PubMed · 7346431
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H C Agarwal, N N Sood, Y Dayal. 1981. Aphakic glaucoma.. https://pubmed.ncbi.nlm.nih.gov/7346431/
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BACKGROUND: In the management of congenital cataracts the correction of aphakia is still an unsatisfactorily solved problem. As far as surgical techniques and materials are concerned, the implantation of an IOL seems to be justified even in younger children; but choosing the refractive power of the lens is somewhat difficult regarding the expected growth of the eye. MATERIALS AND METHODS: A new type of IOL is presented as a solution for this problem. Being composed of a PMMA-fashioned optic and haptic it bears a silicone lens which is fastened on top of it. The supporting lens is made of PMMA (polymethylmethacrylate) with a biconvex surface with modified J-loops. The diameter of the optic is 6 mm, the overall diameter is 11 mm. The supplementary lens is made of the same silicone material as used for foldable intraocular lenses. Its diameter is 4.5 mm. This additional component can be removed from the implanted lens so that the needed reduction of refractive power after completed growth of the eye can be performed. The PMMA-fashioned basic component remains in situ just like a conventional posterior chamber lens. The lens was examined using scanning-electron microscopy. Im- and explantation was performed in isolated porcine eyes. RESULTS: The high quality of the lens could be demonstrated using scanning-electron microscopy. The technical feasibility of this concept could be demonstrated on isolated porcine eyes. DISCUSSION: Currently the sandwich lens is being tested in animal experiments. Our special interest is focussed on biocompatibility, formation of secondary cataract, biological reactions in the interface and the possibility of atraumatic explantation of the silicone lens.
Since 1974, I have used individual sound velocities for each eye condition encountered for axial length measurement. The calculation results in 1,555 M/sec for the average phakic eye. A slower speed of 1,549 M/sec was found for an extremely long (30 mm) eye and a higher speed of 1,561 M/sec was noted for an extremely short (20 mm) eye. This inversely proportional velocity change can best be adjusted for by measuring the phakic eye at 1,532 M/sec and correcting the result by dividing the square of the measured axial length (AL1,532)2 by the difference of the measured axial length (AL1,532) minus 0.35 mm. A velocity of 1,534 M/sec was found for all aphakic eyes regardless of their length, and correction is clinically significant. The velocity of an eye containing a poly(methyl methacrylate) intraocular lens is not different from an average phakic eye but it does magnify the effect of axial length change. I recommend measuring the pseudophakic eye at 1,532 M/sec and adding to the result (AL1,532), + 0.04 + 44% of the IOL thickness. The speed for an eye with a silicone IOL was found to be 1,476 M/sec (or AL1,532 + 0.04 - 56% of IOL thickness) and for glass, 1,549 M/sec (or AL1,532 + 0.04 + 75% of IOL thickness). A speed of 1,139 M/sec was found for a phakic eye with silicone oil filling most of the vitreous cavity and 1,052 M/sec for an aphakic eye filled with oil. For varying volumes of oil, each eye should be calculated individually. The speed was 534 M/sec for phakic eyes filled with gas. Eyes containing a silicone IOL or oil or gas will create clinically significant errors (3 to 10 diopters) if the sound velocity is not corrected.