Effects of topical pilocarpine on ocular growth and refractive development in rabbits.

PURPOSE: This study aimed to investigate whether topical pilocarpine affects ocular growth and refractive development as well as the underlying biochemical processes in early eye development in rabbits. METHODS: Twenty three-week-old New Zealand white rabbits were treated with 0.5% pilocarpine in the right eye for 6 weeks. The left eyes served as contralateral controls. The effects of pilocarpine on refractive error, corneal curvature and ocular biometrics were assessed using streak retinoscopy, keratometry, and A-scan ultrasonography, respectively. Eyeballs were enucleated for histological analysis. The ciliary body and sclera were homogenized to determine the mRNA and protein expression levels of five subtypes of muscarinic receptors. RESULTS: Compared to control eyes, pilocarpine-treated eyes exhibited approximately -1.63 ± 0.54 D myopia accompanied by a 0.11 ± 0.04 mm increase in axial length (AL) (p < 0.001, respectively). The anterior chamber depth (ACD) was reduced, whereas the lens thickness (LT) and vitreous chamber depth (VCD) increased (p < 0.001, respectively). Corneal curvature decreased over time but was not significantly different between treated and control eyes. The mRNA and protein expression levels of five subtypes of muscarinic receptors were upregulated in the ciliary body and downregulated in the sclera. CONCLUSIONS: Based on these results, pilocarpine can induce myopic shift, increase LT, elongate VCD and AL, and reduce muscarinic receptor expression in the sclera early in development. These changes raise the possibility that pilocarpine may promote axial elongation in ocular development and facilitate the emmetropization of hyperopic eyes.

Protective effects of taurine against alloxan-induced diabetic cataracts and refraction changes in New Zealand White rabbits.

The present study examined the protective effects of taurine on alloxan-induced diabetic cataracts and lens damage in male New Zealand White rabbits. The animals were randomly divided into three treatment groups: (1) normal control (vehicle administration); (2) diabetes (100 mg/kg alloxan administration); and (3) diabetes + taurine (1% [w/v] taurine dissolved in drinking water and alloxan administration). The results showed that alloxan-induced diabetes caused significant (p < 0.05) hyperglycemia, hyperopic refraction shifts, cataract formation and lens damage compared with the normal control group. In contrast, the administration of taurine for 24 weeks significantly ameliorated the alloxan-induced elevated levels of blood glucose, level of hyperopic refraction error shifts in the eyes and progression of diabetic cataract formation in the lens in rabbits. Moreover, histopathology showed that the taurine supplement reduced the incidence of lens lesions induced by hyperglycemia. Overall, the studies demonstrate that taurine exhibits potent protective effects against alloxan-induced diabetic cataracts and refraction changes in rabbits.

Refractive state following retinal reattachment and silicone oil tamponade in dogs.

OBJECTIVE: To evaluate the refractive error induced by intraocular administration of silicone oil (SiO) in dogs. ANIMALS: 47 client-owned dogs evaluated for blindness secondary to retinal detachment. PROCEDURES: -3-port pars plana vitrectomy with perfluoro-octane and SiO exchange (1,000- or 5,000-centistoke SiO) was performed in 1 or both eyes for all dogs (n = 63 eyes), depending on which eye or eyes were affected. Dogs were normotensive, had complete oil filling of the eyes, and were examined in a standing position for retinoscopic examination of both eyes (including healthy eyes). RESULTS: The mean refractive error for SiO-filled phakic and pseudophakic eyes was 2.67 and 3.24 D, respectively. The mean refractive error for SiO-filled aphakic eyes was 6.50 D. Dogs in which 5,000-centistoke SiO was used had consistently greater positive refractive errors (mean, 3.45 D), compared with dogs in which 1,000-centistoke SiO was used (mean, 2.10 D); however, the difference was nonsignificant. There was no significant linear relationship between refractive error and the number of days between surgery and retinoscopy. CONCLUSIONS AND CLINICAL RELEVANCE: Hyperopia was observed in all dogs that underwent SiO tamponade, regardless of lens status (phakic, pseudophakic, or aphakic). Aphakic eyes underwent a myopic shift when filled with SiO. Pseudophakic eyes appeared to be more hyperopic than phakic eyes when filled with SiO; however, additional investigation is needed to confirm the study findings.

Different refractive errors in triplets with retinopathy of prematurity treated with bevacizumab.

The authors report refractive errors possibly resulting from intravitreal bevacizumab injection. Triplet A presented with stage 3 retinopathy of prematurity, was treated with intravitreal bevacizumab, and high refractive errors were noted. Triplet B presented with stage 2 retinopathy of prematurity in the right eye and stage 3 retinopathy of prematurity in the left eye, which regressed spontaneously. Triplet C presented with stage 2 retinopathy of prematurity in the right eye and stage 3 retinopathy of prematurity in the left eye, which were treated with intravitreal bevacizumab.

Drug-induced myopia, hyperopia and accommodation disorders.

Myopia, hyperopia and accommodation disorders are common refractive disorders, usually due to anatomical abnormalities or to physiological aging. They can also be functional, however, particularly when provoked by drugs. Drug-induced refractive disorders resolve after treatment cessation. All drugs acting on the autonomic nervous system can affect vision. Other drugs have unpredictable effects: the mechanism is not always known but sometimes appears to involve changes in the hydration of various ocular structures.

Transient hyperopia after intensive treatment of hyperglycemia in newly diagnosed diabetes.

PURPOSE: Our aim was to observe the transient hyperopia during the intense glucose reduction in patients with newly diagnosed diabetes and severe hyperglycemia. STUDY DESIGN: Consecutive cases were observed. RESULTS: Totally 4 men and 1 woman with a mean age of 48 years were enrolled. In the 4 patients who received insulin, the hyperopia developed at 4.2 days after the initiation of treatment on average and reached a peak at 11.7 days; they recovered at 64.0 days. The other subject who received oral hypoglycemia agents revealed a peak change at 17 days and recovered at 70 days. A broader hyperopic change of 6.25 dpt was found in the patient with high myopia (-16 dpt). No significant difference was observed in the corneal curvature, axial length, lens thickness or depth of the anterior chamber during the course. The stable value of the accommodation amplitude and lens thickness may indicate that the cause of refraction change was due to the alteration in the reflection index of the lens. CONCLUSION: Intensive glucose reduction may cause transient hyperopia changes in newly diabetic patients and results in blurred vision.

Refractive changes in silicone oil-filled pseudophakic eyes.

PURPOSE: We examined the refractive changes in pseudophakic eyes of patients with idiopathic macular hole treated with silicone oil injection. METHODS: Twenty consecutive eyes of 19 patients with idiopathic macular hole who had undergone successful pars plana vitrectomy using silicone oil tamponade were studied retrospectively. Lensectomy with intraocular lens (IOL) implantation was performed on each patient before vitreous surgery. Five biconvex type IOL models were used. After pars plana vitrectomy and fluid-air exchange, silicone oil was injected to replace the air completely. Macular hole closure was confirmed by optical coherence tomography, and silicone oil removal was performed. Manifest refractions before silicone oil filling, with silicone oil filling, and after silicone oil removal were determined. RESULTS: A mean hyperopic shift +/- SD in spherical equivalents of +5.69 +/- 1.71 diopters (P < 0.0001) was observed with silicone oil instillation. In contrast, a mean myopic shift +/- SD of -5.63 +/- 1.33 diopters was observed after silicone oil removal (P < 0.0001). The absolute value of the refractive shift showed a strong correlation with the posterior radius of the IOL (r = 0.699, P < 0.0001). CONCLUSION: IOL models with steeper posterior convex curvature result in larger refractive deviations in patients scheduled for silicone oil instillation.

Evidence for a potential role of glucagon during eye growth regulation in chicks.

Eye growth and refraction are regulated by visual processing in the retina. Until now, the messengers released by the retina to induce these changes are largely unknown. Previously, it was found that glucagon amacrine cells respond to defocus in the retinal image and even to its sign. The expression of the immediate-early gene product ZENK increased in this cell population in eyes wearing plus lenses and decreased in minus lens-treated chicks. Moreover, it was shown that the amount of retinal glucagon mRNA increased during treatment with positive lenses. Therefore, it seems likely that these cells contribute to the visual regulation of ocular growth and that glucagon may act as a stop signal for eye growth. The purpose of the present study was to accumulate further evidence for a role of glucagon in the visual control of eye growth. Chicks were treated with plus and minus lenses after injection of different amounts of the glucagon antagonist des-His1-Glu1-glucagon-amide or the agonist Lys17,18,Glu21-glucagon, respectively. Refractive development and eye growth were recorded by automated infrared photorefraction and A-scan ultrasound, respectively. The glucagon antagonist inhibited hyperopia development, albeit only in a narrow concentration range, and at most by 50%, but not myopia development. In contrast, the agonist inhibited myopia development in a dose-dependent fashion. At high concentrations, it also prevented hyperopia development. The amount of glucagon peptide in the retinae and choroids of lens-treated chicks and its diurnal variation was measured by using a radio-immunoassay. Retinal glucagon content decreased after minus lens treatment and choroidal glucagon content increased after plus lens treatment. No diurnal variation in the retinal amount of glucagon was detected. In addition, using an optokinetic nystagmus paradigm, the effect of glucagon and the antagonist des-His1-Glu9-glucagon-amide on suprathreshold contrast sensitivity was studied. Glucagon reduced contrast sensitivity (which might be linked to a signal for growth inhibition) whereas the antagonist des-His1-Glu9-glucagon-amide increased contrast sensitivity. The results of the study are in line with the hypothesis that glucagon plays a role in the visual control of eye growth in the chick.

Effects of retinal dopamine depletion on the growth of the fish eye.

We investigated the suitability of fishes as animal models to study the involvement of the retinal dopaminergic system in the visually guided control of eye growth (emmetropization). Advantages of such a model system are (i) that all dopaminergic cells in the retina can be destroyed without apparent damage to other neurons, (ii) simple optical design and short depth of field of the eye, and (iii) continuous growth throughout life. Depleting the retina of dopamine in Aequidens pulcher (Cichlidae) had no apparent effect on refractive state, since size and focal length of the eye were reduced by the same amount. Furthermore, imposed defocus was compensated at a normal rate in spite of the absence of retinal dopamine. In A. pulcher, the dopaminergic system of the retina trus appears not to have an essential role in emmetropization. Our results furthermore suggest that in eyes of more complicated optical design, manipulation of the retinal dopaminergic system may lead to unrelated effects indistinguishable from direct interference with emmetropization. A major disadvantage of the fish model was that refractive state of the eye could not be measured accurately in vivo with standard methods.

Excimer laser photorefractive keratectomy: one year follow-up.

BACKGROUND AND OBJECTIVE: To confirm the effectiveness of the 193 nm excimer laser to correct low myopia (1.00 to 6.00 D), moderate myopia (6.00 to 10.00 D), and high myopia (10.00 D and above). PATIENTS AND METHODS: One hundred eighty-one eyes of 114 patients underwent excimer laser photorefractive keratectomy (PRK). The minimum follow-up was 12 months. RESULTS: After one year, 96% of the eyes in the low myopia group, 69% in the moderate myopia group and 29% in the high myopia group achieved uncorrected visual acuity of 20/40 or better with one treatment using a single application with a 5 mm optic zone. There were no significant major complications. CONCLUSION: PRK is a safe, effective and relatively accurate procedure to correct low to moderate myopia.

Intraocular lens style and refraction in eyes treated with silicone oil.

The comparatively high refractive index of silicone oil significantly alters the refractive power of the human eye when it is placed into the vitreous cavity during retinal reattachment surgery. If cataract extraction and intraocular lens (IOL) implantation are subsequently performed, significant refractive errors result with most IOL styles if standard formulas are used to determine lens power. Thick-lens optical analysis of four IOL styles showed that the meniscus style yields the smallest difference between predicted (Binkhorst, Sanders-Retzlaff-Kraff formulas) and actual postoperative refraction. This IOL style also minimizes the change in refractive error that accompanies subsequent alterations in the contents of the vitreous cavity, including removal of silicone oil and replacement with balanced salt solution.

Optic nerve drusen and pseudopapilledema.

A case is presented in which unilateral visible optic nerve head drusen and a contralateral visual acuity loss are associated with moderate hypermetropia and the use of oral contraceptives. Optic nerve drusen are known to be responsible for visual field losses, but a reduction in visual acuity is a rare finding. Extensive investigation of this patient revealed no other cause for the visual acuity loss. However, the possibility of misdiagnosis of papilledema and papillitis is suggested by recent onset headache with unilateral visual acuity loss. A tentative diagnosis of buried drusen of the optic nerve in the affected eye is discussed.

PIP: The reported incidence of visible optic nerve drusen range from 3.4/1000-20.4/1000 in the general population, the discrepancy suggesting that many drusen are buried or are too small to be visible clinically. Drusen of the optic nerve head are an important consideration in the differential diagnosis of papilledema, papillitis, and pseudopapilledema. This case report describes a 22-year old white female patient with previously undetectedoptic nerve head drusen. She presented on June 20, 1979 for optometric examination with symptoms and signs suggestive of increased intracranial pressure or optic neuritis, namely reduced visual acuity, recent onset of severe headaches, central visual field loss, and an elevated right optic disc. The patient reported that her general health was good and she was not under any medical treatment; she was taking oral contraceptives for several years with no apparent side effects. Opthalmological examination and fluorescein angiography confirmed the appearance of both optic discs and the drusen in the right optic disc. Optic nerve drusen can cause visual field losses, but reduction in visual acuity is a rare finding. The pills were discontinued as a precaution. Neurological examination revealed no orbital, cranial, or ventricular abnormalities. The neurologist diagnosed muscle contraction (tension headache) and a tricyclic antidepressant was prescribed. In August 1980, visual acuities were unchanged but there was a reduction in the frequency and intensity of the headaches. This case associates unilateral visible optic nerve and head drusen and a contralateral visual acuity loss with moderate hypermetropia and pill use. Complication of pill use, such as venous thrombosis associated with papilledema was a possible diagnosis. However, there were several indications that the right optic disc elevation was in fact congenital anomalous elevation (pseudopapilledema) with drusen. The important point to remember is that anomalous elevation of disc with drusen and hypermetropia must not only be differentiated from papilldema and optic neuritis, but may also occur in association with these conditions.