Purpose
To investigate the accuracy of echography with a 20-MHz probe for evaluation of posterior lens capsule in traumatic cataract before surgery.
Design
Prospective interventional case series.
Methods
This study consisted of 43 eyes with traumatic cataract that were scheduled to undergo surgery. In all cases, cataract was dense enough to prevent visualization of the posterior lens capsule. Echography was performed using a 20-MHz probe to detect rupture of the posterior lens capsule. All patients subsequently underwent cataract extraction and intraoperative findings of the posterior lens capsule were compared with the preoperative echographic findings.
Results
This study included 43 eyes of 43 patients (38 men and 5 women) with a mean age of 35.6 ± 15.3 years (range, 4-68 years). The trauma was either blunt (4 eyes) or sharp (39 eyes); there was closed globe injury in 2 eyes and open globe injury in 41 eyes. By 20-MHz echography, posterior border of the crsytalline lens was clearly visualized in all 43 eyes. By 20-MHz echographic imaging, rupture of the posterior lens capsule was identified in 17 eyes (39.5%). During cataract surgery, it was noted that 14 eyes (32.6%) had rupture of the posterior lens capsule. Sensitivity, specificity, positive predictive value, and negative predictive value were 93%, 86%, 76%, and 96%, respectively, for 20-MHz echography to detect rupture of the posterior lens capsule. Also, the positive likelihood ratio, negative likelihood ratio, and odds ratio were 6.7, 0.08, and 81, respectively.
Conclusion
Echography with 20-MHz probe is an accurate imaging modality for detection of posterior lens capsule rupture in traumatic cataract preoperatively. This technique helps ophthalmologists have an appropriate surgical plan before operating.
Cataract formation is a well-known consequence of blunt and sharp ocular trauma. It results from direct lens injury, contusive ocular damage, or lens dislocation, and it is often associated with traumatic injury to the cornea, iris, and vitreous. A good preoperative evaluation, particularly of the posterior lens capsule, is necessary for determination of the best surgical plan to ensure satisfactory visual outcomes.
After trauma, for various reasons including associated corneal lacerations, hyphema, swollen cortical fibers, fibrin formation, and flocculent lens materials, it may be difficult to have a clear visualization of the posterior lens capsule by slit lamp biomicroscopy. Therefore, it is often necessary to use imaging modalities to evaluate the posterior lens capsule before surgery. However, the best method for evaluation of the posterior lens capsule in traumatic cataract has not been determined.
Echography has been used for a long time to evaluate ocular structures. Various frequencies of ultrasound have been employed in ocular echography for different purposes. Conventional 10-MHz B-scan echography, which is commonly used for evaluation of the posterior segment of the eye, has only limited visualization of the anterior segment structures including posterior lens capsule. Ultrasound biomicroscopy (UBM), which uses a 50-MHz frequency, provides high-resolution images of the anterior segment structures. However, with a 50-MHz transducer, the scan field is limited to 5 × 5 mm 2 with a depth of penetration of 5 mm in tissues. Therefore, because of lack of enough penetration, it provides only visualization of the anterior lens capsule and cannot assess other parts of the crystalline lens, including posterior lens capsule. To evaluate the entire anterior segment in a single scan, 12.5-, 20-, and 35-MHz transducers may be used. However, there are limited data on clinical application of echography with these transducers in evaluation of the posterior lens capsule.
Although in just 1 case report it has been demonstrated that 20-MHz echography is able to assess the posterior lens capsule integrity in traumatic cataract, accuracy of the device for evaluation of the posterior lens capsule remains unknown. Therefore, the purpose of this study was to investigate the accuracy of 20-MHz echography for evaluation of the posterior lens capsule in traumatic cataract before surgery.
Methods
This prospective study included 43 eyes of 43 patients with traumatic cataract who were scheduled to undergo cataract extraction. In all cases, cataract was dense enough to prevent visualization of the posterior lens capsule by slit-lamp biomicroscopy. Patients with significant irregularity of the globe contour, extensive vitreoretinal injuries, remarkable discomfort, or inability to cooperate for the imaging were excluded from the study. In cases with open globe injuries, the laceration was first primarily repaired and then echography was performed before cataract surgery. Patients with open globe injury and obvious rupture of the lens capsule received lens extraction at the time of primary surgery and therefore were excluded from the study. All patients or their parents, in the case of child patients, consented to participate in the study.
A few days before cataract surgery, echography was performed using a commercially available unit (Eye Cubed; Ellex Inc, Osaka, Japan) with a 20-MHz probe, providing 13 frames per second image acquisition rate. The image depth was 12 mm and the scanning width at the focal zone was 15 to 17 mm. Patients were scanned in a supine position using an immersion technique in which a scleral shell filled with saline solution as a coupling agent was used. Imaging was done in axial, longitudinal, and transverse sections to evaluate the crystalline lens, particularly to assess the presence of rupture of the posterior lens capsule, seen as a discontinuity in integrity of the capsule contour.
All patients subsequently underwent cataract extraction through an anterior limbal approach. Intraoperative findings of the posterior lens capsule were compared with the preoperative findings by 20-MHz echography to evaluate the accuracy of the imaging in detection of posterior lens capsule rupture. For this, sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio, negative likelihood ratio, and odds ratio for this imaging were determined. Sensitivity was calculated as true positives/true positives + false negatives; specificity was calculated as true negatives/true negatives + false positives. Positive predictive value and negative predictive value were calculated as true positives/total positives and true negatives/total negatives, respectively. Positive likelihood ratio was calculated as sensitivity/1 − specificity; negative likelihood ratio was calculated as 1 − sensitivity/specificity. Odds ratio was calculated as true positives × true negatives/false positives × false negatives.
Results
This study included 43 eyes of 43 patients (38 men and 5 women) with a mean age of 35.6 ± 15.3 years (range, 4–68 years). The trauma was either blunt (4 eyes) or sharp (39 eyes), resulting in closed globe injury in 2 eyes and open globe injury in the other 41 eyes. The mean visual acuity of patients before cataract surgery was 2.2 ± 0.7 logMAR (light perception to 20/40). All eyes had cataracts dense enough to preclude visualization of the posterior lens capsule by slit lamp biomicroscopy. The surgery was uneventful in all cases with no iatrogenic intraoperative complications.
Echography with a 20-MHz ultrasound probe was performed in all eyes without any complications. The echography was done 19.5 ± 7.8 days (range, 14–25 days) after trauma in eyes with closed globe injury and 9.3 ± 5.9 days (range, 4–17 days) after trauma and its primary repair in eyes with open globe injury. In all 43 eyes, it was possible to clearly visualize the posterior border of the crystalline lens by 20-MHz echography to evaluate its integrity. The posterior border was seen as a continuous, thick, and highly reflective interface clearly distinguishable from other ocular structures ( Figure , Left). By echographic imaging, discontinuity of the posterior lens capsule was identified in 17 eyes (39.5%) ( Figure , Right). However, during cataract surgery, it was noted that 14 eyes (32.6%) had rupture of the posterior lens capsule.
Comparison of the preoperative echographic findings with the intraoperative findings showed sensitivity, specificity, positive predictive value, and negative predictive value of 93%, 86%, 76%, and 96%, respectively, for 20-MHz echography to detect rupture of posterior lens capsule ( Table ). Also, positive likelihood ratio, negative likelihood ratio, and odds ratio were 6.7, 0.08, and 81, respectively.
| Intraoperative Findings | |||
|---|---|---|---|
| Intact PLC | Ruptured PLC | Total | |
| Preoperative 20-MHz echographic findings | |||
| Intact PLC | 25 | 1 | 26 |
| Ruptured PLC | 4 | 13 | 17 |
| Total | 29 | 14 | 43 |
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