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Biomedical subjects

D J Apple

Publications and source records attributed to D J Apple.

At least 19 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

A comparative evaluation of the biostability of a poly (ether urethane) in the intraocular, intramuscular, and subcutaneous environments.

A transparent poly (ether urethane) (PEU) was considered for use as a foldable intraocular lens material. The PEU was found to possess excellent mechanical, optical, and surface characteristics for this application. In vitro hydrolytic and ultraviolet aging studies suggested the PEU to be tolerant to conditions simulating 3-10 years of normal intraocular exposure. Different behavior was obtained, however, from intraocular and subcutaneous implantation of the PEU. After 6 months of intraocular exposure in the feline model, prototype PEU lenses had lost most or all of their optical resolving power. SEM analysis demonstrated scattered pitting and cracking on the lens surfaces. Degradation was found to be more extreme after as little as 30 days of subcutaneous exposure in rabbits. Severe pitting over the entire surface of implanted flat PEU specimens was observed by SEM. Macroscopic examination showed the samples to be frosty in appearance. It was postulated that the subcutaneous implant environment provides an accelerated in vivo model for materials intended for intraocular use. A minimum acceleration of 6-10x was estimated on a preliminary basis. The PEU studied here was found to be unsuitable for use as a foldable intraocular lens material.

Animals↗
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

Scanning electron microscopic study of modern silicone intraocular lenses.

Silicone, as manufactured today, appears to be a biocompatible material. The safety and efficacy of silicone lenses are primarily related to the intraocular lens (IOL) design. We compared the edge finish of two three-piece polypropylene loop foldable silicone IOL designs (Allergan Medical Optics) and three one-piece designs (Staar Surgical Co., CooperVision-Cilco). Except for an early Staar one-piece design, all lenses including the more recent Staar lenses had acceptably smooth edges with minimal molding flash.

Biocompatible Materials↗
PubMed1992

Variations in manufacturing quality of diffractive multifocal lenses.

The new generation of multifocal intraocular lenses (IOLs) based on diffraction optics is characterized by a stepped discontinuity at zone boundaries on the posterior surface of the IOL optic. The step height at the zone boundaries is less than 2 microns. There are approximately 30 zones on a 6 mm diameter lens, requiring manufacturing precision of about 0.02 mm. Various companies produce this type of lens. On two implanted lenses we found, in addition to the 2 microns boundaries, many small circular rims that appeared to be manufacturing artifacts. The presence of these artifacts may explain the variable clinical acceptance of these IOLs.

Aged↗
PubMed1992

The effect of varying wavelength on subconjunctival scleral laser suture lysis in rabbits.

We studied laser suture lysis of subconjunctival scleral sutures in a rabbit eye using selected wavelengths from a dye and diode laser to determine which wavelength caused the least conjunctival damage. We found an oval shaped area of coagulation necrosis surrounding the suture track in the conjunctival substantia propria measuring in depth 61.0 mu for 488 + 514 nm (blue-green), 105.7 mu for 514 nm (green), 148.3 mu for 630 nm (red), and 29.0 mu with 780 + 830 nm (infrared) wavelengths. No observable damage was noted with 585 nm (yellow) or 610 nm (orange) wavelengths. The energy intensity required for suture lysis was similar across each wavelength studied. No damage was observed in the sclera or conjunctival epithelium. These findings suggest that using the yellow or orange wavelength, when performing laser suture lysis clinically, potentially may limit conjunctival damage.

Animals↗
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↗
PubMed1992

[Implantation of IOLs with different diameters].

The intraocular lenses (IOLs) commonly used today are 13.5 to 14 mm in diameter, and this diameter is considered by some to be unnecessarily large. The size of the crystalline lens and the diagonal width between the ciliary sulcus were measured in rabbit eyes and human eyes. Then, IOLs with a smaller diameter (12.5 mm) were evaluated after implantation into rabbit eyes. The mean diameter of the human crystalline lens was 9.6 mm and its thickness was 4.1 mm. The mean width of the ciliary sulcus was 11.1 mm. The crystalline lenses of rabbits were larger than those of humans. Decentration and posterior capsular opacification score were 0.33 mm and 0.63 in 12.5 mm IOL, and 0.47 mm and 0.61 in 14.0 mm IOL. Indicating that the result of implanting the 12.5 mm IOL was not inferior to that of implanting the conventional 14 mm IOL. The average width of the ciliary sulcus is 11.1 mm, indicating that a 12.5 mm IOL is of a sufficient size to be firmly fixed in this sulcus. In addition, a 12.5 mm IOL is considered to be safer, because larger lenses may lead to erosion or vessel compression that could induce ischemia or neovascularization.

Animals↗
PubMed1992

Histologic differences in the conjunctiva of black and white glaucoma patients.

We compared perioperative conjunctival biopsy specimens from 31 consecutive trabeculectomy patients to determine if there were any histologic differences between black and white glaucoma patients. We found a statistically significantly greater mean and distribution of mast cells and neutrophils in the white patients. No significant difference was found in the mean number of goblet cells, eosinophiles, macrophages, fibroblasts, plasma cells, or lymphocytes; or in thickness of the epithelium, vascular density, or collagen or mucopolysaccharide staining. We conclude that histological conjunctival factors that could be evaluated preoperatively probably are not related to the poor results in black patients of filtration surgery noted by some investigators.

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↗