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Biomedical subjects

J Marshall

Publications and source records attributed to J Marshall.

At least 757 records · Page 42Linked to original sources
PubMedDate not supplied

A comparative study of the duration and efficacy of tetracaine 1% and bupivacaine 0.75% in controlling pain following photorefractive keratectomy (PRK).

OBJECTIVE: To evaluate if topical bupivacaine 0.75% provides better pain control after excimer laser over topical tetracaine 1% without affecting corneal wound healing, refractive outcome of visual function. DESIGN: A prospective, double-masked trial was conducted in which 38 patients were randomized to receive either tetracaine or bupivacaine every 30 minutes for 24 hours post-operatively. Pain was recorded over a four day period using a Visual Analogue Pain Scale. The rate of epithelial healing was assessed during digitized retro-illumination photography. Visual performance was recorded using best corrected Snellen acuity, objective measurements of haze, halo and glare over a six month period. RESULTS: Tetracaine afforded better pain control (p = 0.05). Full epithelial closure occurred in all patients within 72 hours and no statistically significant difference was recorded in any of the parameters measured. CONCLUSIONS: Contrary to our expectation, the longer acting anaesthetic, bupivacaine, was inferior to tetracaine. Limited and supervised use of topical anaesthetics is recommended in controlling pain following photorefractive keratectomy.

Adult↗
PubMedDate not supplied

The management of ischaemic and periampuation pain.

This article describes the development and pilot application of a management tool designed to support healthcare practitioners in the management of ischaemic and periamputation pain. The ischaemic management periamputation care (IMPAC) guidelines have been piloted in the authors' clinical area and early results suggest that there are positive benefits accruing to patients and ward staff.

Humans↗
PubMedDate not supplied

Neuroendocrine changes in patients undergoing whole body hyperthermia.

A phase I study of whole body hyperthermia (WBH) (52 treatments/12 patients) utilizing a radiant heat device has been completed. This study incorporated a temperature escalation scheme from 39.5 to 41.8 degrees C for up to 150 min. Pain relief or a sense of well being was observed post-WBH in the first three patients entered in this study. We postulated that WBH might result in increases in the opiate peptide beta-endorphin. Therefore we elected to study prospectively the next six patients entered in this study to test the hypothesis that WBH stimulates the neuroendocrine axis. Results are reported which show thermal-induced increases in plasma levels of beta-endorphin as well as prolactin, ACTH and cortisol.

Adrenocorticotropic Hormone↗
PubMedDate not supplied

The use of cranial electrotherapy stimulation in the treatment of closed-head-injured patients.

This double-blind study sought to discover if cranial electrotherapy stimulation (CES), which is a known treatment of depression, anxiety and insomnia in non-head-injured patients, could be an effective, drug-free treatment of stress-related symptoms in the closed-head-injured (CHI) patient. In this study 10 CHI patients treated for 45 min daily, 4 days a week for 3 weeks, responded significantly on all negative mood factors of the Profile Of Mood States, while five sham-treated and six placebo controls did not. While the majority of the patients were known seizure cases, no patient suffered a seizure during CES therapy. No placebo effects were found, nor were any negative effects from CES treatment seen.

Adult↗
PubMedDate not supplied

Refractive index of the human corneal epithelium and stroma.

BACKGROUND: The refractive index of the cornea must be determined to optically perfect keratorefractive procedures. There are very few empirical measurements of the human corneal refractive index described in the literature. Throughout its depth, the cornea demonstrates regional variations in physiological properties such as swelling/de-swelling characteristics. These properties suggest there may be a difference in the refractive index between the anterior and posterior corneal surfaces. METHODS: The refractive index of the human corneal epithelium of 10 eyes was measured, in vivo, using a modified hand-held refractometer. The refractive indices of the anterior and posterior surfaces of the bare stroma of fresh human corneas were measured using a bench model Abbe refractometer. RESULTS: The mean refractive index of the epithelium, stromal anterior and posterior surfaces were 1.401 (SD +/- 0.005), 1.380 (SD +/- 0.005), and 1.373 (SD +/- 0.001) respectively. CONCLUSIONS: The refractive index of the cornea is not uniform. The calculated dioptric power of the corneal epithelium is approximately -1.40 diopters (D). The varying refractive index does not significantly affect the total dioptric power of the cornea. The varying refractive index of the cornea has the potential to significantly contribute to the overall optical performance of the eye in relation to refractive surgery. The results should be incorporated into mathematical models, comparing and contrasting the optical performance of the eye before and after surgery.

Adult↗
PubMedDate not supplied

Model for deriving the optical performance of the myopic eye corrected with an intracorneal ring.

BACKGROUND: The intracorneal ring has been advanced as a mechanical device for the correction of myopia. The device may reduce refractive error, but the effect on the overall optical performance of the eye has been neglected. This paper addresses this issue by presenting mathematical models that will predict the effect of the intracorneal ring on refractive error, corneal asphericity, and the spherical aberration of the eye. MATERIALS AND METHODS: Algorithms are derived for predicting the corneal apical radius, asphericity, and the change in myopia after inserting intracorneal rings of any thickness and diameter. RESULTS: The model predicts that the magnitude of myopia reduction is a function of both ring thickness and diameter. The large diameter (9 to 10 mm), thin (0.1 to 0.2 mm) intracorneal ring is less likely to adversely affect corneal asphericity and therefore not significantly enhance the spherical aberration of the eye. CONCLUSIONS: An intracorneal ring cannot correct more than 4.00 diopters (D) of myopia without significantly increasing ocular spherical aberration, which, in turn, will compromise the final visual outcome.

Algorithms↗
PubMedDate not supplied

Do topical corticosteroids have a role following excimer laser photorefractive keratectomy?

The article reviews the evidence for and against the use of topical corticosteroids following PRK. Two significant problems after PRK are the development of corneal haze and unpredictability of the refractive outcome. These arise from changes in the anterior stroma, the deposition of new subepithelial tissue, and individual variations in the wound healing response. In rabbits, corticosteroids reduced corneal haze by limiting the synthesis of subepithelial collagen. However, in humans, controlled trials showed that corticosteroids had no lasting effect on either haze or regression, and were associated with an unacceptably high incidence of unwanted effects. The difference between species probably related to the relative absence of collagen and predominance of glycosaminoglycans during corneal wound healing in humans. Some human studies have shown rapid changes in refraction occurring within days of stopping or restarting corticosteroids. This suggests that their transient hyperopic effect is probably mediated by changes in the hydration of the tissue. Therefore, the role of corticosteroids in PRK is very limited. There is no justification for their routine use after PRK for low or moderate myopia. If corticosteroids have a role in improving haze or refractive outcome in selected patients, a means for their early identification must be found.

Administration, Topical↗
PubMedDate not supplied

Effects of ablation diameter, depth, and edge contour on the outcome of photorefractive keratectomy.

PURPOSE: To investigate the effects of the ablation diameter, depth, and edge contour on the outcome of excimer laser photorefractive keratectomy (PRK). METHODS: A prospective study was conducted in which 60 patients (60 eyes) were randomly allocated to 5.00-mm, 6.00-mm, or 5.00 to 6.00-mm multizone treatment groups. All eyes underwent a -6.00 diopter (D) correction using a Summit Omnimed excimer laser. RESULTS: In eyes treated with 6.00-mm diameter zones, the initial hyperopic shift was reduced, with significant differences at 1 and 4 weeks (p < 0.01). At 6 and 12 months, the refractive changes were closer to the intended correction with 6.00-mm diameters. The predictability of PRK was improved with 6.00-mm zones, with a significant reduction in variance of the refractive changes, at all stages postoperatively (p < 0.05 to p < 0.001). Objective measurements of haze were significantly less at 1, 3, and 6 months with 6.00-mm ablations (p < 0.05). There were no differences between the 5.00-mm and the 5.00- to 6.00-mm multizone groups. Computerized measurements of "night" halo were significantly smaller in the 6.00-mm treatment group at 1 week and 1 month (p < 0.05). At 12 months, two patients treated with 5.00-mm zones and three with the 5.00- to 6.00-mm multizone complained of severe night vision disturbances. No 6.00-mm eyes were similarly affected. CONCLUSIONS: Treatment with a 6.00-mm spherical ablation diameter produced less initial overcorrection, improved predictability, and was associated with a reduction in postoperative halos and night vision disturbances. Creating a superficial blend zone with a 5.00- to 6.00-mm multizone treatment had no beneficial effect on the outcome.

Adult↗
PubMedDate not supplied

Corneal asphericity and its implications for photorefractive keratectomy: a mathematical model.

BACKGROUND: Several clinical trials investigating myopic excimer laser photorefractive keratectomy (PRK) report an initial change in refraction from myopia to hyperopia, followed by a gradual regression toward emmetropia and occasionally to recurrent myopia. We examined the effect of corneal shape on refraction following PRK for myopia using a mathematical model. METHODS: We calculated the volume of corneal tissue removed by PRK for -3.00-diopter (D) and -6.00-D corrections with ablation diameters of 5 mm and 6 mm. For all the operating algorithms, the central region of the cornea was considered spherical. Mathematical models were developed based on calculations of the apical radius of the ablated cornea and the final refraction for a range of corneal asphericities. Baker's equation was used to model corneal asphericity. RESULTS: The smaller both the ablation size and desired correction, the smaller the effect of corneal asphericity on the refractive outcome. While corneal asphericity can influence the immediate refraction after PRK, the maximum effect is unlikely to be greater than +0.75 D. CONCLUSIONS: Corneal asphericity marginally affects the initial outcome of PRK. The effect will probably be offset by the healing response of the cornea.

Cornea↗
PubMedDate not supplied

Control of pain after photorefractive keratectomy.

BACKGROUND: The inadequate control of pain after photorefractive keratectomy remains an important issue for both patients and clinicians. METHOD: A survey of postoperative pain regimens used in excimer centers worldwide was carried out. A pilot study to assess the temporal basis of pain after photorefractive keratectomy was done by using a visual analog pain score in 30 patients. A comprehensive literature search was undertaken to ascertain the suitability of topical ophthalmic anesthetics in controlling pain after photorefractive keratectomy. RESULTS: Many drugs, both oral and topical, are used worldwide to control pain after photorefractive keratectomy, but no group has shown satisfactory pain control in all patients. The pilot study revealed that the pain was most severe in the first 24 hours after photorefractive keratectomy and declined to low levels thereafter. Topical anesthetics cause corneal complications when used excessively and for prolonged periods. CONCLUSION: Pain after photorefractive keratectomy is most severe in the first 24 hours. Topical anesthetics would only be needed for this short time and would guarantee pain relief in all patients. We do not anticipate any corneal complications if the anesthetics are used for short times and under close medical supervision.

Anesthetics, Local↗
PubMedDate not supplied

Corneal optical aberrations induced by photorefractive keratectomy.

BACKGROUND: Photorefractive keratectomy causes marked alteration to anterior corneal topography, and is likely to induce major changes to the optical aberrations of the eye. METHODS: Six diopters (D) of myopia correction was attempted on one eye of 50 patients, randomly allocated to one of three different treatments: 5-mm or 6-mm single ablation zone, or a double ablation (multizone; -5.00 D correction over 4.6 mm and -1.00 D over 6 mm). Topographic data was used to estimate corneal aberration coefficients. These were compared for effect of ablation zone, before and 1 year after photorefractive keratectomy. The coefficients were used to derive modulation transfer functions for the anterior corneal surface. RESULTS: Corneal spherical aberrations and coma-like aberrations both increased significantly following photorefractive keratectomy (p < 0.001). The mean spherical aberration coefficient increased from 0.36 +/- 0.11 before, to 0.91 +/- 0.37 after treatment, while the mean coma-like aberration coefficient changed from 0.28 +/- 0.16 before, to 0.60 +/- 0.31 after treatment. Ablation zone form had a significant effect on spherical aberration (p = 0.030), but not for coma (p = 0.96). The spherical aberration coefficient increased least for the 6-mm ablation (by 0.38 +/- 0.17), compared with the 5-mm ablation (0.69 +/- 0.45) and the multizone (0.62 +/- 0.38). Corneal modulation transfer functions were reduced significantly following the photorefractive procedure. The effect was greatest for large pupil diameters and for spatial frequencies between 2 and 15 cycles per degree. CONCLUSIONS: Corneal modulation transfer function calculations suggest that a significant loss of visual performance should be anticipated following photorefractive keratectomy, the effect being greatest for large pupil diameters. Results for three ablation zones show that induced aberrations are least for the largest (6 mm) ablation zone.

Adult↗
PubMedDate not supplied

Loss and recovery of corneal sensitivity following photorefractive keratectomy for myopia.

BACKGROUND: Photorefractive keratectomy affects corneal innervation in a new, and drastic, way. This inevitably results in a significant loss of corneal sensitivity. This paper investigates the pattern of sensitivity loss and recovery following PRK for low to moderate myopia. METHODS: Patients were recruited for two separate studies. Longitudinal Study: 10 patients, treated with a -6.00 D/6 mm PRK ablation, were examined over a 1-year period. Transverse Study: A comparison was made between 35 non-contact lens wearers, 80 contact lens wearers, and 60 patients who underwent five different PRK treatments, 1 year previously. Corneal sensitivity was assessed using the Non-Contact Corneal Aesthesiometer at four corneal locations: centrally, temporally, medially, inferiorly, on all patients. RESULTS: Longitudinal Study: Corneal sensitivity was significantly reduced at week 1, with a further significant reduction at week 2. A gradual recovery in sensitivity then followed to reach preoperative levels by 1 year. Transverse Study: There was no significant difference in corneal sensitivity found as a result of different PRK ablation depths. The depth of ablation was not a factor in corneal sensitivity recovery in low to moderate myopic corrections. Corneal sensitivity in the PRK treated eyes was significantly lower than in the control groups. CONCLUSION: The immediate loss of corneal sensitivity after surgery was due to the total removal of the corneal epithelial nerve supply and a substantial portion of the underlying stromal nerves. The further decrease at week 2 was probably due to the new epithelium acting as barrier to stimulation. The gradual recovery of corneal sensitivity was most likely caused by epithelial reinnervation within the ablation zone, but this was still below normal levels at 1 year after surgery. Corneal nerve function demonstrates a biphasic pattern of loss and recovery following the excimer laser correction of low to moderate myopia.

Adult↗
PubMedDate not supplied

Anterior corneal optical aberrations induced by photorefractive keratectomy for hyperopia.

PURPOSE: Photorefractive keratectomy (PRK) for hyperopia requires both a steepening of the central cornea and a flattening of the mid-periphery to achieve its effect and is likely to affect the optical aberrations of the eye. METHODS: Nine patients underwent PRK to correct between +2.00 and +4.00 D of hyperopia (first eye treated for each patient) using the Summit Technology Apex Plus excimer laser. Anterior corneal aberrations for pupil diameters of 3, 5.5 and 7 mm were estimated from corneal topography data (TMS-1), assuming a uni-index, single surface cornea. Refractive error was assessed using retinoscopy and standard subjective tests. RESULTS: Apart from the intended change in refraction (mean spherical equivalent manifest refraction, +4.60 +/- 1.60 D before surgery and +0.70 +/- 1.60 D at 1 year after surgery), the most significant change was in spherical aberration. Anterior corneal spherical aberration was positive (+1.60 +/- 0.60 D for a 5.5-mm pupil) before surgery and became negative after surgery (-1.80 +/- 1.20 D at 1 year). The change in spherical aberration was related to the achieved change in refractive error. CONCLUSIONS: The large change (approximately 3.00 D) in spherical aberration (from positive to negative aberration) has implications for the optical performance of the whole eye, where the effects of lenticular aberration must also be considered.

Cornea↗
PubMedDate not supplied

Direct and indirect therapy for word sound deafness.

This paper evaluates two therapy programmes conducted with PK, an aphasic individual with word sound deafness. The first aimed directly to improve discrimination skills, using minimal pair tasks supported with lip reading. Disappointingly, there were no changes on discrimination tests after this therapy, even when PK could benefit from lip reading information. The second, indirect, programme of therapy aimed to change the communication behaviours of PK's wife. Strategies such as writing and simplifying information were modelled and practiced. A detailed information booklet, outlining the target strategies and explaining PK's main strengths and weaknesses supported the programme. Evaluation of this therapy involved pre- and post-therapy analysis of interactions between PK and his wife, with biographical questions forming the basis of the interactions. There were several changes after therapy on this measure. The number and length of communication breakdowns were reduced, and more questions were answered accurately. This study suggests that, in some cases of severe word sound deafness, indirect therapies may be most effective.

Aged↗
PubMedDate not supplied

Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze.

BACKGROUND: After photorefractive keratectomy using excimer lasers (193 nm), most corneas show a marginal loss of transparency (haze) and the assessment of its magnitude in clinical studies has been subjective. To address this problem, we have developed a new device for the objective measurement of haze by measuring corneal light scattering. METHODS: A CCD-camera was fixed at 40 degrees to a slit-lamp microscope and connected via frame-grabber to a computer. By incorporating polarizing filters, the system could discriminate between reflected and scattered light. The intensity of light coming from the cornea was measured in gray scale levels using in-house image analysis software. The system was calibrated against three different sizes of microspheres (0.25, 0.50, and 5.00 microns) which corresponded to the size of cellular and extracellular elements known to occur at sites of corneal surgery. Data were obtained from three treated human eyes with measurements before treatment and at five different postoperative intervals with a maximum follow up of 4 months. RESULTS: All three sizes of microspheres caused disturbances in gray scale levels (36 to 255 units) in the same range of those observed in corneal measurements. Disturbances in corneal light scattering were noted from 1 week postoperatively and persisted throughout the period of observation. We observed an increase in reflected and scattered light until the 2nd postoperative month followed by a subsequent decline. CONCLUSIONS: It appears that this device is very useful to defect and measure objectively disturbances in corneal transparency after excimer laser photorefractive keratectomy.

Adult↗
PubMedDate not supplied

Photorefractive keratectomy with an argon fluoride excimer laser: a clinical study.

The results of excimer laser photorefractive keratectomy (PRK) in 16 blind and 120 sighted eyes (136 patients) are presented. Follow up for the blind eyes was 22 months and for the sighted eyes 8 to 18 months (mean, 1 year). A Summit Technology UV200 excimer laser with fluence fixed at 180 mJ/cm2, beam diameter 4 mm, a frequency of 10 Hz, and ablation rate of 0.22 mu per pulse was used. The range of preoperative myopia was - 1.50 diopters to - 17.50 D (spherical equivalent). Ninety percent of patients undergoing a -2.00 D correction and 75% of patients undergoing a -3.00-diopter correction were within +/- 1.00 D of intended refraction at 6 months. This figure fell to 40% and 20% for the groups undergoing -6.00 D and -7.00 D corrections, respectively. While the trend is toward undercorrection, around 70% of patients in all groups have benefited from a reduction of their myopia by at least half that intended. A variable degree of anterior stromal "haze" was detected in 110 patients (92%) despite a rigid high dose topical corticosteroid regime over 3 months. Best spectacle corrected visual acuity, however, was greater than or equal to preoperative levels in 111 patients (93%). Six patients experienced a reduction of one line of Snellen acuity at 6 months and three of the high myopes lost two lines. No patients lost more than two lines of Snellen acuity. Ninety-four patients (78%) noticed a "halo" around lights at night, more marked in the early postoperative period, which we attribute to the 4-millimeter diameter ablation zone. With a large pupil, both central and paracentral cornea can contribute simultaneously to the retinal image. We have demonstrated considerable individual variation in response to this surgery, which is more marked in high myopia. Although follow up at the present time is limited, to date PRK appears to be a safe procedure that holds considerable promise for refractive surgery in the future.

Blindness↗