1 2 3
Increased numbers of Demodex in contact lens wearers
4 5 6
Isabelle Jalbert, OD, PhD, MPH, FAAO
7
Shazana Rejab, BOptom, MOptom
8 9
School of of Optometry and Vision Science, UNSW Australia
10 11 12 13 14
3 tables and 3 figures
15 16
Address for correspondence:
17
Dr Isabelle Jalbert
18
School of Optometry and Vision Science, UNSW Australia, UNSW Sydney NSW
19
2052, Australia
20
Tel: +61 (2) 9385 9816 / Fax : +61 (2) 9313 6243
21
Email:
[email protected]
22 23 24 25
Submitted 15 October 2014
26
More Demodex in contact lens wearers?
27 28 29 30 31 32 33
Everyone seems to have become interested in the Demodex mites over recent years. Yet to date, there have been no studies on whether Demodex is observed in contact lens wearer. We wondered whether Demodex infestation in contact lens wearers could explain some of the discomfort that continues to frequently plague wearers. Demodex was observed in 90% of contact lens wearers and in larger numbers than in non‐contact lens wearers. We used confocal microscopy to detect mites and this was a more sensitive technique than the conventional light microscopy technique. So remember to consider Demodex in your contact lens practice.
34
35
ABSTRACT
36
PURPOSE: The aim of this study was to determine if Demodex infestation is more
37
frequent in contact lens wearers than non wearers. Secondary aims were to evaluate
38
the effects of Demodex on the ocular surface (symptoms and signs) and to evaluate
39
the ability of confocal laser scanning microscopy to detect and quantify the Demodex
40
infestation compared to the conventional light microscopic technique.
41
METHODS: Forty Asian female participants (20 non wearers, 20 lens wearer) aged
42
27 ± 9 years were recruited. Ocular comfort scores (OSDI, OCI, DEQ), vital staining
43
(corneal, conjunctival, lid wiper), tear osmolarity, tear break up time, meibomian
44
gland evaluation were evaluated. Demodex was detected using in vivo confocal
45
microscopy and conventional light microscopy.
46
RESULTS: The number of Demodex was higher in lens wearers than non wearers
47
(7.6 ± 5.8 vs 5.0 ± 3.1; p=0.02). Demodex was observed in a large majority (90%) of
48
lens wearers and in 65% of non wearers using confocal microscopy (p=0.06). The
49
detection rate was lower in both groups using conventional light microscopy
50
(p=0.003) where Demodex could only be confirmed in 70% and 60% of lens and non
51
wearers, respectively. The number of Demodex tended to increase with age (=0.28,
52
p=0.08) but Demodex did not appear to affect ocular comfort or any clinical signs
53
(p>0.05).
54
CONCLUSIONS: Contact lens wearers harbour Demodex as frequently as non
55
wearers and in higher numbers, which is best detected using in vivo confocal
56
microscopy. The significance of these findings is uncertain as no associations were
57
found with any symptoms and signs of dry eye disease.
58
Keywords: Demodex, contact lens, confocal microscopy, dry eye disease,
59
blepharitis
60
The Demodex mite is an ectoparasite found on human skin, most commonly on the
61
eyelids, eyelashes, meibomian glands, face, and external ear.1 Demodex mites have
62
traditionally been considered harmless, non pathogenic residents, however, recent
63
reports have suggested that Demodex may cause unwanted symptoms when
64
present in large numbers.1-3 Two types of Demodex are able to establish
65
relationships with humans; these are D. folliculorum and D. Brevis.1, 4 Both species
66
can be differentiated by their inhabited location and characteristics. D. folliculorom is
67
0.35 to 0.40 mm in length and is found in lash follicles while D. Brevis measures 0.15
68
to 0.20 mm and is found in the deeper sebaceous and meibomian glands.5, 6 Adult
69
female mites lay up to 24 eggs inside a single hair follicle.1 Mites will travel to mate
70
on the surface of the skin at night and will go back inside the skin in the morning; this
71
has been postulated to explain the ocular symptoms of dryness, irritation, foreign
72
body sensation, itching and visual disturbance sometimes reported.7-9
73 74
The reported prevalence of Demodex ocular infestation ranges from as low as 10%
75
to as high as 90% with the majority of studies showing prevalences of 50% to 60% in
76
blepharitis patients and 10% to 20% in controls.8,
77
include age,8, 11 male gender,11, 12 and conditions such as blepharitis,4, 10 chalazia,13
78
and rosacea.1 The cylindrical dandruff present in blepharitis patients is thought to
79
offer the best harbouring site for these mites.4,
80
immunological deficiency1 have also been proposed as potential contributors to the
81
establishment of Demodex infestation. More frequent usage of cosmetic products
82
and cleanser for the skin and eyelid in females has also been suggested to perhaps
83
discourage the establishment of Demodex.11 The mechanical action (rubbing)
84
associated with more frequent use of soaps and cosmetics potentially reduces the
10, 11
14, 15
Risk factors for Demodex
Improper sanitation11 and
85
levels of infestation and promotes better overall lid hygiene. To the best of our
86
knowledge, no studies have explored the prevalence of Demodex in contact lens
87
wearers.
88 89
An invasive sampling and counting technique involving plucking of eyelashes
90
followed by observation using conventional light microscopy is traditionally used to
91
detect and diagnose Demodex.4,
92
confocal microscopy9,
93
biomicroscopy17-19 may be used to detect Demodex mites without the need for lash
94
epilation. More studies are required to confirm the usefulness of these techniques.
16
8, 15
Recent isolated reports suggest that in vivo
and eyelash rotation under high magnification slit lamp
95 96
The primary aim of this study was to determine if Demodex infestation is more
97
frequent in contact lens wearers than non wearers. A first secondary aim was to
98
evaluate the effects of Demodex on the ocular surface (symptoms and signs). An
99
additional secondary aim was to evaluate the ability of confocal laser scanning
100
microscopy to detect and quantify Demodex infestation compared to the
101
conventional sampling and counting light microscopic technique.
102 103
METHODS
104
A cross-sectional study was performed. Forty female patients were recruited
105
between November 2012 and April 2013 from the University of New South Wales
106
(UNSW) Australia campus population and surrounding community. The inclusion /
107
exclusion criteria for this study did not specifically include a particular sex or ethnicity
108
requirement, however female participants of similar ethnic background were
109
preferentially enrolled related to the lead clinician’s religious faith. Patients aged
110
eighteen years and above, with or without ocular discomfort were included. Patients
111
with ocular disease, systemic immune deficient conditions such as AIDS or taking
112
systemic immunosuppressant were excluded. An equal number of lens (soft and
113
rigid gas permeable) and non-lens wearers (those not wearing lenses for the past 6
114
months) were enrolled. This research followed the tenets of the Declaration of
115
Helsinki. Informed consent was obtained from the subjects after explanation of the
116
nature and possible consequences of the study. The research was approved by the
117
Biomedical Human Research Ethics Advisory panel of UNSW Australia.
118 119
The sample size was calculated using G* power 3.1.7 software. Based on a
120
previously demonstrated mean number of Demodex of approximately 5 ± 5 in a
121
female population8, an expected clinically significant increase of 50% to 10 Demodex
122
in contact lens wearers and a 95% confidence level, it was estimated that 17
123
participants in each group would be sufficient to demonstrate a difference.
124 125
The following measurements were conducted in both eyes in the order they are
126
listed below from least invasive to most invasive. A single unmasked examiner (SR)
127
conducted all measurements. Three validated dry eye symptoms questionnaires
128
were self-administered online under supervision. These included the Ocular Surface
129
Disease Index (OSDI),21 the Ocular Comfort Index (OCI)22 and, to specifically
130
address the potential effect of contact lens wear and Demodex on diurnal variation of
131
symptomatology, the full length version of the Dry Eye Questionnaires (DEQ).23
132
Participants were instructed to report symptoms experienced wearing their habitual
133
correction. The Contact Lens Dry Eye Questionnaire (CLDEQ) is identical to the
134
DEQ but contains additional contact lens related questions.24 We chose not to use
135
the CLDEQ to simplify questionnaire administration and scoring. The OSDI was
136
chosen because it has previously been successfully used to demonstrate a
137
relationship between ocular discomfort and Demodex infestation.7,
138
contains three sub-categories sampling ocular symptoms, visual performance, and
139
eye comfort in different environments using a scale from 0 to 4. Total OSDI scores
140
were obtained using the formula A x 25/B where A was the sum of the three sub-
141
scores and B represented the total number of questions answered. The OCI
142
questionnaire was included on the basis that its validated construct may make it
143
better suited to characterise mildly symptomatic populations, such as that expected
144
in this study.22 The OCI score was obtained using the OCI calculator. Although the
145
OSDI and the OCI were not designed for this use, they have been successfully used
146
to discriminate ocular comfort changes in contact lens wearers.25-27 The full length
147
version of the DEQ was evaluated for its total score (DEQ frequency + DEQ intensity
148
+ DEQ bothersome). DEQ frequency was calculated by adding the scores of the 10
149
items: eye discomfort, dryness, grittiness and scratchiness, eye burning and stinging,
150
tired eyes, changeable and blurry vision, eyelid redness, watery eyes, eye mucus
151
and crusting, and closing of the eyes. DEQ intensity of symptoms in the morning and
152
evening was then calculated by adding the scores of the six items: discomfort,
153
dryness, grittiness and scratchiness, burning and stinging, tired eyes and
154
changeable or blurry vision. Total score for DEQ bothersome was then calculated
155
based on the six items described in DEQ intensity. Each of the sub-categories was
156
converted to a percentage before being combined together as total DEQ score.
8
The OSDI
157 158
Tear osmolarity is increasingly recognised as a key marker of ocular surface
159
health.28-30 Thus, to enable evaluation of the effects of Demodex on the ocular
160
surface (secondary aim 1), tear osmolarity was measured using the in situ
161
osmometer (TearLab Osmolarity; TearLab Corporation) .31 A detailed slit lamp
162
observation of the eyelid, cornea, and conjunctiva of both eyes was conducted. The
163
average of three tear break-up time measurements was recorded immediately after
164
instillation of sodium fluorescein. Corneal staining was assessed at the same time
165
and graded using the Oxford scale.32 Contact lens wearers were instructed to
166
remove their lenses before fluorescein dye instillation. Conjunctival staining was
167
measured nasally, temporally, superiorly and inferiorly 2-3 minutes after instillation of
168
lissamine green and graded using the same Oxford scale. Lissamine green was also
169
used to measure lid wiper staining on the upper and lower lid on both eyes and
170
graded in 0.5 steps using a 4 points simplified pictorial severity grading scale where
171
0 = none and 3 = severe.33 In addition, meibomian gland health was graded using
172
the scale described in the Meibomian Gland Workshop report. 34 The grading
173
includes several domains such as the eyelid margin, orifices and expressed
174
secretion. For the eyelid margin assessment, the vascularity and the presence of
175
blepharitis, pouting and plugging of the orificies were graded using a dichotamous
176
scale where 0 = absent and 1= present. The expressed secretions were also
177
characterised based on their foamy characteristic and the quality (0=clear,
178
1=cloudy, 2=granular, 3=toothpaste) and expressibility (1=light, 2=moderate,
179
3=heavy pressure). The lower and upper eyelids were graded separately.
180 181
The eyelid margins and the bases of the eyelashes were imaged using in vivo
182
confocal microscopy with the use of a corneal module (Heidelberg Retina
183
Tomograph II, Rostock Corneal Module; Heidelberg Engineering GmbH). The
184
instrument utilises a diode laser with a wavelength of 670 µm and is said to provide
185
transverse resolution of 2 µm and optic section thickness of 4 µm. The objective of
186
the microscope was an immersion lens covered by a polymethylmethacrylate cap
187
(Tomo-Cap; Heidelberg Engineering). To minimise the risk of corneal injuries during
188
applanation of the eyelid margins, the upper lids of both eyes were everted. For
189
examination of the lower lid, participants were asked to look upwards while their lid
190
was retracted. No anaesthetic was used as the microscope touched only the eyelid
191
area. Viscotears comfort gel (Novartis, North Ryde, Australia) was used as a
192
coupling agent between the applanating lens cap and the eyelid surface. The
193
confocal microscope was set on ‘manual mode’ and the centre of the
194
polymethylmethacrylate cap was applanated onto the eyelid margins and high-
195
quality images of individual eyelashes observed on a computer screen. Focal
196
distance was adjusted manually to allow evaluation of the whole follicle and lash
197
root. The surrounding palpebral conjunctiva and meibomian glands were scanned by
198
moving the applanating objective of the confocal microscope from the nasal to the
199
temporal lid. The operator manually controlled scan depth and image recording in
200
section mode by observing the digital images on a computer screen. The two-
201
dimensional image sizes were 384 x 384 pixels with a 400 x 400 µm field of view.
202
The upper and lower eyelids were scanned on each eye separately. Confocal
203
microscopy examination of both eyelids on both eyes took on average 20 to 30
204
minutes to complete for each participant and did not exceed the manufacturer’s
205
imposed limit of 50 minutes of total exposure to the HRT laser at any single visit. No
206
particular precautions were required to avoid lids flipping back during measurements.
207
No participant reported any significant discomfort following the procedure, nor was
208
any adverse effect observed after an examination in this study. The number of
209
Demodex mites and eggs were subsequently counted on the recorded confocal
210
microscopy images.
211 212
Eight eyelashes (two from each lower and upper lid) were epilated from each
213
participant using fine forceps under the slit lamp biomicroscope with 25X
214
magnification. Whenever possible, eyelashes with distinct cuffs collaring the lash
215
root were specifically targeted for epilation. The epilated eyelashes were immediately
216
placed on either end of a glass slide and mounted with a coverslip and extreme care
217
was taken to minimise the possibility of loss of mites during transport. Fluorescein
218
was then applied using a micropipette to the edge of coverslip to enhance
219
visualisation.35 The number of mites were counted using light microscopy under 40X
220
magnification after approximately 15 minutes, to allow the cylindrical dandruff to
221
dissolve and stimulate Demodex to migrate out of the eyelashes. Images were
222
captured and recorded using a smartphone camera (Samsung GT-S5830) attached
223
to a conventional light microscope.
224 225
The highest of the confocal or light microscopy number was retained for total number
226
of Demodex. Descriptive statistics are reported as means ± standard deviation (SD).
227
Data were compiled and analysed using SPSS software version 16.0 (IBM
228
Corporation). To address the potential issue arising from analysis of paired data from
229
the two eyes, worst eye data was retained for analysis of the osmolarity, tear
230
breakup time, corneal and conjunctival inflammation, lid wiper staining and
231
meibomian gland dysfunction evaluation. The data were tested for normality using
232
Shapiro-Wilk test. Spearman correlation was used to study the association between
233
variables. The Mann-Whitney or Chi-Square tests were used to examine differences
234
between lens and non-lens wearers and examination techniques (confocal versus
235
light microscopy), as appropriate. Significance was determined at a confidence level
236
of 95%.
237 238
RESULTS
239
Fourty study participants were enrolled, nineteen of which were soft contact lens
240
wearers and one rigid gas permeable contact lens wearer. The rigid gas permeable
241
contact lens wearer replaced lenses yearly whereas soft contact lens wearers
242
replaced lenses on a monthly (12), fortnightly (3), or daily (4) basis. The average age
243
of the study participants was 27 ± 9 years (range 21 to 65). There was no age
244
difference between non-lens wearers (27 ± 9 years; range: 21 to 65) and contact
245
lens wearers (28 ± 9 years; range: 22 to 60) (Mann Whitney U, p = 0.45). All patients
246
were female. Thirty-four (85%) of the 40 participants originated from South-East
247
Asia, four (10%) from Oceania and two (5%) from central Asia.
248 249
Two instruments were used to detect Demodex, confocal microscopy and light
250
microscopy. Demodex was observed in almost all contact lens wearers (18 of 20 or
251
90%) using confocal microscopy (Table 1). Interestingly, no Demodex was detected
252
in the single participant wearing rigid gas permeable lenses. Using the same
253
technique, Demodex was detected in just over half of the non wearers (13 of 20 or
254
65%) (Table 1). Although Demodex was found more frequently in lens than non-lens
255
wearers with both techniques, this difference did not reach statistical significance
256
(Chi-Square, p = 0.06 for both instruments).
257
258
Table 1: Number (percentage) of patients with Demodex. Significant differences are shown in
259
bold.
260
Confocal
Non wearers
Lens wearers
Total
p-value
(n=20)
(n=20)
(n=40)
13 (65%)
18 (90%)
31 (78%)
0.06
12 (60%)
14 (70%)
26 (65%)
0.06
0.09
0.02
0.003
microscopy Light microscopy p-value 261 262
When light microscopy was used, Demodex was detected less frequently in contact
263
lens wearers (14 of 20 or 70%) than the 90% detected rate shown above (Chi-
264
square, p = 0.02). Demodex was observed in 60% of non-contact lens wearers using
265
light microscopy compared to the 65% detection rate shown above with confocal
266
microscopy (Chi-square, p = 0.09). Overall when both groups were considered
267
together, a significantly higher prevalence of Demodex was detected using confocal
268
scanning (31 of 40 or 78%) compared to light microscopy (26 of 40 or 65%) (Chi-
269
Square, p = 0.003). In this study involving 40 participants, there were only 4
270
instances where light microscopy yielded a higher number of Demodex than confocal
271
microscopy examination. A trend for a positive correlation on number of Demodex
272
detected by both instruments was shown (Spearman = 0.42, p = 0.07).
273 274
In patients where Demodex was detected, the average number of mites visualised
275
was higher in contact lens wearers (7.6 ± 5.8; range 2 to 25) than in non-lens
276
wearers (5.0 ± 3.1; range 2 to 12) (Mann-Whitney U, p = 0.02). Anecdotally,
277
investigators reported that more Demodex were observed on the upper lid compared
278
to the lower lid but this data were unfortunately not recorded in this study. Figure 1
279
highlights the clinical (top left), confocal microscopy (top right) and light microscopy
280
(bottom left and right) appearance of Demodex mites. Demodex eggs (Figure 1,
281
bottom right) were observed in 1 non-lens wearer and 3 contact lens wearers.
282
Whenever eggs were seen, mites were also observed. In all cases, these eggs were
283
detected using light microscopy, however eggs could only be observed in one of
284
these four cases with confocal microscopy. A short video of a Demodex mite
285
movement captured using light microscopy is also provided (see Video,
286
Supplementary Digital Content 1, which shows examples of the movement of live
287
Demodex folliculorom and Brevis mites observed under light microscopy post
288
epilation).
289
290 291
Figure 1: Demodex. (Top left) Cylindrical dandruff observed at the base of the
292
eyelashes is characteristics of Demodex infestation. (Top right and bottom
293
left) A group of Demodex folliculorum(*) is observed at the eyelash base using
294
in vivo confocal microscopy (top right) and light microscopy (plucked eyelash)
295
(bottom left). (Bottom right) Demodex brevis mites (*) and a Demodex egg
296
(arrow) are observed using light microscopy of a plucked eyelash.
297 298
The clinical results of the study population, including symptomatology sampled using
299
three validated dry eye questionnaires, are presented in Table 2. No changes in
300
symptoms were observed in contact lens wearers with Demodex using the OSDI or
301
OCI (Table 2). Surprisingly, contact lens wearers with Demodex reported less
302
symptoms on the DEQ (p=0.04) than wearers without Demodex (Table 2). However,
303
this finding is based on only 2 wearers without Demodex and requires confirmation
304
with a larger sample size. In non-contact lens wearers with Demodex infestation,
305
there were no differences in any of the questionnaires. Habitual contact lens wearers
306
with Demodex infestation yielded similar tear osmolarity and stability measurements
307
than Demodex-free contact lens wearers (Table 2). In contrast, non-contact lens
308
wearers with Demodex appeared to have lower tear osmolarity (p=0.08) and more
309
stable tears (p=0.06) than Demodex-free non-contact lens wearers, although this did
310
not reach statistical significance (Table 2). Other clinical findings were unremarkable
311
either in contact lens wearers or non-contact lens wearers. This is perhaps not
312
surprising in light of the fact that both groups were not heavily infested with
313
Demodex.
314
315 316
Table 2: Clinical measurements of the study population.
317
Non wearers
Lens wearers
(n=20)
(n=20)
Demodex
None
(n=13)
(n=7)
OSDI
24.3 18.1
20.9 15.4
OCI
33.8 6.3
DEQ Osmolarity (mOsmol/L)
p-value
Demodex
None
p-value
(n=18)
(n=2)
0.87
24.1 17.3
12.5 ± 17.7
0.28
34.3 6.1
0.84
34.3 8.9
29.9 ± 19.9
0.90
37.2 19.5
33.3 17.8
0.41
34.0 ± 24.6
73.6 12.2
0.04
306.5 13.9
325.1 27.2
0.08
305.3 11.5
307.5 4.9
0.49
TBUT (secs)
7.0 3.5
4.0 1.7
0.06
6.5 3.0
7.5 6.4
0.95
MGD (0-18)
2.5 ± 0.7
2.0 0.0
0.07
2.8 ± 0.8
2.0 0.0
0.13
Corneal staining (0-5)
0.4 ± 0.7
0.1 ± 0.4
0.40
0.6 ± 0.7
0.5 ± 0.7
1.00
Conjunctival staining (0-20)
2.0 ± 1.7
1.3 ± 2.0
0.34
1.3 ± 1.5
2.0 ± 2.8
0.74
Lid wiper staining (0-6)
0.9 ± 1.0
1.1 ± 1.5
0.80
0.8 ± 1.2
1.0 ± 1.4
0.77
318
There was a trend for a moderate positive correlation between the number of
319
Demodex mites and increasing age in contact lens wearers (=0.41, p=0.06) but not
320
in non wearers (=0.27, p=0.26) (Figure 2).
321 322
Figure 2: Relationship between Demodex and age in contact lens wearers
323
(open circles) and non-contact lens wearers (closed circles). A trend for an
324
association between number of Demodex and age was observed in contact
325
lens wearers (=0.41, p=0.06) and overall (=0.28, p=0.08) but not in non-
326
contact lens wearers (=0.27, p=0.26).
327 328
Overall, the number of Demodex also trended towards a weak correlation with
329
increasing age (=0.28, p=0.08). The lack of relationship in non wearers may be
330
attributed to the lower levels of mite infestation in these subjects. There were no
331
significant associations between the number of Demodex and ocular comfort
332
measured by OSDI, OCI and DEQ in contact lens wearers and non-contact lens
333
wearers (Figure 3, Table 3).
334 335
Figure 3: Relationship between Demodex and ocular symptoms measured by
336
OSDI (top left), OCI (top right) and DEQ (bottom left) in contact lens wearers
337
(open circles) and non-contact lens wearers (closed circles). There were no
338
significant associations (see Table 3).
339 340
Numerically, more Demodex were detected in the four participants replacing lenses
341
daily than in participants replacing lenses less frequently; however this was not
342
statistically different. This study had too few participants in each wear schedule to
343
allow for measuring the potential impact of wear schedule on Demodex infestation.
344
345
Table 3: Relationship between Demodex infestation and comfort scores (OSDI, OCI and
346
DEQ) in lens wearers and non-wearers. Comfort
Correlation
questionnaire
Coefficient
OSDI
0.02
0.92
OCI
0.01
0.97
DEQ
0.27
0.25
OSDI
0.20
0.41
OCI
-0.31
0.90
DEQ
-0.35
0.13
p-value
Non-wearers (n=20)
Lens wearers (n=20)
347 348 349 350
DISCUSSION
351
The prevalence of Demodex in our study (Table 1) was similar to that of 70%
352
reported in non wearers.8 However, our results suggest that contact lens wearers
353
may harbour more Demodex than non-wearers with up to 90% of contact lens
354
wearers harbouring mites. The clinical significance of this finding is uncertain.
355
Several factors could explain the increased propensity for contact lens wearers to
356
host Demodex. Through its impact on the normal ocular flora and/or lid margin
357
health, contact lens wear may provide a more favourable environment for Demodex
358
mites to proliferate. As discussed in the introduction, blepharitis is known to provide
359
a favourable environment for Demodex infestation1,
360
colonisation of lid margins by microorganisms such as Staphylococcus epidermidis,
361
Propionibacterium
acnes,
Corynebacteria,
and
8, 12
and is associated with
Staphylococcus
aureus.1,
2
362
Intriguingly, the same microorganisms have been detected more frequently in
363
contact lens wearers.36 It is possible that the contact lens may act as a vector for
364
microorganisms that offer an environment more favourable to accumulate excessive
365
bacteria which further may lead towards Demodex infestation.
366 367
A number of factors may explain the slight increased ability of in vivo confocal
368
microscopy to detect Demodex. This mirrors findings of increased detection of D.
369
Brevis and Demodex larvae by confocal microscopy.16 Detection is perhaps
370
facilitated by the higher magnification and resolution provided by the confocal
371
microscope combined with the ability to scan all eyelashes rather than just a limited
372
sample of two per eyelid. In addition, we speculate that exposure of the mites to
373
intense illumination and heat during the in vivo confocal microscopy procedure may
374
entice the mites into moving away from the energy source, making detection easier.
375
Anecdotally, mites were sometimes seen to be moving deeper and burying
376
themselves into sebaceous glands during the confocal microscopy examination.
377
More Demodex mites were observed on the upper lid than the lower lid. This is
378
perhaps due to the larger numbers of eyelashes in the upper than the lower lids
379
(approximately 150 versus 75 eyelashes).37 Confocal microscopy
380
observation of a much larger number of eyelashes than the conventional light
381
microscopy sampling and counting technique and this again may explain the larger
382
detection rate. Additionally, scanning was easier to conduct on upper lid compared to
383
the lower lid, which may have facilitated detection in the upper lids. Mites may also
384
have been lost during epilation and transport of eyelashes to the slide, which would
385
lead to an underestimation of the ability of the conventional light microscopy
386
technique to detect the mite. Although we targeted lashes with cylindrical dandruff for
enables
387
epilation, others have shown that cylindrical dandruff is not always completely
388
removed with the lash during epilation4, 18 and therefore fragments of collarettes still
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harbouring mites may have been retained on the eyelash margins. Whatever the
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reason, the difference between the techniques’ ability to detect Demodex, whilst
391
statistically significant, was very small suggesting that perhaps they may be used
392
interchangeably. In contrast, egg detection seemed to be much easier under light
393
microscopy than confocal microscopy. This is perhaps because eggs were
394
predominantly found embedded in cylindrical dandruff and the usage of fluorescein
395
as part of the light microscopy procedures facilitates the dissolution and expansion of
396
cylindrical dandruff.35 Thus, it allows better visualization of eggs.
397 398
This study confirmed the previously demonstrated significant relationship between
399
Demodex and age.8 Not accounted for in our analysis is the possibility that
400
blepharitis and other age-related conditions may confound these results. Our study
401
population was on average 27 years old, much younger than the majority of the
402
populations previously studied. Interestingly, Lee et al8 have previously concluded
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that “in the less than 30 years of age, ocular surface discomfort is not necessarily
404
evidence of an increased in Demodex.” Our study was conducted on an Asian
405
population. The generalizability of these results to other populations (e.g.
406
Caucasians) in uncertain. Non-random selection of the worst eye for inclusion in the
407
analysis is a possible source of bias which may lead to an overestimation of the
408
significance of our findings.
409 410
Infestation with Demodex mites has been shown to impact a number of ocular
411
symptoms and clinical signs such as conjunctival inflammation and tear break-up
412
time.8,
15
413
foreign body sensation or dryness have been described.1,
414
significant relationship between the number of Demodex and ocular discomfort
415
measured with the OSDI has been reported.7, 8 In support of this pathogenic theory,
416
reports of reduced symptoms and signs of ocular surface inflammation following
417
antiseptic treatment with tea tree oil are emerging.15
Symptoms of ocular discomfort such as irritation, itching, burning, and 7, 8, 19, 20
Additionally, a
418 419
We could not replicate the previously demonstrated association between ocular
420
discomfort and Demodex.8 Surprisingly, no association was found between number
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of Demodex - either in non-contact lens wearers or contact lens wearers - and ocular
422
comfort sampled by OSDI, OCI and DEQ dry eye questionnaires in our study. This is
423
perhaps due to the low levels of infestations found in our sample population. The use
424
of contact lenses by a significant proportion of our population may also have
425
confounded these results. Contact lens wear itself may also be modulating
426
symptoms to a much larger extent than mite infestation is able to do. The
427
unexpected finding of better comfort (measured by DEQ) in contact lens wearers
428
who have Demodex than those who don’t is puzzling and cannot be explained easily;
429
this may be a spurious finding, perhaps due to abnormally high DEQ values in the
430
two contact lens wearers without Demodex. In their study, Lee et al modified the
431
OSDI by adding the following three questions pertaining to chronic blepharitis: “Do
432
your eyes feel itchy?”, “Are you eyelids injected in the morning?” and “Is there a
433
discharge that makes opening the eyes in the morning difficult?” 8 The OSDI was not
434
modified in our study and this may have precluded us from demonstrating a
435
relationships between Demodex and ocular symptoms.
436
437
The relationship between Demodex and the full range of standard signs of ocular
438
surface health, including tear osmolarity was examined. We could not replicate the
439
previously demonstrated relationship between tear breakup time and Demodex,8 nor
440
could we show an association with any other signs of dry eye disease (tear
441
osmolarity, MGD grade, corneal and conjunctival staining, lid staining) (Table 2).
442
Intriguingly and unexpectedly, non-wearers recorded higher tear osmolarity and
443
reduced tear stability in Demodex-free than Demodex-infested group. It was also
444
interesting that the mean values for lid wiper staining were numerically lower (but not
445
significantly different) in Demodex infested subjects than those without Demodex for
446
contact lens wearers and non wearers. We speculate that although symptoms were
447
absent, Demodex infestation might have led to increased tearing and tear production
448
in these subjects. As suggested and reviewed by Milton and colleagues,19 the
449
aqueous deficient sub-type of dry eye may in fact interfere with Demodex infestation.
450
Coating of the eyelid margin by mite waste products or by the mites themselves may
451
provide added protection to the lid margin against surface shearing and dehydration.
452
Studies focused specifically on the possible relationship between Demodex and lid
453
wiper staining would be of interest. Our study was not powered to show differences
454
in these secondary outcome variables. Confirmation of these findings with a larger
455
sample size is required.
456 457
Although we did not intend to treat Demodex in this observational, cross-sectional
458
study, we found that several participants became distressed on being informed of the
459
presence of the parasite on their eyelashes. This was, for the most part, easily
460
managed by providing detailed explanations. One participant with moderate
461
infestation and significant symptoms requested treatment and received two weekly
462
in-office 50% tea tree oil treatments15 before she was lost to follow-up. These
463
treatments caused notable irritation and should not, in our opinion, be undertaken
464
without the pathogenic role of Demodex being well established in individual cases.
465 466
In conclusion, contact lens wearers harbour more Demodex than non wearers and
467
this is perhaps best detected using in vivo confocal microscopy. The significance of
468
these findings is uncertain as no associations were found with any symptoms and
469
signs of dry eye disease.
470
formulate future products with these results in mind.
Manufacturers of contact lens care products may want to
471 472
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SUPPLEMENTAL DIGITAL CONTENT
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Supplemental Digital Content 1: Video that demonstrates the movement of
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live Demodex folliculorom and Brevis mites observed under light microscopy
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post epilation. wmv
