Purchase this article with an account.
PA Good, MA Burdon; B Scan Biometry in Clear Lens Extraction in Myopic Eyes . Invest. Ophthalmol. Vis. Sci. 2002;43(13):383.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Clear lens extraction provides an attractive alternative to corneal laser surgery particularly in high myopia. However, in order to achieve accurate and predictable post operative refractive outcomes an accurate biometry is required. A scan or optical biometry may be inaccurate due to posterior staphylomata or tilted discs. This study investigates the use of B scan biometry methods in the measurement of axial lengths prior to clear lens extraction. Methods: Twelve patients; 8 males, 4 females; age range 24 to 41 years, underwent A and B scan measurement of axial length. Their myopia ranged from -14D to -24D. A BVI Axis II biometer, and BVI CineScan S Scanner were used to perform the measurements. The latter has a specially modified time gain control which allows clear imaging of the anterior segment including the cornea. Anterior chamber depth was confirmed using the A scan biometer, and the macula was located either by measuring 3.5 mm from the optic disc, or by placing the cursor on the shallow indent made by the macula on this high resolution ultrasound. Results: The group mean axial length was 27.4 mm (range 25.2-31.9mm) Posterior staphylomata were noted in 14/28 eyes, and 18/24 eyes had tilted discs. All 12 treated eyes achieved a post operative refraction within 1 Dioptre of the predicted value. Eight eyes were within 0.5 D of the predicted refraction. It was calculated that if A scan measurements had been used alone to measure the axial lengths, only 9/12 eyes would have been within 1D, 5/12 within 0.5 D, and 2 eyes would have been ≷ 3D outside the predicted outcome. Conclusion: B scan measurement of axial length gives a highly accurate means of performing biometry in myopic eyes. The advantage over A scan biometry is that the macula can be precisely located. As clear lens extraction becomes increasingly popular this may be the preferred means of recording axial lengths.
This PDF is available to Subscribers Only