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Intraocular Telescope

2008; Elsevier BV; Volume: 115; Issue: 5 Linguagem: Inglês

10.1016/j.ophtha.2007.12.024

1549-4713

Ümit Beden, Barış Sönmez, Dilek Erkan,

Intraocular Surgery and Lenses

We read the recent article by Orzalesi et al1Orzalesi N. Pierrottet C.O. Zenoni S. Savaresi C. The IOL-Vip System A double intraocular lens implant for visual rehabilitation of patients with macular disease.Ophthalmology. 2007; 114: 860-865Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar concerning rehabilitation of patients with a central scotoma. We think that the article can be strengthened if the following points are clarified. First, there is the possible source of the difference between the simulation results and the final results after the procedure mentioned by the authors in “Discussion.” The authors created a Galilean telescope by implanting −66-diopter (D) and +55-D lenses with a resulting magnifying power of ×1.3. However, we wish the authors would state whether the aphakia created at the beginning of the surgery had been included in the comparison of the magnifying power of the optical system with the simulation results, because in the study the intraocular lenses are implanted after phacoemulsification of the patients' own lenses, which had a +21.00-D power. Thus, the power change for the posterior chamber should be determined as −66.0 D (lens implanted) − 21.0 D (lens extracted) = −87.00 D. In this model, one can calculate the magnifying power of such a telescopic system compared with a normal phakic eye as power of the eye piece/power of the objective = 87/+55 = 1.58. Hence, a greater magnifying power than proposed by the authors can better explain the results obtained after the procedure than with the simulation, which was performed preoperatively with the phakic patient. The equation above is true only if the system is a Galilean telescope; otherwise, real magnifying power can be calculated by a thick lens model, which can be used to reduce the 2 individual systems to a single system with its own cardinal points. However, this model, as a rule, requires determination of the exact distance between the 2 lenses. The authors conclude that better results were obtained with myopic patients because of the increased axial length and increased distance between the 2 lenses.1Orzalesi N. Pierrottet C.O. Zenoni S. Savaresi C. The IOL-Vip System A double intraocular lens implant for visual rehabilitation of patients with macular disease.Ophthalmology. 2007; 114: 860-865Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar To reproduce a parallel light, the initial image obtained by the objective should be placed at the real focal point of the negative eyepiece; hence, the length of the telescope is fixed and determined by the power of the lenses that forms the telescope.2Von Noorden G.K. Visual acuity, geometric optical effects of spectacles and aniseiconia.in: Von Noorden G.K. Binocular Vision and Ocular Motility. 5th ed. Mosby, St. Louis1996: 114-121Google Scholar In a Galilean telescope, the lenses are separated by the difference in focal lengths. This difference according to the power of the lenses implanted would be determined as focal length of the objective lens − focal length of the eyepiece lens = (index of the media/power of the objective lens) − (index of the media/power of the eyepiece lens) = (1.33/55) − (1.33/66) = 2.42 cm − 2.02 cm = 0.40 cm = 4.0 mm. However, this result is true only if the effect of the aphakia is not included in the calculations; that is why we argue that the difference should be calculated as (1.33/55) − (1.33/87) = 2.42 cm − 1.53 cm = 8.9 mm. This (with addition of half thicknesses of the lenses) will add up to a 9.85-mm (8.9 mm + 0.95 mm) length for the entire telescopic system, which is probably not feasible for standard globe anatomy. Bringing the objective lens closer to the eyepiece will result in increase of the negative effect of the eyepiece, and the real magnification of such a system can be calculated by a thick lens model only if the exact distance between 2 lenses is known. This point could be clarified by postoperative biometric measurements of distance between the 2 lenses, which could help to evaluate the effect of deviation of lens positions on the final refractive result. Next, the authors propose that a Galilean telescope with a magnification of ×1.3 (a low magnifying telescope) can provide comfortable binocular vision. However, it is well known that aniseikonia with more than a 4% to 6% difference between two eyes generally results in disruption of binocular vision.2Von Noorden G.K. Visual acuity, geometric optical effects of spectacles and aniseiconia.in: Von Noorden G.K. Binocular Vision and Ocular Motility. 5th ed. Mosby, St. Louis1996: 114-121Google Scholar Thus, a magnification power of ×1.3 (meaning a 30% difference in dimensions perceived by the two eyes) will very likely disrupt the binocularity of these patients. Additionally, if we accept the magnifying power to be 1.58, as suggested above, binocularity would definitely be disrupted. These arguments do not negate the benefits of such a new lens design and procedure for central scotoma but hopefully help journal readers to understand and improve the results of the procedure in further applications. Author replyOphthalmologyVol. 115Issue 5PreviewIn reply to the comments about our article, we stress that the design of the intraocular lens (IOL) is covered by an international patent owned by Lenspecial S.R.L. (Milan, Italy). As a consequence, we had only limited information about the characteristics of this implant. We know that manufacturing the IOL requires special techniques, also covered by the Lenspecial patent. Other comments: Full-Text PDF