Dr. Dilipkumar Batra, B15691, Dr. Chetan
Dhondiram Rathod, Dr. Shah Dhavalkumar
Maheshkumar, Dr. Mehul Ashvin Kumar Shah
IS OCT AN USEFUL TOOL FOR DETECTION OF POST-OPERATIVE ANGIOGRAPHIC MACULAR EDEMA
It is well known that macular oedema may develop after intraocular surgery. Postoperative macular oedema was recognised frequently after intracapsular cataract extraction (ICCE), especially in cases of vitreous loss, which has been named Irvine–Gass syndrome after the discoverers.1
With ICCE, the rate of postoperative macular oedema was around 2–20%, whereas it decreased to 1–2% with the widespread use of extracapsular cataract extraction (ECCE) with intact posterior capsule.2
With phacoemulsification although infrequent (incidence of 0.1-2%), it is still a main cause of unfavourable visual outcome after uneventful cataract surgery in healthy population.2
Two prospective studies did not show central macular edema (CME) causing decreased vision, even with a 9% increase in the mean foveal thickness measured with optical coherence tomography (OCT) and a 9% incidence of angiographic CME at 6 weeks after surgery.3
Pseudophakic clinically significant CMO is defined differently by various authors. When it is associated with a decrease in visual acuity of 20/40 or worse, it is categorized as clinically significant.2
Although the exact pathomechanism is not known, the role of surgical trauma with release of prostaglandins and blood retinal barriers disruption is suspected. Light toxicity and vitreo-macular traction may also have a role.2,4-5
Optical coherence tomography (OCT) is a relatively new method for high-resolution cross-sectional imaging of the retina that directly measures changes in the z-plane (depth of the retina). This method uses near-infrared light to detect relative changes in reflection at optical interfaces by the method of low-coherence interferometry. OCT has the advantages of being noninvasive, comfortable, and can be safely repeated as often as required.6
OCT has been found to be useful for objectively monitoring retinal thickness in patients with macular oedema, macular holes, or epiretinal membranes, with a high degree of reproducibility and repeatability.6,7
Cystoid macular oedema (CMO) is an important complication of cataract extraction, with uncertain aetiology. OCT can demonstrate cystic changes and increased retinal thickness in patients with CMO.6 As OCT has a high resolution of up to 10 mm, it may be able to detect subtle changes in retinal thickness that cannot be seen at clinical examination.
Optical coherence tomography (OCT) has been used to study macular changes after uncomplicated cataract surgery but the results are heterogeneous; retinal thickness is increased in some studies,2 whereas in others a decrease is reported.6 These studies are difficult to compare due to the use of different generations of OCT instruments, data analysis, post-operative treatment regimens and probably a high incidence of measurement artefacts.
The purpose of this study was to determine macular thickness changes by Cirrus HD OCT measurements which are precise and highly repeatable, after uncomplicated cataract surgery in otherwise normal eyes by an experienced surgeon.
AIMS & OBJECTIVES
- To determine the clinically insignificant angiographic macular edema through Optical coherence tomography (OCT) changes in macular thickness after uncomplicated cataract surgery.
We obtained consent from ethical committee.A prospective cohort study.All patients presenting to Cataract clinic at Drashti Netralaya, Dahod, Gujarat from January 2012 to October 2016 with cataract, as diagnosed by the anterior segment specialist were enrolled in this study. All patients had a complete ophthalmic examination which included: Ophthalmic and systemic history, visual acuity testing, intraocular pressure measurement, Cycloplegic refraction, Slit lamp examination of anterior segment bilaterally, Dilated fundus examination bilaterally by either indirect ophthalmoscope or slit lamp biomicroscopy. All patients having uneventful surgical outcome.
Included subjects underwent retinal scanning using Cirrus HD-OCT: The Macular Cube 512×128 Combo protocol was used. The protocol consists of two perpendicular line scans centered at the fovea followed by a cube scan also centered at the fovea. The line scans were 6 mm in the transverse direction, had a 2-mm axial depth, and were composed of 1,000 axial scans each. The cube scan was 6 × 6 mm, had a 2-mm axial depth, and was composed of 512×128 axial scans. Patients underwent cataract surgery either SICS or Phacoemulsification depending on decision taken by the senior operating surgeon. Postoperatively standard protocol was used, patients received moxifloxacin 0.5% three times a day and prednisolone acetate 1% six times a day for 3 days, followed by moxifloxacin 0.5% two times a day and prednisolone acetate 1% four times a day for 1 month. After 1 month prednisolone acetate 1% was tapered weekly.
Patients were evaluated on post-operative days 3, 60 and 90 with Cirrus HD-OCT ,slit lamp biomicroscopy, indirect fundus examination and visual acuity testing.
The data was analyzed using Statistical Package-SPSS-22/Medical.
Between-group comparisons were conducted using the Pearson x2 test for categorical variables.
In our primary analysis, we compared changes in macular thickness after uncomplicated cataract surgery.
SCAN SELECTION CRITERIA:
For the macula database, each eye was scanned three times with the Macular Cube 512×128 scan.
The scans were reviewed for image quality. One best quality scan for each scan type was chosen for each subject per eye.
Scans having the following characteristics were excluded from the normative database:
- Signal Strength of 3 or lower.
- Large eye motion during image acquisition, resulting in a saccade that was within the central 80% of the scan area.
- Area of data loss greater than 10% at the edge of the scan area.
- Presence of floater(s) obscuring macular area on Macular Cube scan.
Our study was a retro-prospective observational cohort study with a total of 262 eyes of 227 patients, who satisfied the inclusion criteria.
All the eyes included were thoroughly examined and cataract surgery was performed in Cataract And Refractive Surgery Department of Drashti Netralaya, Dahod, by the Head of Department.
All the findings were recorded on pre-tested proforma, all data was tabulated and statistically analysed using SPSS 22.
We evaluated a total of 262 eyes of 227 patients of which 113 (43.13%) were males and 149 (56.87 %) were females. Maximum males were in age group 61-70 years and maximum females were in age group 51-60 years.
TABLE 1. Demographics distribution in current study.
(P value< 0.209)
The average preoperative BCVA was significantly poor due to cataract in the eyes scheduled for surgery. At all points, average BCVA of the operated eyes was significantly improved with respect to that of the preoperative BCVA. Table 3 and Graph 3 shows number of patients with visual acuity preoperatively, 3rd day post-operatively, 1 month post-operatively and 3rd day post-operatively.
Preoperatively 77% patients were with best corrected visual acuity poor than 6/24 (Table 4 and Graph 4), which improved to 100 % patients with best corrected visual acuity better than 6/12 on 3rd day post-operatively.
1 month postoperatively 6 patients presented with deterioration of BCVA, out of which 3 patients deteriorated to BCVA less than 6/24 and 3 patients with BCVA 6/12-6/9.
Further, 3rd month postoperatively, 13 patients presented with deterioration of BCVA less than 6/12. Number of patients with BCVA 6/6 were 245(93.5 %) on 3rd postoperative day, 239(91.2%) on 1 month postoperatively and 214(81.7%) on 3rd month postoperatively.
TABLE 2. Distribution of patients preoperatively and postoperatively (3rd day, 1 month and 3rd month) according to BCVA (best corrected visual acuity)
|Visual Acuity||NO OF PATIENTS AT PREOP||NO. OF PATIENTS AT 3RD DAY POST-OP||NO OF PATIENTS AT 1 MONTH POST-OP||NO OF PATIENTS AT 3RD MONTH POST-OP|
CENTRAL MACULAR THICKNESS
The initial preoperative average value of central macular thickness is 236.8 ± 40.6504 µm which increased to 241.2 ± 32.4737 µm postoperatively 3rd day to 249.8 ± 39.8109 µm postoperatively 1 month and 254.8 ± 45.5785 µm postoperatively 3rd month.
The average change in central retinal thickness from preoperative to 3rd day postoperative was 4.4 ± 38.7762 µm, preoperative to postoperative 1 month was 13.0 ± 43.0469 µm and preoperative to postoperatively 3rd month was 18.0 ± 51.1109 µm which is significant.
On comparing preoperative central macular thickness with 3rd day postoperative central macular thickness there were changes in preoperative to 3rd day postoperative with CMT 151-200 µm in 5.7% and 6.1% patients, 201-250 µm in 54.96% and 57.25% patients, 251-300 µm in 33.2% and 32.8% patients, 301-350 µm in 1.9% and 2.7% patients and 351-400 µm in 0.76% and 0.38% patients.
Distribution of patients according to central macular thickness value preoperatively and postoperatively ( 3rd day , 1 month and 3rd month).
|Central Macular Thickness
|Central Macular Thickness(Pre-Op)||Central Macular Thickness(Post Op 3rd day)||Central Macular Thickness(Post-Op 1 Month)||Central Macular Thickness(Post-Op 3rd Month)|
Graph 4. Distribution of patients according to central macular thickness value preoperatively and postoperatively ( 3rd day , 1 month and 3rd month).
Similarly, on comparing 3rd day postoperative central macular thickness with 3rd month postoperative central macular thickness, patients with CMT 151-200 µm was 6.1% and 3.1%, 201-250 µm were 57.3% and 50.8%, 251-300 µm were 32.8% and 37.8%, 301-350 µm were 2.7% and 4.6% and with CMT 351-400 µm were 0.38% and 1.5% respectively. (Table 8)
Comparison of central macular thickness – preoperative with 3rd day postoperative.
| 3rd DAY
| Central Macular Thickness (in µm)
On applying chi square test, the chi square (x2) statistic is 309.277. P value is 0.00 which is statistically significant (p<0.05).
Comparison of central macular thickness – 3rd day postoperative with 3rd month postoperative.
| 3rd month
|Central Macular Thickness (in µm)|
On applying chi square test, the chi square (x2) statistic is 130.224. P value is 0.00 which is statistically significant.
shows relationship between Central Macular Thickness at Post Op 3rd Day and central Macular thickness at Post Op 3rd Months, and the relationship is statistically significant.
Our study included patients from various age groups, including minimum age of 22 years to 80 years of age. Mean age was 59.4 ± 9.7 years and the maximum numbers of patients were between 51-60 years of age.
Stern AL et al 108 studied pseudophakic cystoid maculopathy and found that young patients less than 65 years of age, had a much higher incidence of pseudophakic cystoids maculopathy.
In 2012, Vukicevic M et al 238 studied 80 patients (100 eyes) with cataracts and an age range of 40 to 90 years (mean 76.18 years).
The mean age of patients in the study was correlated with the age of presentation of cataract morbidity.
In our study of the 262 eyes only 3 eyes developed clinically significant macular edema after just 1 month of uncomplicated cataract surgery, all of which are under 65 years of age. This shows a positive correlation between age and postoperative macular edema.
We evaluated a total of 262 eyes of 227 patients of which 113 (43.13%) were males and 149 (56.87 %) were females. Maximum males were in age group 61-70 years and maximum females were in age group 51-60 years. Thus, we found that females are more disposed for the development of cataract.
This can be due to the lack of estrogen in post menopausal years, as estrogen has an inhibitory feedback on cataractogenesis.
Harvey Simon et al 248 have described females to be more at risk for development of cataract in their study on cataract risk factors.
Robert MB et al 249 studied the protective effect of estrogen in age related cataracts and found a positive association between the two.
In our study on 262 eyes, preoperative BCVA was less than 6/24 in 203 eyes (77% patients), which improved to BCVA better than 6/12 in 262 eyes (100 % patients) on 3rd postoperative day after uncomplicated cataract surgery. This was due to removal of cataract which is a leading cause of preventable blindness in developing countries like India.
Park K. defined cataract as a principle cause of blindness in India accounting for 62.6%
The distribution of preoperative visual acuity in the study group ranges from BCVA less than 1/60 to BCVA of 6/9 .
Since OCT is the investigative tool under the study and for satisfying the inclusion criteria we need to have preoperative scans with signal strength of 4 or more so, all patients with dense cataract and very low visual acuity were excluded.
In our study, we found that 3 eyes (1.15%) developing deteoriation of BCVA more than 6/12 after 4 weeks, which increases to 13 eyes (4.96%) at 3rd month postoperatively .
After complete clinico-investigative workup, OCT in these eyes revealed macular edema. This was in accordance with the fact that cystoid macular edema is more prevalent within 12 weeks following surgery.
Development of macular edema can be explained by the fact that in any tissue, edema occurs when the rate of capillary filtration increases more than rate of fluid removal from perivascular interstitium. The development of postoperative CME is based on Starling’s hypothesis and its relationship to the blood-brain barrier [BRB].88-90
The anatomical structure of macula is predisposed to the collection of fluid. The horizontal course of the outer plexiform layer extends transversely from cone nuclei to bipolar cells, and the resultant laxity of this layer predisposes to the formation of a reservoir for the accumulation of transudate94.In addition to this, the avascularity of the foveolar area restricts absorption250 .Another contributing factor is that, the foveal region has large concentrations of cells with a high metabolic activity. Inflammatory, metabolic, or vascular disturbances can lead to increased concentrations of tissue metabolites with angiographic CME in which patients have normal visual acuity, but their FA reveals detectable leakage from the perifoveal capillaries.
Visual acuity does not correlate with the presence of cyst formation, but it correlates with the number, size and location of the cysts. Thus, just the presence of cysts will not affect the visual acuity, it is the characteristic of the cysts that will determine the conversion of angiographic macular edema to clinically significant macular edema.
Carlo Caginia et al239 found that with respect to preoperative values, visual acuity improved significantly postoperatively though there is an asymptomatic increase in macular thickness and volume at 12 weeks after the surgery.
Rathi N et al251 studied the relationship of macular thickness as determined by OCT to best corrected visual acuity (BCVA) and concluded that there is a significant correlation between foveal thickness and BCVA.
Kusbeci T et al238 found that increase in macular thickness did not correlate with BCVA at postoperative 1st and 4th weeks but there was a significant correlation at postoperative 12th and 24th weeks.
Nicholas S et al 252 investigated correlations between optical coherence tomography macular thickness measurements and visual acuity after cataract surgery in 62 patients and concluded that there may be a threshold relationship between degree of foveal anatomic change and significant loss of visual acuity.
Burkhard von Jagow et al 241 studied macular thickness after uneventful cataract surgery by optical coherence tomographyin 33 patients, in whom phacoemulsification and intraocular lens (IOL) implantation was performed in one eye, and the contralateral eye served as control and concluded that after cataract surgery, a mild increase of foveal thickness without impact on visual acuity could be observed, this increase may be due to both subclinical changes and the influence of changes in media opacity on the measurement technique.
They also found that surgical and biometric parameters such as phacotime and energy and axial length did not correlate to the degree of macular thickening.
Brar et al 253 in their study demonstrated that visual acuity was not found to be statistically different across the different etiologies (p = 0.1) and there was no correlation between visual acuity and cystic changes on OCT.
In about 90% of patients with macular edema following cataract surgery, a spontaneous resolution of the edema and a recovery of visual acuity can be observed.
Our study demonstrates increase in macular thickness after uncomplicated cataract surgery as measured by OCT on postoperative 3rd day, 1 month and 3rd month.
The average change in central macular thickness shows increase from preoperative values to postoperative values and this change is found to be significant.
In various studies, similar subclinical macular thickening has been reported after uncomplicated cataract surgery.
Kusbeci T et al238 evaluated the central macular thickness (CMT) and the cystoid macular edema (CME) after uncomplicated phacoemulsification surgery and found statistically significant increase in CMT at postoperative 1st, 4th, 12th, and 24th weeks (p = 0.043). The most significant increase in CMT was seen at 12th weeks (p = 0.028).
In their study the incidence of angiographic CME at postoperative 12th weeks was 3.2% and the appearance of CME in OCT was observed in 5.5% of eyes at postoperative 12th weeks.
They concluded that macular thickness changes after uncomplicated phacoemulsification surgery. Spectral domain OCT is helpful in detecting cystoid abnormalities and any increase in macular thickness at postoperative early periods.
Similarly, Irfan Perentea et al242 evaluated the effect of uncomplicated phacoemulsification surgery on macula by optical coherence tomography (OCT) in a total of 110 eyes of 102 patients, and found that the change in mean central foveal thickness was insignificant at postoperative 1st day (p > 0.05), and significant at 1st week, 1st, 3rd, and 6th months (p < 0.05 for all measurements).
They concluded that statistically significant increase in macular thickness was detected at postoperative early periods, after the 1st week after uncomplicated cataract operation.
In a similar study, M Gharbiyaet al2 studied macular thickness changes after uncomplicated cataract surgery using spectral domain optical coherence tomography (OCT) and demonstrated a significant increase in macular thickness up to 6 months after uncomplicated cataract surgery. The most important finding was the regional pattern of retinal thickening with an early involvement of the parafoveal area.
Z Biro et al 1 measured the foveal and perifoveal thickness of the retina after uneventful phacoemulsiﬁcation and posterior chamber intraocular lens (PC-IOL) implantation and found that no signiﬁcant change of the thickness values could be measured 1 day after surgery. However, a signiﬁcant increase could be detected on the postoperative 7, 30, and 60 days in the perifoveal 3.0 and 6.0mm sectors.
They concluded that OCT enables the detection of minimal increases in perifoveal retinal thickness even 6 months after cataract surgery.
Most of these studies show that there was initial reduction or no significant change in macular thickness in immediate postoperative period followed by increase in macular thickness on further postoperative visits.
This was in accordance with our study where initial postoperative visit was at day 3, and it can be explained by the fact that retinal thickness does not vary or increase due to surgery-induced inﬂammation shortly after cataract extraction.
A signiﬁcant decrease observed in some of the above studies like that of M Gharbiya et al 2 could be related to the inﬂuence of cataract on the preoperative OCT measurements or to an apparent thinning of the retina when the lens is replaced by an IOL because cataract may cause lightscattering effect that may give rise to artefacts in OCT measurements 254 .These studies used the 1st post-operative day measurements as the baseline retinal thickness.
Grewing R, Besker H.255 measured retinal thickness immediately after cataract surgery by optical coherence tomography. The change of retinal thickness was measured in 15 different points of the posterior part of the retina, half an hour after cataract extraction in a small number of patients (10 eyes), and there was no signiﬁcant change (p=0.8) compared to the preoperative values.
In our study, we reported a 4.96% (13 eyes) incidence of OCT detected clinically significant CMO. The incidence was found to be higher as compared with that documented in literature (0-2%).
It may be due to our definition of clinically significant CMO, which was based on ‘any change’ in visual acuity rather than a certain cutoff value in macular thickness. Different dosage regimen and duration of topical steroidal therapy, and the use of topical non-steroidal anti-inflammatory agents may also have a role in the observed difference.
In our study we compared the preoperative CCT with post-operative CCT on day 3 and 90, we found that patients having preoperative CCT between the range of 450-550 µm shows maximum propensity for early post-operative corneal edema i.e. on day 3 and did not show much change at 3rd month (long term post-operative corneal edema) and those with pre-operative CCT of more than 550µm may have a protective factor for the development of early as well as late post-operative corneal edema at 3rd month.
In relation to the pathophysiology inflammation is the central figure which leds to corneal thickening and edema.
With time edema subsides and corneal thickness reaches to the baseline values.
Edema of the corneal epithelium is significantly related to visual recovery after cataract surgery.
Zheng T et al 256 analysed corneal epithelial thickness after cataract surgery and its correlation with epithelial cell changes and visual acuity and found that maximum increase in central epithelial thickness and CCT correlated with the lowest achieved values of BCVA postoperatively.
Calabuig-Goena M et al 257 in a similar study found that immediate postoperative corneal edema following phacoemulsification irregularly affects the cornea at the sublayer level and that initially central and paracentral non-epithelial thickening takes place which is followed by subsequent central and paracentral epithelial thinning. These initial changes occurred more markedly closest to the main incision over the entrance pupil, which may have visual implications.
Interestingly, decline in visual acuity in the post-operative period due to corneal edema may be associated with PCME.
In fact Do JRet al 258 studied the role of transient corneal edema on the development of macular edema post uncomplicated cataract surgery and found that it is a predictive factor in the development of pseudophakic cystoid macular edema (PCME).
In our study we have included all the patients with in the bag PCIOL after uncomplicated cataract surgery but there still exists different schools of thought for the effect of site of IOL implantation over the corneal endothelium.
ACIOLs carry a poor prognosis because of the damage to the angle of the anterior chamber followed by iris claw lenses due to the prostaglandins induced inflammatory cascade.
Numa A et al 259 compared anterior vs posterior chamber lenses and their effect on the endothelium and found that those with anterior chamber lenses had severe endothelial cell loss and morphologic changes.
In our study of 262 eyes, 172 eyes who had undergone phacoemulsification were compared with 90 eyes who had undergone SICS for best corrected snellen’s visual acuity, central macular thickness and central corneal thickness on postoperative 3rd month.
The correlation for all the above variables with the type of surgical procedure was found to be statistically insignificant.
When we analyzed the changes in CCT, CMT and BCVA and its correlation with the type of cataract surgery(phacoemulsification and Manual SICS), we found that in patients who had undergone SICS, central macular thickness and central corneal thickness on 3rd postoperative month were more than those who underwent phacoemulsification but these findings were statistically insignificant (p>0.05).
Also, though we found that there was a small increase in CMT and CCT in patients who underwent SICS it did not have an impact on BCVA.
Von Jagow B et al studied macular thickness after uneventful cataract surgery by optical coherence tomography and found that there occurs a small increase of 3.5–6% in CMT after manual SICS. 241
Kim A et al244 in their study pointed out the importance of BCVA in evaluating macular edema and suggested that findings measured by OCT should be used in correlation with clinical findings and BCVA.
Alio J et al260 compared the different techniques i.e biaxial vs coaxial small-incision clear corneal cataract surgery and found that biaxial MICS was slightly more efficient.
In our study we found that the surgical technique either phacoemulsification or manual SICS, had no effect on our results.
In our study patients without any known predisposing causes for CME, were found to have subclinical increase in postoperative macular thickness in both phacoemulsification and manual SICS. This small amount of increase in macular thickness had no effect on final BCVA in either group.
Advances in HD-OCT technology now allow ophthalmologists to accurately and quickly evaluate the macula with very high resolution and detect changes that are not clinically relevant and that cannot be evaluated at the slit lamp examination.
Although this information is helpful, the clinician must remember that visual function assessment is most important when evaluating macular edema 148 or corneal edema. Therefore, because ultimate BCVA was excellent in both groups, our study does not support the routine use of any one procedure. It should be determined according to surgeons’ decision and expertise of the procedure in surgeons’ hand.
Although it is known that the length of phacoemulsification surgery, the phacotime and the phacoenergy all may influence the outcome, these parameters were not evaluated in our study. An average 40–50% phacoenergy was used in all of the cases.
What was known before
- Conflicting results in macular thickness change measured using optical coherence tomography (OCT) has been reported after uneventful phacoemulsification.
- Difficulty in comparison of the reports in the literature due to the use of older generation OCT instruments and variable data analysis.
What this study adds
- With the use of new technology a precise and highly repeatable OCT measurements of retinal thickness after uncomplicated cataract surgery.
- Our study showed a significant increase in macular thickness with a peculiar regional pattern of distribution over time, where the most significant changes were in the parafoveal areas.
- Our study also adds a fact that there is significant subclinical increase in central corneal thickness with improved BCVA in postoperative period.
- This study also compared the changes in macular thickness as well as central corneal thickness between phacoemulsification and Manual SICS.
Our study had the following limitations:
- The main limitation of our study was the quality of preoperative OCT scans of subjects with dense cataract. The media opacity obscures the signal to the retina and decreases the signal strength, so in our study we have included scans with signal intensity 4 or better.
- Some adjustment in retinal thickness measurement, may be required if the lens status is changed, as OCT measures the retardation of light when traversing through different ocular media. Thus, there is an apparent thinning of the retina when the crystalline lens is replaced by an intraocular lens.
- Due to the normal variation in retinal thickness, a cutoff point has to be determined to differentiate abnormal thickening from normal thickness. If a higher value is used (three SDs greater than the mean value),it would produce false negative results for patients with thinner retinas and if a lower value is used, false positive results would be obtained for patients with thicker retinas.
It is important to note that to determine the range of normal retinal thickness, we should assess the changes in macular thickness accurately. Along with the reliability of the measuring instrument, retinal thickness measurement can be affected by parameters such as axial length, body mass, age, sex, or race of the patients. 261-264
Van Velthoven et al 254 stated that mild nuclear cataracts have no significant influence on the retinal thickness.
Also as reported by Tappeiner et al 265 decrease of transmission to only 30% still allowed reliable analyses of the retinal layers which is required to speculate retinal thickness.
OCT is a new non-invasive technology that gives precise and highly repeatable measurements of retinal thickness after uncomplicated cataract surgery.
Our study shows that over time there is a significant increase in macular thickness after uncomplicated cataract surgery with a peculiar regional pattern of distribution, mainly involving the parafoveal areas.
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