[Continuous intraocular pressure measurement over several days with the Codman Microsensor--a case report].

Abstract

BACKGROUND: In eyes with irregular corneal surface (e.g. following bullous keratopathy, irregular astigmatism, edema or scars and following perforating keratoplasty), applanation tonometry often cannot be performed or results do not correlate with the clinical findings. In these cases, intraocular measurement of intraocular pressure is necessary. By puncturing of the anterior chamber, single measurements can be done for a short time period. Data of the course of intraocular pressure for a long period of time can not be assessed by this method. We report on two patients whom we implanted a continuously measuring probe into the anterior chamber for up to 96 hours instead of puncturing the anterior chamber. PATIENTS AND METHODS: A neurosurgical micro sensor (CODMAN, Norderstedt) was placed into the anterior chamber via a 1.2 mm wide and 4 mm long scleral tunnel. The data were transmitted to the ICP Express Display Monitor (CODMAN, Norderstedt) and displayed. From there, the data were transmitted to the multifunctional monitor DINAMAP Plus 8720 (CRITIKON, Norderstedt). After analog-digital transformation, the data were recorded on a personal computer with Pentium processor for analysis (patient #1: one measurement per minute, patient #2: one measurement per 10 seconds). In the first patient, implantation of the probe was indicated by enormous deviation of applanation tonometric measurements (12 to 20 mmHg) from the measurement results with the finger tips (25 to 30 mmHg). Clinical findings correlated to the higher intraocular pressure. Due to a decompensation of the corneal transplant, a re-keratoplasty was necessary. Within this operation, the micor sensor for continuous measurement of the intraocular pressure was implanted. The probe was explanted the next day. In the second patient, an primary chronical open-angle glaucoma in both eyes was known. In 1997, corneal transplantation has been performed in both eyes due to corneal dystrophy. Postoperatively, intraocular pressure stayed high. Applanation tonometry gave measurements of 16 to 20 mmHg although the measurement results with the finger tips exceeded 30 mmHg. To find out the real intraocular pressure and to have a basis for a rational therapy, we implanted the intraocular measurement probe for five days to determine the intraocular pressure at night and day. After measuring the baseline values, the efficiency of several antiglaucomatous drugs was tested to find out the drugs with the highest effect to prescribe it to the patient after the removal of measuring probe. RESULTS: The intraocular measurement with the CODMAN micro sensor could confirm in both patients that the measurements by applanation tonometry were wrongly too low. The measurement results with finger tips were confirmed by the intraocular measuring. The data had essential implications for the patients. Meanwhile, in both patients pressure lowering surgery was performed. The probe did not cause intraocular problems (1 day respectively 5 days). An irritation of the anterior chamber did not appear. In the first patient, the measuring probe moved from its position with following external filtration. So the probe was explanted only the next day. A movement of the probe tip can be avoided be appropriate subconjunctival suture fixation. CONCLUSION: Continuous measuring and recording of the intraocular pressure may be indicated, if applanation tonometry gives unreliable or even wrong results. Via a long scleral tunnel, a water-proof implantation into the anterior chamber is possible. Because a postoperative irritation could not be seen, we think that the probe only causes a minor falsification of the intraocular pressure. The described pressure measuring system allows measuring intraocular pressure continuously and assessing the individual effect of different antiglaucomatous drugs. Before using the probe as routine procedure, some improvements are necessary, e.g. smaller tip of the probe. The transmission wire to the