IRIS CLAW LENS

letters to the editor This section is an open forum and consists of the opinions and personal commentary of the writers. The views expressed are exclusively those of the writers and do not purport to reflect those of ASCRS or the Journal.

To the Editor: I always read the Consultation Section with interest. However, I would like to voice some criticism of the section in the March 1991 issue (pages 229 to 240). It dealt with the question of which intraocular lens (IOL) to implant in an aphakic eye without a posterior capsule. The journal spent 11 pages on three possibilities, i.e., the angle-fixated anterior chamber lens and a posterior chamber IOL which is either sutured to the sulcus or to the iris (Drews). These answers were to be expected from the colleagues who were asked to respond. A fourth alternative, the iris claw or lobster claw lens, was not mentioned because no surgeon acquainted with this IOL was asked for a contribution. Although the iris claw lens is not available in the United States, the Journal of Cataract and Refractive Surgery is not read only by surgeons in North America and I think it justified to draw attention to this fourth alternative. The iris claw lens has a 5.5 mm optic and is fixated to the anterior surface of the iris by two claws at diagonally opposite ends of the haptic. The lens was designed by Worst in 1978 and since then has been widely used in Holland and in India.l-4 In 1987 I reported my experience with the lens5 and I continue to use it for secondary implantation or when capsule or sulcus fixation is not possible in primary cases. Strobel of Giessen University Eye Clinic performed an investigation with the laser flare cell meter on 68 eyes with iris claw lenses. 6 He found the protein content and the cell count in the anterior chamber of eyes with iris claw lenses as low as in eyes with IOLs after endocapsular implantation. Strobel also examined 23 eyes with iris claw lenses by fluorescein angiography and noted a complete lack of iris vascular leaks. 6 In summary, the impression of those of us who use this lens, based on approximately ten years of experience, is that the iris claw lens is an excellent alternative device for the correction of aphakia in eyes without a posterior capsule. P.U. Fechner, M.D.

Hannover, Germany

REFERENCES 1. Worst JGF. Iris fixated lenses: evolution and application. In: Percival P, ed, A Color Atlas of Lens Implantation, London, Wolfe Publishing Ltd, 1991; 80 2. Sing D. Correspondence on iris claw lens. Eur J Implant Refract Surg 1989; 1:285-287 3. Singh R. Scleral fixated intraocular lenses (letter). J Cataract Refract Surg 1991; 17:242 4. Alpar J, Fechner PU. Intraocular Lenses. New York, Thieme Inc, 1986; 328-335 860

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5. Fechner PU. Die Irisklauen-Linse. Klin Monatsbl Augenheilkd 1987; 91:26-29 6. Fechner PU, Strobel J, Wichmann W. Correction of myopia by implantation of a concave Worst-iris claw lens into phakic eyes. Refract Corneal Surg 1991; 7:286-298

TRANSVERSE ASTIGMATIC KERATOTOMY To the Editor: Regarding the article "Reduction of Corneal Astigmatism at Cataract Surgery" by Hall and colleagues (J Cataract Refract Surg 1991; 17:407-414), I have several questions and one or two comments. The article states that there were no perforations in any case, a total of244 incisions (four incisions for 61 eyes). My observation is that if no perforations occurred, the incisions were not deep enough. The article states that "all incisions were 3 mm in length." This is somewhat like fitting all adult males in size 90 shoes with no consideration for casual or dress styles, width, or arch supports. The paper states that the diamond blades were set at 0.003 mm (30 microns) greater than the "average paracentral (3 mm) optical zone." If pachymetry was d?n~ preoperatively at the 3 mm optical zone, why dldn t you measure the corneal thickness at the site of your proposed incisions? This may be part of the reason that every case was undercorrected. If the blade was set at 0.003 greater than the 3 mm optical zone depth for all incisions regardless of the transverse astigmatic keratotomy optical zone, only the 5.5 mm optical zone would be close to the proper depth and all others would be too shallow. The average cornea increases in thickness about 35 microns per millimeter. I agree with the authors that transverse astigmatic keratotomy (TAK) is an effective way to reduce corneal astigmatism during or after cataract surgery but I would suggest that greater accuracy can be achieved by being more precise in measuring corneal thickness, incision length, and depth. Spencer P. Thornton, M.D. Nashville, Tennessee

Gary W. Hall, M.D., replies: I agree with most of Dr. Thornton's comments. However, I would like to explain why we conducted our study as we did. The final effect of linear incisions on corneal astigmatism depends on several variables. A partial list of these include the following: length of TAK J CATARACT REFRACT

incisions, depth of TAK incisions, distance of TAK incision from optical axis (optical zone), intraocular pressure, elasticity of corneal stroma, capacity of regenerate stromal collagen (healing effect), corneal curvature (keratometry) and/or topography. With current technology and with some margin of error, we have the ability to measure all these except stromal collagen regeneration. (To my knowledge, no method for this has been developed.) Although a theoretical mathematical formula could be developed to predict the immediate effect of these incisions, the margins of error for both the measurement and implementation of surgical procedure are compounded to result in even larger margins of error with the final effect. As Theo Seiler showed in 1988, changing the depth of these incisions can have a profound effect on the final outcome. Similarly, many of us have experienced and reported volatility from incision length and optical zone. Since the quest is to arrive at the most clinically useful and predictable way to alter corneal astigmatism, studies need to be cautious about altering more than one variable at a time. Otherwise, how do we ascertain how much of the results were from the change in incision length or optical zone or incision depth? If something works, perhaps the end justifies the means, but I think we can and will do better. Greater than paracentral depth 0.03 mm is, for example, too shallow to achieve "maximum" effect. If, however, it achieves the desired effect, that is what we want. In a subsequent study (soon to be submitted for publication), we altered depths at the 7.0 mm optical zone with 0.03, 0.04, and 0.05 mm over the paracentral corneal depth. We found the 0.05 mm resulted in a significant number of cases of overcorrection (and microperforation). The 0.03 and 0.04 mm groups gave the "best" results. I agree that the more exactly we can measure and perform the surgical procedure, the better our results. Some of this must be weighed against clinical usefulness and efficiency. We have not, for example, used intraoperative pachymetry for the simple reason that it takes too long. Though we tried measuring pachymetry at the appropriate optical zone preoperatively, we found the margin of error too great to be any better than using a single central or paracentral measurement. In summary, we are dealing with a volatile procedure which needs greater accuracy and predictability. Yet, we would like all cataract surgeons to be able to perform these simply and routinely. The results can be very gratifying and with low complication. Perhaps Dr. Thornton and Dr. Gills are on the right track with penetrating keratotomy incisions which eliminate depth as a factor in the outcome.

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