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At least 469 records · Page 26Linked to original sources
PubMed1984

[Fundus asymmetry--supertraction of the papilla and posterior sclera staphyloma--as a source of error in the calculation of intraocular lenses].

The evaluation of 404 consecutively implanted posterior-chamber intraocular lenses after extra-capsular cataract extraction revealed a mean post-operative refractive error of + 0.52 diopters with a standard deviation of +/- 1.27 diopters. Four calculations attracted attention because of their unusually high refractive error of + 3.4 diopters. A post-operative refractive balance excluded measurement or calculation errors. On the other hand, repeated axial length measurements on these four eyes showed a very high mean variation of 3.27 mm. This high variation can be correlated to such typical elevation changes of the central fundus as a tilted disc or posterior staphyloma. High axial length measurements which do not correspond to appropriate amounts of axial myopia should be handled carefully to avoid high amounts of hyperopia following intraocular implantation.

Fundus Oculi↗
PubMed1977

Visual acuity and contrast sensitivity in multiple sclerosis--hidden visual loss: an auxiliary diagnostic test.

In 48 patients with multiple sclerosis sine-wave gratings were used to test visual sensitivity for coarse, medium, and fine detail rather than measuring visual acuity for fine detail only, as in conventional clinical tests. In 20/48 patients the test revealed a visual defect of neural origin, qualitatively different from that caused by refractive error. In 11 of these 20 patients, visual sensitivity to detail of medium coarseness was markedly degraded, even though sensitivity to both coarse and fine detail was unimpaired. In 3 of these 20 patients visual sensitivity to coarse detail was selectively degraded. These visual defects could not be detected by the Snellen test, yet the patient might experience visual problems in everyday life and also experience distorted visual perception. Possible neural bases for these visual impairments are discussed. Since 8 of the 14 patients with selective loss showed no clinical evidence of visual involvement, the test can aid the earlier diagnosis of multiple sclerosis.

Adolescent↗
PubMed2000

Contact lens fitting difficulties following refractive surgery for high myopia.

PURPOSE: To describe the clinical and optical problems encountered in contact lens fitting following refractive surgery for high myopia. METHODS: Following refractive surgery for high myopia (greater than -10.00 D) we corrected residual refractive errors with contact lenses in the four eyes of two patients. The first patient had undergone bilateral laser in situ keratomileusis (LASIK),with two subsequent LASIK retreatments in the left eye. Ten months later she was fit with rigid gas permeable (RGP) lenses in both eyes. The second patient had undergone a clear lens extraction in the right eye and radial keratotomy followed by photorefractive keratectomy(PRK) in the left eye. She was fit with toric soft lenses six years postoperatively. RESULTS: Final visual acuity obtained with contact lenses was 20/25-20/20 in all eyes. The first patient required significant minus lens power compensation. Furthermore, the RGP lens in the left eye was slightly decentered due to corneal irregularity induced by LASIK. The second patient had regular corneal surfaces and was successfully fit with daily wear toric soft lenses despite the 2.75 D of residual astigmatism in the left eye. CONCLUSIONS: Following refractive surgery for high myopia a proportion of patients will remain undercorrected. In these patients the alterations in corneal architecture that ensue make contact lens fitting more challenging. Patients with regular astigmatism may be fitted successfully with toric soft lenses. Patients with corneal irregularities should be fit with RGP lenses.

Adult↗
PubMed2004

Computerized calculation scheme for toric intraocular lenses.

BACKGROUND AND PURPOSE: While a number of intraocular lens (IOL) power prediction formulae are well established for determination of spherical lenses, no common strategy has been published for the computation of toric IOLs. The purpose of this study is to describe a paraxial computing scheme for tracing an axial pencil of rays through the 'optical system eye' containing astigmatic refractive surfaces with their axes at random. The capabilities of this computing scheme are demonstrated with clinical examples. METHODS: Based on a schematic model eye with spherocylindric surfaces, we use two alternative notations for description of vergences or prescriptions: (1) standard notation (refraction in both cardinal meridians and axis), and (2) component notation (spherical equivalent and cylindric component in 0 degrees and 45 degrees. Refractive surfaces are added to the vergence in component notation, whereas the transformation of the vergence through media is performed in the standard notation for both cardinal meridians. For calculation of the toric lens implant, a pencil of rays is traced through the spectacle and the cornea to the estimated lens position as well as backwards from the retina to the estimated lens position. For calculation of residual spectacle refraction, a pencil of rays is traced backwards from the retina through the toric lens implant and the cornea to the spectacle plane. RESULTS: In example 1 we calculate a 'thin toric lens' for compensation of a corneal astigmatism to achieve a spherical target refraction. In example 2 we compute a 'thick toric lens', which has to compensate for an oblique corneal astigmatism and rotate the spectacle cylinder to the against the rule position to enhance near vision. In example 3 we estimate the residual refraction at the corneal plane after implantation of a thick toric lens, when the cylinder of the lens implant is compensating the corneal cylinder in part and the axis of implantation is not fully aligned with the axis of the corneal astigmatism. CONCLUSION: This novel mathematical concept for computation of toric IOLs or prediction of the refractive outcome with a toric implant in place is a straightforward, computer-based approach, which may substitute for more or less empirical methods of determining toric IOL implants.

Aged↗
PubMed2005

Hyperpolarizabilities for the one-dimensional infinite single-electron periodic systems. II. Dipole-dipole versus current-current correlations.

Based on Takayama-Lin-Liu-Maki model, analytical expressions for the third-harmonic generation, dc Kerr effect, dc-induced second-harmonic optical Kerr effect, optical Kerr effect or intensity-dependent index of refraction, and dc-electric-field-induced optical rectification are derived under the static current-current (J0J0) correlation for one-dimensional infinite chains. The results of hyperpolarizabilities under J0J0 correlation are then compared with those obtained using the dipole-dipole correlation. The comparison shows that the conventional J0J0 correlation, albeit quite successful for the linear case, is incorrect for studying the nonlinear optical properties of periodic systems.

Journal Article↗
PubMed1981

The normal cup-disk ratio.

We determined the cup-disk ratios of 580 individuals, ranging in age from 4 to 91 years, with a Hruby lens; we also determined the cup-disk ratios of 289 of the 580 with a direct ophthalmoscope. All had applanation pressures of 18 mm Hg or less. There was no linear relationship (covariation) between cup-disk ratio and refractive error or intraocular pressure, but there was a tendency toward increasing cup-disk ratio with increasing age. The mean cup-disk ratio in the group examined with the Hruby lens was 0.38 and that in the group examined with the direct ophthalmoscope was 0.25. With either method almost all eyes had cup-disk ratios of 0.7 or less. In 9% of the eyes the cup was ovoid. In only 10% of these cases was the vertical cup-disk ratio greater than the horizontal cup-disk ratio, and in only one case was this difference 0.2 or more. The Hruby lens method consistently gave a slightly larger cup-disk ratio than the direct ophthalmoscope did. However, there was seldom a disparity of more than 0.2. The Hruby lens or biomicroscopic lens should be used to determine the fullest extent of the contour of the cup. Any cup-disk ratio of 0.7 or more, any vertical cup-disk ratio larger than the horizontal cup-disk ratio, and any disparity between the direct ophthalmoscope estimation and Hruby lens estimation of more than 0.2 should be viewed with suspicion.

Adolescent↗
PubMed2004

Time reversal of light with linear optics and modulators.

We introduce a new physical process that can perform a complete time-reversal operation on any electromagnetic pulse. The process uses only small refractive index modulations of linear optical elements. No nonlinear multiphoton effects such as four-wave mixing are required. The introduced process can be implemented on chip with standard semiconductor materials. Furthermore, the same process can be used to compress or expand the spectrum of electromagnetic waves while completely preserving the coherent information. We exhibit the time-reversal process by first-principles simulations of microcavity complexes in photonic crystals.

Journal Article↗
PubMed2002

Lenticular astigmatism in tilted disc syndrome.

PURPOSE: To evaluate whether an abnormal optic disc shape in patients with tilted disc syndrome (TDS) is associated with an abnormal configuration of the crystalline lens measured as lenticular astigmatism. SETTING: Department of Ophthalmology, Inönü University Medical Faculty, Turgut Ozal Medical Center, Malatya, Turkey. METHODS: This cross-sectional masked case-control study comprised 32 eyes of 32 patients with established TDS (13 men, 19 women; mean age 21.31 years +/- 7.05 [SD]) and 20 age- and sex-matched healthy control subjects (8 men, 12 women; mean age 22.65 +/- 7.11 years) with a comparable amount of myopic astigmatism (spherical equivalent) without TDS. The optic disc was morphometrically analyzed by planimetric evaluation of optic disc photographs. The total refractive and keratometric corneal astigmatism was obtained, and lenticular astigmatism was calculated by vector analysis. The Mann-Whitney U test was used for statistical analysis; 1 eye of each patient was evaluated in both groups. A P value less than 0.05 was considered statistically significant. RESULTS: The mean spherical equivalent refraction was comparable in TDS patients (-4.73 +/- 1.12 diopters [D]) and controls (-4.28 +/- 1.29 D) (P =.210). The mean total astigmatism was higher in TDS patients (-2.96 +/- 1.04 D) than in the controls (-2.51 +/- 1.09 D), but the difference was not significant (P =.151). The mean corneal astigmatism was comparable in TDS patients (-2.07 +/- 0.83 D) and controls (-2.28 +/- 0.87 D) (P =.454), but the calculated mean lenticular astigmatism was significantly higher in TDS patients (-1.31 +/- 0.98 D and -0.20 +/- 0.35 D, respectively) (P <.001). Twenty-nine of 32 TDS patients (90.6%) had lenticular astigmatism; in 16 (50%), it was greater than -1.00 D. Lenticular astigmatism was present in 7 controls (35%); in 2 (10%), it was greater than -1.00 D. The mean keratometry was significantly higher in TDS patients (43.84 +/- 1.06 D) than in the controls (42.75 +/- 1.45 D) (P =.011). CONCLUSIONS: Clinically significant lenticular astigmatism was present in TDS patients. If an abnormal optic disc shape is found on ophthalmoscopy, lenticular astigmatism as well as corneal astigmatism should be carefully evaluated to prevent an unsatisfactory refractive outcome, especially in refractive surgery candidates.

Adolescent↗
PubMed2003

Cataracts and glaucoma in patients with oculocerebrorenal syndrome.

BACKGROUND: Oculocerebrorenal syndrome is an X-linked recessive hereditary oculocerebrorenal disorder characterized by congenital cataract, mental retardation, and Fanconi syndrome of the proximal renal tubules. Other ocular findings include glaucoma, corneal opacity (keloid), enophthalmos, and hypotonia. OBJECTIVE: To describe the treatment of 7 patients (14 eyes) with bilateral cataracts associated with oculocerebrorenal syndrome. Method Retrospective review. RESULTS: Seven patients with oculocerebrorenal syndrome had visually significant bilateral cataracts detected on their first full ophthalmic examination. All underwent bilateral cataract surgery. The mean age (of 14 eyes) at cataract extraction was 1.25 (median, 1.1) months. Glaucoma diagnosis and treatment were more variable. The mean age (of 11 eyes) at glaucoma diagnosis was 24.1 (range, 0.2-70.0) months: the mean age was 0.2 month (of 4 eyes) when glaucoma was diagnosed before cataract extraction, and the mean age was 37.7 months (of 7 eyes) when glaucoma was diagnosed after cataract extraction. All eyes were followed up for a mean of 100.8 (range, 38-190) months. Main Outcome Measure Treatment of 7 patients (14 eyes) with bilateral cataracts associated with oculocerebrorenal syndrome. CONCLUSIONS: Early identification and surgical removal of cataracts is recommended in patients with oculocerebrorenal syndrome. Despite this, visual acuity results will only rarely be better than 20/70, and nystagmus is likely. Patients should be monitored closely and regularly for changes in intraocular pressure, optic nerve cupping, and refractive error to rule out the development of glaucoma.

Cataract↗
PubMed1976

Methodologic differences and measurement of cup-disc ratio: an epidemiologic assessment.

A retrospective analysis was undertaken to estimate the effect on measurements of cup-disc ratio (CDR) that result from overall differences among examination methods used by experienced investigators. The findings suggest large inter-observer differences, that is, large differences in measurement attributable to differences in definitions and methods between one observer and another. Extreme caution is indicated before attaching wide clinical or investigative importance to a specific value of CDR. A value of CDR regarded as the dividing line between normalcy and suspicion by one observer may be a highly inappropriate cutoff for another observer. Similarly, if different observers record measurements on the same patient, it may be impossible to determine whether the cup of an individual patient changes with time. Interobserver differences also can cast doubt on conclusions drawn from the comparison of data collected by different investigators. There is a need for standardization of definitions and methods in such clinical or research situations.

Adolescent↗
PubMed1996

Retinitis pigmentosa in a young man with Noonan syndrome: further evidence that Noonan syndrome (NS) and the cardio-facio-cutaneous syndrome (CFC) are variable manifestations of the same entity?

We report on a young man with Noonan syndrome (NS) and retinitis pigmentosa. As far as we know, retinitis pigmentosa has not been reported in NS. However, in the 3 cardio-facio-cutaneous syndrome (CFC) patients in whom electroretinographic studies were performed, retinal anomalies have been found. In addition, decreased vision, refractive errors, strabismus, and optic disc anomalies were reported in CFC patients. This observation suggests that NS and CFC are variable manifestations of the same entity.

Abnormalities, Multiple↗
PubMed2004

Effects of objective numerical apertures on achievable imaging depths in multiphoton microscopy.

Multiphoton microscopy is a powerful technique for achieving three-dimensional submicron imaging in biological specimens. However, specimen optical parameters such as refractive indices and scattering coefficients can result in the loss of image resolution and decreased signal in depth. These factors are coupled to the focusing objective's numerical aperture (NA) in limiting the achievable imaging depths. In this work, we performed multiphoton imaging on aqueous fluorescent solution, human skin, and rat tail tendon to show that, under the same immersion condition, lower NA objectives can examine more deeply into biological specimens and should be used when optimal imaging depths is desired.

Animals↗
PubMed2006

Photorefractive effect of ferroelectric liquid crystals.

This paper reviews our recent work on the photorefractive effect of ferroelectric liquid crystals (FLCs). The photorefractive effect is defined as the optical modulation of the refractive index of a medium as a result of a variety of processes. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. FLCs exhibit fast electric field response, and the orientation of the molecular axis of FLCs changes its direction according to the change in direction of the spontaneous polarization (Ps). When two laser beams interfere in a photoconductive FLC, an orientational grating is formed. The mechanism of the formation of the grating is based on the response of the Ps to the photoinduced internal electric field. The time of formation of the refractive index grating is significantly shorter in FLC materials.

Lasers↗
PubMed1994

Covariation of optic disc measurements and ocular parameters in the healthy eye.

To understand the variations in optic disc topography that may affect the local susceptibility of nerve fibers to glaucomatous damage, we evaluated the correlations between optic disc topography and selected ocular parameters in 210 normal eyes of healthy Japanese. In the total study group, eyes with a longer axial length had a longer distance between the disc and foveola, a larger index of ovalness and a larger disc (P < 0.01). A longer disc-foveola distance correlated with a larger index of ovalness (P < 0.01). The optic discs of severely myopic eyes had a considerably different structure from other eyes. Eyes with a tilted optic disc were unique in that the area of the optic disc was not large despite a positive correlation with long axial length (P < 0.01) a long disc-foveola distance (P < 0.01), and a large index of ovalness (P < 0.01). Eyes with a rotated optic disc were another special case. This eye type correlated in a contradictory fashion with two parameters: a large axial length (P < 0.01) and a short disc-foveola distance (P < 0.01). These findings suggest that changes in optic disc topography or susceptibility to glaucomatous damage correlate with selected ocular parameters but are not completely parallel.

Anthropometry↗
PubMed2004

Magnification-corrected indirect biomicroscopy of the optic nerve head.

BACKGROUND: Proper use of the new Super VitreoFundus and SuperPupil XL non-contact slit-lamp lenses for clinical disc biometry requires knowledge of their comparative magnification. METHODS: The optical performance of each fundus lens is described in terms of axial magnification, lens position, and the correction factor p (in degrees per millimeter) using a calibrated Gullstrand-type model eye adjusted for axial ametropia between -12.5 D and +12.6 D. RESULTS: The total change in axial magnification from myopia to hyperopia was -13.3% to +15.6% (Super VitreoFundus lens), and -13.9% to +14.1% (SuperPupil XL lens). When the fundus lens position was altered with respect to the model eye by +/-2 mm under myopic conditions the change in axial magnification was -5.1% to +7.7% (Super VitreoFundus lens), and -6.5% to +9.7% (SuperPupil XL lens). In the hyperopic condition the change was -3.8% to +5.8%, and -4.9% to +7.3%. Both fundus lenses exhibited a linear relationship between p and degree of ametropia of the model eye, while only the Super VitreoFundus lens displayed a constant relationship between p and ametropia of -5 D to +5 D. CONCLUSIONS: Using the fundus lens correction factor (p), the clinician may be able to estimate the dimensions of optic nerve head features with sufficient accuracy to allow clinical decisions to be made in the evaluation of patients with diagnosed or suspected glaucoma.

Fundus Oculi↗