preferred lenses from Bausch and Lomb. 60% of the lens users preferred soft lenses for cosmetic purpose.

Despite the known effects of long duration of soft contact lens wear on corneal endothelial cell morphology, this study could not draw a significant correlation between them. However, it was seen that all eyes were altered by contact lens wear. Fortunately, a large majority of contact lens wearers enjoyed the benefits of comfort and excellent vision without experiencing any significant ill effects.

 
  References Top

1.MacRae SM, Matsuda M, Yee R. The effect of long term hard contact lens wear on the corneal endothelium. CLAO J 1985;11:322-6.  Back to cited text no. 1
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2.MacRae SM, Matsuda M, Shellans R, Rich LF. The effects of hard and soft contact lenses on the corneal endothelium. Am J Ophthalmol 1986;102:50-7.  Back to cited text no. 2
    
3.Hirst LW, Auer C, Cohen J, Tseng SC, Khoudadost AA. Specular microscopy of hard contact lens wearers. Ophthalmology 1984;91:1147-53.  Back to cited text no. 3
    
4.Stevenson RW, Kirkness CM. Corneal endothelial irregularity with long term contact lens wear. Cornea 1992;11:600-3.  Back to cited text no. 4
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5.Schoessler JP. Corneal endothelial polymegathism associated with extended wear. Int Contact Lens Clin 1983;10:148-55.  Back to cited text no. 5
    
6.Liesegang TJ. Physiologic changes of the cornea with contact lens wear. CLAO J 2002;28:12-27.  Back to cited text no. 6
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7.Holden BA, Sweeney DF, Vannas A, Nilsson KT, Efron N. Effects of long-term extended contact lens wear on the human cornea. Invest Ophthalmol Vis Sci 1985;26:1489-501.  Back to cited text no. 7
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8.Kaufman SC, Hamano H, Beuerman RW, Laird JA, Thompson HW. Transient corneal stromal and endothelial changes following soft contact lens wear: A study with confocal microscopy. CLAO J 1996;22:127-32.  Back to cited text no. 8
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9.Holden BA, Mertz GW. Critical oxygen levels to avoid corneal edema for daily and extended wear contact lenses. Invest Ophthalmol Vis Sci 1984;25:1161-7.  Back to cited text no. 9
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10.Carlson KH, Bourne WM, Brubaker RF. Effect of long-term contact lens wear on corneal endothelial cell morphology and function. Invest Ophthalmol Vis Sci 1988;29:185-93.  Back to cited text no. 10
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11.Nieuwendaal CP, Odenthal MT, Kok JH, Venema HW, Oosting J, Riemslag XF, et al. Morphology and function of the corneal endothelium after long-term contact lens wear. Invest Ophthalmol Vis Sci 1994;35:3071-7.  Back to cited text no. 11
    
12.Holden BA, Merrz GW, McNolly JJ. Corneal swelling response to contact lenses worn under extended wear conditions. Invest Ophthalmol Vis Sci 1983;24:218-26.  Back to cited text no. 12
    
13.Bourne WM, Hodge DO, McLaren JW. Estimation of corneal endothelium pump function in long term contact lens wearers. Invest Ophthalmol Vis Sci 1999;40:603-11.  Back to cited text no. 13
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14.Patel SV, McLaren JW, Hodge DO, Bourne WM. Confocal microscopy in vivo in corneas of long term contact lens wearers. Invest Ophthalmol Vis Sci 2002;43:995-1003.  Back to cited text no. 14
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15.Ventocilla M. Chief Editor: Hampton Roy Sr. In: Ventocilla M, Roy H, Editors. Contact Lens Complications. Available from: http://www.emedicine.medscape.com/article/1196459-overview. [Last updated Oct 17,2012] [Last accessed on 2011 Mar 8].  Back to cited text no. 15
    
16.MacRae SM, Matsuda M, Phillips DS. The long term effects of polymethylmethaacrylate contact lens on the corneal endothelium. Ophthalmology 1994;101:365-70.  Back to cited text no. 16
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17.Lee JS, Park WS, Lee SH, Oum BS, Cho BM. A comparative study of corneal endothelial changes induced by different durations of soft contact lens wear. Graefes Arch Clin Exp Ophthalmol 2001;239:1-4.  Back to cited text no. 17
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]



 

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