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At least 775 records · Page 43Linked to original sources
PubMed1996

The ciliary ganglion and vitreous cavity shape.

PURPOSE: To learn the influence of the ciliary ganglion on the postnatal growth of eyes with unimpaired visual input and of eyes beneath an image diffusing goggle. METHODS: Newborn chicks received unilateral ciliary ganglionectomy or unilateral sham operation and were reared either with or without a goggle ipsilateral to the surgical procedure. Ocular refractions and ultrasound measurements were made on anesthetized chicks; eyes enucleated postmortem were measured in axial and equatorial dimensions with calipers and studied histologically. RESULTS: Excessive growth of open eyes in the equatorial dimensions followed ciliary ganglionectomy and became more pronounced as the chicks grew older. There was only a modest increase in axial growth. Ganglionectomy also induced relative hyperopia; lens thinning contributed to this effect and likely was a direct result of disrupted parasympathetic input to the ciliary muscle. Ganglionectomy also slightly increased the thickness of the choroid in the posterior pole but not in more peripheral locations. CONCLUSION: We conclude that the ciliary ganglion exerts an inhibitory influence on the postnatal growth of open eyes; the main effect is in the equatorial dimension of the vitreous cavity, with a smaller effect on axial length. Ciliary ganglionectomy exerted minimal influence on the development of experimental myopia, known to be induced by the goggle regimen. The amount of equatorial expansion in goggle-induced myopia was greater than after ganglionectomy alone, indicating that other factors besides the ciliary ganglion can influence the equatorial dimension of the vitreous cavity.

Animals↗
PubMed1994

Refractive errors among engineering students in Norway.

This study reveals the prevalence of refractive errors in a group of young adults (mean age 20.6 years) exposed to high educational demands, including much reading. In all, 224 (117 females, 107 males) first-year engineering students were subjectively refracted. A prevalence of myopia of 46.9% (right eye), 49.1% (left eye) and 42.9% (both eyes), and a prevalence of hyperopia of 29.5% (right eye), 28.1% (left eye) and 23.2% (both eyes) was detected. The mean refractive error in the whole group was -0.6 +/- 2.2 D (right eye), -0.7 +/- 2.4 D (left eye) and -0.7 +/- 2.3 D (both eyes). As many as 56.4% (n = 57) of the myopic students had either no corrective lenses (11.9%, n = 12) or had their first corrective lenses prescribed at the age of 16 years or later (44.6%, n = 45). There was no significant difference in the prevalence of myopia between female and male students. No significant difference regarding body height was found among men in the different groups of refractive errors, but a significant difference was detected among women. We found no statistically significant relationship between intraocular pressure and any refractive error among men or women.

Adult↗
PubMed1997

Ocular abnormalities in a patient with partial deletion of chromosome 6p. A case report.

We report on a patient with a de-novo deletion of chromosome 6p. This male infant presented with multiple systemic congenital defects together with an unusual ocular phenotype. Slit-lamp examination revealed thin, opaque, rectilinear bands within the anterior segment partially connecting iris to corneal endothelium. These were associated with bilateral hyperopia and optic nerve hypoplasia. Ocular abnormalities in such patients have been documented although the number of individuals is small and identical cytogenetic defects are rarely encountered. We compare the clinical findings in this case with previously described phenotypes. Characterisation of such cases is important as it is becoming apparent that deletion of genetic information encoded on chromosome 6p has implications for ocular embryogenesis.

Abnormalities, Multiple↗
PubMedDate not supplied

Accommodation in hyperopic and myopic school children.

Binocular accommodation of 150 consecutive hyperopic and 150 myopic school children was measured during the eye examination. There were 99 girls and 51 boys in the hyperopic group and 100 girls and 50 boys in the myopic group. The ages varied from seven to 16 years. Accommodation of the hyperopic children varied from 4 to 20 D (mean 10.6 +/- 3.4), and in the myopic children also from 4 to 20 D (mean 10.9 +/- 2.5). The difference between these means was not statistically significant. However, hyperopic girls aged 12 to 16 years showed low values of accommodation (mean 9.0 +/- 2.7) compared to the other corresponding age groups. In the second part of the study the refraction of 80 children, aged seven to 15 years, with decreased accommodation was studied retrospectively to see if they had a tendency to become myopic. The follow-up time was from one to eight years, and the accommodation at the beginning of the observation time varied from 2 to 7 D. The mean annual change of the refraction of these children was from -0.03 to -0.17 D. In 34 children there was no change at all, and in 12 children the change of refraction was slightly toward more hyperopia. Only three of these 80 children became myopic during the observation time. This incidence is lower than the incidence of myopia at these ages. Thus, accommodative power of hyperopic and myopic school children appears to be on the same level, and low accommodation does not predict the development of myopic refraction in the school years.

Accommodation, Ocular↗
PubMedDate not supplied

Myopic shift after cataract removal in childhood.

BACKGROUND: Children who have had cataract removal tend to have decreasing hyperopia (myopic shift) as they grow older. We wondered if the rate of myopic shift could be determined by age at surgery, cataract type, glaucoma, or other factors. METHODS: We studied 156 aphakic eyes of children who had cataract surgery before age 10 and documented refractions for more than 3 years. Refraction was corrected with contact lenses and spectacles; glaucoma was managed with medicine and surgery. Stepwise multiple regression was used to analyze differences in the rate of myopic shift between subgroups. RESULTS: The average refraction tended to follow a logarithmic decline with age (P < 0.01, R2 = 0.97). The average rate of myopic shift (the slope of spectacle plane refraction vs log of age, where age is in years and log is base 10) was -5.5, with a standard deviation of 3.8. Age at surgery had a small but statistically significant effect on the rate (P < 0.01, R2 = 0.04). No other studied factor reached statistical significance. However, among the 86 eyes with cataract removal after age 6 months, age at surgery was not as significant (P = 0.21), and unilateral cataract eyes tended to have a greater rate than bilateral cataract eyes (-7.7 vs -5.7; P = 0.05, R2 = 0.05). CONCLUSIONS: Aphakic refraction tends to follow a logarithmic decline with age. The rate of myopic shift is determined partly by age at surgery and whether the cataract was unilateral or bilateral, although the effects are small. A wide variation in the rate of myopic shift exists. The following factors made little difference in the rate: cataract type, glaucoma, sex, side, and best corrected visual acuity.

Aging↗
PubMedDate not supplied

Hyperopic shift and myopic regression in a patient 7 years after bilateral refractive keratotomy.

PURPOSE/METHODS: To report a patient who developed hyperopic progression in one eye and myopic regression in the other eye following bilateral, non-simultaneous refractive keratotomy. RESULTS: Uncorrected visual acuity improved to 20/25 and 20/25-2 in the right and left eyes, respectively, 3 months following refractive keratotomy (one procedure in the right eye, two procedures in the left eye). The visual acuity was not stable over time and almost 8 years after surgery, uncorrected distance visual acuity was 20/40- and 20/200. The spherical equivalent refraction of the right eye progressed from -0.50 diopter (D) 3 months after surgery to +1.25 D several years later. The left eye regressed from a spherical equivalent refraction of -0.75 D 3 months after the second surgery to -2.50 D more than 7 years postoperatively. Slit-lamp microscopy disclosed deeper, opaque incisions in the hyperopic eye, and shallower and more transparent incisions in the myopic eye. CONCLUSIONS: The shift toward hyperopia and myopia in an individual suggest that instability of the radial keratotomy wound may be related to local wound healing events that are, in part, related to incision depth.

Adult↗
PubMedDate not supplied

Comparison of two microkeratome systems.

BACKGROUND: Microkeratomes are currently used for keratomiluesis in situ (automated lamellar keratoplasty) for myopia and hyperopia and for laser in situ keratomileusis (LASIK). Visual and refractive complications have been reported with these refractive surgical procedures. We compared two microkeratomes in their ability to resect corneal lamellae to gain insight into possible mechanism(s) of refractive and visual complications following lamellar refractive procedures. METHODS: Using an eyebank eye model, we performed automated lamellar keratoplasty to theoretically correct 10.00 diopters (D) of myopia using the Automated Corneal Shaper, manufactured by Chiron, Inc. and the MicroPrecision microkeratome, manufactured by Eye Technology, Inc. Diameters before (wet) and after fixation, thicknesses of excised tissue, and scanning electron microscopy were measured in a masked evaluation to compare instruments. Ultrasonic corneal pachymetry and a mechanical tissue compression gauge were also used to assess thickness of excised tissue. RESULTS: The Chiron automated corneal shaper created blade chatter marks at the edges of all excisions, smaller than anticipated excision diameters, and a wide range of tissue thicknesses. In contrast, the MicroPrecision microkeratome created smoother resections of all tissues without creating blade marks; tissue diameters and thicknesses were closer to the intended dimensions compared to the Chiron automated corneal shaper. CONCLUSION: Different microkeratomes create different morphologic features as they excise corneal tissue. Differences in instrument design, mechanics of the tissue excision and blade oscillation, and instrument traverse combined with surgical skill influence the configuration of lamellar keratotomies.

Aged↗
PubMedDate not supplied

Hyperopic shift induced by high altitude after radial keratotomy.

BACKGROUND: The collagen fibrils embedded in the ground substance of the stromal lamellae provide the structural support for the cornea. When the stromal lamellae are cut in a radial keratotomy surgical procedure, the remaining uncut lamellae carry the tensile forces. METHODS: We studied two expert climbers who had bilateral radial keratotomy before participating in six climbs of extreme altitude, including Mount McKinley and above 7500 m (24,606 ft) on Mount Everest. RESULTS: Whenever either climber was exposed to altitudes greater than approximately 5000 m (16,405 ft) for more than a day, their refraction would become +3.00 D or more hyperopic and remain so al long as they were at or above this altitude. Visual acuity slowly returned to normal after descent. CONCLUSION: It appears that in the presence of significantly reduced atmospheric pressure and/or oxygen there is a greater effect of radial keratotomy in some patients, making the cornea more vulnerable to changes in shape. The cornea appears to respond by further flattening, exacerbating the intended surgical effect and producing a refractive shift toward hyperopia.

Adult↗
PubMedDate not supplied

Algorithm to correct hyperopic astigmatism with the Nidek EC-5000 excimer laser.

BACKGROUND: The efficacy of a new ablation algorithm for the correction of hyperopic astigmatism with the Nidek EC-5000 excimer laser was evaluated. METHODS: Twenty-five eyes with mean preoperative hyperopia of +3.76 +/- 1.70 D and a mean hyperopic cylinder of 2.20 +/- 0.80 D underwent photorefractive keratectomy (PRK) using a new algorithm with the Nidek EC-5000 excimer laser (software version 3.0). The new algorithm differed from previous algorithms in that less tissue was removed for the same amount of diopters, and there was less of a dioptric gradient between the optical zone and the transition zone. Mean preoperative spectacle-corrected visual acuity was 0.8 +/- 0.09. Minimum follow-up was 6 months. RESULTS: Mean postoperative spectacle corrected visual acuity (geometric mean) increased significantly to 0.89 +/- 0.1. The mean sphere decreased by 3.08 D and the mean cylinder by 1.60 D. CONCLUSION: Hyperopic PRK using the Nidek EC-5000 excimer laser with this new algorithm for hyperopic astigmatism appears to be safe and effective.

Adult↗
PubMedDate not supplied

Intraocular lens power calculation in eyes after corneal refractive surgery.

PURPOSE: The purpose of this review article is to discuss the major reasons for postoperative hyperopia after cataract surgery following radial keratotomy (RK) and photorefractive keratectomy (PRK) and to illustrate potential methods for improvement of intraocular lens (IOL) power prediction after keratorefractive surgery based on exemplary model calculations. METHODS: We previously performed model calculations in eyes after PRK for myopia (-1.50 to -8.00 D, mean -5.40 +/- 1.90 D) using keratometry readings as measured by the Zeiss keratometer and the TMS-1 topography unit and as calculated using the "clinical history method" (spherical equivalent refraction change) and change in anterior surface keratometry readings. RESULTS: We found that after PRK, mean measured keratometry readings were significantly greater than respective calculated values considering the preoperative to postoperative change of anterior corneal surface (P < .001), which itself was significantly greater than calculated keratometry readings considering the preoperative to postoperative change of spherical equivalent refraction (P < .001). IOL power underestimation correlated significantly with the difference between preoperative and postoperative spherical equivalent refraction (P = .001). CONCLUSIONS: For correct assessment of keratometric readings to be entered into more than one modern third-generation IOL power calculation formula (but not a regression formula), the clinical history method should be applied whenever refraction and keratometric diopters before the keratorefractive procedure are available to the cataract surgeon. If preoperative keratometric diopters and refraction are not known, average central power on the postoperative videokeratograph may be used after RK, but refined calculation of keratometric diopters from radius of anterior and posterior corneal surface should be used after PRK and/or LASIK.

Cataract Extraction↗
PubMedDate not supplied

Laser in situ keratomileusis: three unexpected complications.

PURPOSE: To report unexpected outcomes in three patients after uneventful laser in situ keratomileusis (LASIK) performed using the Nidek EC-5000 excimer laser and the Hansatome microkeratome (Bausch & Lomb Surgical). METHODS: LASIK was performed with the Nidek EC-5000 excimer laser and the Hansatome microkeratome (Bausch & Lomb Surgical) in three patients. RESULTS: In three patients, unexpected outcomes were observed. One patient treated for -3.00 D of myopia presented with a central island. One patient treated for +2.00 D (+1.00 x 90 degrees) of hyperopia in both eyes ended up emmetropic in one eye and overcorrected in the fellow eye. The third patient with -12.00 D (-2.00 x 180 degrees) of myopia was treated as -8.60 -1.00 x 180 degrees and at last examination was +4.00 D. During these sessions, all other patients treated were within +/-0.50 D of emmetropia. CONCLUSION: After LASIK with the Nidek EC-5000 excimer laser and the Hansatome microkeratome (Bausch & Lomb Surgical), unexpected outcomes may still occur, despite controlling all the usual variables.

Adult↗
PubMedDate not supplied

Effect of acute biomechanical changes on corneal curvature after photokeratectomy.

PURPOSE: Unintended hyperopic shift is a common yet poorly understood complication of phototherapeutic keratectomy (PTK) that raises fundamental questions about the etiology of corneal curvature change in PRK and LASIK. We investigated the relative contributions of ablation profile and peripheral stromal thickening to intraoperative PTK-induced central flattening, and propose a biomechanical model of the acute corneal response to central ablation. METHODS: Fourteen de-epithelialized eye bank globes from seven donors underwent either broadbeam ablation (approximately 100-microm depth, no programmed dioptric change) or sham photoablation in paired-control fashion. Peripheral stromal thickness changes and the pattern of thickness loss across each ablation zone were evaluated by optical section image analysis as predictors of acute corneal flattening. RESULTS: Relative to sham ablation, keratectomy caused significant anterior corneal flattening (-6.3+/-3.2 D, P = .002). Concomitant peripheral stromal thickening (+57+/-43 microm, P = .01) was a significant predictor of acute hyperopic shift (r = 0.68, P = .047). Ablation pattern bias did not consistently favor hyperopia and was a poor lone predictor of hyperopic shift. CONCLUSIONS: Unintended keratectomy-induced hyperopic shift is replicable in a human donor model and is associated with significant thickening of the unablated peripheral stroma. This biomechanical response may have a considerable impact on early refractive outcomes in PTK, PRK, and LASIK.

Acute Disease↗
PubMedDate not supplied

Comparison of Placido-based, rasterstereography, and slit-scan corneal topography systems.

PURPOSE: Elevation-based topography systems have received growing recognition. We compared a Placido-based (EyeSys), a rasterstereography (PAR), and a slit-scan system (Orbscan) for human subjects. METHODS: Measurements were obtained from 221 eyes of 119 human subjects. We made statistical comparisons central curvature, keratometric curvatures, and meridians between the three systems. We also compared the optical pachymetry of the slit-scan system with an ultrasonic device. We analyzed cases of subclinical keratoconus, central island, photorefractive keratectomy for myopia, and hyperopia correction with arcuate keratotomy. RESULTS: The statistical comparison showed better correlation between the Placido-based and the rasterstereography systems in measurement of central curvature (R=0.95). The slit-scan system showed better correlation with the Placido system in the preoperative and postoperative radial keratotomy group (R=0.73) than in the group that included postoperative PRK eyes (R=0.69). Similar results were obtained for keratometric curvatures and meridians. The Orbscan pachymetry correlation with ultrasonic was R=0.69 and increased when the postoperative PRK eyes were excluded (R=0.95). CONCLUSIONS: Slit-projection topography and pachymetry seemed to be affected by hydration in the postoperative PRK group. The pachymetric map was useful in predicting the final outcome of refractive surgery and in the diagnosis of keratoconus.

Cornea↗
PubMedDate not supplied

Bilateral simultaneous laser in situ keratomileusis with the Aesculap Meditec MEL 60 laser.

PURPOSE: To report the outcome of bilateral simultaneous excimer laser in situ keratomileusis (LASIK) with the Aesculap Meditec MEL 60 laser for the correction of myopia and hyperopia. METHODS: This retrospective study included 338 eyes of 169 patients who had bilateral simultaneous LASIK performed by one surgeon (D.L.V.). RESULTS: Postoperatively, 20/20 or better visual acuity was achieved by 78.5% (186 eyes) in the <-6.00-D group, and 55.6% (54 eyes) in the > or = -6.00-D group. Postoperatively, the mean spherical equivalent refraction was within +/- 0.50 D for 78% (185 eyes) in the <-6.00-D group (range, -2.25 to +1.25 D), 55% (53 eyes) in the > or = -6.00-D group (range, -2.38 to +1.13 D), and one eye in the hyperopic group. Complications at 3 months included regression in five eyes (1.4%), infiltrates in six eyes (1.7%), primary undercorrection in two eyes (0.6%), superficial punctate keratitis in four eyes (1.1%), ten eyes (2.9%) underwent enhancement, two eyes (0.6%) underwent refractive lensectomy, and four eyes (1.1%) underwent astigmatic keratotomy 3 months postoperatively. Two eyes lost two lines of best spectacle-corrected visual acuity. CONCLUSION: Bilateral simultaneous LASIK with the Aesculap Meditec MEL 60 laser was effective and predictable. It was more economical and convenient for the patient than unilateral LASIK and binocular visual rehabilitation was rapidly restored. No sight threatening complications occurred in this group of patients.

Adult↗
PubMedDate not supplied

Refractive lens exchange with an array multifocal intraocular lens.

PURPOSE: To prospectively evaluate safety, efficacy, predictability, stability, complications, and patient satisfaction after refractive lens exchange (clear lens extraction) followed by posterior chamber implantation of a multifocal intraocular lens (IOL). METHODS: Fifty eyes of 25 patients (mean age 51 years, range 44 to 62 years) with preoperative spherical equivalent refraction between -15.50 and +5.75 D and cylinder between 0 and 1.50 D underwent bilateral implantation of a zonal progressive multifocal IOL (Array, AMO). RESULTS: Eyes were divided into group A (n=24; myopia, average preoperative spherical equivalent refraction -7.11 +/- 3.25 D (-1.75 to -15.50 D), and group B (n=26; hyperopia, average preoperative spherical equivalent refraction +3.04 +/- 1.04 D). Follow-up was 6 months in all eyes. Postoperatively, all eyes of both groups were within +/-1.00 D of target refraction. No eye in group A and three eyes in group B sustained a loss of one line of BSCVA. Forty-seven eyes (94%) remained unchanged or gained one or more lines of their preoperative BSCVA. In all eyes, postoperative UCVA was 20/40 or better. When compared to preoperative, uncorrected near visual acuity improved (statistically significant). All patients achieved uncorrected binocular visual acuity of 20/30 and J4 or better. Patient satisfaction was extremely high; no intra- or postoperative complications were reported. CONCLUSION: Six-month results of implantation of the AMO Array multifocal IOL for refractive lens exchange demonstrated safety, efficacy, and predictability in correcting high ametropia and significant improvement of uncorrected near and distance visual acuity.

Adult↗
PubMedDate not supplied

Experimental results of preparing laser-shaped stromal implants for laser-assisted intrastromal keratophakia in extremely complicated laser in situ keratomileusis cases.

PURPOSE: To evaluate the feasibility of laser-shaped stromal implants from a donor eye for correcting extreme high hyperopia with irregular astigmatism and an exceptionally thin corneal bed. METHODS: Thirty-one fresh enucleated porcine eyes were used. The procedure was initiated with mechanical de-epithelialization followed by a lamellar cut with a microkeratome, resulting in a hinged flap (thickness 150 microm, diameter 9.5 mm). The cornea was photoablated with PRK treatment for +8.00 D sphere (hyperopic lenticule group) and -5.00 D sphere (myopic group) by a scanning spot excimer laser. A customized scanning software algorithm was used to create a circumferential cut with a 6.5-mm internal diameter. The lenticule was removed from the stromal bed and measured by a surface profiling system. A clinical case was performed on a patient with previous LASIK and highly irregular hyperopic astigmatism to verify the clinical utility of the experimental setup. RESULTS: Under the microscope, lenticules seemed round, regular, and transparent. The average surface profile of porcine corneas demonstrated good parabolic shape with individual variations as large as 30 microm, probably due to the corneal size and curvature differences between the porcine eye and the human eye--for which the microkeratome is designed. The patient underwent a topography-guided treatment after laser-assisted intrastromal keratophakia (LAIK) and 1-month follow-up showed an increase of UCVA, BSCVA, and central corneal thickness. CONCLUSIONS: The use of modern scanning-spot excimer lasers and microkeratomes enabled us to produce stromal lenticules of good quality, which might be acceptable to implant into a human eye.

Adult↗
PubMedDate not supplied

Effect of hyperopic photorefractive keratectomy on corneal sensitivity: a longitudinal study.

PURPOSE: To investigate corneal sensitivity after photorefractive keratectomy (PRK) for low hyperopia, as measured with a non-invasive stimulus. METHODS: Two experimental groups were recruited: a control group of 17 patients (mean age 61.65 years) who underwent no treatment, and a PRK group of 11 patients (mean age 58.64 years) who underwent one of three attempted hyperopic corrections: +2.00 D (two patients), +3.00 D (four patients), +4.00 D (five patients). Corneal sensitivity was assessed centrally and peripherally, at temporal, medial, and inferior locations, approximately 1 mm from the limbus, using the Non-Contact Corneal Aesthesiometer (NCCA). Measurements were taken at each location for the control group and at preoperative, and postoperative weeks 1 and 2, 1, 3, and 6 months for the PRK group. RESULTS: Comparison of control and PRK groups (preoperative sensation threshold) (t-test): central P=.715, temporal P=.719, medial P=.943, inferior P= .920. Comparison of longitudinal changes in PRK group (one-way ANOVA): central P=.612, temporal P=.997, medial P=.981, inferior P=.993. CONCLUSIONS: Using the Non-Contact Corneal Aesthesiometer, no significant difference was found between the control and PRK groups for preoperative sensation thresholds, and no significant change in corneal sensitivity was found between any of the test time periods at any of the four corneal test locations for the PRK group.

Adult↗
PubMedDate not supplied

Conductive keratoplasty to correct hyperopic astigmatism.

PURPOSE: To evaluate the efficacy of conductive keratoplasty in the treatment of pre-existing and surgically induced hyperopic astigmatism. METHODS: In this prospective, noncomparative case series, four eyes of four subjects, two female and two male (age 25 to 47 yr) were treated for hyperopia (up to +5.50 D) and hyperopic astigmatism (up to +5.75 D) with the Refractec ViewPoint conductive keratoplasty system. The follow-up period was 6 months. Uncorrected and spectacle-corrected visual acuity, manifest and cycloplegic refraction, and videokeratographs were obtained before and after surgery. We treated two patients who had already had LASIK, one of them with a decentered ablation and the other with flap striae, one patient after PRK, and one patient with keratoconus. RESULTS: No complications were observed. No eye lost lines of spectacle-corrected visual acuity. All eyes showed improvement of uncorrected visual acuity of 3 or more lines. Videokeratographs demonstrated improved centration and reduction in keratometric power readings. Each eye was analyzed separately, including a comparative analysis of the proposed nomograms and quality of vision after surgery. CONCLUSIONS: Conductive keratoplasty may be a minimally invasive solution for patients with irregular hyperopic astigmatism, offering improved quality of vision in instances of flap striae by tightening the central cornea.

Adult↗