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Biomedical subjects

Sandra M Brown

Publications and source records attributed to Sandra M Brown.

51 records · Page 3Linked to original sources
PubMed2004

Orbital lymphangioma.

Explore the source record for details and available documents.

Arteriovenous Malformations↗
PubMed2003

Systematic underablation in laser in situ keratomileusis: ablation pattern identified by advanced topographical analysis.

Topographical analysis based on the differential geometry of surfaces-curvature topography-was developed and applied to a patient after laser in situ keratomileusis. The patient had a minimal residual refractive error and normal best corrected visual acuity but had multiple visual aberrations, including ghosting and glare, unless the pupils were maximally constricted. The corneal loci responsible for the aberrations were difficult or impossible to identify on axial topographies but were readily identified with curvature topography. The patient's ablations appeared to be miniature versions of the intended ablation profiles, with small areas of emmetropic central cornea surrounded by annuli of rapidly increasing keratometric power; that is, systematic underablation. This may explain why some patients have visual aberrations with pupil diameters smaller than the programmed optical zones.

Adult↗
PubMed2003

Pupil size and the ablation zone in laser refractive surgery: considerations based on geometric optics.

PURPOSE: To determine whether the currently accepted method of selecting a minimum ablation zone size for refractive surgery based on dark-adapted pupil diameter is substantiated by geometric optical analysis. SETTING: Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA. METHODS: An optical model of the anterior segment was developed to calculate the effective corneal refractive diameter (ECRD), which is the diameter of the area of cornea that refracts all incident light rays arising from objects along the line of sight though the physical pupil (PP). The concept of the entrance pupil (EP) was reexamined and developed, and the ECRD was calculated over a range of corneal curvatures (K), anterior chamber depths (ACDs), and EP sizes. The model was generalized to include oblique light rays. Calculations were performed using MatLab Optimization Toolbox software (The MathWorks). RESULTS: For a given EP size, the ECRD was significantly influenced by K and slightly influenced by ACD. CONCLUSIONS: For objects on the line of sight, the ECRD was smaller than the EP in all cases. Regarding rays from objects in the periphery, the ECRD expanded rapidly as the angle of oblique incidence increased. For objects on the line of sight, the ECRD is always smaller than the clinically measured pupil (EP) because the EP is substantially magnified relative to the PP. Ablation zones larger than the EP should, in theory, prevent scattered or defocused light rays from contributing to the foveal image. When considering objects in the periphery, the increase in ECRD is sufficiently rapid that current refractive procedures cannot stop scattered light from these objects from contributing to the retinal image.

Cornea↗
PubMed2002

Iatrogenic ring scotoma after laser in situ keratomileusis.

A 37-year-old ophthalmologist had bilateral simultaneous laser in situ keratomileusis (LASIK) for moderate myopia with astigmatism using the Alcon Summit LADARVision laser; an ablation zone of 5.5 mm was used. Five months after surgery, the uncorrected visual acuity was 20/20 and 20/25 but despite regular corneal topographies, the patient experienced prominent ghost images under photopic and scotopic conditions. To elucidate the nature of the problem, automated static perimetry was performed, which revealed a significant depression between 10 degrees and 30 degrees compared with a baseline study obtained 3 years earlier. The patient started brimonidine 0.2% 1 drop in both eyes every morning, which caused 1.5 to 2.0 mm of pupillary miosis (tonic pupil size 3.0 to 4.0 mm in dim light) and eradicated the ghost images. Repeat perimetry showed significant improvement in all indices. The mechanism of improvement is unclear but may be due to elimination of light scatter from the transition zone between the ablated and unablated cornea. The issue of perimetric changes after refractive surgery deserves more attention; postoperative testing may be indicated for patients in whom the ablation zone diameter is close to the mesopic or scotopic pupil size to provide an accurate lifetime baseline visual field.

Adult↗
PubMedDate not supplied

Rapid, painless unilateral vision loss in a 37-year-old healthy woman.

A 37-year-old woman experienced painless, progressive vision loss to no light perception in the left eye over the course of 3 days. The right eye was unaffected. On examination, the only other abnormal finding was a +4 left afferent pupillary defect. She was initially diagnosed with retrobulbar optic neuritis and admitted for treatment with intravenous methylprednisolone. Neuro-imaging revealed a large right anterior cerebral artery aneurysm that crossed the midline to compress the left optic nerve. The aneurysm was treated with coil embolization, which was technically successful but which did not lead to significant improvement in vision.

Adult↗
PubMedDate not supplied

Bilateral retinal hemorrhages in an 18-year-old woman.

A previously healthy 18-year-old woman presented with sudden onset of central blurred vision in the right eye. Fundoscopic examination showed retinal venous tortuosity, several flame-shaped hemorrhages bilaterally, and a subhyaloid hemorrhage in the right fovea. Laboratory evaluation and subsequent bone marrow biopsy were consistent with the diagnosis of acute lymphoblastic leukemia. The retinal findings had cleared almost completely by three weeks after initiation of chemotherapy.

Adolescent↗