David B. Denham

In vitro dimensions and curvatures of human lenses

The purpose of this study was to determine dimensions and curvatures of excised human lenses using the technique of shadowphotogrammetry. A modified optical comparator and digital camera were used to photograph magnified sagittal and coronal lens profiles. Equatorial diameter, anterior and posterior sagittal thickness, anterior and posterior curvatures, and shape factors were obtained from these images. The data were used to calculate lens volumes, which were compared with the lens weights. Measurements were made on 37 human lenses ranging in age from 20 to 99 years. These showed that lens dimensions and the anterior radius of curvature increase linearly throughout adult life while posterior curvature remains constant. The relative shape (or aspect ratio) of the posterior lens is unchanged through adult life since both equatorial diameter and posterior thickness increase at the same rate. The ratio of anterior thickness to posterior thickness is constant at 0.70. It is suggested that in vivo forces alter the apparent location of the lens equator, that the in vitro lens shape corresponds to the maximally accommodated shape in vivo and that the shapes of the accommodated and unaccommodated lens progressively converge toward each other due to lens growth with age, with a convergence point located near the age of total loss of accommodation (55-60 years). Together, these observations provide additional support for the Helmholtz theory of accommodation.

Interstitial laser hyperthermia model development for minimally invasive therapy of breast carcinoma.

BACKGROUND This investigation describes the preclinical development of a laser fiberoptic interstitial delivery system for the thermal destruction of small breast cancers. We propose adaptation of this technology to stereotactic mammographic instrumentation currently employed for diagnostic core biopsy to thermally ablate a site of disease with maximal treatment efficacy, minimal observable superficial change, reduced patient trauma, and lowered overall treatment costs. STUDY DESIGN Laser hyperthermia is a clinical modality that seeks to achieve tumor destruction through controlled tissue heating. The advantage of laser-induced hyperthermia over traditionally used heat sources such as ultrasound, microwave, or radiowave radiation lies in the ability to focus heat localization to the specific tumor tissue site. Neodymium:yttrium aluminum garnet (Nd:YAG) laser light transmitted through a fiberoptic cable to a diffusing quartz tip can induce such temperature increases leading to localized tissue destruction. Because breast cancer occurs with greatest frequency in the mature woman whose breast tissue has undergone glandular involution with fatty replacement, this study concentrates on determining the resultant laser energy heat distribution within fat and fibrofatty tissue. This investigation studied the time-temperature responses of ex vivo human breast and porcine fibrofatty tissue, which led to an in vivo subcutaneous porcine model for the practical demonstration of a laser hyperthermia treatment of small volumes of porcine mammary chain tissue. RESULTS Spatial recordings of the resultant temperature fields through time exhibited similar, reproducible thermal profiles in both ex vivo human breast and subcutaneous porcine fat. In vivo laser-produced temperature fields in porcine subcutaneous fat were comparable to those in the ex vivo analyses, and showed a histologically, sharply defined, and controllable volume of necrosis with no injury to adjacent tissues or to overlying skin. CONCLUSIONS Interstitially placed, fiberoptically delivered Nd:YAG laser energy is capable of controlled tissue denaturation to a defined volume for the treatment of small breast cancers. It is hoped that this minimally invasive approach, with further investigation and refinement, may lead to the effective treatment of small, well-defined breast cancers that are commonly diagnosed through stereographic mammography and stereotactic core biopsy. The juxtaposition of such a localized treatment modality with these increasingly used diagnostic tools is of considerable promise.

In Situ temperature measurements with thermocouple probes during laser interstitial thermotherapy (LITT): Quantification and correction of a measurement artifact

Background and Objective: The purpose of this work was to quantify the magnitude of an artifact induced by stainless steel thermocouple probes in temperature measurements made in situ during experimental laser interstitial thermo‐therapy (LITT). A procedure for correction of this observational error is outlined.

Development of stereotactically guided laser interstitial thermotherapy of breast cancer: In situ measurement and analysis of the temperature field in ex vivo and in vivo adipose tissue

The size (0.5–1.0 cm) of early nonpalpable breast tumors currently detected by mammography and confirmed by stereotactic core biopsy is of the order of the penetration depth of near infrared photons in breast tissue. In principle, stereotactically biopsied tumors, therefore, could be safely and efficiently treated with laser thermotherapy. The aim of the current study is to confirm the controlled heating produced by clinically relevant power levels delivered with an interstitial laser fiber optic probe adapted for use with stereotactic mammography and biopsy procedures.

Internal Sclerectomy with an Automated Trephine for Advanced Glaucoma

An automated trephine (trabecuphine) was used to perform an internal sclerectomy in seven glaucoma patients who were aphakic or had undergone previous filtering surgery that had failed or both. A patent fistula was achieved intraoperatively in all seven eyes. Postoperatively, six patients received subconjunctival injection of 5-fluorouracil (5-FI) once daily for an average of 8 days. Five of seven patients have retained a functional bleb and a controlled intraocular pressure (IOP) after surgery (follow-up, 4-24 months). The only intraoperative complication was hemorrhage from the sclerectomy site in a patient with aniridia that resulted in a 20% hyphema. The hyphema cleared quickly, and the bleb has remained functional with a pressure of 12 mmHg for 9 months. The trabecuphine makes it possible to perform a glaucoma filtering operation safely from within the anterior chamber. This technique minimizes conjunctival trauma in the filtration area. The absence of a conjunctival incision overlying the fistula simplifies the adjunctive use of antimetabolites such as 5-FU.

Laser interstitial thermotherapy (LITT) monitoring using high-resolution digital mammography: theory and experimental studies.

Laser interstitial thermotherapy (LITT) is a minimally-invasive laser hyperthermia procedure for the treatment of localized tumours. Real-time monitoring of LITT is essential to control the extent of tumour destruction and ensure safe and effective treatments. The feasibility of using high-resolution digital x-ray mammography to monitor LITT of breast cancer was evaluated. Tissue phantoms including polyacrylamide hydrogel and cadaver porcine tissue were heated using a 980 nm diode laser delivered through optical fibres with diffusing tips. Digital images of the tissue phantoms were recorded with a high-resolution digital stereotactic breast biopsy system during heating. The recorded images were processed and analysed to detect heat-induced changes. No changes were detected during heating of the hydrogel. Pixel-by-pixel subtraction of the initial image from images taken during laser heating shows observable thermally-induced changes around the fibre during laser irradiation that correlate with the thermal denaturation zone observed by gross anatomy. These experiments demonstrate that high-resolution digital x-ray mammography can be used to detect heat-induced tissue changes during experimental LITT in fibro-fatty tissue.

Ablation rate of PMMA and human cornea with a frequency-quintupled Nd: YAG laser (213 nm)

As an alternative to the standard excimer laser used for PRK, we investigated the ablation rate at 213 nm of PMMA, and human corneas under controlled hydration.

Thermal analysis of laser interstitial thermotherapy in ex vivo fibro-fatty tissue using exponential functions

A therapeutic procedure to treat small, surface breast tumours up to 10 mm in radius plus a 5 mm margin of healthy, surrounding tissue using laser interstitial thermotherapy (LITT) is currently being investigated. The purpose of this study is to analyse and model the thermal and coagulative response of ex vivo fibro-fatty tissue, a model for breast tissue, during experimental laser interstitial thermotherapy at 980 nm. Laser radiation at 980 nm was delivered interstitially through a diffusing tip optical fibre inserted into a fibro-fatty tissue model to produce controlled heating at powers ranging from 3.2 to 8.0 W. Tissue temperature was measured with thermocouples placed at 15 positions around the fibre. The induced coagulation zone was measured on gross anatomical sections. Thermal analysis indicates that a finite sum of exponential functions is an approximate solution to the heat conduction equation that more accurately predicts the time-temperature dependence in tissue prior to carbonization (T < 100 degrees C) during LITT than the traditional model using a single exponential function. Analysis of the ellipsoid coagulation volume induced in tissue indicates that the 980 nm wavelength does not penetrate deep enough in fibro-fatty tissue to produce a desired 30 mm diameter (14.1 x 10(3) mm3) coagulation volume without unwanted tissue liquefaction and carbonization.

Temperature-induced corneal shrinkage

Thermokeratoplasty is a procedure utilizing heat to reshape the surface of the cornea through shrinkage of collagen within the stroma. We have constructed an apparatus for measurements of thermally induced corneal shrinkage. Using this apparatus, we have defined the cornea shrinkage rate and examined the relationships between age, shock temperature, and shock temperature duration to the amount of shrinkage on fifteen corneal strips from Eye-Bank eyes. The results show that less heat energy was required to induce shrinkage in older corneas, that acute shrinkage increases with increasing shock temperature and that shrinkage increases with increasing shock temperature duration.

Endothelial Damage by the Corneal Hessburg-Barron Vacuum Trephine

BACKGROUND Tissue damage in corneal transplantation procedures was previously assessed in comparative pilot studies using vacuum-assisted metal blade trephines and a noncontact hydrogen fluoride laser trephine system. With the laser, endothelial damage was less than 20 x 30 microns at the edge of the posterior corneal perforation. METHODS In this study, a second generation vacuum-assisted Hessburg-Barron trephine was evaluated in full-thickness penetrating trephination performed in 16 rabbit eyes and eight fresh human donor eyes. RESULTS We found a relatively large, 150-micrometer wide, annular zone of endothelial damage on the recipient cornea located 1.25 mm away from the trephined opening. Our study demonstrates that endothelial damage is linked to the instruments vacuum fixation ring. CONCLUSION With this trephine, endothelial damage may be avoided by using partial-depth trephination, filling the anterior chamber with viscoelastic and completing the procedure using a metal blade or diamond knife.