Invited Symposium: Glaucoma: Diagnosis and Therapy
Lege, B (University Eye Clinic, Wuerzburg, Germany)
Grehn, F (University Eye Clinic, Wuerzburg, Germany)
Short eyes require a more precise attention to the calculation of intraocular lenses. In order to focus on the retina, the natural lens of these eyes is usually thicker, the corneal diameter as well as the corneal radius of curvature is smaller, and the anterior chamber is shallower than in normal eyes. Due to the small anatomical dimensions, keratometry and ultrasonic measurements are more sensitive to systematic measurement errors. Moreover, depending on the individual A-scan unit used for biometry, a shallow anterior chamber as well as a thick lens might result in faulty measurements since the system does not anticipate such variations in ocular dimensions. Assuming that we have obtained precise measurements, we then have to deal with the necessary high dioptric power of the intraocular lens (IOL). Usually, these powers are not readily available. The lenses even might have to be especially designed and manufactured. High-powered lenses are 'thick' lenses optically, giving rise to calculation problems for the usual IOL algorithms which are based on infinitely thin lenses. In addition, possible errors due to different power-labelling policies (total power vs (back) vertex power) of lens manufacturers become more pronounced for high power IOLs. In acute angle closure glaucoma, we normally are faced with an extreme situation of the above increased thickness of the lens and small corneal diameter and radii. Corneal edema may contribute to problems occuring with keratometry. We retrospectively analyzed the results of IOL implantations in patients with short eyes, among them cases with non-glaucomatous short eyes as well as patients with a history of angle closure glaucoma. Factors (like differences in anterior chamber depth, lens thickness and axial length) contributing to the quality of IOL calculation will be demonstrated and discussed in detail for both groups.
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|Haigis, W; Lege, B; Grehn, F; (1998). IOL Calculation Difficulties in Short Eyes with Special Attention to Angle Closure Glaucoma Patients.. Presented at INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Invited Symposium. Available at URL http://www.mcmaster.ca/inabis98/nemeth/haigis0830/index.html|
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