Biomedical subjects
G R Snibson
Publications and source records attributed to G R Snibson.
A comparison of different depth ablations in the treatment of painful bullous keratopathy with phototherapeutic keratectomy.
AIM: To study the efficacy of phototherapeutic keratectomy (PTK) for pain relief for patients with painful bullous keratopathy and poor visual potential. METHODS: Patients with painful bullous keratopathy and poor visual potential were treated with superficial PTK (8-25 microm), intermediate (50-100 microm) or deep PTK (25% stromal thickness) using the Nidek EC5000 excimer laser after manual epithelial debridement. Follow up ranged from 1 to 24 months (mean 6.5 months). Outcome measures included symptomatic relief and need for further treatment. RESULTS: In the superficial PTK group five of eight (62%) patients improved symptomatically after treatment. The three (38%) who did not improve went on to have penetrating keratoplasty for pain relief. In the intermediate depth group only two of five (40%) patients had symptom alleviation. The three others (60%) required further procedures. 20 of 24 (83%) patients treated with deep PTK had significant or total alleviation of symptoms. Of these, one developed acute anterior uveitis 9 months after PTK and two required botulinum ptosis for persistent corneal epithelial defects, one of whom had three consecutive episodes of microbial keratitis. Three of 24 suffered occasional discomfort and one patient required a penetrating keratoplasty for continued pain. CONCLUSION: PTK can be a useful therapeutic measure in painful bullous keratopathy with poor visual potential. Deep PTK appears to be more successful in pain management than superficial treatment.
Evaluation of the myocilin (MYOC) glaucoma gene in monkey and human steroid-induced ocular hypertension.
PURPOSE: Glucocorticoid-induced ocular hypertension (the steroid response) may result in optic nerve damage that very closely mimics the pathologic course of primary open angle glaucoma (POAG). In addition, patients with glaucoma and their relatives are much more likely to exhibit the steroid response than unaffected individuals, suggesting a potential link between the steroid response and POAG. Recently, the expression of a gene (MYOC) in the trabecular meshwork was shown to be steroid-induced. MYOC variations thought to be disease-causing also were found in 3% to 5% of POAG cases. The purpose of this study was to determine whether some variations in MYOC might be involved in steroid-induced ocular hypertension. METHODS: Seventy human steroid responders and 114 control subjects were screened for variations in the coding sequence and promoter of MYOC. Also, topical doses of dexamethasone (DEX) were administered to cynomolgus monkeys to determine their steroid responsiveness, and the MYOC orthologue was cloned from the cynomolgus monkey. RESULTS: Overall, 109 instances of 20 different sequence variations were identified in the human myocilin gene. However, only four of these (each observed in a single individual) met the study criteria for a possible phenotype-altering variation. Three of these were present in steroid responders and one in a control patient, a distribution that was not statistically significant (P: = 0.3). In addition, the allele frequency of a closely flanking marker was compared between the steroid responders and the control subjects, and no evidence for linkage disequilibrium was observed. Reproducible and reversible ocular hypertension was induced in approximately 40% of the monkeys treated with DEX, similar to that seen in man. Ten monkeys were screened for MYOC mutations with single-strand conformation polymorphism (SSCP) analysis. Overall, 37 instances of 13 different sequence variations were observed. Four of these changes met the study criteria for a possible phenotype-altering variation, and these were equally distributed between responder and nonresponder monkeys. CONCLUSIONS: This study identified no statistically significant evidence for a link between MYOC mutations and steroid-induced ocular hypertension.
Excimer laser refractive surgery.
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Pterygium surgery in Victoria: a survey of ophthalmologists.
AIM: To determine the surgical approaches and adjunctive therapy es currently used by Victorian ophthalmologists for the treatment of primary and recurrent pterygia. METHOD: Ophthalmologists practising in Victoria were asked to complete a written survey relating to their experience with pterygium surgery. RESULTS: Responses were received from 142 of 165 ophthalmologists surveyed (86%). Of these, 107 (75%) had performed at least one pterygium operation during the preceding 2 years. Excision followed by beta irradiation was the most commonly performed procedure for both primary (57%) and recurrent (35%) pterygia. The next most commonly performed procedure for primary pterygia was excision leaving bare sclera (15%) and, for recurrent pterygia, excision with autologous conjunctival transplantation (26%). Considerable variation was observed in surgical technique, choice of adjunctive therapy, postoperative care and in the surgeons' estimates of the frequency of major complications. CONCLUSION: Although there is little consensus regarding the surgical management of pterygium, beta irradiation remains the most commonly used adjunctive therapy in Victoria.
Pyogenic granuloma of the cornea.
BACKGROUND: Ocular pyogenic granulomata are uncommon and are often associated with a chalazion or previous ocular and adnexal surgery The avascular nature of the cornea may explain the rarity of pyogenic granulomata at this site. We report on a case of corneal pyogenic granuloma following previous corneal surgery. METHODS: Ophthalmologists who had treated the patient previously were contacted and earlier clinical notes and histopathological examinations were reviewed. The clinical course following excision of the pyogenic granuloma is described, as are the histopathological findings. RESULTS: Histological examination confirmed the diagnosis of pyogenic granuloma. Excision was followed by a clinical recurrence at a different site with spontaneous resolution. CONCLUSIONS: Pyogenic granulomata of the cornea are rare. However, the present case illustrates the importance of considering benign inflammatory causes in the differential diagnosis of a corneal mass lesion so as to avoid unnecessarily aggressive intervention. To our knowledge, spontaneous resolution of a corneal pyogenic granuloma has not been previously described.
Corneal and conjunctival infections.
Recent advances in the field of infectious conjunctivitis and keratitis include new diagnostic methods, the identification of new pathogens, and novel therapeutic agents. Tandem confocal microscopy has been used to diagnose Acanthamoeba keratitis, and polymerase chain reaction has proven to be a rapid and sensitive technique for detecting specific viral antigens, particularly in cases where cultures yield no growth. Two new antiviral agents, ganciclovir and carbocyclic oxetanocin G, have been shown to be as effective as acyclovir in treating herpetic epithelial disease. The fluoroquinolones, especially ofloxacin, have become the antimicrobial agents of choice in the initial management of selected cases of bacterial keratitis.
Delayed microbial keratitis following radial keratotomy.
BACKGROUND: We report on the case of a 46-year-old female who presented with delayed microbial keratitis 10 years after uncomplicated radial keratotomy. METHODS: The pre- and postoperative clinical record was reviewed following her presentation to the Corneal Clinic. Slit-lamp examination revealed a stromal inflammatory infiltrate at the site of an earlier radial keratotomy incision. The lesion was scraped and a coagulase-negative Staphylococcus aureus was cultured in enrichment broth. RESULTS: The keratitis was treated successfully with combination fortified topical antibiotics without loss of vision. CONCLUSIONS: Although microbial keratitis is a well documented complication of incisional refractive procedures, it is rarely encountered as late as one decade after surgery. Patients should be warned of this possibility and the need for prompt treatment.
Retreatment after excimer laser photorefractive keratectomy. The Melbourne Excimer Laser Group.
PURPOSE: To determine the risk factors for undercorrection of myopia after photorefractive keratectomy and to evaluate the efficacy and safety of retreatment. METHODS: A VISX Twenty/Twenty excimer laser was used to treat myopia and myopic astigmatism of up to -15.00 diopters (spherical equivalent) at the corneal plane. Retreatments were performed primarily for undercorrection with or without coexistent corneal haze or abnormalities on videokeratoscopy. Not every patient who was undercorrected requested retreatment. RESULTS: Of 645 eyes (440 patients) followed up for more than 12 months, 58 eyes (9%) required retreatment. The retreatment rate increased with increasing myopia: 17 (5%) eyes with myopia of less than -5.00 diopters, 30 (13%) eyes with myopia of -5.01 to -10.00 diopters, and 11 (19%) eyes with myopia of greater than -10.00 diopters required a second procedure. A higher retreatment rate was observed after astigmatic corrections than after spherical corrections. Corneal haze after retreatment was no greater than that observed after initial procedures. Twelve months after primary procedures, 378 (75%) of 504 eyes were within 1.00 diopter of emmetropia, whereas 27 (69%) of 39 eyes attained this result after retreatment. A total of 383 (76%) of 504 eyes attained uncorrected visual acuity of 20/40 or better after primary procedures, compared with 25 (64%) of 39 eyes after retreatment. CONCLUSIONS: The risk of undercorrection requiring retreatment after photorefractive keratectomy increases with the magnitude of the primary treatment. Although less successful than initial procedures, retreatment appears to enhance the results of photorefractive keratectomy.
Association of keratoconus with granular corneal dystrophy.
A 23-year-old woman presented with a history of reduced vision and foreign body sensation in both her eyes. Ocular examination revealed the simultaneous presence of bilateral keratoconus and granular corneal dystrophy. To our knowledge, bilateral concurrent occurrence of keratoconus and typical granular corneal dystrophy has not been reported previously. In such a case, penetrating keratoplasty performed for keratoconus may also carry the risk of recurrence of the granular dystrophy.
One-year evaluation of excimer laser photorefractive keratectomy for myopia and myopic astigmatism. Melbourne Excimer Laser Group.
OBJECTIVE: To evaluate prospectively the efficacy and safety of excimer laser photorefractive keratectomy in the treatment of myopia and myopic astigmatism. METHODS: Up to 15 diopters (D) of myopia with or without astigmatism of less than 6 D was treated with an excimer laser (VISX Twenty/Twenty). One hundred fifty procedures have been followed up for more than 12 months. RESULTS: Postoperative refractions were generally stable after 3 months without significant early overcorrection. Of those eyes treated with spherical equivalents of 5 D or less, 96% were within 1 D of the targeted refraction after photorefractive keratectomy and 88% had uncorrected visual acuities of 20/40 or better. At 12 months, 77% of all 150 eyes treated achieved an uncorrected visual acuity of 20/40 or better and 81% were within 1 D of the intended correction. Nine eyes (6%) lost 2 or more lines of best corrected visual acuity and 14 (9%) gained 2 or more lines. Adverse reactions were reported in 12 patients (8%) during the postoperative period. CONCLUSIONS: Photorefractive keratectomy is capable of correcting low and moderate myopic errors with a relatively high degree of accuracy and safety. The predictability and stability of the postoperative refraction during the first 12 months seem to be good.
Ocular surface residence times of artificial tear solutions.
Solutions of hydroxypropylmethylcellulose (HPMC) and polyvinyl alcohol (PVA) are widely used as artificial tears. However, their usefulness is limited by the short duration of their effect. Dilute sodium hyaluronate (SH) solutions exhibit non-Newtonian rheology with high viscosities at low shear rates, which would be expected to enhance their ocular surface residence time. Using quantitative gamma scintigraphy, estimates of the ocular surface residence times of 0.3% HPMC, 1.4% PVA, and 0.2% SH were made in six patients with keratoconjunctivitis sicca. The sodium hyaluronate solution had a mean half-life on the ocular surface of 321 s, significantly longer than hydroxypropylmethylcellulose (44 s; p = 0.012) and polyvinyl alcohol (39 s; p = 0.013).
Meibomian gland disease. Classification and grading of lid changes.
In recent years attention has been paid to meibomian gland dysfunction (MGD) as a distinct clinical entity responsible for chronic symptoms and signs and occurring independently or in association with atopy, cicatrising mucosal disorders and rosacea. Attempts to correlate MGD with microbiological and lipid biochemical changes are confounded by the absence of a clear descriptive language for the disorder and its associated changes. Such a language is crucial for the conduct of cross-sectional and natural history studies and therapeutic clinical trials. We present a comprehensive classification and grading scheme of meibomian gland disease, supporting our observations with illustrations.
Precorneal residence times of sodium hyaluronate solutions studied by quantitative gamma scintigraphy.
Sodium hyaluronate solutions have been advocated in the management of a variety of dry-eye states. By virtue of their non-Newtonian rheological properties, formulations exhibiting high zero-shear viscosities may be used as an artificial tear with the expectation of prolonged precorneal residence times and improved tolerance. Quantitative gamma scintigraphy was used to evaluate the residence times of 0.2% and 0.3% sodium hyaluronate solutions and a polymer-free solution of buffered saline in 12 patients with keratoconjunctivitis sicca and a group of six normal volunteers. Using several indices of residence time, mean values for the sodium hyaluronate solutions were significantly longer than those for buffered saline. Parallel changes in tear film thickness were also demonstrated using a technique based on laser interferometry.