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Biomedical subjects

N Alpins

Publications and source records attributed to N Alpins.

11 recordsLinked to original sources
PubMed2001

Astigmatism analysis by the Alpins method.

PURPOSE: To determine the effectiveness of correcting astigmatism by laser refractive surgery by a vectorial astigmatism outcome analysis that uses 3 fundamental vectors: target induced astigmatism vector (TIA), surgically induced astigmatism vector, and difference vector, as described by the Alpins method. METHODS: A data set of 100 eyes that had laser in situ keratomileusis to correct myopia and astigmatism (minimum preoperative refractive astigmatism 0.75 diopter) was analyzed. The data included preoperative and 3 month postoperative values for manifest refraction and standard keratometry. Using the ASSORT or VectrAK analysis program, individual and aggregate data analyses were performed using simple, polar, and vector analysis of astigmatism and an analysis of spherical change. Statistical analysis of the results was used for means and confidence limits, as well as to examine the differences between corneal and refractive astigmatism outcomes. RESULTS: At an individual patient level, the angle of error was found to be significant, suggesting variable factors at work, such as healing or alignment. A systematic error of undercorrection of astigmatism is prevalent in the treatment of these 100 patients by a factor of between 15% and 30%, depending on whether refractive or corneal values are examined. Spherical correction showed systematic undercorrection of 11%, and parallel indices demonstrated it to be more effective than the astigmatic correction. CONCLUSION: This method of astigmatism analysis enables the examination of results of astigmatism treatment measured by both refractive and corneal measurements using vector analysis. By examining individual vector relationships to the TIA (ie, the correction index, index of success, and flattening index), a comprehensive astigmatism analysis is completed. Each index provides information necessary for understanding any astigmatic change. Astigmatic outcome parameters are more favorable when measured by subjective refractive than objective corneal methods.

Astigmatism↗
PubMed2000

Management of irregular astigmatism.

Using a liberal definition of corneal irregularity, modern videokeratoscopy may define approximately 40% of normal corneas with a toric refractive error as possessing primary irregular astigmatism. The causes of secondary forms of irregular astigmatism include corneal surgery, trauma, dystrophies, and infections. Internal refractive surface and media irregularity or noncorneal astigmatism (ocular residual astigmatism) contribute to irregular astigmatism of the entire refractive path of which crystaline lenticular astigmatism is usually the principal contributing component. Treatment options have increased in recent years, particularly, though not exclusively, through the advent of tailored corneal excimer laser ablations. However, discussion continues concerning the systematic approach necessary to enable treatment to achieve an optimal optical surface for the eye. Discussion also continues as to what constitutes the optimal corneal shape. Some refractive procedures may increase higher order aberrations in the attempt to neutralize refractive astigmatism. The way to further refinement of the commonly performed refractive techniques will ultimately lie in the integrated inclusion of a trio of technologies: topographic analysis of the corneal surface, wavefront analysis of ocular refractive aberrations, and vector planning to enable the appropriate balance in emphasis between these two diagnostic modalities. For the uncommon, irregularly roughened corneas, the ablatable polymer techniques show some promise.

Animals↗
PubMed1996

Astigmatic change 1 year after excimer laser treatment of myopia and myopic astigmatism. Melbourne Excimer Laser Group.

PURPOSE: To evaluate the surgically induced astigmatism (SIA) 1 year after excimer laser photorefractive astigmatic keratectomy (PARK) and photorefractive keratectomy (PRK). SETTING: Royal Victorian Ear and Eye Hospital, Melbourne, Australia. METHODS: This study comprised 333 PARK patients and 155 PRK patients treated with a VISX 20/20 excimer laser and followed prospectively for 12 months. Vector analysis of the change in astigmatism was used to calculate the SIA in the PRK group and the percentage of astigmatism corrected in the PARK group. RESULTS: Among patients with low cylinders astigmatic correction varied greatly, particularly in those treated for large amounts of myopia. The spherical PRK treatments yielded a mean induced postoperative astigmatism of 0.47 diopter. There was a linear relationship between this inadvertent SIA and increasing myopia. CONCLUSION: Excimer laser surgery for myopia creates a low degree of random, unpredictable SIA that may be the result of irregular epithelial thickening during postoperative healing. This creates a background noise of astigmatic change upon which the targeted astigmatic correction is superimposed.

Adult↗
PubMed1994

Excimer laser correction of myopic astigmatism.

The excimer laser allows the controlled ablation of corneal tissue to correct refractive error. By using a combination of spherical and slit apertures, it is possible to correct both myopia and astigmatism. We report the results of 139 consecutive eyes that had photoastigmatic refractive keratectomy (PARK) for myopic astigmatism (myopia < or = -15.00 diopters [D] with astigmatism < or = -6.00 D) and compare these results with 107 consecutive and concurrent eyes that received photorefractive keratectomy (PRK) for myopia (< or = -15.00 D). The same excimer laser was used by 27 different surgeons. All patients were followed for at least three months. In the PARK group, 68% were within +/- 1.00 D at six months and 77% were within +/- 2.00 D. In the PARK group, these figures were 87% and 97%, respectively. Uncorrected visual acuity of 20/40 or better was achieved in 72% of PARK and 90% of PRK patients at six months. Minor adverse reactions occurred in 6% of PARK and 11% of PRK patients. No significant surgeon effect was seen. Photoastigmatic refractive keratectomy provides a realistic approach to the surgical correction of myopic astigmatism and is comparable to PRK in safety and efficacy.

Adult↗
PubMed1978

The supranuclear disturbances of gaze in kernicterus.

Five patients with kernicterus and ocular motility disturbances are reported. All of the patients showed some defect in vertical gaze but not always upgaze. The most severely affected patient exhibited slowness of horizontal saccades in addition to a total vertical gaze palsy. In general, the severity of the ocular motility disturbance paralleled the severity of hearing loss. It is suggested that damage to the periaqueductal area accounts for disturbances in vertical gaze and the infrequent horizontal saccadic disturbances results from interruption of the descending centrifugal fibers. It is emphasized that kernicterus must be included in the differential diagnosis of any supranuclear vertical gaze disturbance.

Athetosis↗