Highly precise and maintenance-free bearing technology for slit lamps in ophthalmology

What the drill is to the dentist, the slit lamp is to the ophthalmologist. It allows an insight into the different areas of the eye with up to 40x magnification and thus enables a holistic diagnosis and the detection of various eye diseases. The technical demands on the mechanical design of the medical device are high. One critical point is the movement of the microscope arm. The lamp must be very easy to move and the axes must be guided with high precision, as every irregularity and every clearance is communicated to the doctor via the microscope with 40-fold amplification. However, minimal travel is essential if the ophthalmologist is looking for haemorrhages on the retina, for example. At the same time, he must also be able to securely fix the microscope arm.
However, the slit lamps tested by the medical technology manufacturer A.R.C. focussed either on smooth operation or on precision. Both aspects were all the more difficult to achieve because the microscope is around 250 millimetres away from the bearing of the movable arm, creating a lever that makes precise and clearance-free positioning difficult.
It was also important for the plain bearing material to be homogeneous so that the sliding properties are always the same, even with machined components. Noiseless movement and freedom from lubricants are also important: the ophthalmologist does not want to have to relubricate under any circumstances. Last but not least, service life is a key criterion, as slit lamps are often in daily use for decades.

While searching for an optimal bearing solution, the A.R.C. designers came across the iglidur ® bearings. These bearings have already proven themselves in other areas of medical technology. If they perform infeed movements, bearings with the standard fit E 10 are usually sufficient. In the case of the A.R.C. slit lamp, however, significantly higher requirements had to be met. Here we are at the limits of what can be produced mechanically. For this reason, a customised solution was developed in close cooperation with A.R.C., which ensures an optimum fit with the smallest possible clearance and at the same time extremely smooth running and the possibility of fixing. The material pairing was also adapted to this bearing solution.
The plain bearings used are components made of iglidur® J - the bearings supplied as bar stock are machined with high precision down to the μm range in the A.R.C. production department in order to achieve the desired fit. During the design process, attention was also paid to minimising the wall thickness of the plastic bearings in order to ensure maximum dimensional stability. To make matters worse, A.R.C. makes openings in the bearing bushes so that electrical cables can be fed through the slit lamp arms.
A.R.C. also uses the plastic plain bearings at other bearing points of the slit lamp and is very satisfied with them. In combination with the stainless steel and brass materials used, perfect results are achieved there. This example impressively demonstrates that any reservations about the use of plastic bearings in medical technology are misplaced. On the contrary, these bearings can be used to achieve maximum precision, and the absence of lubricants is very advantageous for reasons of hygiene. The intensive endurance tests carried out by A.R.C. over a period of months also prove the durability of the precision bearing on the microscope arm.