Polymethylmethacrylate (PMMA) is a rigid, relatively inert, lightweight material with a water content of less than 1%. It is durable and resistant to changes caused by aging and climate.1 Polymethylmethacrylate is still the standard intraocular lens (IOL) material against which newer materials are compared. The material has good tensile strength. Single-piece all-PMMA IOLs can withstand the level of stress necessary for implantation; however, excessive pressure on a haptic can lead to a fracture, usually at the optic–haptic junction, which is the weakest point of the IOL. Inside the eye, a PMMA IOL can withstand the physiological stress induced by fibrosis of the capsule.
To our knowledge, traumatic fracture of a PMMA single-piece posterior chamber (PC) IOL has not been reported. We present a case in which the IOL haptic was fractured at the optic–haptic junction following trauma.
An 18-year-old man presented to the cornea clinic of L.V. Prasad Eye Institute, Hyderabad, India, with a history of trauma to the left eye as a result of a fist injury. He had been a patient of the institute for some years. A review of the medical records showed that a corneal laceration caused by a stick injury in the same eye had been repaired 5 years earlier. Two months after the repair, a traumatic cataract in the eye had been extracted and a rigid single-piece PMMA PC IOL implanted. The surgical notes indicated that a posterior capsule tear occurred during cataract extraction. This necessitated an anterior vitrectomy, which was followed by uneventful implantation of the PC IOL with 1 haptic behind the anterior capsule flap (in the bag) and the other haptic in the sulcus at the 3 o'clock and 9 o'clock position. The patient was followed regularly. During these visits, the IOL was in the posterior chamber. At the last evaluation, 2 years postoperatively, the best corrected visual acuity (BCVA) was 20/20 and the IOL was well centered.
At the most recent presentation, the visual acuity in the left eye was 20/160, which improved to 20/100 with pinhole. Slitlamp examination of the eye revealed a linear full-thickness corneal scar above the pupil and pigment dispersion on the endothelium, confined to the inferior half of the cornea. The rest of the cornea was clear. The anterior chamber was deep, and the PC IOL optic with 1 attached haptic was anterior to the iris and pupil. The other haptic was visible behind the pupil (Figure 1). The posterior capsule had a tear, and the fundus examination was within normal limits. Examination of the right eye did not reveal any abnormality.
The PC IOL in the left eye was explanted; an anterior vitrectomy was performed, and a rigid single-piece PC IOL was implanted through a superior incision. During surgery, the broken haptic and the IOL with attached haptic were removed. There was no significant capsule fibrosis. At the last examination, the BCVA was 20/50. The decreased vision was primarily due to secondary glaucoma.
Fracture of an IOL after implantation is relatively rare. Shammas and Milkie2 report the traumatic fracture of a rigid Choyce-style anterior chamber IOL. Subsequently, there have been reports of traumatic2,3 and spontaneous4,5 fracture of anterior chamber IOLs. Although PMMA is a stable and relatively inert material, it inherently lacks flexibility. This lack of flexibility of the haptics varies with the molecular weight of the polymer and the variables involved in the manufacturing process, such as cooling rates, polishing, and finishing. Most modern single-piece all-PMMA IOLs have highly flexible and compressible haptics. However, the stress of conventional surgical manipulation could cause a fracture in a susceptible IOL.
Lambert and Grossniklaus6 report fracture of 1 or both haptics after IOL implantation in neonatal rhesus monkeys. The haptic fracture was related to the stress on the optic–haptic junction of the single-piece all-PMMA IOLs caused by rapid growth of the neonatal eye.7 We did not find any other report of fracture of a PC IOL at the optic–haptic junction secondary to trauma. The trauma in our case did not cause serious direct mechanical damage to the eye structures, although the eye had a corneal scar from a previously repaired corneal laceration. Under these circumstances, we think the fracture occurred because the IOL was fixated asymmetrically, with 1 haptic in the sulcus and the other in the bag. During blunt trauma, the rebound energy forced the IOL optic and the haptic in the sulcus anteriorly through the pupil, resulting in fracture of the enmeshed haptic at its junction with the optic. Since most of the energy was absorbed by the IOL, other ocular structures were not damaged.
In conclusion, although the current generation of rigid all-PMMA IOLs have more flexible haptics and reduced brittleness, the kinetic energy of blunt trauma may result in dislocation and fracture of the IOL.
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