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A Comparison of Corneal Light Shields for the Prevention of Photoxicity

R. Gary Lane, MD 1 , J. Michael Jumper, MD 1 , Yu Hyon Kim, MD 1 , John Taboada, PhD 2 1 Wilford Hall Medical Center, San Antonio, TX, 2 Brooks AFB, San Antonio, TX . A Comparison of Corneal Light Shields for the Prevention of Photoxicity. Authors have no financial Interest.

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A Comparison of Corneal Light Shields for the Prevention of Photoxicity

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  1. 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 A Comparison of Corneal Light Shields for the Prevention of Photoxicity Authors have no financial Interest.

  2. IntroductionPhoticmaculopathy • Operating microscope induced photicmaculopathy after cataract surgery was first reported in 1983. • Has been observed in other procedures, including glaucoma, refractive, corneal, and retinal surgeries. • Photicmaculopathy 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%

  3. IntroductionCorneal Light Shields • 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”.

  4. Methods • 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.

  5. MethodsCorneal Shields Used 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).

  6. MethodsPorcine eyes preparation 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. 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

  7. MethodsFormation of a “hot spot” • 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.

  8. Results The actual amount of light attenuation (mV) for each shield is shown on the x-axis. A percentage attenuation was also calculated after subtracting out background illumination. ANOVA (p<0.001)

  9. Results 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).

  10. ResultsFormation of “Hot spots” 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.

  11. ResultsSummary • Highest attenuation levels: • Hessburg 8.5mm shield • 8.5mm brown surgical glove • Several shields ineffective • Less than 10% total light (5/9) • Less than 75% 505nm light (6/9) • 8.5mm shields are more effective.

  12. Conclusion • 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 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 commercially available Hessburg shield. • 4mm Lindstrom keratoplasty shield was not effective in our study. • Do not become complacent after placing a light shield

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