|Year : 2015 | Volume
| Issue : 1 | Page : 6-9
The effects of rigid gas-permeable contact lens wear on tear film of eyes with keratoconus
Nuha Fath-Elrahman1, Ibrahim Merghani1, Mustafa Abdu1, Kamal Hashim Binnawi2
1 Department of contact lenses, Faculty of Optometry and Visual Science, Al-Neelain University, Khartoum, Sudan
2 Faculty of Medicine, Al-Neelain University, Khartoum, Sudan
|Date of Web Publication||17-Jun-2015|
Department of contact lenses, Faculty of Optometry and Visual Science, Al-Neelain University, Khartoum
Aim: This is a comparative retrospective study aimed to determine the effect of contact lens wearing on the tear film of patients with keratoconus. Material and Methods: A total number of 150 were screened and 66.67% (100 patients) were found to fulfill the criteria of selection (35.7% males and 64.3% females). The patients were divided into two groups wearing RGP (medium Dk) (50%) and not wearing contact lenses (50%). The tear film quality and quantity were evaluated using tear break-up time (TBUT) and Schirmer test. Results: One hundred patients were included in the study, of which 66% were in the age group of 21 - 31 years. Eighty eight percent of the patients wearing contact lenses between 6 months and one year, and 82% of them have moderate keratoconus. Ninety one percent (46% wearing contact lens and 45% not wearing contact lenses) were found with tear break up time less than normal. About 65% (36% wearing contact lenses and 23% not wearing contact lenses) of patients showed abnormal tear volume (6% dry eye and 59% watery eye). Independent sample t- test showed significant differences in TBUT and Schimer test between males and females wearing and not wearing contact lenses (p < 0.05). Conclusion: Tear quality and quantity were abnormal in patients with keratoconus wearing contact lenses than those with keratoconus not wearing contact lenses. Eye care practitioner may benefit from these findings in the care and management of keratoconus patients.
Keywords: Contact lenses, keratoconus, Schirmer test, tear break up time
|How to cite this article:|
Fath-Elrahman N, Merghani I, Abdu M, Binnawi KH. The effects of rigid gas-permeable contact lens wear on tear film of eyes with keratoconus. Sudanese J Ophthalmol 2015;7:6-9
|How to cite this URL:|
Fath-Elrahman N, Merghani I, Abdu M, Binnawi KH. The effects of rigid gas-permeable contact lens wear on tear film of eyes with keratoconus. Sudanese J Ophthalmol [serial online] 2015 [cited 2021 Sep 20];7:6-9. Available from: https://www.sjopthal.net/text.asp?2015/7/1/6/158989
| Introduction|| |
Keratoconus, which was first described in detail in 1854, derives from the Greek words Kerato (cornea) and Konos (cone).  Keratoconus is the most common primary ectasia. The condition is noninflammatory, self-limiting ectasia of the axial portion of the cornea. It is characterized by thinning and steepening of the central or paracentral cornea that leads to a reduction in vision.  Corneal thinning normally occurs in the inferio-temporal and central part of the cornea. A superior portion also has found to be affected.  The incidence appears to be similar between females and males, with slightly higher incidence in males.  Keratoconus is always bilateral with 2% to 7% of the cases being unilateral. 
The cause of keratoconus is unknown. Some studies have found that keratoconus runs in families,  and it found to be happening more often in people with certain ocular and systemic conditions such as allergic conditions, chronic eye rubbing, but most often, there is no eye injury or disease that could explain why the eye starts to change. ,,
Keratoconus usually begins in the teenage years,  but it can also start in childhood or up to about age of 30 years. The changes in the shape of the cornea occur slowly and gradually, usually over several years. 
In the early stages, keratoconus can be treated with spectacles or regular soft contact lenses.  Custum soft toric contact lenses as keratosoft lenses and Novakone lenses are designed to treat mild to moderate keratoconus.  However, as the disease progresses the cornea becomes more irregular and spectacles or soft lenses no longer can treat it, so that rigid gas-permeable (RGP) contact lenses are the options used to correct moderate and advanced keratoconus.  Some patients with mild or advanced keratoconus cannot tolerate RGP contact lenses they can be corrected with piggy baking contact lenses in which RGP contact lenses are fitted over soft lenses.  Different hybrid contact lenses were designed specifically for keratoconus. These hybrid contact lenses combine rigid center with a soft peripheral skirt to increase comfort and tolerance. 
Contact lens wear can increase dry eye symptoms because all contact lens materials significantly and adversely affected tear physiology by increasing the evaporation rate and decreasing tear thinning time.  Keratoconus was reported to affect significantly tear functions, which seem to get worse with the extent of keratoconus.  Few studies have reported the effect of RGP contact lens wear on tear film of eyes with keratoconus. This study aimed to evaluate the effect of RGP contact lens wear on the tear film quality and quantity among keratoconic patients.
| Materials and methods|| |
The study is a cross-sectional hospital based study. All keratoconus patients (wearing and not wearing RGP contact lenses) who attended Makka Eye Complex and Alfaisal Eye Hospital were included in this study. Subjects with ocular or systemic diseases or those who use any drugs that may interfere with the tear film were excluded.
Patients' demographic data (age, gender, and history of wearing contact lenses, general and ocular health) were taken. The inner eyes were examined using Heine ophthalmoscope. Shinn-Nippon corneal topographer was used for corneal mapping to determine the presence and severity of keratoconus. Based on the modified Amsler-Krumeich scale, keratoconus was classified to mild (>45.00 D), moderate (>45.00 D and <52.00 D), advanced (>52.00 D and <62 D), and severe (>62.00 D). Hagg Streit slit lamp was used to examine the outer eye, assess the fitting of contact lenses. To evaluate the tear volume a 35 mm × 5 mm Schirmer test strips was placed at the junction of medial 2/3 and lateral 1/3 of the lower lid in the fornix of the patients eye for 5 min, and after that the strip was removed and the length of moisture part was recorded in millimeters according to Khurana,  then the results were graded as normal (10-15 mm), dry eye (<10 mm) and watery (>15 mm). The test was done for both eyes. 
Tear film breakup time (TBUT) test was carried using Haag-Streit slit lamp in a bright light and cobalt blue filter. The subject's inferior bulbar conjunctiva of the eye was swiped with a saline wetted fluorescein strip (Fluorescein, Haag-Streit International, Switzerland). The patient was asked to blink several times after that he was asked to stop blinking and his eye was observed thought the slit lamp. The time between last blink and the appearance of the spots or streaks in the tear film was taken as the TBUT. Three readings were taken with stopwatch, recorded, and then the reading was calculated from the average of these readings. The results were then graded as normal (≥10 s) and abnormal (<10 s).
Informed consent was signed by all participants. Data were statistically analyzed using SPSS software version 18 (SPSS Inc).
| Results|| |
One hundred and fifty patients were screened, 100 patients (50 wearing Rose-K contact lenses and 50 not wearing contact lenses) were found to full fit the criteria of selection (42% males and 58% females). Subject's mean age was 19.71 ± 4.69 years and 66% of them were found between 10 and 21 years. Around 90% of the patients in contact lens wearer group wearing their contact lenses between 6 months and 1-year. About 82% of patients had moderate keratoconus [Table 1].
|Table 1: Classification of KC according to modified Amsler-Krumeich Scale (2009)|
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Regarding tear stability, 91 of subjects showed TBUT below the normal (46 of them from the contact lens wearer group). An independent sample t-test showed significant differences in mean TBUT between RGP contact lens wearer (M = 6.60, standard deviation [SD] = ±1.83) and those who never worn contact lenses (M = 7.52, SD = ±1.74), t (49) = −2.37, P = 0.02 [Table 2]. The test also showed significant difference in mean TBUT between females (M = 5.88, SD = ±1.38) who wearing RGP contact lenses and females (M = 8.04, SD = ±1.42) who never worn contact lenses, t (34) = −5.95, P < 0.001. No significant difference was found between males RGP contact lens wearer (M = 8.26, SD = ±1.75) and those males but noncontact lens wearer (M = 7.07, SD = ±1.34), t (14) =2.04, P = 0.06 [Table 3].
|Table 2: TBUT findings in contact lens and noncontact lens wearer groups|
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In term of tear volume, 65% of patients were found with dry eye (6% <10 mm/s and 59% had watery eye >18 mm/s). An independent sample t-test showed insignificant difference in mean Schirmer test outcomes between RGP contact lens wearer (M = 18.66, SD = ±3.28) and noncontact lens wearer group (M = 17.34, SD = ±3.77), t (49) =1.47, P = 0.15 [Table 4]. The significant difference was found only between females wearing RGP contact lens (M = 17.94, SD = ±3.64) and females not wearing contact lenses (M = 21.04, SD = ±1.66), t (22) = −14.33, P < 0.001 [Table 5].
|Table 4: Schirmer test findings in contact lens and noncontact lens wearer groups|
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| Discussion|| |
Tear film integrity helps to maintain an optically uniform interface between air and the anterior surface on contact lens that would affect visual function. Dogru et al.  and Mohd-Ali et al.  reported that keratoconus patients have poor tear stability compared to normal people.
Few studies have reported the effect of RGP contact lens wear on the tear film of eyes with keratoconus. Results from this study showed that prolonged RGP contact lens wear had a significant effect on tears quality of keratoconic eyes. This agreed with a study reported by Moon et al.  who found that tear film changes in keratoconus could be directly related to contact lens wear. In their study of keratoconus RGP wearers, myopic RGP wearers, Keratoconus noncontact lens wearers, and normal control, they noted that TBUT was significantly lower in contact lens wearer groups (keratoconus = 10 ± 3.28 s and myopic = 11.21 ± 2.52 s) compared to that of noncontact lens wearers (keratoconus = 12.1 ± 3.15 s and control = 12.94 ± 2.15 s). Furthermore, they found that TBUT in keratoconus who wore RGP lenses was significantly lower when compared to noncontact lens wearing keratoconus subjects. The finding from this study also agreed with Thai et al.  who stated that all contact lenses materials significantly and adversely affected tear physiology by increasing evaporation rate and decreasing tear thinning time
Results from this study agreed Mohd-Ali et al.  who found minimal changes in tear characteristics after 6 months of continuous wear of hyper Dk RGP (Menicon Z) contact lenses among nonkeratoconic subjects. In their study, 35 neophyte subjects were fitted with continuous wear hyper Dk RGP contact lenses in both eyes. Using data from phenol red thread test (PRT), -TBUT and tear meniscus height test, the authors found statistically significant differences in tear volume for PRT indicating a low impact of hyper Dk RGP contact lens on tear characteristics. This may indicate that the induced changes in tear film in our study could also attributed to contact lens materials as we used medium Dk material RGP contact lenses.
Females were found to be more affected than males in this study and this can be referred to that females have other contributing factors such as hormonal changes beside keratoconus and contact lenses. These finding also agreed with that stated by other researchers. ,
| Conclusion|| |
Keratoconus patients who wear RGP contact lenses have poor tear stability which needs to be considered appropriately during management of such patients, so both systemic and ocular signs of dry eye condition should be managed prior and during contact lens wear.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]