3 research outputs found
Age related variations in anterior ocular characteristics and response to short term contact lens wear
The purpose of this thesis was to investigate age related variations in anterior ocular
characteristics and their effect on the response to short-term (one-hour) open eye
orthokeratology (OK) lens wear and overnight hydrogel lens wear.
Sixty-three volunteer subjects were divided into three groups comprising children (Group
I), young adults (Group II) and older adults (Group III). Anterior ocular characteristics that
were measured included corneal topography with the Medmont corneal topographer, total,
stromal and epithelial thickness with the Holden-Payor optical pachometer, microscopic
cell characteristics with the confocal microscope, corneal aesthesiometry, corneal modulus
of elasticity, and tear film, palpebral and eyelid characteristics.
The older cornea was found to be more spherical in shape (asphericity Q = -0.24 ± 0.07 in
group III compared to -0.34 ± 0.09 and -0.32 ± 0.17 in groups I and II respectively) and
showed a tendency from with-the-rule to against-the-rule astigmatism. Older subjects also
had a decreased endothelial cell density (2596 ± 111 cells/mm2 in group III compared to
2793 ± 138 cells/mm2 in group II) and reduced eyelid tension compared to the younger
groups. Children were found to have lower blink rates than adults. It was concluded that
these changes might have a significant impact on contact lens wear. The responses to two
contact lens based techniques, orthokeratology (OK) and hydrogel overnight wear (ON),
were studied.
Sixty subjects (20 per group) wore reverse-geometry lenses (BE, Ultravison Aust Pty Ltd)
of Boston XO material in one eye under open eye conditions for one hour in one eye only.
Changes in unaided visual acuity, corneal curvature, corneal thickness and confocal
microscopic variables were measured after OK lens wear. All subject groups showed
statistically significant improvements (p < 0.05) in unaided visual acuity, a trend for more
positive (less prolate) corneal asphericity, increase in apical corneal radius and decrease in
central total corneal thickness, after OK lens wear. When the groups were stratified,
statistical significance was obtained between the older group and the other two younger
groups for change in apical corneal radius (0.23 ± 0.01 mm in group I, 0.15 ± 0.01 mm for
group II, 0.06 ± 0.33 for group III). The change in asphericity also showed significant
differences between the older age group (0.10 ± 0.08 mm) and the young adult group (0.21
± 0.13). Central corneal thinning obtained after one hour of OK lens wear revealed
significant differences between the older adult group (-1.9 ± 3.2 μm) and the other two
groups (-5.0 ± 5.9 μm in group I, -5.0 ± 2.0 μm for group II).
Sixty subjects wore hydrogel lenses (One-Day Acuvue, Johnson and Johnson Visioncare
Pty Ltd) made of etafilcon A in one eye only overnight during sleep at their home.
Changes in unaided visual acuity, corneal curvature, corneal thickness, confocal
microscopic variables and slitlamp variables were measured after ON lens wear. All
subjects showed significant thickening (p < 0.05) of the cornea with ON wear, more in the
lens-wearing eye. This study reported that the edema response induced by Acuvue contact
lenses is stromal in origin. The edema response of the older group (33.9 ± 11.5 μm) was
lower than the other two groups as demonstrated by the difference in the change in central
stromal thickness (49.3 ± 20.3 μm for group I and 51.0 ± 20.0 μm for group II). However,
a statistically significant difference in the change in thickness was not reached either for
the central total corneal thickness or for other topographic locations.
Corneal and visual changes found in this study confirm previous reports of the effects of
short term OK and hydrogel ON lens wear. Older lens wearers showed a reduced or
delayed response to short-term lens wear. Studies investigating the effects of age with long
lens-wearing durations are warranted to quantify these effects further
EUROSENSORS XVII : book of abstracts
Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)
A cumulative index to the 1977 issues of a continuing bibliography on aerospace medicine and biology
This publication is a cumulative index to the abstracts contained in the Supplements 164 through 175 of Aerospace Medicine and Biology: A Continuing Bibliography. It includes three indexes-- subject, personal author, and corporate source