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M C Knorz

Publications and source records attributed to M C Knorz.

At least 37 records · Page 2Linked to original sources
PubMed1996

Contrast sensitivity with monofocal and bifocal intraocular lenses.

Bifocal intraocular lenses (BIOLs) reduce image contrast. We measured contrast sensitivity (CS) to evaluate the clinical significance of the loss in image contrast. Four groups were compared: 15 patients with a monofocal IOL, 13 with the True Vista BIOL, 13 with the AcuraSee BIOL, 11 with the diffractive BIOL. CS was measured using the Mentor B-VAT II-SG. Distance CS was slightly better in monofocal eyes than in all bifocal eyes, and distance CS was considerably better than near CS in eyes with the True Vista or the AcuraSee BIOL. With the diffractive BIOL, values were about the same at distance and near focus. Our results demonstrate that BIOLs reduce CS. thereby performing differently: both True Vista and AcuraSee favor distance vision, while the diffractive BIOL provides about the same contrast at distance and near focus.

Aged↗
PubMed1996

[Diode laser coagulation of stage 3+ retinopathy of prematurity].

BACKGROUND: Laser photocoagulation in retinopathy of prematurity (ROP) appears to have fewer adverse effects and to be at least as effective as cryotherapy. METHODS: To evaluate the efficacy and safety of diode laser photocoagulation we examined 50 eyes affected by stage 3+ ROP in 30 very low birth weight infants (gestational age 24-29 weeks, mean +/- SD 26.5 +/- 1.4 weeks; birth weight 480-1400 g, 898 +/- 208 g) in a prospective (uncontrolled) clinical study. Photocoagulation treatment was performed using a diode laser (810 nm) with a laser indirect ophthalmoscope delivery system. Follow-up ranged from 3 to 23 months (10.5 +/- 6.4 months). RESULTS: In 46 (92%) of the 50 eyes ROP regressed after a single laser treatment and the outcome was a flat, attached retina. Two eyes (4%) had a second laser session and one other eye (2%) had additional retinal detachment surgery, resulting in the regression of ROP and a flat, attached retina. Thus, the success rate was 98% (49 out of 50 eyes). In 1 (2%) of the 50 eyes treatment failed and ROP progressed to stage 5, although additional retinal detachment surgery was performed. No adverse side effects of diode laser treatment were noted, except for a small amount of retinal/preretinal bleeding in the ridge in 8 eyes (16%) and slight postoperative anterior chamber bleeding in 1 eye (2%) with dense tunica vasculosa lentis. There were neither lenticular opacities nor cataract formation. CONCLUSION: Diode laser photo coagulation using the laser indirect ophthalmoscope for stage 3+ ROP was easy to administer. Laser treatment had only minor side effects and was at least as effective as cryotherapy.

Female↗
PubMed1996

[Vector analysis of surgically-induced astigmatism in cataract operation with 4 tunnel incision techniques].

UNLABELLED: Evaluation of astigmatism induced by cataract surgery requires the calculation of surgically induced astigmatism using vector analysis. This method was performed for four tunnel-incision techniques and compared with the results of computer-assisted videokeratoscopy. METHODS: Phacoemulsification with IOL implantation was performed in 59 eyes using four different incisions (4- or 5- to 6-mm scleral tunnel and 4- or 5.5-mm clear cornea). Surgically induced astigmatism was calculated by vector subtraction using the formulas of Retzlaff. In addition, corneal topography was performed and astigmatism was calculated within three concentric corneal zones (3 mm, 3-5 mm, 5-7 mm). RESULTS: Surgically induced astigmatism after a 4-mm scleral tunnel incision was 0.55 D (pre-op 0.58 D, post-op 0.72 D), the 5-6-mm incision induced 0.89 D (pre-op 0.97 D and post-op 1.02 D). The 4-mm clear cornea incision induced 2.00 D (from 0.89 D to 1.56 D), the 5.5-mm corneal incision, performed in the steepest meridian to reduce preexisting astigmatism, induced 3.57 D; pre-op 3.38 D, post-op 2.09 D. Corneal topography revealed a slight increase in astigmatism within all corneal zones (4-mm scleral tunnel: 0.26 D, 5-6-mm scleral tunnel: 0.36 D and 4-mm clear cornea incision: 0.22 D). After a 5.5-mm clear cornea incision, however, astigmatism of the central 3-mm zone was reduced by 1 D, while astigmatism of the 5-7 mm zone increased by 0.22 D. CONCLUSION: The 4- and 5- to 6-mm scleral tunnel as well as the 4-mm clear cornea incision were shown to be nearly astigmatism-neutral. The 5.5-mm clear cornea incision reduced astigmatism of the central cornea by about 35%, but induced irregular astigmatism in the periphery.

Astigmatism↗
PubMed1996

[The True-Vista bifocal intraocular lens. Current results of the European multicenter study].

In a prospective multicenter study we evaluated vision with the True Vista bifocal IOL. At 12-14 months after operation. 391 patients ("best cases") were available for follow-up. Without (with) correction, 14.4% (37.9%) had a distance acuity of 20/20 or better, 28% (69.6%) had 20/25 or better, 70% (96.9%) had 20/40 or better, and 30% (3.1%) had a distance acuity of less than 20/40. Near acuity without (with) correction was 20/20 or better in 18.7% (57.5%), 20/25 or better in 42.9% (80.8%), 20/40 or better in 84% (97.5%), and less than 20/40 in 16% (2.5%). Our results demonstrate that corrected distance and near acuity with the True Vista bifocal IOL is good. However, due to surgically induced astigmatism and inaccuracies of IOL power calculation, uncorrected acuities are still disappointing. Thus, when implanting bifocal IOLs, careful patient selection, control of astigmatism and IOL power calculation seems crucial.

Accommodation, Ocular↗
PubMed1995

Diode laser photocoagulation for stage 3+ retinopathy of prematurity.

BACKGROUND: Laser photocoagulation in retinopathy of prematurity (ROP) appears to have fewer adverse effects than cryotherapy and seems to be at least as effective. METHODS: To evaluate the efficacy and safety of diode laser photocoagulation, we included 42 eyes with stage 3+ ROP of 24 preterm infants (gestational age 24-29 weeks, mean +/- SD 26.6 +/- 1.3 weeks; birth weight 480-1400 g, 896 +/- 196 g) in a prospective clinical study. Photocoagulation treatment was performed using a diode laser (810 nm) with a laser indirect ophthalmoscope delivery system. Follow-up ranged from 3 to 16 months (8.8 +/- 4.0 months). RESULTS: In 39 (93%) of 42 eyes ROP regressed after a single laser treatment and the outcome was a flat, attached retina. One eye (2%) had a second laser session and another eye (2%) had additional retinal detachment surgery, resulting in the regression of ROP and a flat, attached retina. Thus, the success rate was 41 (98%) out of 42 eyes. In one (2%) of the 42 eyes treatment failed and ROP progressed to stage 5, although additional retinal detachment surgery was performed. No adverse side effects of diode laser treatment were noticed except for a small amount of retinal/preretinal bleeding in the ridge in five eyes (12%) and a small postoperative anterior chamber hemorrhage in one eye (2%) with dense tunica vasculosa lentis. Neither lenticular opacities nor cataract formation were encountered. CONCLUSION: Diode laser photocoagulation for stage 3+ ROP showed only minor side effects and was at least as effective as cryotherapy treatment.

Female↗
PubMed1995

Diode laser photocoagulation for threshold retinopathy of prematurity in eyes with tunica vasculosa lentis.

PURPOSE: To determine possible side effects of diode laser photocoagulation for threshold retinopathy of prematurity in eyes with tunica vasculosa lentis. METHODS: In a prospective clinical study, threshold retinopathy of prematurity was treated in 14 eyes of seven consecutive preterm infants with tunica vasculosa lentis (birth weight, 480 to 980 g; mean +/- S.D., 777 +/- 175 g; gestational age, 24 to 27 weeks; mean +/- S.D., 25.7 +/- 0.9 weeks) by using the diode laser indirect ophthalmoscope. Main outcome measure was the incidence of adverse treatment effects. Follow-up included anterior segment examination with a hand-held slit lamp and ranged from seven to 17 months (12.6 +/- 3.5 months). RESULTS: The tunica vasculosa lentis did not interfere with photocoagulation in any of the 14 eyes. Laser power ranged from 200 to 400 mW (260 +/- 52 mW). Duration of a single spot was 200 msec. Number of burns ranged from 1,060 to 2,132 (1,556 +/- 315). Retinopathy of prematurity regressed in all eyes, and the outcome was a flat, attached retina. A small amount of postoperative anterior chamber bleeding was noticed in one eye (7% of the eyes, 14% of the patients). There were neither lenticular opacities nor cataract formation. CONCLUSION: Diode laser photocoagulation with the laser indirect ophthalmoscope can be used safely in eyes with tunica vasculosa lentis. At the laser energy levels used in our study, no transient lens opacities or cataract formation occurred. However, the results of this study are limited by a relatively small number of patients and a relatively short follow-up.

Capillaries↗
PubMed1994

A controlled clinical trial of light and retinopathy of prematurity.

Bright continuous light has been implicated in the pathogenesis of retinopathy of prematurity. To investigate the influence of light on the incidence and severity of retinopathy of prematurity, we enrolled 127 preterm infants (birth weight < or = 1,500 g; gestational age < or = 32 weeks) in a controlled clinical study. Randomization was done separately for three birth-weight groups (< 1,000 g; 1,000 to 1,249 g; 1,250 to 1,500 g). The babies' eyes were patched all day and night from birth to a gestational age of 35 weeks. The infants in the control group were exposed to cycled lighting conditions (that is, reduced light level during the night). Of 62 infants with patched eyes, 26 (42%) developed retinopathy of prematurity. In the control group, 25 of 65 infants (39%) showed retinopathy of prematurity (P = .596). There were also no statistically significant differences in the incidences of retinopathy of prematurity in the birth-weight subgroups or in the severity of retinopathy of prematurity. Thus, patching of the eyes from birth to 35 weeks of postconceptional age does not decrease the risk of retinopathy of prematurity in preterm infants when compared to a control group exposed to cycled lighting conditions.

Female↗
PubMed1994

Effect of pupil size and astigmatism on contrast acuity with monofocal and bifocal intraocular lenses.

We conducted a bicenter study to evaluate the effect of pupil size and corneal astigmatism on best corrected contrast acuity (BCCA) in patients with the True Vista bifocal intraocular lens (IOL) and compared the results with those in a matched group of monofocal patients. Best corrected contrast acuity was measured using the Regan Charts (96%, 50%, 25%, 11%) at four pupil sizes (2.0, 2.5, 3.5, 6.0 mm) in three groups (Group 1: corneal astigmatism 0-0.50 D [n = 11]; Group 2: 0.75-1.50 D [n = 11]; Group 3: 1.75-2.50 D [n = 4]). In monofocal eyes, BCCA between these astigmatic groups did not differ significantly at any contrast step or at any pupil size tested. However, BCCA decreased slightly with increasing pupil size in each group, and differences between 2.00 mm and 6.0 mm pupils were significant at each contrast level. In all bifocal groups, BCCA decreased significantly with increasing pupil size and also decreased with increasing corneal astigmatism; differences were significant at most pupil sizes and contrasts tested. In Group 1, BCCA was lower in eyes with bifocal IOLs than in eyes with monofocal IOLs at 25% and 11% contrast with a 2.5, 3.5, and 6.0 mm pupil; with a 2.0 mm pupil it did not differ significantly. In Groups 2 and 3, BCCA in eyes with bifocal IOLs was lower at all contrast steps and all pupil sizes tested. Our results indicate that corneal astigmatism in excess of 0.50 D reduces quality of vision in eyes with bifocal IOLs, while eyes with monofocal IOLs are not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

[Ocular findings in former premature infants at the age of 11 to 14 years].

BACKGROUND: Functional disturbances as well as morphologic changes can be various in regressed retinopathy of prematurity (ROP). PATIENTS AND METHODS: To investigate the incidence and the degree of such changes, we examined prematurely born infants in the age of 11 to 14 years. Of the 142 prematures (birthweight < or = 2000 g), who were cared for in their first weeks of life in the University Children's Hospital at the Klinikum Mannheim in 1977 to 1979, 48 could be reexamined. RESULTS: Of 48 infants (mean birth weight 1808 +/- 211 g, gestational age 34.6 +/- 3.1 weeks) six (12.5%; birth weight 1742 +/- 218 g, gestational age 32.2 +/- 2.5) had had acute ROP (stage 2 or 3). When reexamined in school age 10 (21%) of the children had physical deficits. Eight (17%) visited a school for handicapped children. Eight (17%) children had a squint. In 13 out of 96 (14%) eyes visual acuity was reduced to 0.8 or less. Thirteen eyes (14%) were emmetropic, 67 (70%) hyperopic, 16 (17%) myopic and 15 (16%) astigmatic. The intraocular pressure was normal in all eyes (15 +/- 4 mm Hg). The anterior segments did not show findings caused by ROP. The fundus findings in the 12 eyes, in which the diagnosis of acute ROP was established in the first weeks of life, showed in 5 (42%) eyes a slightly reduced angle kappa between the vascular arcades and avascular retina in the temporal fundus periphery in all of the 12 (100%) eyes. In 1 (8%) eye the retinal periphery showed extensive scarring after cryotherapy because of acute ROP. None of the eyes which had had acute ROP showed macular ectopia or retinal folds (amotio falciformis). In 16 of the 84 (19%) eyes, which did not have a history of acute ROP, minor changes of the retinal periphery, the peripheral retinal vessels and the pigment epithelium were present, which were caused by prematurity. CONCLUSION: Prematurely born infants examined in school age, who were comparatively mature preterms at birth (mean birth weight 1800 g; mean gestational age 34.6 weeks), did not show a higher risk of refractive errors, i.e. myopia. However, they were at higher risk having squint. The functional disturbances found in the prematurely born infants in this study were not caused by morphologic changes due to ROP.

Adolescent↗
PubMed1994

A theoretical model to predict contrast sensitivity with bifocal intraocular lenses.

Bifocal intraocular lenses (BIOLs) cause a reduction in image contrast. However, the clinically measurable reduction is much lower than that predicted by experimental results. We therefore compared monofocal IOLs, the True Vista BIOL, and the diffractive BIOL. We measured the modulation transfer function (MTF) of all IOLs in a model eye. Clinically, we determined the contrast sensitivity (CS). For a comparison of the results, the MTF was converted into the theoretical CS of the eye using the age-corrected values of retinal CS. The calculated CS of the BIOLs was similar to the values measured clinically. However, the calculated CS of monofocal IOLs was considerably higher than the clinical values. This difference should be due to the MTF of the normal eye; the MTF of monofocal IOLs was considerably higher than that of the normal eye, whereas the MTF of the BIOLs was lower. Thus, the MTF of the normal eye becomes the limiting factor of this system. The proposed model takes into account the retinal CS and the MTF of the normal eye. Using the MTF of an IOL, the clinical CS can be calculated, and the clinical performance of new IOL designs may be predicted before clinical trials commence.

Adult↗
PubMed1994

[Eye manifestations of shaken baby syndrome. A case presentation].

UNLABELLED: Violent shaking is a type of child abuse which may cause intracranial hemorrhages combined with retinal and vitreous bleeding. Fundus bleeding is similar to that in Terson syndrome. However, in the shaken baby syndrome the intraocular hemorrhages may precede both the clinical and radiologic recognition of subdural haematoma. CASE REPORT: We present a 4-months-old baby with convulsions and additional extensive bleeding of the fundus. Neither the ocular findings nor the seizures could be explained by minimal lesions of external trauma. Repeated cranial computed tomography showed increasing intracerebral bleeding with consecutive brain atrophy. Fundus bleeding completely disappeared. CONCLUSION: When child abuse is suspected, ophthalmological examination is most important to detect fundus bleeding, which, in the absence of birth trauma or any other supportive evidence of external trauma or other diseases, is the leading symptom of the shaken baby syndrome.

Battered Child Syndrome↗
PubMed1993

Results of a European multicenter study of the True Vista bifocal intraocular lens.

The True Vista intraocular lens (IOL), a three-zone refractive bifocal lens, was implanted in 446 patients in a prospective study. Visual acuity, pupil size, and astigmatism were determined. Contrast acuity was measured in a randomized subgroup of best-case patients (n = 60; Regan charts); subjective assessment of vision was compared in 41 best cases with a monofocal fellow eye. Two hundred twenty-seven best-case patients were available for four to six months follow-up, and 145 for seven to eleven months. Best corrected distance acuity was 20/40 or better in 96% and 98%, respectively. Near acuity was 20/30 or better in 93% and 92% with near add, in 64% and 69% uncorrected, and in 79% and 78% with distance correction, respectively. Distance and near acuity decreased with increasing astigmatism and increasing age. Contrast acuity at distance focus was lower than for monofocal IOLs (11% contrast); values at near focus were considerably lower at all contrast steps tested. Of the patients with a monofocal fellow eye, 96% rated their distance vision with glasses in the monofocal eye as good, compared with 78% in the bifocal eye. The True Vista IOL favors distance vision while near acuity is still sufficient. As high image contrast at distance is usually more important than at near, this might be a good compromise. However, bifocal IOLs should probably not be implanted in patients with a monofocal fellow eye.

Aged↗
PubMed1993

Comparison of the optical and visual quality of poly(methyl methacrylate) and silicone intraocular lenses.

We evaluated experimentally the optical quality of poly(methyl methacrylate) (PMMA) (Storz 68UV, AMO PC58) and silicone (AMO SI19, Adatomed 90D) intraocular lenses (IOLs) and compared the results with our clinical data. We measured surface and image quality using the Zygo laser interferometer and modulation transfer function (MTF) using the Ealing EROS MTF analyzer. Contrast acuity was tested clinically with glare and without glare (Regan charts); AMO PC58, n = 18; AMO SI19, n = 7; Adatomed 90D, n = 18). Modulation transfer function and image quality were slightly better with PMMA IOLs but the reduction of MTF with silicone lenses was within the 1/8 diopter defocus range. Surface quality of silicone IOLs was superior to that of PMMA IOLs. Contrast acuity measured clinically was also slightly better with PMMA IOLs at low contrast and with glare but differences were not significant. Our results suggest that optical and visual quality of silicone IOLs is slightly lower than with PMMA IOLs. Experimental and clinical results correlated closely. However, the small differences observed are unlikely to be significant clinically.

Aged↗
PubMed1993

Evaluation of contrast acuity and defocus curve in bifocal and monofocal intraocular lenses.

We compared visual quality of the following intraocular lenses in a prospective study: monofocal, True Vista bifocal, 3M diffractive bifocal, and Nordan aspheric VariFocal silicone. Four to six months postoperatively we measured distance acuity, Snellen near acuity (Lighthouse chart), reading acuity (Nieden chart), and contrast acuity at far and near focus (Regan charts: 96%, 50%, 25%, 11% contrast) with different pupil sizes. A defocus curve was obtained by spectacle defocus (+1 diopter [D] to -5 D). Eleven patients had True Vista in one eye and monofocal in the fellow. Contrast acuity at far focus decreased with decreasing contrast and increasing pupil size. This decrease was more pronounced with the True Vista than with the monofocal lenses. These differences were significant, with a 4.5 mm pupil at lower contrast (25%, P = .02; 11%, P = .01). Depth of focus was 4.5 D (+1.0 D to -2.0 D) with True Vista lenses and 2.5 D (+1.0 D to -1.5 D) with monofocal lenses. Corrected distance acuity was 20/22 with True Vista, 20/25 with 3M, and 20/20 with VariFocal. Distance corrected Snellen near acuity was 20/39 with True Vista, 20/34 with 3M, and 20/57 with VariFocal. Distance corrected reading acuity was 20/29 with True Vista, 20/23 with 3M, and 20/44 with VariFocal (P = .005). Contrast acuity at far focus was best with the VariFocal IOL, followed by True Vista and 3M. At near focus it was best with 3M, followed by True Vista and VariFocal. Contrast acuity at near focus was lower than at far focus. Average acuity differences were as follows: VariFocal 0.43, P = .01; True Vista 0.19, P = .05; 3M 0.04, P = .3. Depth of focus was 4.5 D (+1.0 D to -3.5 D) with True Vista and 3M and was 3 D (+1.0 D to -2.0 D) with VariFocal. Each design offers unique features. VariFocal is best at distance, but near vision is not sufficient. The 3M lens is best at near vision but distance contrast acuity is somewhat reduced. The True Vista lens provides a good compromise as distance contrast acuity is good and near vision is sufficient.

Aged↗
PubMed1993

[Indications and contraindications for implantation of bifocal intraocular lenses].

BACKGROUND: Bifocal intraocular lenses (BIOLs) performed satisfactorily in a certain number of patients only. This paper therefore provides an overview of the indications and contraindications of BIOLs. CONCLUSIONS INDICATIONS: BIOLs are indicated in younger and active patients without ocular pathologies. BIOLs should be implanted bilaterally, corneal astigmatism should be less than 1 dpt, emmetropia should be the target refraction, pupil size and responsiveness must be normal, and IOL decentration should be avoided. CONTRAINDICATIONS: Corneal astigmatism in excess of 1 dpt, very small or atonic pupils, ocular pathologies, and a monofocal fellow eye are definite contraindications. In addition, BIOLs are contraindicated in patients who require maximum resolution at low contrast. Relative contraindications include very old patients, eyes with an axial length of more than 24.5 mm or less than 22 mm, and patients who may not tolerate the visual side effects (halos, glare).

Aged↗
PubMed1993

[Contrast sensitivity and defocus curve with various bifocal-IOL].

Simultaneous vision, the basic principle of all bifocal intraocular lenses (IOLs), provides increased depth of focus but also causes a loss in contrast. We therefore measured contrast acuity (CA) (Regan Charts) and the defocus curve at different pupil sizes in 14 patients with a TRUE VISTA bifocal IOL (TV) (Storz Co.), 10 patients with a 3M diffractive bifocal IOL (3M) (3M Co.) and 9 patients with a Nordan Aspheric Varifocal Silicone IOL (VF) (Wright Medical Inc.). CA at distance focus was best with VF; next was TV, and 3M showed the lowest values. At near focus, CA was best with 3M; next was TV, and VF showed the lowest values. Differences between VF and 3M were significant (P = 0.05; t-test). CA at near focus was significantly lower than at distance focus with TV and VF (TV: P = 0.0001; VF: P = 0.005). Pseudoaccommodation was 4.5 D with TV and 3M and 3D with VF. In conclusion, distance CA was best with VF but pseudoaccommodation was not sufficient for reading. Near CA was best with 3M while distance CA was somewhat reduced. TV showed good distance CA while near CA was still sufficient. TV therefore seems to provide a good compromise.

Accommodation, Ocular↗
PubMed1993

Vision with bifocal intraocular lenses.

The laboratory and clinical results of tests of different bifocal intraocular lenses (BIOLs) are compared. Included are two-zone refractive BIOLs with a central near zone and an annular distance zone (group 1); three-zone refractive BIOLs with a central distance zone, an annular near zone, and a peripheral distance zone (group 2); diffractive BIOLs (group 3); multizone refractive BIOLs (group 4); and other BIOLs (group 5). All BIOLs cause a significant loss of image contrast and acuity at low contrast. The incidence of visual side effects (e.g., halos, glare) varies but is significantly higher than that obtained with monofocal IOLs. On the other hand, BIOLs provide a depth of focus of 3-4 D as compared with only 1.5 D for monofocal IOLs. In group 1, distance vision is reduced in bright light, which limits the clinical use of these BIOLs. In group 2, distance vision is better than near vision. Thus, a temporary near add is required in some cases. In group 3, distance and near vision are similar, but the incidence of visual side effects is higher than that in group 2. Only BIOLs of groups 2 and 3 can be recommended for clinical use in selected patients. Not enough data are currently available on the other groups. Patient selection is the most critical factor for BIOLs. Ideal patients are relatively young and active, are highly motivated, show no ocular pathology, and have a normal pupil, an axial length of 22-24.5 mm, and a corneal astigmatism of less than 1 D. Reduced image contrast, mainly at near focus, and visual side effects must be acceptable. Bilateral implantation yields the best results. A monofocal fellow eye is a definite contraindication. In summary, BIOLs cannot replace monofocal IOLs. However, they provide a valuable alternative in selected patients.

Accommodation, Ocular↗