Int Ophthalmol DOI 10.1007/s10792-014-9985-x
ORIGINAL PAPER
The conjunctival sensitivity in soft contact lens wearers Tsutomu Igarashi • Masafumi Ono • Chiaki Fujimoto • Hisaharu Suzuki • Hiroshi Takahashi
Received: 28 March 2014 / Accepted: 1 August 2014 Ó Springer Science+Business Media Dordrecht 2014
Abstract We determined the influence of soft contact lenses (SCLs) on conjunctival sensitivity. A total of 26 volunteers (11 males, 15 females; mean age 28.3 ± 4.6 years; range 22-39 years) without dry eye were enrolled in the study. Subjects with a low corneal touch threshold, atopic keratoconjunctivitis, or vernal keratoconjunctivitis were excluded. In 26 participants, 12 were disposable SCL wearers. Touch thresholds were determined using a Cochet–Bonnet esthesiometer with a 0–60 mm nylon monofilament in 5 mm increments. The length (mm) was converted to tension (g/mm2). Mean touch sense thresholds in the SCL wearers (n = 12) and non-wearers (n = 14) were 10.7 ± 2.57 and 24.6 ± 7.3 g/mm2 in the whole conjunctiva, and 9.07 ± 3.02 and 19.2 ± 7.8 g/mm2 in the upper palpebral conjunctiva, respectively. Significant differences were observed in all locations (p \ 0.01). The enhanced conjunctival sensitivity associated with SCL use may contribute to the dry eye-like symptoms in SCL users who do not have dry eye.
Introduction The use of soft contact lenses (SCLs) has become the principal means of refractive correction for hundreds of millions of people around the world [1]. However, SCL use can lead to complications such as corneal ulcers, corneal neovascularization, or giant papillary conjunctivitis. One of the reported risk factors associated with SCL use is a reduction of the corneal nerve function. Although corneal sensitivity is commonly used to assess the reduction, the mechanism responsible for these changes remains unknown [2]. Paradoxically, many SCL users who complain about corneal stimulation or dry eye-like symptoms rarely have dry eye. This suggests that factors other than corneal sensitivity may be related to the cause of these symptoms. Even so, we speculate that the conjunctival sensitivity does play a role in the overall phenomenon. Therefore, we measured the conjunctival sensitivity in volunteers and analyzed the effect of wearing SCLs.
Keywords Conjunctiva Cornea Sensitivity Contact lens Cochet–Bonnet esthesiometer
Methods
T. Igarashi (&) M. Ono C. Fujimoto H. Suzuki H. Takahashi Department of Ophthalmology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8602, Japan e-mail: [email protected]
This study was a prospective, clinic-based study conducted in compliance with the regulations of our Institutional Review Board, and the tenants of the Declaration of Helsinki. Informed consent was obtained from all participants before any clinical evaluations were performed.
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A total of 26 healthy volunteers (11 males, 15 females; mean age 28.3 ± 4.6 years; range 2239 years) were enrolled in the study. Out of the 26 participants, 12 wore disposable low oxygen permeable SCLs (5 males, 7 females) and 14 did not wear any CLs (6 males, 8 females). Conjunctival papillae were observed in 14 subjects (6 males, 8 females); while 12 others exhibited no papillae (5 males, 7 females). All participants wore SCLs at least 8 h per day, 6–7 days per week, and had been wearing these types of lenses for more than 1 year. The contact lens wearers were required to remove their SCLs on the night before the examinations. As it is known that corneal sensitivity is age-dependent, this study only enrolled subjects who were in their twenties and thirties [3]. Prior to being enrolled in the study, all participants underwent examinations to confirm they did not have dry eye, as diagnosed by the 2006 Japanese criteria [4]. Subjects were excluded from the study if a Cochet-Bonnet esthesiometer determined the corneal touch threshold was less than 5 mm. We also excluded subjects who had atopic keratoconjunctivitis or vernal keratoconjunctivitis, as these patients have been reported to have a significantly lower corneal sensitivity than healthy subjects [5]. Since 14 participants who did not exhibit any symptoms were found to have tarsal conjunctival papillae that were less than 1 mm, we further examined the influence of the papillae by comparing these 14 subjects to 12 other subjects without any papillae. None of the participants had a history of Stevens-Johnson syndrome, or any prior chemical, thermal, or radiation injury. In addition, none of the subjects exhibited any other systemic disorders or had previously undergone any ocular surgeries that could induce ocular surface problems. Contact lens wearers were required to remove their SCLs on the night before the examinations. Touch thresholds in all subjects were determined using a Cochet-Bonnet esthesiometer with a 0-60 mm nylon monofilament in 5 mm increments. All of the lengths (mm) were converted to tension (g/mm2). During this evaluation, subjects were asked to indicate exactly when the stimulus was first felt. Sensitivity was defined as the length of the filament that gave a 50 % positive response for a minimum of three stimulus applications. The touch threshold was determined in the upper and lower palpebral, and in the nasal and temporal bulbar conjunctiva in both eyes of all subjects. The mean length was calculated based on
123
Table 1 The contingency table for SCL wear and the presence/absence of conjunctival papillae in the 26 participants
the results of the three individual tests that were performed. A single ophthalmologist (T.I.) performed the measurements in all of the subjects. An unpaired Student’s t test was used for all analyses (Table 1).
Results Effect of wearing SCLs The mean conjunctival thresholds for all locations tested in the SCL (n = 12) and non-SCL wearers (n = 14) were 10.7 ± 2.57 and 24.6 ± 7.3 g/mm2 (p = 0.0001), respectively (Fig. 1a). The mean thresholds for the SCL and non-SCL wearers in the upper palpebral conjunctiva were 9.07 ± 4.81 and 19.15 ± 11.481 g/mm2 (p = 0.0001), while they were 12.33 ± 3.02 and 45.31 ± 42.77 g/mm2 (p = 0.0003) in the lower palpebral conjunctiva, 10.89 ± 7.91 and 18.7 ± 11.6 g/mm2 (p = 0.004) in the nasal bulbar conjunctiva, and 10.38 ± 5.91 and 15.34 ± 10.64 g/mm2 (p = 0.024) in the temporal bulbar conjunctiva, respectively (Fig. 1b). There were no significant differences observed between the male and female subjects. The mean thresholds in the male and female SCL wearers were 12.38 ± 2.89 and 10.67 ± 3.04 g/mm2 (p = 0.13), while the thresholds for the male and female non-SCL wearers were 24.55 ± 11.3 and 24.68 ± 10.0 g/mm2 (p = 0.98), respectively.
Effect of the conjunctival papillae The mean conjunctival thresholds for all locations tested in the subjects with (n = 14) and without conjunctival papillae (n = 12) were 19.5 ± 7.96 and 17.1 ± 6.21 g/mm2 (p = 0.3), respectively (Fig. 2a).
Int Ophthalmol Fig. 1 Conjunctival sensitivity in soft contact lens wearers and noncontact lens wearers. The average tension from the whole conjunctiva is shown in (a). The average tension from the upper palpebral, lower palpebral, nasal bulbar and temporal bulbar conjunctiva is shown in (b)
Fig. 2 Conjunctival sensitivity in subjects with conjunctival papillae and non-conjunctival papillae. The average tension from the whole conjunctiva is shown in (a). The average tension from the upper palpebral, lower palpebral, nasal bulbar and temporal bulbar conjunctiva is shown in (b). p? with conjunctival papillae; p- nonconjunctival papillae
The thresholds for the subjects with and without the papillae in the upper palpebral conjunctiva were 14.38 ± 9.49 and 16.8 ± 12.36 g/mm2 (p = 0.18), while they were 31.99 ± 36.958 and 26.13 ± 32.47 g/mm2 (p = 0.36) in the lower palpebral conjunctiva, 16.81 ± 11.74 and 12.33 ± 8.32 g/mm2 (p = 0.0883) in the nasal bulbar conjunctiva, and 13.18 ± 7.91 and 13.16 ± 9.78 g/mm2 (p = 0.36) in the temporal bulbar conjunctiva, respectively (Fig. 2b). There were no significant differences observed between the male and female subjects. The mean thresholds for males and females with conjunctival papillae were 18.58 ± 7.19 and 19.53 ± 11.63 g/mm2 (p = 0.59), while the thresholds in the male and female subjects
without conjunctival papillae were 20.69 ± 14.06 and 14.09 ± 9.29 g/mm2 (p = 0.35), respectively.
Discussion One side effect of wearing SCLs is a reduction of the corneal sensitivity [2, 6–10], although the exact mechanism has yet to be elucidated. In addition, another study has reported a finding that SCL wearers have a decreased sensitivity in the limbal zone [11]. In contrast, there have been quite a few reports on the sensitivity in the conjunctiva. Golebiowski et al. reported that while inferior conjunctival sensitivity
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in low oxygen permeable SCL wearers was not different from the sensitivity in the control nonwearers, there was decreased sensitivity in the high oxygen transmissible SCL wearers [12]. However, Stapleton et al. found that wearing high oxygen permeable SCLs resulted in an increased inferior conjunctival sensitivity, while wearing low oxygen permeable SCLs had no effect on the sensitivity [13]. Even though the SCLs used by all of the participants in the current study were disposable low oxygen permeable SCLs, we found a significant enhancement of the conjunctival sensitivity for all locations in the SCL users. This enhancement was particularly noted in the palpebral conjunctiva (Fig. 1). Thus, contrary to the findings of the Stapleton study, our current results suggest that this type of SCL does enhance the conjunctival sensitivity. These different findings may be related to both the measurement locations and the method used in each of the studies. In the previous studies, the authors measured the sensitivity of the inferior conjunctiva (2 mm below the limbus) using an air-jet esthesiometer [12, 13]. In the current study, however, we used a Cochet-Bonnet esthesiometer to evaluate the sensitivity in the upper and lower palpebral, and nasal and temporal bulbar conjunctiva. Thus, these methodological differences could have led to the contrasting results observed between the two studies. Since SCLs often cause papillae in the palpebral conjunctiva [14], we evaluated the difference of conjunctival sensitivity between SCL wearers with and without papillae. Our results indicated that there were no significant differences (data not shown; p = 0.3). Furthermore, when only the effect of the papillae was evaluated, we also observed no significant difference in the conjunctival sensitivity (Fig. 2). Thus, our findings suggest that the conjunctival sensitivity may not be affected by conjunctival papillae less than 1 mm, regardless of SCL use. Previous studies have hypothesized that the change in the conjunctival threshold in CL wearers is related to the gender of the subject [15–17]. However, we observed no gender differences in our current study. Conjunctival sensation changes in long-term SCLs wearers, adding consideration of reports of ocular surface using In Vivo Confocal Microscopy (IVCM) [18–20] and the review of two of TFOS [21, 22]. Other recent IVCM studies have also revealed that there are subtle changes of the ocular surface at the cellular
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level in vivo in the conjunctiva and meibomian glands (MGs) of CL wearers. In the eyelid, it has been reported that there is an increase of epithelial cell density, and a loss and hypofunction of the MG [18–20]. Additionally, bulbar conjunctiva, thinning of the epithelium, and squamous conversions that are similar to those seen in Sjo¨gren’s syndrome [20] have been reported to occur in SCL wearers [21]. The results of our current study suggest that the pathological changes that occurred due to the mechanical stimulation associated with long-term SCL use might have caused the decreases of the conjunctival threshold. Small papillae have been found to occur in healthy individuals as well as CL wearers. However, consistent with our current results, there have yet to be any direct links found between CL discomfort and these typical non-pathological changes [22]. Most of the sensory nerve fibers innervating the cornea and the bulbar conjunctiva are polymodal nociceptors, which can be activated by noxious mechanical energy, heat, and a large variety of chemical mediators. In addition, the sensitivity of the tarsal conjunctiva has been especially difficult to evaluate due to technical issues [21]. The reason for the differences between the results of the previous reports and our current findings could be that different techniques were used in each of the studies. In conclusion, the current study found enhanced conjunctival sensitivity in SCL users. This phenomenon may contribute to the dry eye-like symptoms in SCL users who do not have dry eye. Further examinations will need to be undertaken in order to elucidate the reason for this increased conjunctival sensitivity in SCL users. Acknowledgments This work was supported in part by a Grant-in-Aid for Young Scientists (B) (23792014) from MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan). Conflict of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper.
References 1. Key JE (2007) Development of contact lenses and their worldwide use. Eye Contact Lens 33:343–345; discussion 362-343
Int Ophthalmol 2. Murphy PJ, Patel S, Marshall J (2001) The effect of longterm, daily contact lens wear on corneal sensitivity. Cornea 20:264–269 3. Norn MS (1973) Conjunctival sensitivity in normal eyes. Acta Ophthalmol (Cph) 51:58–66 4. Shimazaki J, Tsubota K, Kinoshita S, Ohashi Y (2007) Definition and diagnosis of dry eye: 2006 [in Japanese]. J Eye 24:181–184 5. Hu Y, Matsumoto Y, Dogru M, Okada N, Igarashi A, Fukagawa K, Tsubota K, Fujishima H (2007) The differences of tear function and ocular surface findings in patients with atopic keratoconjunctivitis and vernal keratoconjunctivitis. Allergy 62:917–925 6. Epstein AB (2006) Contact lens care products effect on corneal sensitivity and patient comfort. Eye Contact Lens 32:128–132 7. Millodot M (1978) Effect of long-term wear of hard contact lenses on corneal sensitivity. Arch Ophthalmol 96:1225–1227 8. Millodot M, Henson DB, O’Leary DJ (1979) Measurement of corneal sensitivity and thickness with PMMA and gaspermeable contact lenses. Am J Optom Physiol Optom 56:628–632 9. Sanaty M, Temel A (1998) Corneal sensitivity changes in long-term wearing of hard polymethylmethacrylate contact lenses. Ophthalmologica 212:328–330 10. Velasco MJ, Bermudez FJ, Romero J, Hita E (1994) Variations in corneal sensitivity with hydrogel contact lenses. Acta Ophthalmol (Cph) 72:53–56 11. McGowan DP, Lawrenson JG, Ruskell GL (1994) Touch sensitivity of the eyelid margin and palpebral conjunctiva. Acta Ophthalmol (Cph) 72:57–60 12. Golebiowski B, Papas EB, Stapleton F (2012) Corneal and conjunctival sensory function: the impact on ocular surface sensitivity of change from low to high oxygen transmissibility contact lenses. Invest Ophthalmol Vis Sci 53:1177–1181
13. Stapleton F, Tan ME, Papas EB, Ehrmann K, Golebiowski B, Vega J, Holden BA (2004) Corneal and conjunctival sensitivity to air stimuli. Br J Ophthalmol 88:1547–1551 14. Takamura E, Uchio E, Ebihara N, Ohno S, Ohashi Y, Okamoto S, Kumagai N, Satake Y, Shoji J, Nakagawa Y, Namba K, Fukagawa K, Fukushima A, Fujishima H (2011) Japanese guideline for allergic conjunctival diseases. Allergol Int 60:191–203 15. Millodot M, Lamont A (1974) Influence of menstruation on corneal sensitivity. Br J Ophthalmol 58:752–756 16. Sanaty M, Temel A (1998) Corneal sensitivity changes in long-term wearing of hard polymethylmethacrylate contact lenses. Ophthalmologica 212:328–330 17. Macri A, Pflugfelder S (2000) Correlation of the Schirmer 1 and fluorescein clearance tests with the severity of corneal epithelial and eyelid disease. Arch Ophthalmol 118:1632–1638 18. Efron N, Al-Dossari M, Pritchard N (2010) Confocal microscopy of the bulbar conjunctiva in contact lens wear. Cornea 29:43–52 19. Villani E, Ceresara G, Beretta S et al (2011) In vivo confocal microscopy of meibomian glands in contact lens wearers. Invest Ophthalmol Vis Sci 52:5215–5219 20. Villani E, Baudouin C, Efron N et al (2014) In vivo confocal microscopy of the ocular surface: from bench to bedside. Curr Eye Res 39:213–231 21. Efron N, Jones L, Bron AJ (2013) The TFOS international workshop on contact lens discomfort: report of the contact lens interactions with the ocular surface and adnexa subcommittee. Invest Ophthalmol Vis Sci 54:TFOS98– TFOS122 22. Stapleton F, Marfurt C, Golebiowski B (2013) The TFOS international workshop on contact lens discomfort: report of the subcommittee on neurobiology. Invest Ophthalmol Vis Sci 54:TFOS71–TFOS97
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ORIGINAL PAPER
The conjunctival sensitivity in soft contact lens wearers Tsutomu Igarashi • Masafumi Ono • Chiaki Fujimoto • Hisaharu Suzuki • Hiroshi Takahashi
Received: 28 March 2014 / Accepted: 1 August 2014 Ó Springer Science+Business Media Dordrecht 2014
Abstract We determined the influence of soft contact lenses (SCLs) on conjunctival sensitivity. A total of 26 volunteers (11 males, 15 females; mean age 28.3 ± 4.6 years; range 22-39 years) without dry eye were enrolled in the study. Subjects with a low corneal touch threshold, atopic keratoconjunctivitis, or vernal keratoconjunctivitis were excluded. In 26 participants, 12 were disposable SCL wearers. Touch thresholds were determined using a Cochet–Bonnet esthesiometer with a 0–60 mm nylon monofilament in 5 mm increments. The length (mm) was converted to tension (g/mm2). Mean touch sense thresholds in the SCL wearers (n = 12) and non-wearers (n = 14) were 10.7 ± 2.57 and 24.6 ± 7.3 g/mm2 in the whole conjunctiva, and 9.07 ± 3.02 and 19.2 ± 7.8 g/mm2 in the upper palpebral conjunctiva, respectively. Significant differences were observed in all locations (p \ 0.01). The enhanced conjunctival sensitivity associated with SCL use may contribute to the dry eye-like symptoms in SCL users who do not have dry eye.
Introduction The use of soft contact lenses (SCLs) has become the principal means of refractive correction for hundreds of millions of people around the world [1]. However, SCL use can lead to complications such as corneal ulcers, corneal neovascularization, or giant papillary conjunctivitis. One of the reported risk factors associated with SCL use is a reduction of the corneal nerve function. Although corneal sensitivity is commonly used to assess the reduction, the mechanism responsible for these changes remains unknown [2]. Paradoxically, many SCL users who complain about corneal stimulation or dry eye-like symptoms rarely have dry eye. This suggests that factors other than corneal sensitivity may be related to the cause of these symptoms. Even so, we speculate that the conjunctival sensitivity does play a role in the overall phenomenon. Therefore, we measured the conjunctival sensitivity in volunteers and analyzed the effect of wearing SCLs.
Keywords Conjunctiva Cornea Sensitivity Contact lens Cochet–Bonnet esthesiometer
Methods
T. Igarashi (&) M. Ono C. Fujimoto H. Suzuki H. Takahashi Department of Ophthalmology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8602, Japan e-mail: [email protected]
This study was a prospective, clinic-based study conducted in compliance with the regulations of our Institutional Review Board, and the tenants of the Declaration of Helsinki. Informed consent was obtained from all participants before any clinical evaluations were performed.
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Int Ophthalmol
A total of 26 healthy volunteers (11 males, 15 females; mean age 28.3 ± 4.6 years; range 2239 years) were enrolled in the study. Out of the 26 participants, 12 wore disposable low oxygen permeable SCLs (5 males, 7 females) and 14 did not wear any CLs (6 males, 8 females). Conjunctival papillae were observed in 14 subjects (6 males, 8 females); while 12 others exhibited no papillae (5 males, 7 females). All participants wore SCLs at least 8 h per day, 6–7 days per week, and had been wearing these types of lenses for more than 1 year. The contact lens wearers were required to remove their SCLs on the night before the examinations. As it is known that corneal sensitivity is age-dependent, this study only enrolled subjects who were in their twenties and thirties [3]. Prior to being enrolled in the study, all participants underwent examinations to confirm they did not have dry eye, as diagnosed by the 2006 Japanese criteria [4]. Subjects were excluded from the study if a Cochet-Bonnet esthesiometer determined the corneal touch threshold was less than 5 mm. We also excluded subjects who had atopic keratoconjunctivitis or vernal keratoconjunctivitis, as these patients have been reported to have a significantly lower corneal sensitivity than healthy subjects [5]. Since 14 participants who did not exhibit any symptoms were found to have tarsal conjunctival papillae that were less than 1 mm, we further examined the influence of the papillae by comparing these 14 subjects to 12 other subjects without any papillae. None of the participants had a history of Stevens-Johnson syndrome, or any prior chemical, thermal, or radiation injury. In addition, none of the subjects exhibited any other systemic disorders or had previously undergone any ocular surgeries that could induce ocular surface problems. Contact lens wearers were required to remove their SCLs on the night before the examinations. Touch thresholds in all subjects were determined using a Cochet-Bonnet esthesiometer with a 0-60 mm nylon monofilament in 5 mm increments. All of the lengths (mm) were converted to tension (g/mm2). During this evaluation, subjects were asked to indicate exactly when the stimulus was first felt. Sensitivity was defined as the length of the filament that gave a 50 % positive response for a minimum of three stimulus applications. The touch threshold was determined in the upper and lower palpebral, and in the nasal and temporal bulbar conjunctiva in both eyes of all subjects. The mean length was calculated based on
123
Table 1 The contingency table for SCL wear and the presence/absence of conjunctival papillae in the 26 participants
the results of the three individual tests that were performed. A single ophthalmologist (T.I.) performed the measurements in all of the subjects. An unpaired Student’s t test was used for all analyses (Table 1).
Results Effect of wearing SCLs The mean conjunctival thresholds for all locations tested in the SCL (n = 12) and non-SCL wearers (n = 14) were 10.7 ± 2.57 and 24.6 ± 7.3 g/mm2 (p = 0.0001), respectively (Fig. 1a). The mean thresholds for the SCL and non-SCL wearers in the upper palpebral conjunctiva were 9.07 ± 4.81 and 19.15 ± 11.481 g/mm2 (p = 0.0001), while they were 12.33 ± 3.02 and 45.31 ± 42.77 g/mm2 (p = 0.0003) in the lower palpebral conjunctiva, 10.89 ± 7.91 and 18.7 ± 11.6 g/mm2 (p = 0.004) in the nasal bulbar conjunctiva, and 10.38 ± 5.91 and 15.34 ± 10.64 g/mm2 (p = 0.024) in the temporal bulbar conjunctiva, respectively (Fig. 1b). There were no significant differences observed between the male and female subjects. The mean thresholds in the male and female SCL wearers were 12.38 ± 2.89 and 10.67 ± 3.04 g/mm2 (p = 0.13), while the thresholds for the male and female non-SCL wearers were 24.55 ± 11.3 and 24.68 ± 10.0 g/mm2 (p = 0.98), respectively.
Effect of the conjunctival papillae The mean conjunctival thresholds for all locations tested in the subjects with (n = 14) and without conjunctival papillae (n = 12) were 19.5 ± 7.96 and 17.1 ± 6.21 g/mm2 (p = 0.3), respectively (Fig. 2a).
Int Ophthalmol Fig. 1 Conjunctival sensitivity in soft contact lens wearers and noncontact lens wearers. The average tension from the whole conjunctiva is shown in (a). The average tension from the upper palpebral, lower palpebral, nasal bulbar and temporal bulbar conjunctiva is shown in (b)
Fig. 2 Conjunctival sensitivity in subjects with conjunctival papillae and non-conjunctival papillae. The average tension from the whole conjunctiva is shown in (a). The average tension from the upper palpebral, lower palpebral, nasal bulbar and temporal bulbar conjunctiva is shown in (b). p? with conjunctival papillae; p- nonconjunctival papillae
The thresholds for the subjects with and without the papillae in the upper palpebral conjunctiva were 14.38 ± 9.49 and 16.8 ± 12.36 g/mm2 (p = 0.18), while they were 31.99 ± 36.958 and 26.13 ± 32.47 g/mm2 (p = 0.36) in the lower palpebral conjunctiva, 16.81 ± 11.74 and 12.33 ± 8.32 g/mm2 (p = 0.0883) in the nasal bulbar conjunctiva, and 13.18 ± 7.91 and 13.16 ± 9.78 g/mm2 (p = 0.36) in the temporal bulbar conjunctiva, respectively (Fig. 2b). There were no significant differences observed between the male and female subjects. The mean thresholds for males and females with conjunctival papillae were 18.58 ± 7.19 and 19.53 ± 11.63 g/mm2 (p = 0.59), while the thresholds in the male and female subjects
without conjunctival papillae were 20.69 ± 14.06 and 14.09 ± 9.29 g/mm2 (p = 0.35), respectively.
Discussion One side effect of wearing SCLs is a reduction of the corneal sensitivity [2, 6–10], although the exact mechanism has yet to be elucidated. In addition, another study has reported a finding that SCL wearers have a decreased sensitivity in the limbal zone [11]. In contrast, there have been quite a few reports on the sensitivity in the conjunctiva. Golebiowski et al. reported that while inferior conjunctival sensitivity
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in low oxygen permeable SCL wearers was not different from the sensitivity in the control nonwearers, there was decreased sensitivity in the high oxygen transmissible SCL wearers [12]. However, Stapleton et al. found that wearing high oxygen permeable SCLs resulted in an increased inferior conjunctival sensitivity, while wearing low oxygen permeable SCLs had no effect on the sensitivity [13]. Even though the SCLs used by all of the participants in the current study were disposable low oxygen permeable SCLs, we found a significant enhancement of the conjunctival sensitivity for all locations in the SCL users. This enhancement was particularly noted in the palpebral conjunctiva (Fig. 1). Thus, contrary to the findings of the Stapleton study, our current results suggest that this type of SCL does enhance the conjunctival sensitivity. These different findings may be related to both the measurement locations and the method used in each of the studies. In the previous studies, the authors measured the sensitivity of the inferior conjunctiva (2 mm below the limbus) using an air-jet esthesiometer [12, 13]. In the current study, however, we used a Cochet-Bonnet esthesiometer to evaluate the sensitivity in the upper and lower palpebral, and nasal and temporal bulbar conjunctiva. Thus, these methodological differences could have led to the contrasting results observed between the two studies. Since SCLs often cause papillae in the palpebral conjunctiva [14], we evaluated the difference of conjunctival sensitivity between SCL wearers with and without papillae. Our results indicated that there were no significant differences (data not shown; p = 0.3). Furthermore, when only the effect of the papillae was evaluated, we also observed no significant difference in the conjunctival sensitivity (Fig. 2). Thus, our findings suggest that the conjunctival sensitivity may not be affected by conjunctival papillae less than 1 mm, regardless of SCL use. Previous studies have hypothesized that the change in the conjunctival threshold in CL wearers is related to the gender of the subject [15–17]. However, we observed no gender differences in our current study. Conjunctival sensation changes in long-term SCLs wearers, adding consideration of reports of ocular surface using In Vivo Confocal Microscopy (IVCM) [18–20] and the review of two of TFOS [21, 22]. Other recent IVCM studies have also revealed that there are subtle changes of the ocular surface at the cellular
123
level in vivo in the conjunctiva and meibomian glands (MGs) of CL wearers. In the eyelid, it has been reported that there is an increase of epithelial cell density, and a loss and hypofunction of the MG [18–20]. Additionally, bulbar conjunctiva, thinning of the epithelium, and squamous conversions that are similar to those seen in Sjo¨gren’s syndrome [20] have been reported to occur in SCL wearers [21]. The results of our current study suggest that the pathological changes that occurred due to the mechanical stimulation associated with long-term SCL use might have caused the decreases of the conjunctival threshold. Small papillae have been found to occur in healthy individuals as well as CL wearers. However, consistent with our current results, there have yet to be any direct links found between CL discomfort and these typical non-pathological changes [22]. Most of the sensory nerve fibers innervating the cornea and the bulbar conjunctiva are polymodal nociceptors, which can be activated by noxious mechanical energy, heat, and a large variety of chemical mediators. In addition, the sensitivity of the tarsal conjunctiva has been especially difficult to evaluate due to technical issues [21]. The reason for the differences between the results of the previous reports and our current findings could be that different techniques were used in each of the studies. In conclusion, the current study found enhanced conjunctival sensitivity in SCL users. This phenomenon may contribute to the dry eye-like symptoms in SCL users who do not have dry eye. Further examinations will need to be undertaken in order to elucidate the reason for this increased conjunctival sensitivity in SCL users. Acknowledgments This work was supported in part by a Grant-in-Aid for Young Scientists (B) (23792014) from MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan). Conflict of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper.
References 1. Key JE (2007) Development of contact lenses and their worldwide use. Eye Contact Lens 33:343–345; discussion 362-343
Int Ophthalmol 2. Murphy PJ, Patel S, Marshall J (2001) The effect of longterm, daily contact lens wear on corneal sensitivity. Cornea 20:264–269 3. Norn MS (1973) Conjunctival sensitivity in normal eyes. Acta Ophthalmol (Cph) 51:58–66 4. Shimazaki J, Tsubota K, Kinoshita S, Ohashi Y (2007) Definition and diagnosis of dry eye: 2006 [in Japanese]. J Eye 24:181–184 5. Hu Y, Matsumoto Y, Dogru M, Okada N, Igarashi A, Fukagawa K, Tsubota K, Fujishima H (2007) The differences of tear function and ocular surface findings in patients with atopic keratoconjunctivitis and vernal keratoconjunctivitis. Allergy 62:917–925 6. Epstein AB (2006) Contact lens care products effect on corneal sensitivity and patient comfort. Eye Contact Lens 32:128–132 7. Millodot M (1978) Effect of long-term wear of hard contact lenses on corneal sensitivity. Arch Ophthalmol 96:1225–1227 8. Millodot M, Henson DB, O’Leary DJ (1979) Measurement of corneal sensitivity and thickness with PMMA and gaspermeable contact lenses. Am J Optom Physiol Optom 56:628–632 9. Sanaty M, Temel A (1998) Corneal sensitivity changes in long-term wearing of hard polymethylmethacrylate contact lenses. Ophthalmologica 212:328–330 10. Velasco MJ, Bermudez FJ, Romero J, Hita E (1994) Variations in corneal sensitivity with hydrogel contact lenses. Acta Ophthalmol (Cph) 72:53–56 11. McGowan DP, Lawrenson JG, Ruskell GL (1994) Touch sensitivity of the eyelid margin and palpebral conjunctiva. Acta Ophthalmol (Cph) 72:57–60 12. Golebiowski B, Papas EB, Stapleton F (2012) Corneal and conjunctival sensory function: the impact on ocular surface sensitivity of change from low to high oxygen transmissibility contact lenses. Invest Ophthalmol Vis Sci 53:1177–1181
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