INTERACTIVE IOL CALCULATION IN THE WORLD WIDE WEB
HAIGIS W
University Eye Clinic, D-97080 Wuerzburg, Germany
w.haigis@augenklinik.uni-wuerzburg.de
Introduction
The Internet or World Wide Web (WWW) with its vast possibilities for communication and information interchange is attracting growing public interest. More and more hospitals, research institutes and other institutions from the ophthalmological field are going online to be globally represented on the Web. Mostly, the web is used as a big data warehouse providing information to users in the form of digital documents or files. To offer interactive services like the calculation of intraocular lenses, which involves user-activated program execution, one has to has full control over an internet host. Therefore, we set up our own web server and launched our internet presence in July, 1996.
Web Server of the University Eye Hospital of Würzburg
Our server consists of a standard no-name IBM compatible PC with 80486/50 CPU, 16 MB RAM and 50 MB IDE HD, running the well-known web demon Windows httpd V1.4c ((C) by Robert B. Denny, Pasadena, USA, URL: http://tech.west.ora.com/win-httpd/) under Microsoft Windows 3.11. Any computer with standard software and internet access can contact this host under the address (URL)
http://www.augenklinik.uni-wuerzburg.de
On our homepage - in German, since this is a German site - different options may be selected. One of them is the 'Service' link, characterized by additional English language support. Following this link will lead to the page of the Department of Echography. Here, different services are offerered through HTML documents in German as well as in English. Among them are image databases for conventional and high frequency diagnostic ultrasound and, as a novel and special service, interactive calculation of intraocular lenses.
Online IOL calculation
The document providing this service is characterized by the URL
http://www.augenklinik.uni-wuerzburg.de/uslab/iolfrme.htm
(English version). It may be accessed by selecting 'IOL calculation' on the page of the Department of Ultrasound. Further hyperlinks on this document lead to a description of the algorithms used for the calculations and to literature references.
Calculations may be performed for two user-defined intraocular lenses on the basis of different algorithms. At the moment, the SRK II formula (URL: http://www.augenklinik.uni-wuerzburg.de/uslab/ioltxt/srk2e.htm) and the calculation according to HAIGIS (URL: http://www.augenklinik.uni-wuerzburg.de/uslab/ioltxt/haie.htm) are implemented. We plan to offer additional IOL calculation algorithms in the future.
To perform an individual calculation, an input mask (Fig.1) embedded into the document has to be filled in. On first access, all data fields in the mask are initialized with dummy data now to be replaced by real patient data. Likewise, the IOL types (IOL #1 and IOL #2) for which the calculations should be carried out need to be characterized. This is done by entering the lenses' A- or ACD-constants and by marking which one of these constants is to be used for the calculation. Finally, the IOL formula itself has to be selected.
Having come so far, calculation is initiated by a click on the 'Perform calculation' button. This causes the calculation program to be executed on our server. If erroneous data is detected, an error message is sent back. If not, our server returns the results as shown in Fig.2 for the calculation according to HAIGIS. Apart from the original input data on the left side, the results for the 2 IOLs selected are given as tables, stating IOL power, resultant refraction and expected aniseikonia. Of course, aniseikonia assessment works only if the respective data for the fellow eye had been entered before.
IOL calculation algorithms
Whereas the SRK II algorithm is a well-known regression expression described in the literature (SANDERS, RETZLAFF & KRAFF, 1988), the formula behind the calculation according to HAIGIS (e.g. HAIGIS, 1996) is the standard thin lens formula underlying all popular theoretical IOL formulas. Special about our implementation is the way the optical ACD is calculated: We are making use of the preoperatively measured acoustical ACD and axial length and do effectively use three IOL constants: a0, a1 and a2. Thus, our algorithm may be applied in either of two ways: in standard and individualized mode. In standard mode, a0, a1 and a2 are given default values. In individualized calculation mode, these 3 constants are optimized for each lens and each surgeon from an analysis of his/her individual postop results. These results, of course, have to be sent back to our server prior to be able to benefit from the individualized calculation. To make use of this service, another document on our server (URL: http://www.augenklinik.uni-wuerzburg.de/uslab/refbfrme.htm) has to be accessed.
Server Statistics
Since the launch of our server on July 19, 1996 to April 1, 1997, the overall access count reaches nearly 12 000 with a volume of transferred data of 94 MByte. We have served about 800 unique sites. Our service document ranks number 2 as per access, superseded only by our research documents. IOL calculation accesses decreased slightly from a startup peak of 20 to 10 accesses per month in December 1996, only to increase again significantly and reaching 40 accesses per month in March 1997.
Panta Rei
The INTERNET is a highly vivid, dynamical system. Hosts appear, disappear, reappear; new servers show up in ever-increasing numbers. Information is added, edited, withdrawn, modified or erased. All this and more also happens to our server, its documents and its services. Insofar does this report not give a static picture, but rather a snapshot of real life on and around this computer. Everything is changing - nevertheless, it is worthwhile to visit our homepage and have a look. So, just drop by !
References
HAIGIS W: Einfluß der Optikform auf die individuelle Anpassung von Linsenkonstanten zur IOL-Berechnung. In: 9. Kongress d. Deutschen Ges. f.Intraokularlinsen Implant., Kiel 1995 , hrsg.v. R Rochels, GIW Duncker, Ch Hartmann, Springer Heidelberg, 183-189, 1996
SANDERS DR, RETZLAFF J, KRAFF MC: Comparison of the SRK II formula and other second generation formulas. J Cataract Refract Surg 14: 136-141, 1988
Figures
