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Biomedical subjects

E I Assia

Publications and source records attributed to E I Assia.

16 recordsLinked to original sources
PubMed1992

Side-view analysis of the lens. I. The crystalline lens and the evacuated bag.

A new technique for studying the anatomy of the lens and other anterior chamber structures in human eyes obtained post mortem is described. An oblique or side view is achieved by creating a uveoscleral window. This provides a clear three-dimensional view of such structures as the crystalline lens, zonular apparatus, and ciliary body. The crystalline lens is shown to be approximately 4.5 mm thick and 9.5 mm in diameter. The equator of the lens is 0.2 to 0.3 mm from the center of the ciliary body. After removal of lens substance, the capsular bag collapses, its thickness approaches zero, and the total diameter increases to 10.5 mm. Filling of the capsular bag with a viscoelastic material restores the configuration of the lens to its original state. This technique is also useful for demonstrating the dynamics of surgical procedures during cataract operation.

Anterior Chamber↗
PubMed1992

Side-view analysis of the lens. II. Positioning of intraocular lenses.

The uveoscleral window technique is useful for studying the position and fixation of posterior chamber intraocular lenses (IOLs). Studies using this technique show that the configuration of an IOL in the capsular bag largely depends on three factors: size, shape, and relative rigidity of the IOL. The general configuration of the capsular bag is that of a flattened saucer created by radial expansion of the haptic. Zonules at the fixation site are relaxed, eliminating the possibility of accommodation with thin IOLs. Downsized IOLs (total diameter of 12.0 mm) provide stable fixation with less tension on the capsule than larger IOLs.

Cataract Extraction↗
PubMed1992

Posterior continuous curvilinear capsulorhexis. An experimental study with clinical applications.

The posterior continuous curvilinear capsulorhexis technique has been advocated in cases of posterior capsule rupture during extracapsular cataract extraction. The authors compared posterior continuous curvilinear capsulorhexis with posterior capsular sharp-edged tears. Two different types of forces were experimentally created on the posterior capsule of 30 human eyes obtained after death: (1) implantation and dialing of posterior chamber intraocular lenses (PC IOLs) and (2) increased intravitreal pressure by injection of balanced salt solution. All posterior capsular tears extended toward the equator, causing major capsular defects. In contrast, the posterior continuous curvilinear capsulorhexis remained intact in all cases. This experimental study proves that in cases where an inadvertent posterior capsular tear occurs, a posterior continuous curvilinear capsulorhexis is useful in preventing further capsular damage. Also, in cases where a posterior capsulotomy is indicated, a smooth edge created by a posterior continuous curvilinear capsulorhexis may be useful to maintain the integrity of the capsular bag for PC IOL capsular implantation.

Aged↗
PubMed1992

Prospective experimental study of factors related to posterior chamber intraocular lens decentration.

The effect of posterior chamber intraocular lens (IOL) dimensions, design, style, loop fixation, and anterior capsular tears on decentration were investigated in an experimental model. Nine posterior chamber IOLs of various designs and styles with loop diameters between 12.0 and 14.0 mm and optic diameters between 5.0 and 7.0 mm were implanted in human eyes obtained post mortem. Symmetrical and asymmetrical fixation were investigated in eyes with and without radial tears using the Miyake posterior view technique. Location of IOL loops proved to be the most significant factor in IOL decentration. Decentration was least with symmetrical bag/bag fixation and no radial tears (mean = 0.20 +/- 0.05 mm). Asymmetrical bag/sulcus fixation in the presence of anterior capsular tears was associated with the highest decentration rate (mean 0.68 +/- 0.28 mm). Optic size and total loop diameter had no apparent effect on IOL centration in the immediate postoperative period.

Cataract Extraction↗
PubMed1992

Removal of viscoelastic materials after experimental cataract surgery in vitro.

The one significant complication of viscoelastic materials is that they may cause postoperative intraocular pressure rise. We investigated the rate and ease of removal of various viscoelastics using the Miyake video technique. Five viscoelastics were investigated: sodium hyaluronate (Healon), Healon GV, chondroitin sulfatesodium hyaluronate (Viscoat), hydroxypropylmethylcellulose (Occucoat), and polyacrylamide (Orcolon). The viscoelastics were dyed with fluorescein and, after filling the capsular bag with a viscoelastic material, a posterior chamber intraocular lens (IOL) was implanted. The viscoelastic was then aspirated using an automated irrigation/aspiration device. Healon and Healon GV were completely removed within 20 to 25 seconds. Viscoat adhered to the lens capsule and to the posterior surface of the IOL and cooplete removal required approximately 3.5 minutes. Most Occucoat and Orcolon was aspirated within one minute; however, removal was completed only after three minutes. Removal of Healon and Healon GV was faster and more complete than removal of the other viscoelastics. Whether a small amount of viscoelastic left in the eye or trapped behind the IOL optic has any clinical significance has to be studied.

Acrylic Resins↗
PubMed1992

Loop memory of posterior chamber intraocular lenses of various sizes, designs, and loop materials.

Looped intraocular lenses (IOLs) fixate by exerting centripetal pressure on the ocular tissues. The ability of the flexible loops to maintain pressure depends on their rigidity (i.e., resistance to flexion) and their "memory" (i.e., ability to restore original configuration after a long period of compression). We studied the memory of 30 different posterior chamber IOLs, with loops made of polypropylene (PP) and poly(methyl methacrylate) (PMMA), of various diameters, styles, and designs. The lenses were inserted into plastic wells, 9.5 mm in diameter, and immersed in water (37 degrees C) for one month. They were then placed on an open plate and allowed to re-expand for one month. Loop memory was calculated as the difference in diameter between the initial (pretest) measurement and measurements taken during the compression and release periods. The results showed that short (12.0 to 12.5 mm) IOLs had relatively better memory than longer (13.5 to 14.0 mm) IOLs. Those with PP loops expanded more and for longer periods than those comparable size and design with PMMA loops. One-piece, all-PMMA lenses exhibited the best loop memory. These lenses have the high rigidity of the PMMA material and the good memory of the design. Thus, the total IOL diameter can be reduced to 12.0 mm while providing long-term constant pressure on the capsular bag to maintain stable fixation.

Equipment Design↗
PubMed1992

[Comparison of various capsulectomy techniques in cataract surgery. An experimental study].

Radial tears at the edge of an anterior capsulectomy are often associated with the occurrence of intraocular lens (IOL) loops coming out of the capsular bag with subsequent IOL decentration. We analyzed the incidence of radial tear formation in 40 human eyes obtained postmortem. These eyes were randomly assigned to four groups: "can opener," linear capsulotomy, capsulopuncture ("postage stamp"), and continuous curvilinear capsulorhexis (CCC). The CCC appeared to be much less likely to be associated with anterior capsular radial tears as opposed to the other three techniques. With the nucleus expression technique used in this study, radial tears occurred in all cases of "can opener," linear capsulotomy and capsulopuncture, whereas no tears occurred with the CCC technique. The results of this study show that CCC is currently the best available anterior capsulectomy procedure for minimizing the incidence of radial tears and sequelae such as decentration.

Aged↗
PubMed1991

The elastic properties of the lens capsule in capsulorhexis.

We investigated the ability of the anterior lens capsule to stretch and allow removal of lens substance and intraocular lens implantation through a continuous circular capsulorhexis. Capsulorhexis of various sizes (2.5 to 7.5 mm) were performed in 50 eyes obtained post mortem from 31 patients. The nucleus and cortex were removed by either phacoemulsification (35 eyes) or manual extracapsular cataract extraction (15 eyes). The opening of the capsule was then gradually enlarged, using a modified caliper with two pins attached to its tips, until the margins were torn. The capsule was torn when the circumference at the time of rupture was 1.6 times larger than the circumference of the original circular capsulectomy or 5.0 times larger than the diameter of the capsulectomy. Manual extraction of a lens nucleus with profile circumference (sagittal or anteroposterior) of 18.0 to 22.0 mm can be performed through a 5.5-mm opening and a 6.0- to 7.0-mm optic intraocular lens (profile circumference of 13.0 to 17.0 mm) can be implanted through a 4.5-mm capsulectomy.

Aged↗
PubMed1991

An experimental study comparing various anterior capsulectomy techniques.

Radial tears at the margin of an anterior capsulectomy may be associated with the exit of at least one loop of an intraocular lens out of the capsular bag ("pea pod" effect) and subsequent decentration. Many ophthalmologists have gained a clinical impression that the anterior capsule is more likely to remain intact if the continuous circular capsulorhexis (CCC) technique is used. However, controlled comparison of the incidence of radial tears with the use of different capsulectomies under standardized conditions has not been performed, to date. In this study, we analyzed the incidence of radial tear formation in 40 human eyes that were obtained post mortem. These eyes were randomized to four technique groups: (1) "can opener," (2) linear capsulotomy, (3) capsulopuncture, and (4) CCC. We demonstrated that the CCC technique is much less likely to cause or be associated with anterior capsular radial tears as opposed to the other three techniques. With the technique of nuclear expression used in this study, radial tears occurred in 100% of cases treated with the can opener, linear capsulotomy, and capsulopuncture techniques, whereas no tears occurred with the CCC technique. This study provides convincing evidence that the CCC is the best available anterior capsulectomy procedure to minimize the incidence of radial tears.

Aged↗
PubMed1991

Mechanism of radial tear formation and extension after anterior capsulectomy.

The mechanisms of anterior capsular radial tear formation and extension around the equator onto the posterior capsule were investigated in 57 eyes obtained postmortem. Experimental radial tears were created by gradual opening of a caliper. In 95% of cases, the tear immediately reached the equator but none extended to the posterior capsule. The elastic forces of the zonules attached to or crossing the edges of the tear resisted a widening of the gap between the edges and thus limited the radial progression of the rupture. A significantly stronger force and severing of the zonules were necessary for a tear to extend around the equator. The authors have determined that radial tears in the anterior capsule seldom extend around the equator, providing the zonules bridging the tear are intact. There is a diminution of the tearing force when the flaps are widely open. Careful surgery with preservation of the integrity of the capsular-zonular apparatus is a major factor in preventing major complications such as posterior capsular ruptures.

Aged↗
PubMed1991

Anterior capsular tears and loop fixation of posterior chamber intraocular lenses.

Two hundred fifty consecutive postmortem eyes containing posterior chamber intraocular lenses (PC IOLs) were analyzed according to the presence and number of radial anterior capsular tears. Over 90% of cases had been done with the "can opener" technique. A surprisingly high percentage of cases, 86%, had one to five radial tears. Furthermore, our analysis showed that the most consistent and most permanent in-the-bag fixation was achieved when only one tear or less was present in the anterior capsule. Because this study shows that the incidence of radial tears is very high after nuclear expression with "can opener" capsulectomy, it provides a scientific basis supporting the transition toward the continuous circular capsulorhexis technique that is slowly evolving. The latter technique has been shown to minimize the incidence of anterior capsular radial tears. This may ultimately serve to decrease the incidence of PC IOL decentration, an important goal if the use of bimultifocal IOLs and IOLs with small or aspheric optics is to be successful.

Aged↗
PubMed1991

An analysis of flexible anterior chamber lenses with special reference to the normalized rate of lens explantation.

A survey of 1204 closed-loop anterior chamber intraocular lenses (AC-IOLs) and 310 open-loop AC-IOLs accessioned between November 1982 and January 1990 was conducted at the Center for Intraocular Lens Research. An analysis of complication rates was done after normalization of data with respect to market share totals. The results establish that an unacceptable complication rate is associated with the closed-loop design when compared with either the tripod or quadripod lens styles. Furthermore, the closed-loop designs, while comprising an estimated 45% of the total number of AC-IOLs estimated to be implanted in the United States (n = 674,000), were responsible for 80% of the AC-IOLs explanted after complications and accessioned at the authors' center. A rethinking of the extreme condemnation of all anterior chamber IOLs that has surfaced in recent years is warranted. This is particularly true with respect to indications for use of sutured posterior chamber (PC) IOLs as well as with regard to possible use of open-loop AC-IOLs in less-industrialized nations.

Anterior Chamber↗
PubMed1991

A comparison of neodymium: yttrium aluminum garnet and diode laser transscleral cyclophotocoagulation and cyclocryotherapy.

The cyclodestructive effects of cyclocryotherapy and of the neodymium:yttrium aluminum garnet (Nd:YAG) and diode laser transscleral cyclophotocoagulation were investigated in phakic and pseudophakic cadaver eyes using a modified Miyake posterior-view technique and light microscopy. Cyclocryotherapy to -80 degrees C was applied with a 2.5-mm diameter tip, 1 and 2 mm from the limbus. Freezing at the ciliary processes was evident after 10-15 sec and reached a diameter of 3-4 mm by 30 sec. No visible changes were evident grossly in the ciliary processes, crystalline lens, or intraocular lens. Histologically increased separation of cells was observed. Effective noncontact Nd:YAG and diode laser applications to the ciliary processes were observed grossly as tissue blanching and shrinking and pigment dispersion. This effect was obtained by aiming 0.5-1.0 mm behind the limbus at a 1-mm defocus using 4 J of energy for the Nd:YAG and 1.2 J for the diode laser. The diode laser spot size did not affect the tissue response. No damage was observed in the crystalline or intraocular lens with either type of laser. Histologic changes using both lasers were coagulation necrosis with fragmentation and detachment of the ciliary body epithelium. This study suggested that the gross and histologic thermal effects produced by the diode and Nd:YAG laser were similar in the ciliary body. Also, at the time of surgery, these cyclodestructive procedures potentially cause little alteration of the crystalline or intraocular lens.

Ciliary Body↗
PubMed1991

The relationship between the stretching capability of the anterior capsule and zonules.

The stretching capability of the zonules was studied in 40 human eyes obtained postmortem from 27 patients. A continuous circular capsulorhexis (CCC) (2.2-6.8 mm) was performed, and the lenses were removed by either phacoemulsification (26 eyes) or planned extracapsular cataract extraction (ECCE) (14 eyes). Maximal zonular stretch was calculated as the difference in distance between the ciliary processes and the zonular insertion at rest and after maximal stretch. This zonular stretch test showed that zonules can stretch to a mean distance of 3.82 mm before rupturing. Capsular elasticity was measured in 35 of the eyes by gradually opening a modified caliper until the capsular opening was torn. The ratio between the circumference at rupture and the circumference at rest was used as an index of capsular elasticity. Circumference of the intact capsulorhexis could be enlarged an additional 62% before a radial tear occurred. In most cases, no significant correlation was seen between the capsular and zonular capability to stretch. Maximal zonular stretch decreased significantly with age by approximately 0.5 mm for every 5 yr, whereas capsular elasticity did not show a significant correlation with age. Two eyes with pseudoexfoliation had relatively friable zonules but the capsular elasticity was within normal limits. Patient age is probably the best indicator of the stretching capability of the zonules.

Age Factors↗
PubMedDate not supplied

Posterior capsule opacification.

A complication of extracapsular cataract extraction with or without posterior chamber intraocular lens (PC-IOL) implantation is posterior capsule opacification. This condition is usually secondary to a proliferation and migration of residual lens epithelial cells. Opacification may be reduced by atraumatic surgery and thorough cortical clean-up. Clinical, pathological and experimental studies have shown that use of hydrodissection, the continuous curvilinear capsulorhexis and specific IOL designs may help reduce the incidence of this complication. Capsular-fixated, one-piece all-polymethylmethacrylate PC-IOLs with a C-shaped loop configuration and a posterior convexity of the optic are effective. Polymethylmethacrylate loops that retain "memory" create a symmetric, radial stretch on the posterior capsule after in-the-bag placement, leading to a more complete contact between the posterior surface of the IOL optic and the taut capsule. This may help form a barrier against central migration of epithelial cells into the visual axis. Various pharmacological and immunological methods are being investigated but conclusive data on these modalities are not yet available.

Cataract↗