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Biomedical subjects

F W Fitzke

Publications and source records attributed to F W Fitzke.

At least 127 records · Page 7Linked to original sources
PubMed1988

Sorsby's pseudoinflammatory macula dystrophy--Sorsby's fundus dystrophies.

The findings are presented on the updated Kempster pedigree with Sorsby's fundus dystrophy. The study confirms the features described in other families: autosomal dominant inheritance with complete penetrance, loss of central vision due to subfoveal ingrowth of new vessels, and progressive peripheral chorioretinal atrophy. By contrast to other reports the family in the current study have peripheral retinal dysfunction, a deposit of a subretinal yellow material throughout the fundus and a tritan colour defect, all prior to the loss of central vision; in some patients there was loss of central vision from atrophic disease, rather than from ingrowth of subretinal new vessels; and, there was a different temporal progression of the central subretinal neovascular complex. These features suggest the possibility of genetic heterogeneity.

Adult↗
PubMed1988

Image size in the fundus: structural evidence for wide-field retinal magnification factor.

A simple geometrical method is described of calculating the retinal magnification factor (micrometres/degree) at the ora serrata of the human eye. At the ora the magnification factor is some 176 microns/deg., whereas at the posterior pole it is 276 microns/deg. This result may be of clinical use in examinations where dimensions of tears and holes near the ora serrata are estimated.

Humans↗
PubMed1987

Retinal magnification factor at the ora terminals: a structural study of human and animal eyes.

A geometrical method of calculating retinal magnification factor at the limits of the retinal field, adjacent to the ora terminalis, is described. The method is applied to the eyes of 11 mammalian and avian species, using new anatomical measurements and data from the literature. In the human and monkey eye, magnification at the far periphery is substantially smaller than at the posterior pole; in cat, rabbit, rat and mouse there is lesser reduction; in pigeon, tawny owl and starling magnification is closely similar at the far periphery and posterior pole.

Adult↗
PubMed1987

Retinal dysfunction in central serous retinopathy.

Patients with acute and chronic central serous retinopathy (CSR) were studied by psychophysical and photochemical means to establish the extent of visual depression and to investigate the basis of rod dysfunction in this disorder. In acute disease with serous detachment of the retina, the loss of sensitivity attains 3 log units and parallels the height of retinal elevation as does its recovery with resolution of the episode. Immediately after resolution, there is a residual 0.5 log unit threshold elevation. In chronic disease, marked loss of function exists over areas of abnormal retinal pigment epithelium in the absence of clinically detectable serous detachment. Although rhodopsin levels are low in both acute and chronic CSR, this relative lack of visual pigment does not totally account for the functional deficits in either situation.

Fluorescein Angiography↗
PubMed1986

A morphological analysis of experimental myopia in young chickens.

Devices that degrade vision were applied to the left eyes of 3-day old chicks. The dome device affected the entire visual field, and the arch device, only the lateral field. Control chicks wearing a circumorbital ring and untreated chicks were also examined. The dome device produced -15D and the arch device -4D of mean refractive error, while the ring and untreated chicks were emmetropic. Morphological measurements were made from macrophotographs of the intact and hemisected eyes fixed as for electron microscopy. The effects of the devices were analysed from the mean differences between the left (treated) and right (control) eyes. Nearly linear growth of the normal eye was found during the period in which measurements were taken (age 20-55 days). The ring device did not affect eye growth. The arch device significantly increased the dorsoventral equatorial diameter of the eye. The dome device had the greatest effect, and resulted in increases in both axial length and equatorial diameter during the treatment period. Dome eyes had a bulging cornea, increased anterior chamber depth, more open angle, and greater corneal diameter than controls. The axial length and equatorial diameter of the posterior segment also were increased. Two inflammatory responses of the eye were found, particularly in dome eyes; about 50% of treated eyes exhibited choroidal swelling, and vitreal clouding was found less frequently. The association between inflammation and excessive accommodation in producing the observed changes is discussed.

Animals↗
PubMed1985

Electrophysiological optometry using Scheiner's principle in the pigeon eye.

A new electrophysiological optometer has been developed, based on Scheiner's principle. Using two light-emitting diodes driven in counterphase, and grating stimuli in Maxwellian view, the system has been used to refract the photoreceptor plane of the pigeon eye. When a grating is conjugate with the photoreceptors, the electroretinographic response (e.r.g.) is minimal, and the image is stationary. As defocus is introduced, so image shift occurs, and the e.r.g. rises on each side of the refractive minimum. Two experiments were devised to test whether a derived minimum point is primary, by using gratings of bar width 3, 5 and 7 units, and by using random checkerboard stimuli. Ray tracing was used to compute the lobe width of dioptric profiles for gratings of spatial frequency 1.47, 0.88 and 0.63 cycles/deg. The computed lobe widths agree well with experimentally determined e.r.g. profiles. Examination of the lateral visual field, on the horizon, shows that the pigeon eye is emmetropic, and well corrected for astigmatism.

Animals↗
PubMed1985

Refractive sectors in the visual field of the pigeon eye.

Scheiner's principle has been used in electroretinographic optometry to refract the photoreceptor plane in different regions of the visual field of the pigeon eye. Along the horizon and in the upper visual field the eye is emmetropic, or nearly so. Below the horizon the eye becomes progressively more myopic at more negative elevations, refractive state falling to -5D at -90 deg. Lower field myopia is not an artifact of oblique astigmatism, nor of an aberration symmetrical about the optical axis. It is suggested that lower field myopia is a biological adaptation suited to keep the photoreceptors in the upper retina conjugate with the ground. Refractive state below the horizon can be fitted with a sine function by varying a parameter H (eye-ground height). The value of H agrees well with directly measured eye-ground height.

Animals↗
PubMed1985

Experimental myopia in chicks: ocular refraction by electroretinography.

Application of devices that degrade the retinal image has been reported to produce enlargement of the ocular globe in young domestic chicks. Two such device types (domes and arches) were applied to 3-day-old chicks. The domes affected the entire visual field whereas the arches affected only the lateral field. A third group wore a thin circumorbital ring to control for possible mechanical impediments to growth. Untreated control chicks comprised a fourth group. At ages ranging from 3 to 7 wk, the chicks were refracted in their lateral visual fields with a Maxwellian view optometer based on Scheiner's principle, which yields an objective assessment of the refractive state of the photoreceptor image plane. One to seven measurements were taken from each of 48 urethane-anesthetized chicks. These indicated that the mean refractive states of the untreated eyes and the ring eyes were -0.20 D and -0.19 D, respectively, which did not differ significantly from emmetropia. In contrast, the mean refractive states of the arch eyes and the dome eyes were -4.11 D and -14.88 D, respectively, which differed significantly from emmetropia and from each other. The results indicate that early retinal image degradation can result in the relatively rapid development of a substantial myopia in these experimental animals.

Animals↗
PubMedDate not supplied

Effect of decreased retinal illumination on frequency doubling technology.

PURPOSE: To investigate the effect of changes in retinal illumination on Frequency Doubling Technology (FDT). METHODS: Five eyes, of 5 adults who were free from identifiable ocular pathology, were examined using the Snellen chart and the Pelli-Robson chart, conventional automated perimetry, and the full threshold N-30 program of FDT. Each test was performed with and without a 0.9, 1.5, or 2.4 log unit neutral-density (ND) filter placed before the eye. Furthermore, the influence of pupil diameter on FDT test results was compared after treatment with pilocarpine or cyclopentolate with the influence of ND filters. RESULTS: All tests showed a decrease in sensitivity with decreasing retinal illumination. Frequency Doubling Technology showed an especially pronounced and significant decrease in sensitivity. The maximum mean threshold difference in FDT results with ND filter was 31.2 dB while that with the Humphrey Field Analyzer and the Pelli-Robson chart were 13.3 dB and 0.66 log contrast, respectively. The mydriatic state of the pupil increased the sensitivity of FDT and the miotic state decreased it to about the same extent as the the 0.9 ND filter. CONCLUSION: The change in retinal illumination has more impact on FDT than on spatial contrast tests and conventional automated perimetry. It is important to take this into account in evaluating FDT results.

Adaptation, Ocular↗
PubMedDate not supplied

Electrophysiological findings in dominant optic atrophy (DOA) linking to the OPA1 locus on chromosome 3q 28-qter.

Pattern and flash visual evoked cortical potentials (PVEP, FVEP), and pattern electroretinograms, (PERG) were recorded in 13 affected individuals from 8 families with DOA. These were selected as representative from 87 affected members of 21 pedigrees with DOA who were examined, and who underwent genetic linkage analysis. Linkage to the OPA1 locus on chromosome 3q 28-qter was demonstrated in all families. VA ranged from 6/9 to HM: visual fields showed a variable centro-caecal defect; SLO (when performed) showed diffuse nerve fibre loss; MRI (when performed) showed small intra-orbital optic nerves. In 9/13 patients the PVEP was absent in one or both eyes. Most recordable PVEPs were of abnormal latency, but the delays were not marked (peak times 116-135 msec); amplitudes were low or subnormal. PERG fell within the normal range in 9 eyes of 7 patients. 14 eyes showed an abnormal N95:P50 ratio in keeping with ganglion cell dysfunction. Some severely affected eyes showed P50 component involvement, but in no eye was the PERG extinguished. Significant interocular asymmetries in at least one electrophysiological measure were present in 6/13 patients. Colour contrast thresholds were significantly elevated for all three colour confusion axes, with tritan being most affected.

Adolescent↗
PubMedDate not supplied

Corneal haze after excimer laser refractive surgery: objective measurements and functional implications.

Postoperative changes in corneal transparency is a major concern after PRK. Data were obtained from 69 human eyes treated with excimer laser photorefractive keratectomy in order to evaluate a relationship between objective measurements of corneal transparency and visual performance. A CCD-camera device was employed and by using polarizing filters the system could discriminate between reflected and scattered light. We observed two groups of postoperative behaviour in corneal transparency. Each group showed an increase in both scattered and reflected light signals with a maximum at around two months postoperatively. In the majority group (70%) this was followed by a subsequent decline of the scattered light signal, whereas the combined signal generated by reflected and scattered light showed a biphasic curve with a second peak at around 4 to 5 months postoperatively. In the minority patient group (30%) the timebase variations in pattern of both signals were indistinguishable throughout the period of observation. In all patients we observed a good correlation between the signal generated by scattered light alone and the reduction in the 5% contrast visual acuity performance, whereas correlation was poor when the combined signal of reflected and scattered light was considered. These disturbances in low contrast visual performance were only significant during the first three to four months postoperatively and thereafter most patients returned to their preoperative value. Eighteen percent of our patients discontinued topical steroids postoperatively. No differences in either corneal transparency or final refraction was observed. We consider that PRK is an effective form of refractive surgery and the marginal loss of corneal transparency should only be a problem during the first three or four months postoperatively.

Adult↗
PubMedDate not supplied

Night vision after excimer laser photorefractive keratectomy: haze and halos.

A series of 85 patients with myopia, up to -6.00D, was treated by photorefractive keratectomy (PRK), using a 5 mm diameter ablation zone. At six months, 38 patients (45%) reported slight disturbances of night vision, nine (11%) of whom had significant problems. Perturbations of night vision after PRK are seen as starbursts and halos around lights. Corneal haze produces the starbursts, which are usually transient. In contrast, halos are myopic blur circles and may be persistent. Using a computer program, halos after PRK were found to be significantly larger than those in emmetropes and myopes corrected with spectacles (p < 0.01). The halos were diminished by using either artificial pupils or negative lens over-correction. In patients with identical bilateral PRK corrections, except for the ablation zone size, the magnitude of the halo was less with 5 mm than 4 mm zones (p < 0.01). Patients treated with 5 mm reported fewer problems attributable to halo than with the 4 mm ablation diameters (p < 0.01). Halos and pupil diameters were measured in nine patients with significant impairment of night vision haze. Those with starbursts had small hyperopic shifts, minimal halos and high haze and light scatter measurements, whilst patients with halos had large hyperopic shifts, little haze and large pupil diameters. Patients with persistent halo problems benefited from either negative lens over-correction or miotics at night.

Adult↗
PubMedDate not supplied

Refractive index of the human corneal epithelium and stroma.

BACKGROUND: The refractive index of the cornea must be determined to optically perfect keratorefractive procedures. There are very few empirical measurements of the human corneal refractive index described in the literature. Throughout its depth, the cornea demonstrates regional variations in physiological properties such as swelling/de-swelling characteristics. These properties suggest there may be a difference in the refractive index between the anterior and posterior corneal surfaces. METHODS: The refractive index of the human corneal epithelium of 10 eyes was measured, in vivo, using a modified hand-held refractometer. The refractive indices of the anterior and posterior surfaces of the bare stroma of fresh human corneas were measured using a bench model Abbe refractometer. RESULTS: The mean refractive index of the epithelium, stromal anterior and posterior surfaces were 1.401 (SD +/- 0.005), 1.380 (SD +/- 0.005), and 1.373 (SD +/- 0.001) respectively. CONCLUSIONS: The refractive index of the cornea is not uniform. The calculated dioptric power of the corneal epithelium is approximately -1.40 diopters (D). The varying refractive index does not significantly affect the total dioptric power of the cornea. The varying refractive index of the cornea has the potential to significantly contribute to the overall optical performance of the eye in relation to refractive surgery. The results should be incorporated into mathematical models, comparing and contrasting the optical performance of the eye before and after surgery.

Adult↗
PubMedDate not supplied

Model for deriving the optical performance of the myopic eye corrected with an intracorneal ring.

BACKGROUND: The intracorneal ring has been advanced as a mechanical device for the correction of myopia. The device may reduce refractive error, but the effect on the overall optical performance of the eye has been neglected. This paper addresses this issue by presenting mathematical models that will predict the effect of the intracorneal ring on refractive error, corneal asphericity, and the spherical aberration of the eye. MATERIALS AND METHODS: Algorithms are derived for predicting the corneal apical radius, asphericity, and the change in myopia after inserting intracorneal rings of any thickness and diameter. RESULTS: The model predicts that the magnitude of myopia reduction is a function of both ring thickness and diameter. The large diameter (9 to 10 mm), thin (0.1 to 0.2 mm) intracorneal ring is less likely to adversely affect corneal asphericity and therefore not significantly enhance the spherical aberration of the eye. CONCLUSIONS: An intracorneal ring cannot correct more than 4.00 diopters (D) of myopia without significantly increasing ocular spherical aberration, which, in turn, will compromise the final visual outcome.

Algorithms↗
PubMedDate not supplied

Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze.

BACKGROUND: After photorefractive keratectomy using excimer lasers (193 nm), most corneas show a marginal loss of transparency (haze) and the assessment of its magnitude in clinical studies has been subjective. To address this problem, we have developed a new device for the objective measurement of haze by measuring corneal light scattering. METHODS: A CCD-camera was fixed at 40 degrees to a slit-lamp microscope and connected via frame-grabber to a computer. By incorporating polarizing filters, the system could discriminate between reflected and scattered light. The intensity of light coming from the cornea was measured in gray scale levels using in-house image analysis software. The system was calibrated against three different sizes of microspheres (0.25, 0.50, and 5.00 microns) which corresponded to the size of cellular and extracellular elements known to occur at sites of corneal surgery. Data were obtained from three treated human eyes with measurements before treatment and at five different postoperative intervals with a maximum follow up of 4 months. RESULTS: All three sizes of microspheres caused disturbances in gray scale levels (36 to 255 units) in the same range of those observed in corneal measurements. Disturbances in corneal light scattering were noted from 1 week postoperatively and persisted throughout the period of observation. We observed an increase in reflected and scattered light until the 2nd postoperative month followed by a subsequent decline. CONCLUSIONS: It appears that this device is very useful to defect and measure objectively disturbances in corneal transparency after excimer laser photorefractive keratectomy.

Adult↗
PubMedDate not supplied

Discrimination between the origins and functional implications of haze and halo at night after photorefractive keratectomy.

A series of 84 eyes with up to -6.00 diopters (D) of myopia were treated by photorefractive keratectomy (PRK) using a 5.00 mm ablation zone. Three months postoperatively, 43 eyes (51%) complained of disturbed night vision, compared to 12 (14%) preoperatively. Ten (12%) had significant problems, ie, interference with driving at night. At 12 months, there were 32 patients (38%) with minor disturbances of night vision, 4 (5%) with significant problems.

Automobile Driving↗
PubMedDate not supplied

Model for predicting the optical performance of the eye in refractive surgery.

BACKGROUND: Predicting the outcome of refractive surgical procedures is one of the chief goals of the refractive surgeon. Besides perfecting the change required to nullify a refractive error, the optical quality of the postsurgical eye should be maximized. METHODS: A model eye useful for predicting the likely effects on the optical performance of the eye as a result of refractive surgical intervention is presented. The model features aspheric ocular interfaces, a gradient refractive index within the lens, and a uni-index cornea. The dimensions of the model parameters are taken from the literature. Baker's method of ray tracing through aspheric surfaces is used to predict the lateral spherical aberration of the eye for specific pupil sizes. The results for various operational conditions such as number of lens layers and corneal shape were calculated. RESULTS: The model predicts that optimal optical imagery is produced when the corneal profile is represented by a flattening ellipse (shape factor = .65 to .85). Ideally, in refractive surgery involving the cornea, the postoperative corneal contour should conform to this flattening ellipse.

Cornea↗