Directional region-based feature point matching algorithm based on SURF.

Feature point matching is one of the fundamental tasks in binocular vision. It directly affects the accuracy and quality of 3D reconstruction. This study proposes a directional region-based feature point matching algorithm based on the SURF algorithm to improve the accuracy of feature point matching. First, same-name points are selected as the matching reference points in the left and right images. Then, the SURF algorithm is used to extract feature points and construct the SURF feature point descriptors. During the matching process, the location relationship between the query feature point and the reference point in the left image is directed to determine the corresponding matching region in the right image. Then, the matching is completed within this region based on Euclidean distance. Finally, the grid-based motion statistics algorithm is used to eliminate mismatches. Experimental results show that the proposed algorithm can substantially improve the matching accuracy and the number of valid matched points, particularly in the presence of a large amount of noise and interference. It also exhibits good robustness and stability.

A novel uncertainty evaluation method based on the particle filter and beta distribution for data with unknown distribution.

Uncertainty evaluation for unknown distribution data is a key problem to be solved in uncertainty evaluation theory. To evaluate the measurement uncertainty of data with unknown distributions, a novel uncertainty evaluation method based on the particle filter (PF) and beta distribution is proposed in this paper. A beta distribution with wide adaptability was adopted as the distribution type of measurement results, the parameters of the beta distribution were taken as the parameters to be estimated, and a state-space model was established. The PF method, suitable for non-Gaussian data, was utilized to obtain the estimates of the parameters of the beta distribution according to the measurement results. Finally, the best estimates of the measurement results and their uncertainty were calculated using the beta distribution parameters. Simulation results show that the proposed method is adaptive to accurately evaluate the measurement uncertainties of data, especially for non-Gaussian distribution data or asymmetrically distributed data. Multiple evaluation results show that the method has good robustness. The experimental results for the drift errors of a laser interferometer show that the uncertainty result of the proposed method is consistent with the Monte Carlo method. This method is suitable for a variety of distribution types that can be characterized through beta distribution and can solve the optimal estimation and uncertainty evaluation of most measurement results with unknown distribution types.

High-Precision Fabrication of Micro Monolithic Tungsten Ball Tips via Arc Discharge and the Taguchi Method.

A micro ball tip is a core component of high precision coordinate measuring machines. The present micro ball tips cannot satisfy the high-precision measuring requirements of high aspect ratio microstructures due to their large diameter and low accuracy. In the previous study, we fabricated a micro monolithic tungsten ball tip by using arc discharge and surface tension principles. However, the fabrication success rate of forming a micro ball tip is less than 10%. In the present study, the Taguchi method has been applied to increase the fabrication success rate, and it has increased to 57.5%. The output response is evaluated in terms of the diameter, roundness, and center offset of the tungsten probe ball tips. The smaller-the-better signal-to-noise ratio is applied to analyze the influence of various parameters. The proposed parameters can be used to increase the fabrication success rate and accuracy of the monolithic probe ball tip.

Drift Reduction of a 4-DOF Measurement System Caused by Unstable Air Refractive Index.

Laser beam drift greatly influences the accuracy of a four degrees of freedom (4-DOF) measurement system during the detection of machine tool errors, especially for long-distance measurement. A novel method was proposed using bellows to serve as a laser beam shield and air pumps to stabilize the refractive index of air. The inner diameter of the bellows and the control mode of the pumps were optimized through theoretical analysis and simulation. An experimental setup was established to verify the feasibility of the method under the temperature interference condition. The results indicated that the position stability of the laser beam spot can be improved by more than 79% under the action of pumping and inflating. The proposed scheme provides a cost-effective method to reduce the laser beam drift, which can be applied to improve the detection accuracy of a 4-DOF measurement system.

Modeling and Optimal Design for a High Stability 2D Optoelectronic Angle Sensor.

The structural deformations caused by environmental changes in temperature, vibration, and other factors are harmful to the stability of high precision measurement equipment. The stability and optimal design method of a 2D optoelectronic angle sensor have been investigated in this study. The drift caused by structural deformations of the angle sensor has been studied and a drift error model has been achieved. Key components sensitive to thermal and vibrational effects were identified by error sensitivity analysis and simulation. The mounts of key components were analyzed using finite element analysis software and optimized based on the concept of symmetric structures. Stability experiments for the original and optimized angle sensors have been carried out for contrast. As a result, the stability of the optimized angle sensor has been improved by more than 63%. It is verified that the modeling and optimal design method is effective and low-cost, which can also be applied to improve the stability of other sensors with much more complex principles and structures.

A Scanning Probe Microscope for Surface Measurement in Nano-Scale.

A tapping mode scanning probe microscopy (TM SPM) system for surface measurement in nanoscale is developed, of which the main element is a scanning probe consisting of quartz tuning fork and a long sharp tungsten tip. Quartz tuning fork is a very good resonant element with piezoelectrical characteristic, and it acts as an actuator and a force sensor simultaneously in the probe. The vertical spatial resolution of the TM SPM is up to sub-nanometer (0.11 nm) and the measuring force is in micro Newton magnitude (about 30 µN). In the scanning operation, the probe vibrates at its resonant frequency, so that the amplitude or frequency (or phase) of the resonant tuning fork is very sensitive to external forces (Its quality factor in air is about 3138). Using the TM SPM constructed by this probe, silicon samples are scanned. Their topography and phase images which indicate the surface material characteristics are reconstructed effectively with a high resolution and low destructiveness. Soft materials, such as Protein structure can also be scanned theoretically without damage. In addition, because of the using of the long sharp tungsten tip, the system has the capacity of measuring micro structures with large aspect ratio, such as large micro steps, deep micro trenches, etc.

GABAAα1 and GABAAρ1 subunits are expressed in cultured human RPE cells and GABAA receptor agents modify the intracellular calcium concentration.

PURPOSE: Gamma-aminobutyric acid A (GABAA) receptors (GABAARs), which are ionotropic receptors involving chloride channels, have been identified in various neural (e.g., mouse retinal ganglion cells) and nonneural cells (e.g., mouse lens epithelial cells) regulating the intracellular calcium concentration ([Ca(2+)]i). GABAAR ß-subunit protein has been isolated in the cultured human and rat RPE, and GABAAα1 and GABAAρ1 mRNAs and proteins are present in the chick RPE. The purpose of this study was to investigate the expression of GABAAα1 and GABAAρ1, two important subunits in forming functional GABAARs, in the cultured human RPE, and further to explore whether altering receptor activation modifies [Ca(2+)]i. METHODS: Human RPE cells were separately cultured from five donor eye cups. Real-time PCR, western blots, and immunofluorescence were used to test for GABAAα1 and GABAAρ1 mRNAs and proteins. The effects of the GABAAR agonist muscimol, antagonist picrotoxin, or the specific GABAAρ antagonist 1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA) on [Ca(2+)]i in cultured human RPE were demonstrated using Fluo3-AM. RESULTS: Both GABAAα1 and GABAAρ1 mRNAs and proteins were identified in cultured human RPE cells; antibody staining was mainly localized to the cell membrane and was also present in the cytoplasm but not in the nucleus. Muscimol (100 µM) caused a transient increase of the [Ca(2+)]i in RPE cells regardless of whether Ca(2+) was added to the buffer. Muscimol-induced increases in the [Ca(2+)]i were inhibited by pretreatment with picrotoxin (300 µM) or TPMPA (500 µM). CONCLUSIONS: GABAAα1 and GABAAρ1 are expressed in cultured human RPE cells, and GABAA agents can modify [Ca(2+)]i.

GABAB receptor antagonist CGP46381 inhibits form-deprivation myopia development in guinea pigs.

The aim was to investigate the effects of the GABAB receptor antagonist, CGP46381, on form-deprivation myopia (FDM) in guinea pigs. Twenty-four guinea pigs had monocular visual deprivation induced using a diffuser for 11 days (day 14 to 25). The deprived eyes were treated with daily subconjunctival injections (100 µl) of either 2% CGP46381, 0.2% CGP46381, or saline or received no injection. The fellow eyes were left untreated. Another six animals received no treatment. At the start and end of the treatment period, ocular refractions were measured using retinoscopy and vitreous chamber depth (VCD) and axial length (AL) using A-scan ultrasound. All of the deprived eyes developed relative myopia (treated versus untreated eyes, P < 0.05). The amount of myopia was significantly affected by the drug treatment (one-way ANOVA, P < 0.0001). The highest dose tested, 2% CGP46381, significantly inhibited myopia development compared to saline (2% CGP46381: -1.08 ± 0.40 D, saline: -4.33 ± 0.67 D, P < 0.01). The majority of these effects were due to less AL (2% CGP46381: 0.03 ± 0.01 mm, saline: 0.13 ± 0.02 mm, P < 0.01) and VCD (2% CGP46381: 0.02 ± 0.01 mm, saline: 0.08 ± 0.01 mm, P < 0.01) elongation. The lower dose tested, 0.2% CGP46381, did not significantly inhibit FDM (P > 0.05). Subconjunctival injections of CGP46381 inhibit FDM development in guinea pigs in a dose-dependent manner.

GABAB receptors are expressed in human aortic smooth muscle cells and regulate the intracellular Ca(2+) concentration.

The aim of this study was to investigate the expression of GABAB receptors, a subclass of receptors to the inhibitory neurotransmitter gamma-aminobutyric acid (GABAB), in human aortic smooth muscle cells (HASMCs), and to explore if altering receptor activation modified intracellular Ca(2+) concentration ([Ca(2+)]i) of HASMCs. Real-time PCR, western blots and immunofluorescence were used to determine the expression of GABABR1 and GABABR2 in cultured HASMCs. Immunohistochemistry was used to localize the two subunits in human left anterior descending artery (LAD). The effects of the GABAB receptor agonist baclofen on [Ca(2+)]i in cultured HASMCs were demonstrated using fluo-3. Both GABABR1 and GABABR2 mRNA and protein were identified in cultured HASMCs and antibody staining was also localized to smooth muscle cells of human LAD. 100 µM baclofen caused a transient increase of [Ca(2+)]i in cultured HASMCs regardless of whether Ca(2+) was added to the medium, and the effects were inhibited by pre-treatment with CGP46381 (selective GABAB receptor antagonist), pertussis toxin (a Gi/o protein inhibitor), and U73122 (a phospholipase C blocker). GABAB receptors are expressed in HASMCs and regulate the [Ca(2+)]i via a Gi/o-coupled receptor pathway and a phospholipase C activation pathway.

GABAB receptors expressed in human aortic endothelial cells mediate intracellular calcium concentration regulation and endothelial nitric oxide synthase translocation.

GABAB receptors regulate the intracellular Ca2+ concentration ([Ca2+]i) in a number of cells (e.g., retina, airway epithelium and smooth muscle), but whether they are expressed in vascular endothelial cells and similarly regulate the [Ca2+]i is not known. The purpose of this study was to investigate the expression of GABAB receptors, a subclass of receptors to the inhibitory neurotransmitter γ-aminobutyric acid (GABA), in cultured human aortic endothelial cells (HAECs), and to explore if altering receptor activation modified [Ca2+]i and endothelial nitric oxide synthase (eNOS) translocation. Real-time PCR, western blots and immunofluorescence were used to determine the expression of GABAB1 and GABAB2 in cultured HAECs. The effects of GABAB receptors on [Ca2+]i in cultured HAECs were demonstrated using fluo-3. The influence of GABAB receptors on eNOS translocation was assessed by immunocytochemistry. Both GABAB1 and GABAB2 mRNA and protein were expressed in cultured HAECs, and the GABAB1 and GABAB2 proteins were colocated in the cell membrane and cytoplasm. One hundred µM baclofen caused a transient increase of [Ca2+]i and eNOS translocation in cultured HAECs, and the effects were attenuated by pretreatment with the selective GABAB receptor antagonists CGP46381 and CGP55845. GABAB receptors are expressed in HAECs and regulate the [Ca2+]i and eNOS translocation. Cultures of HAECs may be a useful in vitro model for the study of GABAB receptors and vascular biology.

Inhibition of form-deprivation myopia by a GABAAOr receptor antagonist, (1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA), in guinea pigs.

PURPOSE: To investigate the effects of the relatively selective GABAAOr receptor antagonist (1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA) on form-deprivation myopia (FDM) in guinea pigs. METHODS: A diffuser was applied monocularly to 30 guinea pigs from day 10 to 21. The animals were randomized to one of five treatment groups. The deprived eye received daily sub-conjunctival injections of 100 µl TPMPA at a concentration of (i) 0.03 %, ( ii) 0.3 %, or (iii) 1 %, a fourth group (iv) received saline injections, and another (v) no injections. The fellow eye was left untreated. An additional group received no treatment to either eye. Prior to and at the end of the treatment period, refraction and ocular biometry were performed. RESULTS: Visual deprivation produced relative myopia in all groups (treated versus untreated eyes, P < 0.05). The amount of myopia was significantly affected by the drug treatment (one-way ANOVA, P < 0.0001); myopia was less in deprived eyes receiving either 0.3 % or 1 % TPMPA (saline = -4.38 ± 0.57D, 0.3 % TPMPA = -3.00 ± 0.48D, P < 0.01; 1 % TPMPA = -0.88 ± 0.51D, P < 0.001). The degree of axial elongation was correspondingly less (saline = 0.13 ± 0.02 mm, 0.3 % TPMPA = 0.09 ± 0.01 mm, P < 0.01, 1 % TPMPA = 0.02 ± 0.01 mm, P < 0.001) as was the VC elongation (saline = 0.08 ± 0.01 mm, 0.3 % TPMPA = 0.05 ± 0.01 mm, P < 0.01, 1 % TPMPA = 0.01 ± 0.01 mm; P < 0.001). ACD and LT were not affected (one-way ANOVA, P > 0.05). One percent TPMPA was more effective at inhibiting myopia than 0.3 % (P < 0.01), and 0.03 % did not appreciably inhibit the myopia (0.03 % TPMPA versus saline, P > 0.05). CONCLUSIONS: Sub-conjunctival injections of TPMPA inhibit FDM in guinea pig models in a dose-dependent manner.

Identification of GABA receptors in chick retinal pigment epithelium.

PURPOSE: The retinal pigment epithelium (RPE) is a multifunctional, monolayer of cells located between the neural retina and the choroicapillaris. γ-Aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the retina and GABA receptors are known to be present in chick retina, sclera and cornea. There is a report of genes involved in GABA receptor signaling being expressed in human RPE, however, whether GABA receptors are present in chick RPE is unknown. METHODS: Real time PCR and western blot were used to determine the expression of GABA receptors (alpha1 GABAA, GABABR2, and rho1 GABAC receptors) in isolated chicken RPE. Immunofluorescence using antibodies against one of the GABA receptor sub-types was used to determine receptor localization. RESULTS: Both real-time PCR and western blot demonstrated that alpha1 GABAA, GABABR2 and rho1 GABAC receptors were expressed in isolated chick RPE. Immunofluorescence further demonstrated that GABA receptors were localized to the cell membrane and plasma of RPE cells. CONCLUSIONS: Alpha1 GABAA, GABABR2 and rho1 GABAC receptors were expressed in chick RPE. The purpose of the GABA receptors within the RPE remains to be explored.

Identification of GABA receptors in chick cornea.

PURPOSE: The cornea has an important role in vision, is highly innervated and many neurotransmitter receptors are present, e.g., muscarine, melatonin, and dopamine receptors. γ-aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the retina and central nervous system, but it is unknown whether GABA receptors are present in cornea. The aim of this study was to determine if GABA receptors are located in chick cornea. METHODS: Corneal tissues were collected from 25, 12-day-old chicks. Real time PCR, western blot, and immunohistochemistry were used to determine whether alpha(1) GABA(A), GABA(B), and rho(1) GABA(C) receptors were expressed and located in chick cornea. RESULTS: Corneal tissue was positive for alpha(1) GABA(A) and rho(1) GABA(C) receptor mRNA (PCR) and protein (western blot) expression but was negative for GABA(B) receptor mRNA and protein. Alpha(1) GABA(A) and rho(1) GABA(C) receptor protein labeling was observed in the corneal epithelium using immunohistochemistry. CONCLUSIONS: These investigations clearly show that chick cornea possesses alpha(1) GABA(A), and rho(1) GABA(C) receptors, but not GABA(B) receptors. The purpose of the alpha(1) GABA(A) and rho(1) GABA(C) receptors in cornea is a fascinating unexplored question.

ρ1 GABAC receptors are expressed in fibrous and cartilaginous layers of chick sclera and located on sclera fibroblasts and chondrocytes.

rho(1) GABA(C) receptor antagonists inhibit myopia in chick but the site of this effect is not known. The sclera ultimately determines the shape and size of the globe and thus an untested possibility is that GABA agents have a scleral mechanism. Whether rho(1) GABA(C) receptors are expressed and located in chick sclera is unknown. Real-time PCR, western blot and immunohistochemistry were used to determine whether rho1 GABA(C) receptors are expressed and located in chick fibrous and cartilaginous sclera. Both layers of the chick sclera were positive for rho1 GABA(C) receptor mRNA (PCR) and protein (western blot) expression and labeling was observed in both fibroblasts and chondrocytes of the fibrous and cartilaginous layers (immunohistochemistry). These investigations clearly show that chick sclera possesses rho(1) GABA(C) receptors. The sclera is thus a potential previously unrecognized site for activity of rho(1) GABA(C) agents.

Seven-year follow-up of LASIK for moderate to severe myopia.

PURPOSE: To evaluate long-term refractive outcomes of LASIK for correcting moderate to severe myopia. METHODS: A long-term (7-year) prospective follow-up study of visual and refractive outcomes in patients who underwent myopic LASIK surgery in 1998 and 1999. Fifty-nine patients (104 eyes) of the original cohort of 75 patients underwent detailed clinical assessment at 1 and 7 years postoperatively. The main outcome measures were predictability, efficacy, safety, and stability. Topography, corneal thickness, and postoperative complications were recorded at 7 years. All patients completed a questionnaire assessing their satisfaction with the procedure. RESULTS: At 7 years postoperatively, 89.4% of eyes were within 0.50 diopters (D) of attempted correction, and 90.4% were within 1.00 D. All eyes had 20/40 or better vision and 94.2% had 20/20 or better. Best spectacle-corrected visual acuity was unchanged or improved in 80.8% of eyes. Eyes did not regress in refraction between 1 and 7 years postoperatively. Complications were rare and patient satisfaction with the surgery was high. CONCLUSIONS: LASIK surgery has predictable and stable results in refractive and visual outcomes in correcting moderate to high myopia on long-term follow-up. Refractive stability is maintained over 7 years, with no evidence of progressive late-onset complications.

Long-term prospective follow-up study of myopic photorefractive keratectomy.

The aim of this study was to evaluate the long-term outcome of excimer laser myopic photorefractive keratectomy (PRK). We undertook an 11-year prospective follow-up study of visual and refractive outcomes in 46 patients (85 eyes). The main outcome measures were predictability, efficacy, stability and safety of PRK. At 11 years after the operation, 56.5% of eyes were within +/-0.5 D of attempted correction and 81.2% were within +/-1.0 D; 87% had vision of 20/40 or better, and 52% had 20/20 or better. The best spectacle-corrected visual acuity was unchanged or improved in 91% of eyes at 11 years. Eyes with moderate and severe myopia showed a significant change between 3 and 11 years. PRK surgery for myopia shows predictable and stable results in the long term, with a slight regression in refraction, mainly for patients with severe myopia.

Effect of flap thickness on higher order wavefront aberrations induced by LASIK: a bilateral study.

PURPOSE: To investigate the effect of flap thickness on wavefront aberrations induced by LASIK. METHODS: LASIK was performed on 56 eyes of 28 patients with refraction errors that were well matched between the right and left eyes. For each patient, a planned 160-microm flap was created for one randomly selected eye using the Moria M2 microkeratome (130-microm head; thick flap group), and a 110-microm flap was created for the contralateral eye with the same microkeratome (90-microm head; thin flap group). Flap thickness was measured using ultrasonic pachymetry. Wavefront aberrations were measured in the anterior cornea using the Orbscan II (Bausch & Lomb) and in the whole eye using the Wavefront Supported Custom Ablation (WASCA) aberrometer (Carl Zeiss Meditec) preoperatively and at 1 month and 1 year postoperatively. RESULTS: Mean flap thickness was 155 +/- 13 microm in the thick flap group and 112 +/- 11 microm in the thin flap group. Mean root-mean-square of higher order wavefront aberrations were changed for the different test times in the cornea (F = 29.9, P < .0001) and the whole eye (F = 48.0, P < .0001). There was no significant difference between the two flap groups for the cornea (F = 0.76) or for the whole eye (F = 0.07). Similar results were observed for higher order Zernike aberrations such as spherical aberration and comas. CONCLUSIONS: The results suggest higher order wavefront aberrations induced by LASIK are independent of flap thickness. Complications in visual outcome for patients with different flap thickness should be attributed to factors other than aberrations.

[Influence of diameter of optical zone ablation on LASIK-induced higher order optical aberrations in myopia].

OBJECTIVE: To analyze the effects of optical zone ablation diameter on LASIK-induced higher order optical aberrations in myopia. METHODS: Four hundred and sixty-one eyes of 236 patients treated with LASIK for myopia were divided into high, moderate and low myopia group according to preoperative spherical equivalent diopter. In each group, eyes were divided into four subgroups according to optic zone ablation diameter. Before and after surgery 6 months, monochromatic wavefront aberrations of each eye were objectively measured using WASCA Analyzer Aberrometer. F test and q test were used to analyze the difference of total high order, horizontal coma, vertical coma, and spherical aberrations among four subgroups in each group at 4, 5, and 6 mm pupil size. RESULTS: Before surgery no significant difference of higher order aberrations among four subgroups was found. After surgery, there was significant difference of total high order, and spherical aberrations among four subgroups. Total high order, and spherical aberrations in larger optical zone ablation diameter subgroup were significantly lower than that in smaller one. The difference was significant at 4, 5, and 6 mm pupil size in high myopia group, and 6 mm pupil size in low myopia group. At 6 mm pupil size, the difference was significant between each subgroup in high myopia group and subgroup I and subgroup IV in low myopia group. There was no significant difference of horizontal coma, and vertical coma aberrations among four subgroups. CONCLUSIONS: Optical zone ablation diameter has influence on LASIK-induced higher order optical aberrations. Larger optical zone can decrease total higher order and spherical aberrations after LASIK. The effects are more significant in high myopia group than in low myopia group.

[Effects of flashing light on ocular growth and development of myopia in pigmented guinea pigs].

OBJECTIVE: To investigate the effects of flashing light exposure on ocular growth and development of myopia in guinea pigs. METHODS: Thirty 4-week-old pigmented guinea pigs were randomly divided into three groups. Animals in group I were reared with the flashing light continuously and lasted for 6 weeks. The flashing frequency was 15 times per minutes and every flash includes 2 seconds light on and 2 seconds dark. Animals in group II and III were reared with normal light on, and the illumination cycle was 12 hours light/12 hours dark in group II and 24 hours light in group III. After 6 weeks, the effects of flashing light on eye development were assessed by cycloplegic retinoscopy, a-scan ultrasonography and eye weight. The histopathology changes of sclera, choroids and retina in posterior pore of the eye were examined using light microscope and transmission electron microscope. RESULTS: At the end of the treatment period, guinea pigs reared in flashing light exhibited -7.00 D myopia, eye axial elongated 0.56 microm, and the weight increased 68 mg. The histopathology examination showed that the posterior sclera fibroblast become more active, the cell number increased, and the place between fibers became larger, the posterior choroids became thinned, and the outer membrane of photoreceptor cells became shorter and irregular, when compared with the control groups. CONCLUSION: Flashing light can promote ocular growth and induce myopia in pigmented guinea pigs.

[Effect of time limited form deprivation on the development of myopia in guinea pigs].

OBJECTIVE: To investigate the effect of time limited form deprivation on the development of form-deprived-myopia (FDM) in guinea pigs. METHODS: Four-week-old guinea pigs (n = 20) were randomly divided into four groups. Group I was used as normal control without any treatment. In group II-IV, unilateral form deprivation was produced with eye patch for 4 weeks. In group II, eye occlusion was fitted continuously. In group III and IV, occlusion was removed each day for 1 or 4 hours. Refractive development was monitored by retinoscopy and A-scan ultrasonography before and after experiment. RESULTS: After 4 weeks, varied degree of axial myopia was developed in the groups II and III with eye occlusion. Continuous form deprivation produced -5.49 D of relative myopia and the fellow eyes produced +0.76 D of relative hyperopia. One hour of unrestricted vision was sufficient to reduce the degree of FDM by about 50%. The eyes allowed 4 hours of unrestricted vision did not result in myopia. CONCLUSION: Long periods of form deprivation can be counterbalanced by quite short periods of unrestricted vision.