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Abstract
Purpose: To report on the incidence and clinical characteristics of mechanical
complications observed with silicone hydrogel contact lenses worn on a 29 night continuous
wear basis, and to determine risk factors if any for the development of these events.
Materials and Methods: Two hundred and ten participants were enrolled in a prospective
clinical trial to wear silicone hydrogel contact lenses on a 29 night continuous wear schedule.
The study was conducted for 6 months. Adverse events seen during the study period were
categorised as infective, inflammatory and mechanical events. The time in lens wear at time
of event, signs and symptoms of the condition were documented and the events monitored
until resolution. The severity of the events as an eye disease were rated on a scale of 0-4. The
incidence of adverse events were calculated as number of events per 100 patient eye years.
Univariate analysis using ANOVA followed by multivariate analysis using logistic regression
was performed to determine the risk factors. Significance was set at p<0.05.
Results: A single infective event (microbial keratitis), 33 inflammatory and 46 mechanical
events were observed during the study period. The incidence was 27 and 19 per 100 patient
eye years for mechanical and inflammatory events respectively. The mechanical events seen
were 16 events of corneal erosions, 15 events of Superior Epithelial Arcuate Lesions (SEAL)
and 16 events of Contact Lens Papillary Conjunctivitis (CLPC) and accounted for an
incidence of 9.4, 8.2 and 9.4 events per 100 patient eye years respectively. When only the
first events were considered, the incidence was 7.0, 7.6 and 8.2 for erosions, SEALs and
CLPC respectively. A greater number of mechanical events (26%) were asymptomatic
compared to inflammatory events (3%), however these were mostly SEALs. Events of
Corneal erosions presented as acute events with symptoms of pain and watering and CLPC
events presented with itching, discomfort and blurred vision with lenses. When rated for
severity as an eye disease, inflammatory events were found be more severe (mean: 2.01 ±
0.53) compared to mechanical events (mean: 1.48 ± 0.51). Of the mechanical events, a
majority of the erosions (70%) and SEALs (62%) were observed in the first month of lens
wear. There were more local events of CLPC (75%) than generalised CLPC (25%). A
greater number of mechanical events were observed in males and all the mechanical events
were managed just by temporary interruption in lens wear. SEALs and erosions are found to
resolve much faster compared to CLPC. When all mechanical events were grouped together,
reduced bulbar redness at baseline, an increase in palpebral roughness prior to event, corneal
staining in the superior quadrant of the cornea and contamination of lower lid with gram
positive bacteria were found to be significant risk factors. Of these, increased palpebral
redness prior to the event was significant for events of CLPC , increased extent and depth of
corneal staining in the superior quadrant was significant for SEALs and gram positive
bacteria at lower lid was significant for events of corneal erosions (p<0.001). Also an
association with gender, with males developing the event was significant for CLPC
(p=0.006).
Conclusion: A greater number of mechanical than inflammatory events were seen with
continuous wear of silicone hydrogels. However, the individual mechanical events varied
with regards to the onset of the condition, symptoms, resolution and underlying risk factors.
Whilst they were in general less severe than inflammatory events, the acute nature of some of
these events and periods of discontinuations required for management of the condition have
the potential to lead to discontinuation from lens wear.