Transcript A Comparison of Corneal Light Shields for the Prevention

R. Gary Lane, MD1, J. Michael Jumper, MD1, Yu Hyon Kim,
MD1, John Taboada, PhD2
1Wilford Hall
Medical Center, San Antonio, TX, 2Brooks AFB,
San Antonio, TX
Authors have no financial Interest.
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Operating microscope induced photic
maculopathy after cataract surgery was first
reported in 1983.
 Has been observed in other procedures, including
glaucoma, refractive, corneal, and retinal surgeries.
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Photic maculopathy remains an important
problem in ophthalmic surgery
Duration of surgery closely correlates with
injury:
 Less than 100 minutes – 0.9% risk
 Greater than 100 minutes – 39%
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Cheapest and most common method for prevention of
light toxicity.
 Especially important for microscopes without oblique lighting
or an eclipse feature.
 Light shields may directly block light headed for the macula.
 Defocus the light which is concentrated onto a macular “hot
spot” by the cornea and the lens.
Although various light shields have been described and
used for many years, there have been no clinical measures
of their effectiveness.
 We compare the ability of various corneal light shields to
block light from reaching the macula.
 We also describe the ability of shields to diffuse light and
prevent the formation of a “hot spot”.
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A cadaveric model was prepared using 20 porcine eyes
mounted on glass slides with a surgically created
posterior scleral window to allow light transmission
through the ocular media.
Four commonly used ad hoc materials were fashioned
into corneal light shields of 6.0mm and 8.5mm. Two
commercially available light shields were also examined.
Radiometric measurements were made with a UDT
silicone photodiode detector placed behind the eye. .
Light intensities were recorded with and without each
shield in place with unfiltered light from an operating
microscope at full intensity focused on the iris plane and
also with a 505nm filter in place.
Four commonly used ad hoc materials were fashioned into corneal light shields
of 6.0mm and 8.5mm as well as two commercially available light shields
(Hessburg and Linstrom).
Using a trephine, a
10mm window was
surgically created in
the macula to allow
light transmission
through the ocular
media.
The eyes were
mounted on a glass
microscope slide with
putty to block stray
light contamination
Anterior view of the eye
model with the back of
the eye cut away,
showing the clear path
from the cornea to the
scleral window, where
the light detector will
sit.
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Assessed the ability of corneal light shields to
defocus light and prevent the formation of a
“hot spot”, a red glow in the sclera.
A non-surgically altered, intact pig eye was
placed under the operating microscope.
The corneal light shields were placed on the
cornea.
The size of the “hot spot” was measured.
The actual amount of light attenuation (mV) for each shield is shown on the xaxis. A percentage attenuation was also calculated after subtracting out
background illumination. ANOVA (p<0.001)
Attenuation of light (mV) in the blue-green region is shown in the x axis.
Also shown are percentage of the reduction of the voltages after placement
of the corneal shields. ANOVA (p<0.001).
Before and after photos of pig eyes
using a 1000 drape corneal shield. The
shield defocuses the hot spot slightly
and its dimensions increased to 3x5mm.
8.5mm instrument wipe completely
darkens the hot spot.
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Highest attenuation levels:
 Hessburg 8.5mm shield
 8.5mm brown surgical glove
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Several shields ineffective
 Less than 10% total light (5/9)
 Less than 75% 505nm light (6/9)
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8.5mm shields are more effective.
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Not all corneal light shields are created equal.
The overall percentage of light blocked by the shields
was lower than expected.
 Ranges from 25 to 75% for the filtered and lower for the
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unfiltered light.
 Increases dramatically with increasing diameter
 Choose a minimum of 8.5 mm when working with dilated
pupils.
Several commonly used shields provide unacceptably
low levels of protection.
 Brown surgical gloves work just as well as the
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commercially available Hessburg shield.
 4mm Lindstrom keratoplasty shield was not effective in
our study.
Do not become complacent after placing a light shield