Influence of Elevated Intraocular Pressure on the Posterior Chamber–Anterior Hyaloid Membrane Barrier During Cataract Operations

LABORATORY SCIENCES Influence of Elevated Intraocular Pressure on the Posterior Chamber–Anterior Hyaloid Membrane Barrier During Cataract Operations

Shiro Kawasaki, MD; Yoshitaka Tasaka, MD; Takashi Suzuki, MD; Xiaodong Zheng, MD, PhD; Atsushi Shiraishi, MD; Toshihiko Uno, MD; Yuichi Ohashi, MD

Objective: To investigate the influence of elevated in- (Spearman rank correlation; r=0.703, PϽ.001). In ex- traocular pressure on the posterior chamber–anterior hya- periment 2, mean peak intraocular pressure was signifi- loid membrane (PC-AHM) barrier during cataract op- cantly greater in the ruptured capsule–type eyes than in erations in ex vivo porcine eyes. the AC-, zonule of Zinn–, AHM (PϽ.001), or AHM- tear– (P=.02) type eyes, as well as in the AHM- and AHM- Methods: A pressure transducer was connected to por- tear–type eyes compared with the AC and zonule of Zinn cine eye anterior chambers (ACs). In experiment 1, ACs type eyes (PϽ.001). Intraocular pressure was signifi- were perfused for 20 seconds with balanced salt solu- cantly higher in eyes infused with ophthalmic viscosur- tion containing 1.0-µm fluorescein beads (10 eyes per gical devices with a higher molecular weight or sodium bottle height: 45, 85, 145, and 285 cm). In experiment hyaluronate concentration (PϽ.05). 2, 5 ophthalmic viscosurgical devices with different molecular weights and sodium hyaluronate concentrations Conclusions: Stress on the PC-AHM barrier increases were infused into the ACs (20 eyes per ophthalmic vis- as intraocular pressure increases. Ophthalmic viscosur- cosurgical device). After continuous curvilinear capsu- gical devices with a higher molecular weight or sodium lorrhexis, hydrodissection was performed. After both ex- hyaluronate concentration might induce increased IOP periments, PC-AHM barrier staining was evaluated during cataract operations. through the Miyake-Apple view. Clinical Relevance: To maintain normal PC-AHM bar- Results: Types of fluorescein staining patterns were clas- rier function, excessive intraocular pressure should be sified as AC, zonule of Zinn, AHM, AHM tear, and rup- avoided during cataract operations. tured capsule. In experiment 1, plateau intraocular pressure and staining type were positively correlated Arch Ophthalmol. 2011;129(6):751-757

HE SPACE BETWEEN THE Hydrodissection is necessary to sepa- posterior capsule of the rate the lens nucleus and capsule.3-5 How- lens and the anterior ever, in humans, this procedure has been hyaloid membrane (AHM) reported to cause posterior capsule rup- is thought to act as a ture,6 lens nucleus dislocation,7 and de- mechanicalT barrier separating the physi- tachment of the AHM.8 Rapid fluctua- ological and functional anterior portion tions in the IOP or elevated perfusion of the eye from the posterior portion of pressure during hydrodissection might the eye. This barrier is referred to herein cause AHM detachment or tears.1 as the posterior chamber–anterior hyaloid The magnitude of increased IOP dur- Author Affiliations: membrane (PC-AHM) barrier. During ing hydrodissection is strongly influ- Departments of Ophthalmology normal phacoemulsification and aspira- enced by the characteristics of the oph- (Drs Kawasaki, Tasaka, Suzuki, tion operations, the function of the thalmic viscosurgical device (OVD) filling Zheng, Uno, and Ohashi), PC-AHM barrier is well maintained and the anterior chamber (AC). For example, Ophthalmology and intraocular perfusion fluid does not flow when a viscoadaptive OVD is used, the IOP Regenerative Medicine into the vitreous cavity.1 However, in has been reported9 to increase to 170.9 (Dr Shiraishi), Cell Growth and recent years, significant increases in mm Hg in a porcine eye model. Tumor Regulation intraocular pressure (IOP) have been To our knowledge, there have been no (Dr Shiraishi), and Infectious 2 Diseases (Dr Ohashi), Ehime reported during phacoemulsification, studies on the effect of OVDs of different University Graduate School of especially during hydrodissection, molecular weights (MWs) on the PC- Medicine, Shitsukawa, nucleus fragmentation, irrigation and AHM barrier in porcine eyes. The pur- Toon-City, Ehime, Japan. aspiration, and intraocular lens insertion. pose of this experiment was to evaluate the

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©2011 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/28/2021 effect of 2 factors on the integrity of the PC-AHM bar- inserted under the anterior capsule at the 6-o’clock position, rier in isolated porcine eyes: perfusion pressure and in- contralateral to the corneal incision, and a mixture of fluores- creases in IOP during hydrodissection in ACs filled with cein bead solution and balanced salt solution was rapidly in- OVDs. fused at a rate of 3.0 mL per 10 seconds. Hydrodissection was performed by a surgeon (S.K.) who had no knowledge of which OVD had been used. The experiment was conducted on 20 eyes METHODS with each OVD and, immediately after the hydrodissection, the eyes were enucleated and examined as in experiment 1. Porcine eyes were selected as previously reported1 and examined with a slitlamp microscope. Eyes with corneal trauma or STATISTICAL ANALYSES other obvious abnormalities were not used. Spearman rank correlation tests were used to determine whether EXPERIMENT 1 a significant correlation existed between IOP and the staining type, a measure of AHM impairment. The Jonckheere trend test The effects of the pressure exerted on the PC-AHM barrier by was used to investigate these trends in more detail. Analysis of intraocular perfusion were investigated. To monitor the IOP, variance (ANOVA) was used for comparisons between multiple groups; when a significant difference was found by ANOVA a 16-gauge needle attached to a pressure sensor (DI-151RS; Ͻ DATAQ Instruments, Inc, Akron, Ohio) was introduced into (P .05), the Tukey-Kramer multiple comparison test was per- the AC at the 9-o’clock position of the cornea 1.5 mm inside formed. Data are given as mean (SD) unless otherwise indi- the limbus. A closed-eye condition was maintained, and there cated. was no leakage of the infusion fluid from the 16-gauge needle or pressure sensor. RESULTS A 27-gauge needle was attached to a bottle containing perfusion fluid consisting of balanced salt solution (BSS Plus; Al- con Laboratories, Fort Worth, Texas) and 1.0-µm fluorescein EXPERIMENT 1: EFFECT OF PERFUSION bead solution (Fluoresbrite Carboxylate YG 1.0-µm Micro- PRESSURE ON THE PC-AHM BARRIER spheres; Polysciences Inc, Warrington, Pennsylvania) at a ra- tio of 100:3.0 mL. The 27-gauge needle was introduced into Classification of Staining Patterns the AC at the 12-o’clock position of the cornea. Each eye was Observed via Miyake-Apple View perfused for 20 seconds, using bottle heights of 45, 85, 145, and 285 cm. Ten eyes were tested at each height. The fluorescein bead staining patterns of the zonule of At the end of the perfusion, when the 27-gauge needle was Zinn, ciliary body, AHM, and vitreous cavity observed removed, IOP returned to a normal level after 4 to 5 seconds via the Miyake-Apple view were classified into 4 types: in most eyes, with continuous leakage from the wound. Any the AC, zonule of Zinn (Zinn), AHM, and AHM tear IOP that remained relatively high was allowed to return to a normal level before the 16-gauge needle was removed. As a re- (AHT). The AC type was designated as a staining pat- sult, the AC did not collapse. tern in which fluorescein beads remained in the AC After the procedure, the eyes were cut horizontally at the (Figure 1A). When the fluorescein beads reached the equatorial region using a razor blade; the fluorescein staining zonule of Zinn, such eyes were classified as the Zinn type of the zonule of Zinn, ciliary body, AHM, and vitreous cavity (Figure 1B). Eyes in which the fluorescein beads were was then examined by ophthalmic surgical microscope via the situated in the space between the zonule of Zinn and the Miyake-Apple view10,11 and videotaped (camera: DXC-C33; Sony AHM were classified as the AHM type (Figure 1C); eyes Corp, Tokyo, Japan; lens: ML-0310VF; Moritex Corp, Tokyo). in which beads reached the vitreous cavity through tear formation in the AHM were classified as the AHT type EXPERIMENT 2 (Figure 1D). Formation of an AHM tear was visually con- firmed at the time of dissection.1 The influence of the pressure exerted on the PC-AHM barrier Eyes were also examined by scanning electron mi- during hydrodissection was investigated. A 2.8-mm corneal in- croscopy. In the AC-type eyes, a small number of fluo- cision was made at the 12-o’clock position in the porcine eyes, rescein beads were found in the zonule of Zinn (Figure 1E) and 0.4 mL of a viscoelastic substance was infused into the AC. and almost no beads were found in the ciliary body Four types of OVDs with different MWs and concentrations of sodium hyaluronate were tested: a very low-viscosity disper- (Figure 1I). In Zinn-type eyes, a large number of fluo- sive OVD (OVD-A: MW, 600 000 to approximately 1 200 000 rescein beads were found in the zonule of Zinn Da; 10 mg/mL), a medium-viscosity dispersive OVD (OVD-B: (Figure 1F), but almost no beads were seen in the cili- MW, 1 530 000-2 130 000 Da; 10 mg/mL), a viscous cohesive ary body (Figure 1J). In AHM-type eyes, many fluores- OVD (OVD-C: MW, 1 900 000-3 900 000 Da; 10 mg/mL), and cein beads were found in both the zonule of Zinn a viscoadaptive OVD (OVD-D: MW, approximately 4 000 000 (Figure 1G) and the ciliary body (Figure 1K). In AHT- Da; 23 mg/mL). In addition, 1 medium-viscosity dispersive OVD type eyes, the zonule of Zinn was partially damaged near (OVD-E) containing 30 mg/mL of hyaluronate and 40 mg/mL the AHM tear (Figure 1H). Because beads were found of chondroitin sulfate was used. The MW of hyaluronate in 12 mostly in the torn portions of the zonule of Zinn, the dam- OVD-E was 500 000 Da. After infusing the OVDs, a continu- age was thought to have occurred during hydrodissec- ous curvilinear capsulorrhexis was made, with an average diameter of 6.5 mm. tion rather than during processing of the samples. As in experiment 1, a 16-gauge needle attached to a pres- The degree of penetration of fluorescein beads was des- sure sensor was inserted through the peripheral cornea at the ignated as grade 1 to grade 4 based on the staining pat- 9-o’clock position. Hydrodissection was then performed (Naga- terns and scanning electron microscopic findings. A higher hara cannula; ASICO Llc, Westmont, Illinois). The cannula was grade indicated deeper penetration of the fluorescein beads

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E F G H

I J K L

M N O P

Figure 1. Miyake-Apple view images (A-D), scanning electron microscopy of the zonule of Zinn (E-H) and ciliary body (I-L), and schematic diagrams of staining patterns (M-P). The anterior chamber– (A, E, I, and M), zonule of Zinn– (B, F, J, and N), anterior hyaloid membrane– (C, G, K, and O), and anterior hyaloid membrane tear– (D, H, L, and P) type eyes. White arrowheads in H indicate tears in the anterior hyaloid membrane–type eyes.

A B C D

100 mm Hg Intraocular Pressure, 0 10 0 10 0 10 0 10 Time, s Time, s Time, s Time, s

Figure 2. Plateau intraocular pressures (A, 32.28; B, 52.23; C, 102.58; and D, 199.09 mm Hg) were reached after 18.0 seconds (A), 16.1 seconds (B), 13.5 seconds (C), and 9.9 seconds (D) for bottle heights of 45, 85, 145, and 285 cm, respectively. Black arrows indicate the start of perfusion.

in the posterior direction. Schematic figures for each stain- The mean (SD) plateau IOPs were 30.00(2.59) mm Hg ing grade are as follows: grade 1,AC type (Figure 1M); at a bottle height of 45 cm, 56.12(3.73) mm Hg at 85 grade 2,Zinn type (Figure 1N); grade 3,AHM type cm, 105.72(3.91) mm Hg at 145 cm, and 210.51 (Figure 1O); and grade 4,AHT type (Figure 1P). (15.34) mm Hg at 285 cm. The differences in the plateau IOPs of the 4 groups were statistically significant Relationship Between Bottle Height and IOP (PϽ.001, ANOVA). The IOP began to increase when perfusion began and reached a plateau at a time that varied The IOP values determined during perfusion at each bottle depending on the bottle height. The times required for height are shown in Figure 2. The IOP was highest at a the IOP to reach a plateau at each bottle height were 17.8 bottle height of 285 cm, followed by 145, 85, and 45 cm (0.8) seconds for a height of 45 cm, 16.6(0.7) seconds (all PϽ.001, Tukey-Kramer multiple comparison test). for 85 cm, 13.8(1.2) seconds for 145 cm, and 10.1(1.0)

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Staining Type (Grade)

AC (1) Zinn (2) AHM (3) AHT (4) Bottle height, cm, No. of eyesa 45 6 2 2 0 85 1 1 8 0 145 0 2 7 1 285 0 0 8 2 Plateau IOP, mm Hgb 32.28 (8.88) 63.39 (36.23) 117.00 (67.47)c 185.35 (71.50)d,e

Abbreviations: AC, anterior chamber; AHM, anterior hyaloid membrane; AHT, anterior hyaloid membrane tear; IOP, intraocular pressure; Zinn, zonule of Zinn. a Each group included 10 eyes. b Values are expressed as mean (SD). Staining type and plateau IOP were correlated (Spearman rank correlation; r=0.703, PϽ.001). c ACϽAHM (P=.01, Tukey-Kramer multiple comparison test). d ACϽAHT (P=.003, Tukey-Kramer multiple comparison test). e ZinnϽAHT (P=.04, Tukey-Kramer multiple comparison test).

A B C D E

F G H I J

Figure 3. Schematic diagrams of staining patterns observed using the Miyake-Apple view following hydrodissection. Diagrams are shown for the anterior chamber (grade 1) (A and F), zonule of Zinn (grade 2) (B and G), anterior hyaloid membrane (grade 3) (C and H), anterior hyaloid membrane tear (grade 4) (D and I), and rupture (no grade assigned) (E and J) eye types.

seconds for 285 cm. The differences in the time re- and the AHT-type eyes (P=.003, Tukey-Kramer mul- quired for each group to reach the plateau IOP were sig- tiple comparison test). The plateau IOP in Zinn-type eyes nificant (PϽ.001, ANOVA). The 45-cm group took the was significantly lower than that in AHT-type eyes (P=.04, longest time to reach the plateau IOP, followed by the Tukey-Kramer multiple comparison test). 85-cm group (P=.04), 145-cm group (PϽ.001), and Ͻ 285-cm group (P .001, Tukey-Kramer multiple com- EXPERIMENT 2: parison test). EFFECT OF HYDRODISSECTION ON THE PC-AHM BARRIER Relationship Between IOP and Staining Pattern Classification of Staining Patterns The relationship between the plateau IOP and the stain- Following Hydrodissection ing pattern seen at each bottle height is given in Table 1. A significant correlation was found between plateau IOP The 4 types of staining patterns designated in experi- and the staining grade (Spearman rank correlation; ment 1 were also observed after hydrodissection was per- r=0.703, PϽ.001). The Jonckheere trend test indicated formed in experiment 2. In addition, a new staining pat- that the staining grade became significantly higher as IOP tern was recognized in which the posterior lens capsule increased (PϽ.001). Moreover, a significant difference was ruptured. This was designated as the rupture type was found among the plateau IOPs of the 4 types of eyes and was not assigned a numeric grade because the rup- (P=.001, ANOVA); the plateau IOP in the AC-type ture occurred in an anatomically distant site, indepen- eyes was significantly lower than that in the AHM-type dent of bead penetration. Typical examples of each stain- eyes (P=.01, Tukey-Kramer multiple comparison test) ing pattern are shown in Figure 3.

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©2011 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/28/2021 Table 2. Staining Types and Peak IOP During Hydrodissection Performed With Each Viscoelastic Substancea

OVD

OVD-A OVD-B OVD-C OVD-D OVD-E P Valueb Amount of BSS injected, mL 1.38 (0.79) 1.29 (0.83) 1.05 (0.67) 1.50 (1.02) 1.45 (1.02) 0.47 Initial IOP, mm Hg 3.58 (1.61) 4.28 (1.91) 4.24 (1.25) 4.25 (1.33) 3.61 (1.34) 0.34 Peak IOP, mm Hg 15.49 (12.42) 21.08 (8.90) 40.96 (33.20) 115.33 (64.92) 56.08 (47.85) Ͻ.001 Staining type, No. of eyesc AC 16 15 7 0 10 . . . Zinn 4 2 9 2 3 . . . AHM032133... AHT 0 0 2 2 4 . . . Rupture 0 0 0 3 0 . . .

Abbreviations: AC, anterior chamber; AHM, anterior hyaloid membrane; AHT, anterior hyaloid membrane tear; BSS, balanced salt solution; ellipses, not calculated for the staining types; IOP, intraocular pressure; OVD, ophthalmic viscosurgical device; rupture, ruptured capsule; Zinn, zonule of Zinn. a Values are expressed as mean (SD) unless otherwise indicated. b Tukey-Kramer multiple comparison test. c Each group included 20 eyes.

A B C D E

100 Intraocular Pressure, mm Hg 0 2.0 0 2.0 0 2.0 0 2.0 0 2.0 Time, s Time, s Time, s Time, s Time, s

Figure 4. Increase in intraocular pressure during hydrodissection. Black arrows indicate start of hydrodissection. White arrows indicate peak intraocular pressure: 16.21 mm Hg (A), 19.47 mm Hg (B), 38.48 mm Hg (C), 137.80 mm Hg (D), and 56.06 mm Hg (E).

Relationship Between Staining Pattern (P=.01, Tukey-Kramer multiple comparison test) or the and Peak IOP During Hydrodissection OVD-B group (P=.048, Tukey-Kramer multiple com- Performed With Each OVD parison test).

Staining types and peak IOP values observed during hy- Relationship Between Peak IOP drodissection with each OVD are summarized in Table 2. and Staining Pattern Representative graphs of the change in the IOP during hydrodissection with each type of OVD are shown in The mean peak IOPs among the staining patterns were Figure 4. When OVD-A or OVD-B was used, the mean 21.19 (11.91) mm Hg (range, 4.03-50.61 mm Hg) for peak IOPs were only slightly elevated to 15.49(12.42) the AC-type eyes, 29.76 (15.91) mm Hg (range, 3.81- mm Hg and 21.08(8.90) mm Hg, respectively. In con- 57.05 mm Hg) for the Zinn-type eyes, 86.59 (60.31) trast, when OVD-C, OVD-D, or OVD-E was used, the IOP mm Hg (range, 16.21-245.62 mm Hg) for the AHM- increased to mean peak values of 40.96(33.20) mm Hg, type eyes, 122.47 (43.41) mm Hg (range, 75.18-211.48 115.33(64.92) mm Hg, and 56.08(47.85) mm Hg, respec- mm Hg) for the AHT-type eyes, and 189.47 (40.82) tively, within 2 seconds after hydrodissection was initiated. mm Hg (range, 142.42-215.38 mm Hg) for the rupture- No significant differences were found among the 5 type eyes. groups in the amount of balanced salt solution required A significant difference was found among the peak for hydrodissection (P=.47, ANOVA) or the IOP before IOP values of the 5 staining types (PϽ.001, ANOVA). hydrodissection (P=.34, ANOVA); however, there was The peak IOP in rupture-type eyes was significantly greater a significant difference among the groups with regard to than in AC- (P Ͻ .001), Zinn- (P Ͻ .001), AHM- the peak IOP recorded during hydrodissection (PϽ.001, (PϽ.001), or AHT- (P=.02) type eyes. Moreover, the peak ANOVA). A significantly higher peak IOP value was found IOP for AHT-type eyes was significantly greater than that in the OVD-D group compared with the other OVD groups of the AC- (PϽ.001) or Zinn- (PϽ.001) type eyes, and (PϽ.001, Tukey-Kramer multiple comparison test). In the peak IOP for AHM-type eyes was also significantly addition, the peak IOP value in the OVD-E group was higher than that of the AC- (PϽ.001) or Zinn- (PϽ.001) significantly higher than that in either the OVD-A group type eyes (all Tukey-Kramer multiple comparison test).

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©2011 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/28/2021 A significant correlation was found between mean peak cult for these OVDs to leave the eye. Because OVDs with IOP and the staining grade (Spearman rank correlation; higher concentrations of sodiumaluronate and high MW r=0.706, PϽ.001) and, as in the perfusion pressure ex- are less likely to leak from the AC during surgical ma- periment, the staining grade became significantly higher nipulation, careless maneuvers may lead to failure of the as IOP increased. PC-AHM barrier, as shown in the OVD-D or OVD-E groups. When such OVDs are used, it is necessary to avoid sealing the wound during hydrodissection. In contrast, COMMENT when using very low- or medium-viscosity dispersive OVDs, such as OVD-A and OVD-B, there is little need As modern cataract repair evolved into a sophisticated closed- to watch for rises in IOP. Thus, as minimal-incision cata- eye procedure, critical new surgical techniques were inte- ract operations become more widespread, the space- grated. Some of these techniques, such as hydrodissection occupying effect of OVDs should become less of a pri- and lens nucleus processing, are accompanied by in- ority and a different strategy for choosing OVDs may be creases in IOP. Because it is difficult to evaluate the effect warranted in general cataract cases. of increased IOP during these procedures, especially on the It is well known that the Miyake-Apple view is useful PC-AHM barrier, little information has been gathered. How- for examining the effects of surgical manipulations of the ever, by using fluorescein beads and porcine eyes, we were lens capsule and the zonule of Zinn during cataract opera- able to demonstrate that, as IOP increases, the PC-AHM tions. This technique allows the researcher to observe barrier is exposed to increasingly larger amounts of pres- movements of these structures that cannot be seen by the sure. Observation of fluorescein bead staining via the Mi- surgeon during nucleus separation or intraocular lens in- yake-Apple view allowed us to identify 5 different stain- sertion.11 As shown in this study, this technique, combined ing patterns: AC, Zinn, AHM, AHT, and rupture types, listed with fluorescein bead perfusion, offers a new approach for from the type experiencing the lowest pressure to that ex- evaluating the effect of IOP on the PC-AHM barrier. periencing the highest pressure. Among these patterns, the Because the fluorescein beads used in this study were AHT and rupture types are dangerous in terms of vitreal 1.0 µm in diameter, similar in size to bacteria, distribu- contamination because the PC-AHM barrier has broken tion of the beads may mimic bacterial contamination. For down in these situations. instance, in AC- or Zinn-type eyes, bacterial contamina- Previous studies have demonstrated that hydrodis- tion would be expected to remain within the AC, the cap- section produces large increases in IOP2,9 and damage to sule, or the zonule of Zinn. The 3-layered zonule of Zinn the zonule of Zinn or posterior capsule.6,7 For example, forms a tightly organized meshwork over the posterior Khng et al2 reported that IOP during hydrodissection chamber and acts as a filter to prevent further bacterial ranged from 78.6 mm Hg to 223.2 mm Hg in 4 human invasion. However, in the current study, because the eye cadaver eyes, and Ohnuma et al9 reported that it in- was exposed to higher amounts of pressure, the beads creased up to 170.9 mm Hg in porcine eyes. In this study, were prone to slip through the zonule of Zinn and ap- we also demonstrated that AHM tears and even rup- proach the AHM. Under conditions of higher pressure, tures of the posterior capsule are prone to occur owing the fluorescein beads either filled the posterior cavity or to excessive increases in IOP. Scanning electron micros- spread into the vitreous cavity through a tear formed in copy showed that tear formation in the AHM (Figure 1H) the AHM. Because formation of AHM tears offers a di- was associated with damage to the corresponding por- rect path to the vitreous cavity, these tears may be an im- tion of the zonule of Zinn in AHT-type eyes, indicating portant risk factor for endophthalmitis, equal to the risk that this region experienced a high amount of pressure. with posterior capsule rupture.18 We assume that AHM Our results indicate that eyes subjected to pressure higher tears may be one of the predisposing factors for postop- than 75 mm Hg during hydrodissection are at increased erative endophthalmitis in eyes that underwent a seem- risk for AHM tears, and those subjected to pressure higher ingly uneventful operation. than 140 mm Hg are at greater risk for posterior capsule This study has some limitations. First, although the rupture, emphasizing the importance of monitoring IOP general trends observed in porcine eyes are probably simi- in clinical practice, especially during hydrodissection. lar to those in humans, the IOP changes observed in our Our study also showed that the magnitude of in- model may not exactly reflect the changes in human eyes crease in IOP during hydrodissection varied widely de- because of the absence of aqueous flow. Second, the ana- pending on the type of OVD used. During cataract op- tomic structure of the anterior segment, especially the erations, the OVD plays a role in maintaining a surgical zonule of Zinn, is similar to that of a human eye, but the space in which continuous curvilinear capsulorrhexis can integrity of the tissue may be weakened in an enucle- be performed and the intraocular lens can be inserted. ated porcine eye. Third, we performed hydrodissection The OVD also protects the corneal endothelium. Re- by rapidly infusing balanced salt solution into the AC to cently, OVDs with different properties have been devel- examine the effect of increased IOP on the integrity of oped to accommodate a variety of clinical situations.13-17 the PC-AHM barrier in experimental conditions. How- Previous studies9 have found that IOP tends to increase ever, in clinical situations, breakdown of the PC-AHM more easily when a viscoadaptive OVD (OVD-D) is used barrier does not occur at such a high rate because, in most during hydrodissection. Similarly, the OVD-D13 and the cases, surgeons release the OVD from the AC during hy- medium-viscosity dispersive OVD (OVD-E)14 were as- drodissection to avoid unnecessary IOP elevation. sociated with significantly higher increases in IOP in the In conclusion, use of OVDs with higher MWs or higher postoperative period. This suggests that it is more diffi- concentrations of sodium hyaluronate predisposes the eye

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©2011 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/28/2021 to an increased risk of PC-AHM impairment during hy- 5. Vasavada AR, Singh R, Apple DJ, Trivedi RH, Pandey SK, Werner L. Effect of drodissection. Although AHM tears or rupture of the pos- hydrodissection on intraoperative performance: randomized study. J Cataract Re- fract Surg. 2002;28(9):1623-1628. terior capsule may be infrequent in the clinical setting, 6. Allen D, Wood C. Minimizing risk to the capsule during surgery for posterior po- our study shows that breakdown of the PC-AHM bar- lar cataract. J Cataract Refract Surg. 2002;28(5):742-744. rier is possible any time that IOP increases significantly, 7. Ota I, Miyake S, Miyake K. Dislocation of the lens nucleus into the vitreous cav- potentially leading to postoperative endophthalmitis fol- ity after standard hydrodissection. Am J Ophthalmol. 1996;121(6):706-708. lowing an otherwise uneventful operation. Thus, sur- 8. Torii H, Takahashi K, Yoshitomi F, Miyata K, Ishii Y, Oshika T. Mechanical detachment of the anterior hyaloid membrane from the posterior lens capsule. geons should carefully monitor IOP during cataract op- Ophthalmology. 2001;108(12):2182-2185. erations. 9. Ohnuma O, Matsushima H, Senoo T, Obara Y. Intraocular pressure change during phacoemulsification and aspiration [in Japanese]. Atarashii Ganka. 2006; Submitted for Publication: February 22, 2010; final re- 23(9):1225-1227. 10. Miyake K, Miyake C. Intraoperative posterior chamber lens haptic fixation in the vision received September 29, 2010; accepted October human cadaver eye. Ophthalmic Surg. 1985;16(4):230-236. 19, 2010. 11. Apple DJ, Lim ES, Morgan RC, et al. Preparation and study of human eyes ob- Correspondence: Shiro Kawasaki, MD, Department of tained postmortem with the Miyake posterior photographic technique. Ophthalmology, Ehime University Graduate School of Ophthalmology. 1990;97(6):810-816. Medicine, Shitsukawa, Toon-City, Ehime 791-0295, Japan. 12. Arshinoff SA, Jafari M. New classification of ophthalmic viscosurgical devices—2005. J Cataract Refract Surg. 2005;31(11):2167-2171. Author Contributions: Drs Kawasaki and Tasaka con- 13. Rainer G, Stifter E, Luksch A, Menapace R. Comparison of the effect of Viscoat tributed equally as co–first authors. and DuoVisc on postoperative intraocular pressure after small-incision cataract Financial Disclosure: None reported. surgery. J Cataract Refract Surg. 2008;34(2):253-257. 14. Oshika T, Eguchi S, Oki K, et al. Clinical comparison of Healon5 and Healon in phacoemulsification and intraocular lens implantation: randomized multicenter REFERENCES study. J Cataract Refract Surg. 2004;30(2):357-362. 15. Oshika T, Okamoto F, Kaji Y, et al. Retention and removal of a new viscous dis- 1. Kawasaki S, Suzuki T, Yamaguchi M, et al. Disruption of the posterior chamber– persive ophthalmic viscosurgical device during cataract surgery in animal eyes. anterior hyaloid membrane barrier during phacoemulsification and aspiration as Br J Ophthalmol. 2006;90(4):485-487. revealed by contrast-enhanced magnetic resonance imaging. Arch Ophthalmol. 16. Bissen-Miyajima H. In vitro behavior of ophthalmic viscosurgical devices during 2009;127(4):465-470. phacoemulsification. J Cataract Refract Surg. 2006;32(6):1026-1031. 2. Khng C, Packer M, Fine IH, Hoffman RS, Moreira FB. Intraocular pressure dur- 17. Koch DD, Liu JF, Glasser DB, Merin LM, Haft E. A comparison of corneal endo- ing phacoemulsification. J Cataract Refract Surg. 2006;32(2):301-308. thelial changes after use of Healon or Viscoat during phacoemulsification. Am J 3. Faust KJ. Hydrodissection of soft nuclei. J Am Intraocul Implant Soc. 1984;10(1): Ophthalmol. 1993;115(2):188-201. 75-77. 18. Hatch WV, Cernat G, Wong D, Devenyi R, Bell CM. Risk factors for acute en- 4. Fine IH. Cortical cleaving hydrodissection. J Cataract Refract Surg. 1992;18(5): dophthalmitis after cataract surgery: a population-based study. Ophthalmology. 508-512. 2009;116(3):425-430.

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