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Biomedical subjects

D J Apple

Publications and source records attributed to D J Apple.

At least 127 records · Page 7Linked to original sources
PubMed1994

[Area of contact of the artificial lens and posterior capsule. Systematic study of various haptic parameters].

New techniques in cataract surgery, namely the small and tunnel incisions, have led to intraocular lens (IOL) designs with haptics angulated anteriorly as low as 0 degrees. Clinical and animal studies strongly support the inhibitory influence of contact between the optic and the posterior capsule on the formation of posterior capsular opacification. Human cadaver eyes were used to examine the effect of different haptic angulations (1 degree, 5 degrees, 10 degrees, 15 degrees), different haptic diameters (11.5 mm, 12.0 mm, 12.5 mm), and different optic diameters (5.0 mm, 6.0 mm) on the area of contact between optic and posterior capsule. Exciting fluorescein with a Wood light visualized the space between the IOL and the posterior capsule. Only IOLs with haptics bent forward at more than 10 degrees could achieve contact between IOL and posterior capsule. The haptic and optic diameters had only a limited effect.

Humans↗
PubMed1994

[Reasons for the explantation of posterior chamber lenses].

In this study we analysed the overall incidence and the types of complications seen after cataract surgery and implantation of posterior chamber intraocular lenses (PC-IOLs) based on a review of 1460 explanted PC-IOLs. Of these explanted PC-IOLs, 1072 (73.4%) were three-piece PMMA IOLs with Prolene haptics, 261 (17.9%) were one-piece all-PMMA IOLs, 81 (5.6%) were silicone IOLs and 46 (3.1%) were of various other designs (multifocal IOLs, disc IOLs etc.). The mean implant duration for all IOLs was 25.57 +/- 29.24 months. The two most important reasons for explantation were IOL decentration (622/1460, 42.6%) and inflammation (347/1460, 23.77%). There was no difference in reasons for explantation between one-piece and three-piece IOLs. Operative techniques such as "can opener" capsulotomy and sulcus fixation have more influence on IOL decentration than the IOL design alone. Modern operative techniques such as continuous curvilinear capsulorhexis, phacoemulsification and symmetrical in-the-bag fixation of "capsular IOLs" should decrease the explantation and complication rate in the future.

Follow-Up Studies↗
PubMed1994

[Complications after implantation of anterior chamber lenses. An analysis of 4,100 explanted intraocular lenses].

In this study we analyzed the incidence and types of complications seen after cataract surgery and implantation of anterior chamber intraocular lenses (AS-IOLs). This report is based on a review of 4104 explanted AC-IOLs that were submitted to the Center for IOL Research over the past 10 years. The results from pathological examinations were correlated with clinical information. Of the 4104 IOLs, 50% were closed-loop designs (n = 2095/4104), and 22% were open-loop lenses (919/4104). The IOLs most frequently explanted were the closed loop designs Leiske (n = 847) and Stableflex (n = 808). The most important reason for explantation was corneal pathology. Closed-loop IOLs had a much higher complication rate than open-loop lenses. Flexible open-loop AC-IOLs showed the highest explantation rate during the first postoperative year due to surgical problems. The complication rate of closed-loop AC-IOLs increased with implant duration and were responsible for 80% of the corneal pathology. Flexible open-loop AC-IOLs can be an alternative for secondary or exchange implantation. Furthermore, they could also be a viable alternative for cataract surgery in developing countries in order to help catch up with the overwhelming backlog of cases that exist there.

Aged↗
PubMed1994

[Capsulorhexis technique in pediatric cataract. Presented in the rabbit model].

Continuous curvilinear capsulorhexis (CCC) has become a standard procedure in cataract surgery. In pediatric cataracts, however, this technique is difficult to perform. Because of the elasticity and tension of the pediatric anterior lens capsule the danger of radial tears is high. Similar conditions are found in the rabbit model. The anterior lens capsule of young albino rabbits is very elastic. We have developed a CCC technique in rabbits that allows a controlled round capsular opening. This technique was used in an experimental study with 16 rabbits (32 eyes). The mean capsulorhexis diameter was 4.9 +/- 0.9 mm. A radial tear occurred in only 2/32 cases. The technique permits a controlled circular anterior capsulectomy for capsules with high surface tension and elastic properties. This can readily be applied to human pediatric cases.

Animals↗
PubMed1994

Comparison of diode and argon laser trabeculoplasty in cadaver eyes.

PURPOSE: To evaluate differences in the effects of diode and argon trabeculoplasty on cadaver eye trabecular meshwork. METHODS: The argon laser was used at a 50 mu spot size, 500 to 100 mW of power, and a 0.1 second time interval, and the diode laser was used at a 0.1 to 0.2 second time interval, 100 mu spot size, and 400 to 1200 mW of power. Analysis was performed using videography, microscopy, and scanning electron microscopy. RESULTS: This study found grossly that burns with the argon laser caused tissue blanching and pigment dispersion, whereas no reaction was observed with the diode laser. The diode laser made no observable histologic alterations, but the argon caused fragmentation and coagulation of trabecular beams. Scanning electron microscopy showed that the diode laser caused an area of trabecular beam coalescence measuring 50 to 100 mu in diameter with energies > or = 0.12 J. A surrounding zone of more superficial trabecular beam fragmentation measuring 200 to 400 mu in diameter also was observed. Similar energy levels from the argon laser caused hole formation 200 to 400 mu in diameter. Lower argon energy levels (0.05 J) caused inconsistent coalescence 50 to 100 mu in diameter similar to the diode laser. CONCLUSIONS: This study suggests that in the trabecular meshwork the diode laser causes a reaction at, but not at less than, energy levels shown previously to produce a clinical ocular hypotensive effect. Also, at similar energy per area, the tissue effects of the diode and argon laser are comparable.

Argon↗
PubMed1993

Anophthalmic socket pain.

We examined and treated four patients with anophthalmic socket pain. Conditions responsible for this problem in this series included scleritis after evisceration, amputation neuroma, pain from a skull-base meningioma, and chemical dependency with drug-seeking behavior. The pain associated with the scleritis after evisceration responded to removal of the scleral remnant. The pain associated with the amputation neuroma responded to removal of the orbital implant and its pseudocapsule in which the amputation neuroma was embedded. The pain associated with the meningioma was intractable. The pain associated with the chemical dependency remained a persistent problem. A careful history and physical examination are critical in the evaluation of anophthalmic socket pain. Computed tomography or magnetic resonance imaging may be helpful in some cases.

Adult↗
PubMed1993

Clinicopathologic study of the effect of radial tears and loop fixation on intraocular lens decentration.

PURPOSE: The purpose of this study is to determine the effect of loop fixation and anterior capsular tears on intraocular lens (IOL) decentration. METHODS: A retrospective measurement of IOL decentration was performed on 144 human eyes with posterior chamber (PC) IOLs obtained after death. RESULTS: Decentration in eyes with asymmetrical bag-sulcus fixation (mean +/- standard deviation, 0.64 +/- 0.39 mm) was significantly higher than eyes with symmetrical fixation. In the presence of radial tears, symmetrically fixated IOLs in either the capsular bag or the ciliary sulcus decentered to a similar degree, 0.35 +/- 0.25 mm and 0.4 +/- 0.26 mm, respectively. The least decentration was observed with capsular fixation and no radial tears (0.18 +/- 0.09 mm). This was significantly less decentration than with any other form of fixation in the presence of radial tears. CONCLUSION: This study shows that capsular fixation with no radial tears, as can be achieved by using the continuous curvilinear capsulorhexis, is associated with the least decentration.

Adult↗
PubMed1993

Inhibition of posterior capsule opacification: the effect of colchicine in a sustained drug delivery system.

We investigated the effect of colchicine in a sustained drug delivery system on posterior capsule opacification (PCO) in rabbit eyes. A polymer matrix wafer, which diffused colchicine at a steady rate, was implanted in the capsular bag of 34 eyes after the lens material was removed by endocapsular phacoemulsification. Three different drug concentrations were used in the rabbit eyes, which were compared with control eyes containing the polymer matrix wafer without colchicine. The mean PCO score was highest in the control group without colchicine and increased steadily over 12 weeks. The rate of PCO formation in all eyes treated with colchicine was significantly lower than in the control group. There was no statistically significant improvement in PCO inhibition with the higher colchicine dosages. Side effects included inflammatory anterior chamber reaction and corneal and retinal complications and were most notable with the highest drug concentration. Slow release of colchicine reduces PCO formation in the rabbit. The optimal biocompatible dosage must be carefully determined and warrants further investigation.

Animals↗
PubMed1993

[Configuration of the capsular sack after implantation of posterior chamber lenses].

The effect of posterior chamber intraocular lenses (PC-IOLs) on the capsular bag was investigated in human cadaver eyes. Short-term changes were observed with different PC-IOLs directly after experimental implantation. Long-term results were obtained from postmortem eyes with PC-IOLs. Mean implant duration was 2.5 years. The average diameter of the capsular bag in the loop axis was 11.0 mm for 12.0 mm IOLs and 11.5 mm for 13.5-14.0 mm IOLs in the short-term study. Longer loops caused more ovaling of the bag with stress lines on the posterior capsule. The average diameter of the capsular bag in the long term study was 10.6 mm. Secondary processes such as capsular fibrosis and lens epithelial cell proliferation caused the capsular bag to shrink and thus to assume a more circular configuration. The area of contact between the IOL loops and the capsular equator was significantly lower in eyes with radial tears and IOLs with J-loop design when compared to C-loops. The maximal capsular diameter in both the long-term and short-term observations never exceeded 12.0 mm. The results of our study suggest that a 12.0 mm total diameter IOL is sufficient for stable fixation, provided that capsular bag implantation can be assured.

Aged↗
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↗