PubMed · 10794896
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D J Coleman, R H Silverman, M J Rondeau. 2000. Ophthalmology.. https://doi.org/10.1016/s0301-5629(00)00185-x
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OBJECTIVE: To compare the optical properties of bifocal diffractive and multifocal refractive intraocular lenses. METHODS: A model eye with a pupil 4.5 mm in diameter was used to determine the point spread function (PSF) of the distance focus and near focus of a diffractive bifocal intraocular lens (IOL) (model 811E; Pharmacia Inc, Columbus, Ohio) and of a refractive multifocal IOL (model SA40N; Allergan Optical Inc, Irvine, Calif) to compare them with PSFs of foci of corresponding monofocal lenses. For interpreting the PSFs the through focus response, the modulation transfer function, and the Strehl ratio were evaluated. RESULTS: The intensity of the distance focus of the bifocal diffractive lens reached 58.5% and the near focus attained 42.7% of the intensity of a corresponding monofocal lens. The maximal halo intensity surrounding both foci was approximately 4.5%. The distance peak of the refractive multifocal IOL was 73.4% and the near peak 25.1% of a corresponding monofocal lens. The out-of-focus image overlaying the distance focus of the refractive multifocal IOL was approximately 3% of the light intensity of the distance focus, whereas the PSF of the near focus of the multifocal IOL is substantially affected by out-of-focus images. The computed modulation transfer functions show better results for the monofocal lenses, similar results for the tested distance foci, and clear advantages for the bifocal diffractive near focus. CONCLUSIONS: Modulation transfer functions reveal comparable properties for distance vision and a superiority of the bifocal diffractive lens over the refractive multifocal lens for near vision.
PURPOSE: To describe a patient whose "normal tension glaucoma" appears to have been produced by a long-standing habit of repetitive, bilateral eye rubbing. DESIGN: Observational case report. METHODS: A 46-year-old man presented with a "haze" over the left eye and had progressive bilateral optic neuropathy associated with bilateral normal intraocular pressure, pathological cupping of the optic disks, and nerve fiber bundle visual field defects. RESULTS: Over a 4-year period, vision in the left eye deteriorated to no light perception. Progressive deterioration in the right eye stopped only after the patient ceased a 20-year habit of forceful rubbing of his eyes. After that, the decline in vision was terminated and both visual acuity and visual field were stabilized over an 8-year follow-up. CONCLUSION: It may be appropriate to include "eye rubbing" in the differential diagnosis of unexplained progressive optic neuropathy in presumed normal tension glaucoma.
Two principal theories for the pathogenesis of glaucomatous optic neuropathy (GON) have been described--a mechanical and a vascular theory. Both have been defended by various research groups over the past 150 years. According to the mechanical theory, increased intraocular pressure (IOP) causes stretching of the laminar beams and damage to retinal ganglion cell axons. The vascular theory of glaucoma considers GON as a consequence of insufficient blood supply due to either increased IOP or other risk factors reducing ocular blood flow (OBF). A number of conditions such as congenital glaucoma, angle-closure glaucoma or secondary glaucomas clearly show that increased IOP is sufficient to lead to GON. However, a number of observations such as the existence of normal-tension glaucoma cannot be satisfactorily explained by a pressure theory alone. Indeed, the vast majority of published studies dealing with blood flow report a reduced ocular perfusion in glaucoma patients compared with normal subjects. The fact that the reduction of OBF often precedes the damage and blood flow can also be reduced in other parts of the body of glaucoma patients, indicate that the hemodynamic alterations may at least partially be primary. The major cause of this reduction is not atherosclerosis, but rather a vascular dysregulation, leading to both low perfusion pressure and insufficient autoregulation. This in turn may lead to unstable ocular perfusion and thereby to ischemia and reperfusion damage. This review discusses the potential role of OBF in glaucoma and how a disturbance of OBF could increase the optic nerve's sensitivity to IOP.