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PubMed2005

Monocular deprivation in an identical twin.

PURPOSE: The scientific literature contains minimal human studies of the effect of monocular deprivation on a single eye of twins. This report examines the effects of early visual deprivation on axial length measurements by comparing the refractive findings and axial length measurements of identical twins' 4 eyes, 1 visually deprived and 3 nondeprived. METHODS: A retrospective record review was performed on the medical records of identical 6-year-old Hispanic female twins. Both patients had received eye care at the University Optometric Center, State University of New York, for a period of at least 5 years. Subsequently, an Internal Review Board-approved prospective study was undertaken. Each twin received a comprehensive eye examination and an A-scan. RESULTS: The findings of the 3 nondeprived eyes were compared with those of the 1 deprived eye. The 3 nondeprived eyes had at least 20/20 visual acuity, low hyperopia or astigmatism, low with the rule keratometric findings, 12-mm corneal diameters, and A-scan results ranging from 21.0 to 21.55 mm. The remaining eye, which was visually deprived secondary to congenital cataract from birth to 6 months of age, had an aphakic refractive condition, decreased visual acuity, glaucoma, esotropia, and borderline microcornea. Keratometric findings were comparable with those of the other 3 eyes, whereas the A-scan finding was 25.16 mm. CONCLUSION: This case presented a unique opportunity to directly examine the effect of visual deprivation on axial elongation. Although other factors, such as glaucoma and borderline microcornea, may influence axial elongation, the findings in this patient indicate that a substantial portion, if not all, of the axial elongation can be attributed to early monocular deprivation.

Cataract↗
PubMed2004

A paraxial schematic eye model for the growing C57BL/6 mouse.

PURPOSE: The mouse eye has potential to become an important model for studies on the genetic control of eye growth and myopia. However, no data are published on the development of its optical properties. We developed a paraxial schematic model of the growing eye for the most common laboratory mouse strain, the C57BL/6 mouse, for the age range between 22 and 100 days. METHODS: Refractive development was followed with eccentric infrared photorefraction and corneal curvature with infrared photokeratometry. To measure ocular dimensions, freshly excised eyes were immediately frozen after enucleation to minimize distortions. Eyes were cut with a cryostat down to the bisecting horizontal plane, until the optic nerve head became visible. The standard deviations were +/-10 microm for repeated measurements in highly magnified videographs, taken in several section planes close to the equator in the same eyes. To evaluate inter-eye and inter-individual variability, a total of 20 mice (34 eyes) were studied, with 3-4 eyes for each of the 9 sampling ages. Schematic eye models were developed using paraxial ray tracing software (OSLO, LT Lambda Research Corporation, and a self-written program). RESULTS: The measured refractive errors were initially +4.0+/-0.6 D at approximately 30 days, and levelled off with +7.0+/-2.5 D at about 70 days. Corneal radius of curvature did not change with age (1.414+/-0.019 mm). Both axial lens diameter and axial eye length grew linearly (regression equations: lens, 1619 microm +5.5 microm/day, R=0.916; axial length, 2899 microm +4.4 microm/day, R=0.936). The lens grew so fast that vitreous chamber depth declined with age (regression equation: 896 microm -3.2 microm/day, R=0.685). The radii of curvature of the anterior lens surface increased during development (from 0.982 mm at day 22 to 1.208 mm at day 100), whereas the radii of the posterior lens surface remained constant (-1.081+/-0.054 mm). The calculated homogeneous lens index increased linearly with age (from 1.568 to 1.605). The small eye artifact, calculated from the dioptric difference of the positions of the vitreo-retinal interface and the photoreceptor plane, increased from +35.2 to +39.1 D, which was much higher than the hyperopia measured with photorefraction. Retinal image magnification increased from 31 to 34 microm/deg, and the f/number remained < or =1 at all ages, suggesting a bright retinal image. A calculated axial eye elongation of 5.4-6.5 microm was sufficient to make the schematic eye 1 D more myopic. CONCLUSIONS: The most striking features of the mouse eye were that linear growth was slow but extended far beyond sexual maturity, that the corneal curvature did not increase, and that the prominent lens growth caused a developmental decline of the vitreous chamber depth.

Animals↗
PubMed2005

Longitudinal changes of optical aberrations in normal and form-deprived myopic chick eyes.

We performed measurements of refraction (with retinoscopy), axial length (with ultrasound biometry) and ocular aberrations (with a custom-built Hartmann-Shack aberrometer) on seven awake White-Leghorn chicks occluded monolaterally with diffusers for two weeks. Treatment started on the first day after hatching (day 0) and measurements were conducted on several days between day 0 and 13. Non-occluded eyes experienced normal emmetropization (decreasing hyperopia at 0.2 +/- 0.09 D/day and increasing axial length at 0.05 +/- 0.03 mm/day), while occluded eyes developed axial myopia (1.50 +/- 0.2 D/day and 0.12 +/- 0.02 mm/day). Interocular differences in refraction and axial length by day 13 were on average 17.43 D and 0.86 mm, respectively. Monochromatic high order aberrations decreased with age in both eyes. Average RMS (for 1.5 mm pupil diameter) decreased from 0.11 +/- 0.03 at day 0 to 0.06 +/- 0.03 microm (day 13) in occluded eyes, and from 0.12 +/- 0.05 to 0.03 +/- 0.01 microm in non-occluded eyes. MTF-based optical quality metrics also show an improvement with age. However, while this improvement occurs in both eyes, after day 8 myopic eyes tend to show significantly higher amounts of aberrations (and consequently worse best-corrected optical quality) than normal eyes. The degradation imposed by aberrations is small compared to that imposed by defocus and the diffuser. These results suggest a decrease of aberrations during development which does not seem to be visually guided. Myopic eyes showed slightly worse optical quality than normal eyes, suggesting that the geometrical changes resulting from excessive ocular axial growth also affect the optical quality of the ocular components.

Animals↗
PubMed2005

Corneal topography, refractive state, and accommodation in harbor seals (Phoca vitulina).

Corneal topography of a harbor seal measured with a Placido's disc shows a central flattened stripe in the vertical meridian. Together with a pupil that can form a vertical slit, the flat vertical meridian can minimize the optical effects caused by the transition from water to air. Using infrared (IR) photoretinoscopy, we analyzed the refractive state of harbor seals and revealed a high degree of myopia and astigmatism in air, but emmetropia or slight hyperopia with little astigmatism underwater. The brightness distribution in the pupils suggest the presence of a multifocal dioptric apparatus in air and underwater. We found a first indication for accommodation by dynamic recordings underwater.

Accommodation, Ocular↗
PubMed2005

ZENK expression of retinal glucagon amacrine cells in chicks: the effect of defocus presented in vivo, in vitro and under anesthesia.

PURPOSE: The transcription factor ZENK, expressed in glucagon amacrine cells in the retina in the chicken, has been shown to respond selectively to the sign of imposed defocus. To find out whether the retina by itself is able to perform the underlying image processing, we used ZENK to probe responses of amacrine cells to defined amounts of imposed defocus, both in vitro and in vivo. METHODS: To stimulate in vitro, retinal punches (8mm diameter), whole eyecups, or complete excised globes were stimulated with digitally generated video movies that were presented with defined amounts of defocus for 15, 30 or 45 min. Infrared photoretinoscopy was used to control the defocus of the projected movies. Furthermore, both anesthetized and alert chickens were stimulated with the differently focused video movies, or they were exposed to the visual environment of the laboratory for 4 days, wearing spectacle lenses for 45 or 90 min per day. Anesthetic effects per se were determined by using two different anesthetic protocols. After the stimulation, ZENK-immunoreactivity in glucagon amacrine cells was quantified. Eye growth and refractive development were recorded by A-scan ultrasound and infrared photoretinoscopy, respectively. RESULTS: In the isolated retina (stimulated in vitro), no consistent changes in ZENK expression could be induced by defocus, with a baseline expression similar in alert chicks. Placing a diffuser into the light path during optical stimulation did not lower ZENK expression, although diffusers are known to reduce ZENK expression in alert chicks. Imposed defocus in vitro caused merely a higher variability in ZENK expression in some cases. Defocus produced significant changes in ZENK expression only in the case of 4D of imposed hyperopia, but these changes were in the opposite direction to what was previously observed in vivo. Also in isolated eye cup or eye balls, no changes in ZENK expression could be induced by defocus. Most strikingly, neither ZENK expression, nor eye growth were affected by imposing defocus under anesthesia. Only alert chickens displayed the expected changes in ZENK expression and eye growth during imposed defocus, both with video stimulation and the "real world". CONCLUSIONS: In vitro, the chicken retina can still process some spatial features (since ZENK expression in the isolated retina was changed by imposed defocus with video stimulation), but the directions of the changes were no longer related to the sign of defocus. Also in intact animals, though under anesthesia, ZENK and eye growth did not respond to the sign of imposed defocus. Some stimulus for emmetropization appears to be important which is available only in alert animals.

Aging↗
PubMed2001

Management of the corneal flap in laser in situ keratomileusis after previous radial keratotomy.

PURPOSE: To report a method of managing the corneal flap in patients having laser in situ keratomileusis for the treatment of residual refractive errors after radial keratotomy. DESIGN: Retrospective case series. METHODS: Intraoperative dehiscence of radial keratotomy wounds occurred in 7 eyes of 6 patients treated with laser in situ keratomileusis for residual myopia or astigmatism or hyperopia 5 to 15 years after radial keratotomy. To minimize extension of these tears, the flap was initially rolled like a carpet toward the hinge before the ablation and then rolled away from the hinge to its original position after the ablation. RESULTS: Using this method of managing the laser in situ keratomileusis flap in patients with previous radial keratotomy, all eyes had successful laser in situ keratomileusis, with 1-year postoperative uncorrected visual acuity ranging between 20/16 and 20/25. No eye had loss of spectacle-corrected vision or interface epithelial ingrowth. CONCLUSIONS: Laser in situ keratomileusis has proved to be an effective treatment for correction of residual refractive errors after radial keratotomy. The surgical technique used in these cases was targeted at minimizing shearing forces in lifting the corneal flap to avoid extension of radial keratotomy wound dehiscence, which could lead to epithelial ingrowth and loss of best-corrected vision.

Adult↗
PubMed2003

Interlenticular opacification associated with asymmetric haptic fixation of the anterior intraocular lens.

PURPOSE: To describe the occurrence of interlenticular opacification in association with asymmetric haptic fixation of the anterior intraocular lens in a patient who had two intraocular lenses (IOLs) inserted for axial hyperopia. DESIGN: Observational case report. METHODS: An 83-year-old patient underwent uncomplicated cataract extraction and piggyback IOL insertion. The posterior IOL was placed within the capsule, but one of the haptics of the anterior IOL was inadvertently placed in the ciliary sulcus and the other in the capsule. RESULTS: Interlenticular opacification was localized to the interlenticular area near the anterior lens haptic placed within the capsule and absent from the interlenticular area near the anterior lens haptic fixated in the ciliary sulcus. CONCLUSION: This case report supports the idea that sulcus placement of the anterior IOL helps to prevent interlenticular opacification.

Aged↗
PubMed1992

Ocular findings in Cockayne syndrome.

The ocular findings in eight patients with Cockayne syndrome included enophthalmos, hyperopia, poor pupillary dilation, and retinal dystrophy in all patients. Four patients had strabismus. Two patients had cataracts. Three patients had nystagmus. Visual acuity was relatively well preserved in six patients, including a 25-year-old man with a visual acuity of 20/60 in each eye despite advanced retinal pigmentary changes. Failure of DNA and RNA synthesis to recover after ultraviolet light exposure as well as selective loss of repair of transcriptionally active DNA may account for the ocular abnormality in this progeric syndrome.

Adult↗
PubMed1990

Ocular and systemic findings in the Aarskog (facial-digital-genital) syndrome.

The Aarskog (facial-digital-genital) syndrome is an X-linked disorder in which short stature is accompanied by hypertelorism, digital anomalies, and shawl scrotum. Except for hypertelorism and blepharoptosis, ophthalmic abnormalities have been rarely noted in this condition. We examined four patients who had Aarskog syndrome and unilaterally or bilaterally decreased vision on initial examination. Three family members had V-pattern esotropia, latent nystagmus, inferior oblique overaction, and amblyopia. A fourth patient had bilateral blepharoptosis and severe astigmatism. Other ocular features included hyperopia, anisometropia, deficient ocular elevation, blue sclerae, and posterior embryotoxon. These findings underscore the need for ophthalmic examination in asymptomatic patients with Aarskog syndrome to rule out treatable causes of visual loss.

Abnormalities, Multiple↗
PubMed1978

Familial foveal retinoschisis associated with a rod-cone dystrophy.

A brother and sister born of a consanguinous marriage had bilateral foveal retinoschisis and a generalized rod-cone dysfunction. This was associated with nyctalopia, hyperopia, minimal vitreous opacities in the sister, a paramacular tapetal sheen reflex, normal retinal vessels, an abnormal electroretinogram, and a normal electro-oculogram in the less affected brother. Foveal retinoschisis is not pathognomonic for x-chromosome-linked juvenile retinoschisis. It may be seen as a manifestation of a macular dystrophy or associated with a generalized tapetoretinal dystrophy.

Adult↗
PubMed1990

Optic disk elevation in Down's syndrome.

Of five children who had Down's syndrome with optic nerve head elevation, without associated intracranial lesions, three underwent enhanced computed tomography for which no abnormalities were found. Partial, complete, or intermittent resolution of the optic disk elevation occurred in three children. In none of the children were retinal vessel dilation, splinter hemorrhages, optic nerve drusen, subsequent optic atrophy, or apparent visual loss noted. All of the children were hyperopic, but only one child had a hyperopia of greater than 3.50 diopters.

Child, Preschool↗
PubMed2000

Evaluation of the iScreen digital screening system for amblyogenic factors.

BACKGROUND: A digital photoscreener, the iScreen screening system, is now available to detect amblyogenic factors. We carried out a prospective study to evaluate the accuracy of the device in detecting anisometropia, significant refractive error, strabismus and opacities of the ocular media. METHODS: A total of 449 consecutive patients (median age 7 years) from a private pediatric ophthalmology practice underwent screening with the iScreen photoscreener operated by a minimally trained technician. The results were compared to the masked clinical examination of a pediatric ophthalmologist. RESULTS: The iScreen device had a sensitivity of 92.4%, specificity of 89.1%, positive predictive value of 94.1% and false-negative rate of 13.8%. Of the 21 patients with a false-negative result, 12 had myopia of less than -1.50 dioptres. High hyperopia was missed in two patients, high astigmatism in one, unequal cylindrical error in one and strabismus in five. INTERPRETATION: The iScreen digital photoscreener produced accurate and timely screening for potentially amblyogenic defects in the study population.

Adolescent↗
PubMedDate not supplied

Changes in refraction caused by induction of acute hyperglycemia in healthy volunteers.

PURPOSE: To determine whether the myopic changes and ocular hypotension after a glucose load are caused by hyperglycemia. METHODS: Oral glucose tolerance tests were conducted on seven healthy young subjects with normal vision. The changes in the hematologic parameters and the refractive system were measured periodically for 150 minutes after the glucose load. RESULTS: After the glucose load, there was an increase in plasma glucose level and the level of plasma osmosis, ocular hypotension, a myopic change in refractive power, shallowing of the anterior chamber, and a thickening of the lens. The degree of the myopic change exceeded the power of the residual accommodation. Normalization of the plasma glucose level led to a normalization of the intraocular pressure and a reversal of the myopic changes. CONCLUSIONS: These findings suggest that the myopic changes that accompanied hyperglycemia were caused by a thickening of the lens resulting from a decrease in the tension of the zonule fibers of Zinn, and were secondary to ocular hypotension. Hyperopia appeared to be caused by the reversal of the myopia after normalization of plasma glucose levels.

Accommodation, Ocular↗
PubMed1986

Kenny syndrome: evidence for idiopathic hypoparathyroidism in two patients and for abnormal parathyroid hormone in one.

We report three unrelated patients with Kenny syndrome. Clinical symptoms included severe dwarfism, with internal cortical thickening and medullary stenosis of the tubular bones, normal bone age, macrocephaly, absent diploic space, delayed closure of the anterior fontanel, and normal intelligence; two of the patients had hyperopia and papillary edema. The patients also had episodic hypocalcemic tetany and low serum levels of magnesium. In two patients the diagnosis of idiopathic hypoparathyroidism was established on the basis of undetectable serum parathyroid hormone (PTH) levels (N- and C-terminal RIAs); one of these had normal urinary cyclic adenosine monophosphate (cAMP) response to exogenous PTH. Circulating calcitonin was undetectable in either patient. In a third patient, who had abnormal body proportions, serum levels of PTH were increased in an RIA detecting predominantly intact PTH (N-RIA) and undetectable in another RIA recognizing carboxy-terminal fragments (C-RIA). Administration of PTH promptly increased urinary cAMP excretion. In this patient, serum levels of calcitonin were increased, whereas values for 25-OHD and 1,25(OH)2D were normal.

Abnormalities, Multiple↗
PubMedDate not supplied

Excimer laser photorefractive keratectomy.

Excimer laser photorefractive keratectomy has been used for the correction of myopia, hyperopia and astigmatism. This laser removes tissue through a process termed photoablative decomposition, in which incident photon energy is sufficient to break molecular bonds. Selective removal of tissue across the anterior corneal surface results in a change in anterior corneal curvature. The surgical outcome may be influenced also by interindividual variability in wound healing and pharmacologic interventions. The nature of the excimer laser-tissue interaction, and clinical outcomes of predictability, stability and complications of surgery for myopia are discussed in detail.

Animals↗
PubMedDate not supplied

Uveal lymphoid neoplasia: a clinical-pathologic correlation and review of the early form.

We report three cases of uveal lymphoid neoplasia that were diagnosed early in their course. One case exhibited a posterior form, presenting with progressive hyperopia from a serous-macular detachment and choroidal involvement along with retrobulbar involvement. This patient was treated with proton beam irradiation. Two cases displayed an anterior form, with fixed fleshy epibulbar masses resembling salmon patches, and choroidal involvement. The histologic findings from biopsy of these anterior masses are presented. One of these patients was treated with complete excision of the mass and double freeze-thaw cryotherapy of the scleral bed, and the other patient was treated with conventional photon beam irradiation. The clinical features of uveal lymphoid neoplasia in its early form are discussed. Evaluation and treatment strategies for these early forms of uveal lymphoid neoplasia are reviewed.

Aged↗
PubMedDate not supplied

The clinical spectrum of schwannomas presenting with visual dysfunction: a clinicopathologic study of three cases.

Schwannomas (neurilemomas) are benign tumors that arise from Schwann cells in the peripheral nervous system. The most commonly involved nerves that cause neuro-ophthalmic manifestations are cranial nerves V and VIII. In this series of three women, schwannomas presented as intraconal masses that mimicked a cavernous hemangioma, a superior orbital mass transgressing the superior orbital fissure, and an expansive frontal lobe mass with clinical symptoms and signs of increased intracranial pressure. Although all three complained of visual blurring, none of our patients presented with Vth or VIIIth cranial nerve dysfunction. Histopathologic studies demonstrated well-circumscribed, encapsulated spindle-cell lesions with classic Antoni A and B patterns. Histopathologic examination is essential to confirm the diagnosis of a schwannoma that may be otherwise clinically confusing. Direct optic nerve compression, globe indentation with induced hyperopia, or increased intracranial pressure with optic nerve compromise may be responsible for visual symptoms. A multidisciplinary approach is often required because of the size and location of schwannomas.

Adult↗
PubMed2001

Emmetropization in chicks uses optical vergence and relative distance cues to decode defocus.

When visual information is confined to one object plane, the emmetropization end-point is adjusted in accord with the corresponding incident optical vergence at the eye [Proceedings of the 7th International Conference on Myopia (2000) 113]. We now report the effect of adding extra visual information beyond the target plane. Visual conditions were controlled using a cone-lens system: black Maltese cross targets on white opaque backgrounds (OMX) were attached to the open faces of 2.5 cm translucent cones fitted with either 0, +25 or +40 D imaging lenses. An alternative target (TMX) was made by substituting the opaque target background for a transparent background, which allowed access to visual information beyond the target plane. The imaging devices were applied to 7-day-old chicks and worn for 4 days. Prior to this treatment, on day 2, some chicks underwent ciliary nerve section (CNS) to preclude accommodation. All treatments were monocular. Refractive errors and axial ocular dimensions were measured using retinoscopy and A-scan ultrasonography under halothane anesthesia. Treatment effects were specified as mean ( +/-S.D.) interocular differences. Eyes with the OMX/+40 D lens combination remained emmetropic (+0.73 +/-3.57 D), consistent with the target plane being approximately conjugate with the retina. Switching to the TMX caused a hyperopic shift in refractive error (+3.78 +/-3.41 D). This relative shift towards hyperopia in switching from the OMX to the TMX target also occurred for the other two lens powers. Thus, the OMX/+25 D lens induced myopia (-7.00 +/-5.88 D), corresponding to the imposed hyperopic defocus (target plane now imaged behind the retina), and switching to the TMX resulted in a reduction in myopia (-1.73 +/-5.36 D). The OMX/0 D lens combination produced the largest myopic shift, and here, switching to the TMX condition almost eliminated the myopic response (-15.50 +/-6.62 D cf. -0.56 +/-1.24 D). This relative hyperopic shift associated with switching from the OMX to the TMX target was eliminated by CNS surgery. Thus, the two CNS/TMX groups were both more myopic than the equivalent no CNS/TMX groups (+40 D lens: -2.66 +/-2.34 D; +25 D lens: -7.97 +/-6.87 D). When the visual information is restricted to one plane, incident optical vergence appears to direct emmetropization. Adding visual information at other distances produces a shift in the end-point of emmetropization in the direction of the added information. That these effects are dependent on the integrity of the accommodation system implies that accommodation plays a role in emmetropization and represents the first reported evidence of this kind.

Accommodation, Ocular↗