On the prediction of optical aberrations by personalized eye models.

PURPOSE: The purpose of this study is to develop and analyze a method to obtain optical schematic models of individual eyes. Each model should be able to reproduce the measured monochromatic wave aberration with high fidelity. METHODS: First, we choose a generic eye model as the input guess and then apply a two-stage customization procedure. Stage 1 consists of replacing, in the initial generic model, those anatomic and optical parameters with experimental data measured on the eye under analysis. The set of experimental data was that provided by a standard clinical preoperative examination, namely lens topography, ultrasound biometry, and total wave aberration. Then, the second stage is to find the unknown lens structure that would reproduce the measured wave aberration through optical optimization. Two totally different initial eye models have been compared; one considers a simpler constant refractive index for the lens, whereas the second model has a gradient-index (GRIN) lens. RESULTS: This automatic customization method has been applied to 19 eyes with different degrees of spherical ametropia (from +0.4 D to -8 D). Two models have been obtained for each eye (constant and gradient index lens). The results were highly satisfactory, with 100% convergence, and with average RMS prediction errors approximately lambda/100. This is one order of magnitude lower than typical measurement errors. The models with a constant refractive index lens tended to overestimate surface curvatures, whereas for the GRIN model, lens surfaces were too flat. CONCLUSIONS: The proposed method is highly efficient and robust giving a high-fidelity reproduction of the wavefront in all cases attempted so far. Limitations found in reproducing the geometry of the lens seem to be associated with the use of inaccurate models of its refractive index.     

Dislocated intraocular lens after biodegradation of fixation loops. A case report

A boy aged 3 years had a Worst Medallion intraocular lens with loops made of nylon 6 implanted in his right eye after aspiration of traumatic cataract. Post-operatively, the eye was irritated and showed increased tendency to secondary membrane formation. The patient was lost to follow-up 3 months post-operatively. He returned 5 years later because of 4 days of pain and redness in his right eye. On examination, the optic part of the intraocular lens was seen to lie free in the anterior chamber. The loops were broken near their insertions in the lens body. The distal ends of the broken loops could not be detected in the pupillary region. No traces of the iris fixation suture were to be seen. The lens was removed and subjected to scanning electron microscopy which revealed extensive biodegradative changes in the 3 loop stumps, the 4th being totally dissolved. The young age of the patient and the chronic inflammation may have had an accelerating effect on the nylon degradation. We conclude that children with eyes implanted with nylon-loop lenses should stay under regular ophthalmological control.     

Periocular migration of an intraocular lens.

A woman presented with a painful eye 6 weeks after cataract extraction and intraocular lens implantation. In the past she had had a sector iridectomy for iris bombé caused by chronic anterior uveitis. On examination the three central corneal sutures were absent, whilst the medial and lateral sutures had broken and were protruding from the section. The eye was quiet and the section intact. Combined clinical and ultrasound examination failed to locate the intraocular lens. Four months postoperatively, while being fitted for contact lenses for the correction of aphakia, the intraocular lens appeared from the superior fornix.     

Morphology of the cataract in albino mutant quails (Coturnix coturnix japonica)

Morphological changes in cataractous albino quail lens were studied by light microscopy. In some animals, a pin-head opacity in the lens could first be detected with the naked eye 2 months after hatching. Faint anterior or posterior cortical opacity was observed in many lenses at 3 months of age. Most lenses had turned opaque 12 months after hatching. Lens dimensions were markedly enlarged at 6 months of age. Vacuoles were present in the posterior surface just beneath the capsule and equatorial epithelium, before the cells became degenerative. Many swollen lens fibers and abnormally migrated cells were observed in the posterior cortical region. The lens was covered with several layers of epithelioid cells in the mature cataract.     

Effect of infusion bottle height on lens power after lens refilling with and without a plug

PURPOSE: To evaluate the influence of intraoperative infusion bottle height on the power of refilled pig lenses. SETTING: Research Laboratory, Pharmacia Intraocular Lens Manufacturing Plant, Groningen, The Netherlands. METHODS: This study comprised 2 groups of pig eyes. In 1 group, the lens was refilled with silicone oil using a plug to close the capsulorhexis; in the other group, no plug was used. The anterior chamber depth, lens thickness, and vitreous chamber depth were measured by A-scan ultrasound. The total refraction was measured with a Hartinger refractometer. Measurements were performed with the infusion bottle at 0 cm, 25 cm, 50 cm, 75 cm, and 100 cm above eye level. Calculations using a model eye were performed to evaluate the change in lens power based on empirical data. RESULTS: The mean change in the power of refilled lenses caused by varying the height of the infusion bottle was 1.8 diopters. Lenses refilled with a plug had a thickness similar to that of natural lenses. Lenses refilled without a plug were significantly thinner (P<.05). The power of lenses refilled with a plug was significantly higher that of lenses refilled without a plug (P<.05). CONCLUSIONS: During lens refilling, infusion bottle height influenced the resulting lens power. Using a plug to close the capsulorhexis resulted in refilled lens dimensions similar to those of the natural lens.     

Recovery from contact lens-induced edema is prolonged in the diabetic rabbit cornea

The recovery of the cornea from contact lens-induced edema has been proposed as a clinical test for the assessment of corneal hydration control, with prolonged times being seen in aged subjects and in conditions associated with endothelial dysfunction. Because diabetes is known to be associated with altered endothelial morphology, a study was performed to determine the influence of diabetes on recovery times from contact lens-induced edema. Corneal edema was produced in 10 normal and 10 diabetic rabbits by the monocular wear of a thick hydrogel contact lens on a closed eye for a period of 2 h. Corneal thicknesses measured by ultrasound pachometry at the end of the wearing period showed significantly (p less than 0.0001) more edema in the normal (75 +/- 11 microns) than in the diabetic group (56 +/- 11 microns). Open eye and closed eye recovery times from the induced edema were calculated for both groups using linear and nonlinear regression analysis. The calculated edema recovery rates for the diabetic cornea were significantly slower than those of the normal in both the open eye and closed eye deswelling conditions. The results of this study indicate that the cornea of a diabetic rabbit has a decreased ability to recover from contact lens-induced edema, and suggests that the practitioner should remain aware of the blood glucose levels of his poorly controlled diabetic contact lens patients.     

Long-term follow-up of obsolete design: iris-clip glass intraocular lens

An enucleated eye obtained post-mortem from a 95-year-old donor who had a 4-loop, iris-fixated (iris-clip) glass intraocular lens (IOL) that had been implanted 22 years earlier was analyzed. The patient had a history of mild corneal edema, glaucoma, and macular degeneration/macular pucker. High-frequency ultrasound showed a well-centered iris-fixated IOL. Gross and light microscopic analyses of the eye and the IOL showed fragments of iris tissue attached to the haptics, pigment dispersion within the eye, with pigmented epithelial cells attached to the lens haptics and interruptions of the iris pigmented epithelial layers, and signs of corneal decompensation.     

Relative afferent pupillary defect in patients with asymmetric cataracts

PURPOSE: To prospectively investigate the incidence, associated factors, and prognostic significance of relative afferent pupillary defects (RAPDs) in eyes with less severe cataract than in contralateral eyes. SETTING: Department of Ophthalmology, Seoul Municipal Boramae Hospital, College of Medicine, Seoul National University, Seoul, Korea. METHODS: Forty patients with asymmetric cataract and a differences of 3 or more lines of Snellen visual acuity between eyes had detailed ophthalmic examinations including visual acuity, slitlamp evaluation, a swinging flashlight test before and after cataract surgery, and color vision assessment. RESULTS: Twenty-three of 40 patients (58%) had an RAPD (mean extent 0.39 log unit +/- 0.17 [SD]) in the eye with less severe cataract. The RAPD resolved or switched to the other eye after cataract extraction. All 5 patients with a unilateral totally opaque lens had a contralateral RAPD, confirming the relationship between totally opaque cataracts and RAPDs. The difference in visual acuity between the 2 eyes did not differ between patients with RAPD and those without RAPD. There was no association between the presence of RAPD and postoperative visual acuity. CONCLUSIONS: More than half the patients with asymmetric cataract had an RAPD that resolved in the eye with less severe cataract after cataract extraction. All patients with a unilateral totally opaque lens had an RAPD. The presence of a preoperative RAPD was not related to postoperative visual acuity.     

Human traumatic cataract. A quantitative microradiographic and electron microscopic study.

Six cases representing different stages of cataract formation secondary to eye trauma were subjected to quantitative microradiographic or electron microscopic examination. Anterior and posterior subcapsular cataracts were found to contain extensively swollen lens fibers in the subcapsular cortex. Microradiographic measurements revealed a reduced concentration of dry mass in the subcapsular cortex around the whole circumference of the lens. The inner cortex and the nucleus appeared normal both microradiographically and electron-microscopically. Two of the examined cases had an opaque-cataract membrane and one had a Soemmerring's ring. The opaque membranes consisted of irregular masse of degenerated lens fiber material as well as regenerated lens epithelial cells. A wide range of dry mass concentration was found in the opaque membrane that was studied microradiographically. Alterations in morphology and dry mass concentration are more than sufficient to explain the development of opacification in traumatic cataract.     

Simultaneous defocus integration during refractive development

PURPOSE: To determine the effects of simultaneously presented myopic and hyperopic defocus on the refractive development of chicks. METHODS: A novel form of dual-power lens was designed. Normal chicks 7 to 8 days of age were fitted with a dual-power lens over one eye and a plano lens over the fellow (control) eye. Dual-power lenses of +20/-10, +10/-10, +5/-10, and plano/-10-D were tested, along with +10/-10-D lenses having differing ratios (50:50, 33:67, and 25:75) of surface area devoted to each power. Ocular refraction and axial ocular component dimensions were assessed after 6 days of lens wear, by retinoscopy and high-frequency ultrasound, respectively. In a separate experiment designed to test the effect of dual-power lens wear on the refractive development of myopic eyes, chicks were fitted with a dual-power +10/-10-D lens for 6 days, after myopia had been induced by 6 days of -10-D lens wear. RESULTS: For each of the dual-power lenses tested, the refractive end point of the treated eye was found to lie between the two optical powers of the lens (but with the response weighted in favor of the effect of myopic defocus). Refractive development appeared to be modulated by the sign, dioptric magnitude, and relative contribution (relative contrast) of the imposed optical defocuses through an integrative mechanism. Chicks with myopia induced by -10-D lens wear recovered when treated with a +10/-10-D dual-power lens. CONCLUSIONS: The chick retina can discern both the sign and the magnitude of optical defocus. Chick eyes were able to integrate blur cues from simultaneously presented images focused either side of the photoreceptors and to modulate their refractive development accordingly. This implies that the complex nature of defocus in the visual environment may play a critical role in the pathogenesis of myopia. The results suggest a rational method for arresting or reversing the development of myopia, which may be useful in the treatment of human myopia if the primate retina is also capable of responding to simultaneously presented opposing defocus cues.     

Clinical aspects of the measurement of oxygen flux into the cornea.

A comparison was firstly done of the oxygen flux through the Bausch and Lomb Plano T lens, the Bausch & Lomb U3 lens, and the Duragel 75 lens with a sensor on the normal eye. The results showed that the Bausch and Lomb Plano T lens was the best for use with the sensor probe. The sensor was then used to obtain a comparison with the normal oxygen flux through a therapeutic lens on keratoplastic eyes and eyes with bullous keratopathy. The results showed that both conditions had a lower oxygen consumption than normal and that eyes with bullous keratopathy predictably had the lowest value.     

The effect of ultrasonic oscillations of different frequencies on radionuclide accumulation in the eye tissues

The paper describes results of experimental investigations in 25 rabbits for the purpose to study permeability of eye tissues under the action of ultrasound of different frequencies (127, 295, 470, 660, 880, 1000, 2750 kHz). The following radioactive nuclides were used: 99mTc--pertechnetate, 125I in a form of KI and 45CaCl2. In investigations with 99mTc--pertechnetate and 45CaCl2, their accumulation in the aqueous humor, vitreous body, cornea, iris, sclera, crystalline lens, choroid and retina was studied. It was found that permeability of eye tissues depends, to a great extent, on ultrasound frequency. The highest amount of radionuclides penetrate into the eye media and eye tissues under the action of ultrasound with 470, 660, 880 kHz frequencies. With increase or decrease of ultrasound frequency the permeability decreases. This fact should be considered when applying phonophoresis.     

Axial length following implantation of posterior chamber lenses

We used ultrasound to measure axial length in 66 eyes before and three months after extracapsular cataract extraction with implantation of a posterior chamber lens. An ultrasound velocity of 2,718 m/s for poly(methyl methacrylate) was assumed. The intraindividually measured difference (postoperative--preoperative axial length) ranged from -0.4 mm to 0.6 mm and averaged 0.11 mm. The lengthening of the eye was statistically significant (P less than .001; two-tailed, paired t-test). Statistical analysis of the regression equation between the preoperative and the postoperative axial lengths disclosed that this correlation was not more accurate than simply substituting the two measurements. Assuming no real change in axial lengths, our data suggest an ultrasound velocity of 1,679 m/s for the natural lens or an average velocity of 1,560 m/s for the phakic eye. We conclude that the preoperatively measured axial length may be used as a fairly accurate estimate of the postoperative distance in intraocular lens power calculation formulas.     

Confocal microscopic observations of the human cornea following overnight contact lens wear

Background: Striae and folds are observed with a slidamp biomicroscope in the cornea following overnight contact lens wear. These phenomena are poorly understood. The aim of this study is to employ confocal microscopy to observe and document these and other morphological changes in die human cornea following overnight contact lens wear. Methods: Slitlamp biomicroscopy, slit‐scanning confocal microscopy and ultrasonic pachometry were performed on both eyes of 13 subjects (3M, 10F, age 24 ± 3 years) before and after eight hours overnight wear of a ‐3.00 D Bausch & Lomb one day disposable soft contact lens (Dk/t = 15.1 times 10^‐9 (cm/sec) x {ml O²/ml x mmHg)) in one eye; the other non‐lens‐wearing eye acted as a control. Results: Following sleep, both corneas were swollen (lens‐wearing eye 11.8 ± 3.8 per cent; control eye 2.1 ± 1.9 per cent) and the stroma of both corneas displayed an apparent reduction in keratocyte density (lens‐wearing eye 21 per cent; control eye 10 per cent). Folds were observed with the slidamp biomicroscope and long, straight, dark, orthogonal lines were observed widi die confocal microscope, in the posterior stroma of the oedematous lens‐wearing eyes. Such features were not observed in die control eyes. The keratocytes appeared less distinct with greater levels of corneal oedema. Conclusion: The apparent loss of keratocytes following overnight lens wear is an optical artefact that can be explained in terms of corneal oedema causing volumetric tissue expansion and a loss of optical clarity, which hampers keratocyte detection. These findings place the onus on researchers postulating a loss of stromal keratocytes following clinical interventions, such as contact lens wear, to account for the effects of oedema.     

Ultrasound biomicroscopy in uveitis-glaucoma-hyphema syndrome

PURPOSE: To assess anterior segment anatomy in uveitis-glaucoma- hyphema syndrome. DESIGN: Retrospective case series. METHODS: Nine pseudophakic eyes (nine patients) with complete or incomplete uveitis-glaucoma-hyphema syndrome underwent ultrasound biomicroscopy. RESULTS: Ultrasound biomicroscopy revealed intraocular lens malposition in each case. Of the eight eyes with posterior chamber intraocular lenses, haptics were in contact with the iris pigment epithelium (four eyes) or the pars plicata (three eyes) or prolapsed into the angle recess near a filtration bleb internal ostium (one eye). All other posterior chamber intraocular lens haptics were located in the ciliary sulcus with the exception of two in the capsular bag. Both haptics in the eye with the anterior chamber intraocular lens had eroded into the ciliary body. CONCLUSION: By its ability to detect haptic position, ultrasound biomicroscopy can assist in elucidating the cause of uveitis-glaucoma-hyphema syndrome and in deciding on the course of treatment.     

Significance of immediate affixation of a hard contact lens in the emergency treatment of severe alkali burns of the cornea (case report)

BACKGROUND: Severe alkali burns lead to massive limbal stem cell damage resulting in persistent epithelial defects, infiltration and stromal melting early in the disease process. A glued-on hard contact lens may serve as an "artificial epithelium" and protect the cornea from these complications. CASE REPORT: A 39-year-old male presented with severe lime burns in both eyes one week after injury. The right eye showed a totally denuded cornea and conjunctiva with circular paralimbic ischemia. In the left eye "only" two thirds of the cornea and adjacent conjunctiva and limbus were affected with less ischemia. Amniotic membrane transplantation was performed in both eyes but failed after four days already in the right eye. A hard contact lens was therefore glued on the right eye and allowed for visual acuity of 0.4 without correction in this primarily most heavily afflicted eye for 12 months duration. After removal of the contact lens, reepithelisation was quick, and function remained stable with addition of autologous serum eye drops. The primarily far less injured left eye, however, for which the amniotic membrane surgery was primarily judged to be adequate, could not be stabilised. The cornea perforated 4 weeks later necessitating a mini-keratoplasty plus a glued-on contact lens, and correctable vision never became better than 1/35. CONCLUSION: The clinical course confirms former observations that a glued-on hard contact lens is an effective treatment early after alkali burn and prevents the cornea from infiltration and melting. Moreover, two aspects merit consideration: first, with proper technique and timing of the gluing-on a patient may retain useful vision throughout the period of wearing the contact lens; second, for the long period during which the cornea was sealed by the contact lens, improper repopulation by conjunctival epithelium was inhibited, and proper corneal epithelium was given a chance for repopulation after recovery of the limbal area resulting in a stable surface and useful vision without additional keratoplasty measures.     

试析10 MHzB超水浴法眼前节探查价

目的 探讨分析10MHzB超水浴法眼前节探查的价值.方法 以IOMHzB超分别采用水浴法和直接法对眼前节探查,并对声像图进行对比分析.结果 共探查261例(522只眼),10MHzB超水浴法探查发现异常57例(90只眼),其中晶状体混浊45例(78只眼);晶状体内异物1例(1只眼);晶状体半脱位1例(1只眼);人工晶状体半脱位2例(2只眼);晶状体后囊破裂2例(2只眼);睫状体脱离2例(2只眼);前房积血4例(4只眼).眼前节成像远离超声近场,无干扰及伪像,成像清晰.结论 水浴法探查拓展了10MHzB超的探查范围,使其前节观察成为可能,是一项具有临床实用价值的眼科超声检查方法.     

Effect of interrupted lens wear on compensation for a minus lens in tree shrews.

BACKGROUND: When a young animal wears a monocular minus (concave) lens that shifts the focal plane away from the cornea, the vitreous chamber elongates over a period of days, shifting the retinal location to compensate for the altered focal plane. We examined the effect of removing the lens for a portion of each day on the amount of compensation in tree shrews. METHODS: Starting 24 days after natural eye opening, juvenile tree shrews wore a goggle frame that held a -5 D lens in front of one eye, with an open frame around the fellow control eye. The goggle was removed for 0, 0.5, 1, 2, or 7 h each day (N = 5, 5, 5, 5, and 3 animals per group, respectively), starting 0.5 h after the start of each 14 h light-on period. After 21 days of treatment, measures were made of the cycloplegic refractive state (streak retinoscopy) and the ocular component dimensions (A-scan ultrasound). Normal animals that experienced 14 h each day with no lens (N = 3) were also examined. RESULTS: The treated eyes of the 0 h group developed full refractive compensation for the lens (treated eye - control eye, mean +/- SEM = -5.8+/-1.1 D) and had increased vitreous chamber depth (0.13+/-0.02 mm) and axial length (0.12+/-0.02 mm) relative to the untreated control eye. The groups in which the lens was removed for 0.5 and 1 h each day showed partial compensation for the -5 D lens, both in refractive state (-4.2+/-0.4 D; -2.9+/-1.6 D) and in vitreous chamber depth (0.12+/-0.02 mm; 0.09+/-0.02 mm). The 2, 7, and 14 h (normal) groups showed no significant refractive or axial compensation. In the 0.5 and 1 h groups, A-scan ultrasound showed a thinning of the region between the front of the retina and back of the sclera. CONCLUSIONS: The eyes of tree shrews can tolerate altered monocular visual stimulation produced by a minus lens worn for 12 h of a 14-h light cycle without developing an induced myopia. However, when the lens is worn more than 12 of 14 h each day, compensation appears to increase linearly with decreased lens-off time. If the eyes of human children respond similarly to defocus from near work or other sources, it would seem that the defocus must be present almost all the time to induce myopia. If defocus contributes to human myopia through a compensation mechanism, then an increase in the amount of time that focused images are present should reduce myopic progression.     

Ultrasound axial length measurement in biphakic eyes

To determine the calculations to correct the error in ultrasound measurement of a phakic eye with a phakic intraocular lens (IOL) (biphakic eye) to increase the accuracy of IOL power calculation should cataract surgery become necessary.Mathematical derivations were performed to calculate the error caused by a phakic IOL while measuring an eye using an average sound velocity. A simple model was developed to allow correction of the axial length (AL).If the eye is measured at an average velocity of 1555 meters/second, the following calculation can be used depending on the material of the phakic IOL: AL(corrected) = AL(1555) + X x T, where T is the central thickness of the phakic IOL and X = +0.42 (0.41 - 0.42) for poly(methyl methacrylate), -0.59 (0.56 - 0.59) for silicone, +0.11 (0.10 - 0.12) for Collamer, and +0.23 (0.23 - 0.24) for acrylic.By obtaining the dioptric power of the phakic IOL and central thickness from the manufacturer and knowing the material of the lens, a mathematical correction can be made to arrive at the true ultrasound AL in a biphakic eye.