Retinal Neuroprotection against Ischemic Injury Mediated by Intraocular Gene Transfer of Pigment Epithelium-Derived Factor

PURPOSE

To determine whether intraocular gene transfer of pigment epithelium-derived factor (PEDF) protects the retina from ischemia-reperfusion injury.

METHODS

Four days before induction of pressure-induced ischemia, Lewis rats received intravitreous injection of 3 x 10(9) particles of an adenovirus vector expressing PEDF (AdPEDF.11) in one eye and 3 x 10(9) particles of an empty adenovirus vector (AdNull.11) in the contralateral eye. Seven days after reperfusion, eyes were enucleated and processed for morphometric analysis. Apoptotic cells stained by TdT-dUTP terminal nick-end labeling (TUNEL) in the retina were counted 12 hours after initiation of reperfusion. Retina levels of PEDF were measured by enzyme-linked immunosorbent assay.

RESULTS

PEDF levels in retinal homogenates from eyes receiving AdPEDF.11 injection were well above the background levels in the untreated baseline and control eyes (P = 0.04). Retinal thickness was preserved in AdPEDF.11-treated eyes. Retinal cell density was significantly greater in the ganglion cell layer (GCL; P = 0.014), inner nuclear layer (INL; P = 0.008), and outer nuclear layer (ONL; P = 0.008) of AdPEDF.11-treated eyes compared with the corresponding layers in AdNull.11-treated eyes. AdNull.11-treated eyes also had significantly more TUNEL-positive cells in these layers than AdPEDF.11-treated eyes (P < 0.05).

CONCLUSIONS

Adenoviral vector-mediated intraocular expression of PEDF significantly increases cell survival after ischemia-reperfusion injury of the retina. The protective effect may result from inhibition of ischemia-induced apoptosis. This study provides proof of concept for a gene transfer approach directed at interrupting programmed cell death induced by retinal ischemic insult.

Transpupillary thermotherapy threshold parameters: funduscopic, angiographic, and histologic findings in pigmented and nonpigmented rabbits

PURPOSE

To evaluate the effect of pigmentation on threshold fluence levels, needed to produce visible and angiographic lesions, of transpupillary thermotherapy (TTT) in rabbits.

METHODS

Six pigmented and nine nonpigmented rabbits underwent TTT with an 810-nm diode laser coupled to a slit-lamp biomicroscope using a spot size of 2 or 3 mm. The power ranged from 80 to 200 mW with 1 to 3 minutes of laser exposure for pigmented rabbits and 750 to 1800 mW with 1 minute of exposure for albino rabbits. These parameters were also evaluated after compression of the globe using the contact lens to induce blanching of the optic nerve head. After the experiment, the eyes were enucleated under deep anesthesia, and the animals were killed immediately.

RESULTS

In pigmented rabbits, the threshold fluence with the 2-mm spot size was 229 J/cm2 without compression and 153 J/cm2 with compression. With the 3-mm spot size, the threshold decreased from 200 to 150 mW as the duration of exposure lengthened (2 or 3 minutes), increasing the fluence from 170 to 382 J/cm2. In nonpigmented rabbits, the threshold fluence with the 2-mm spot size was 2,865 J/cm2 without compression and 2,674 J/cm2 with compression. With the 3-mm spot size, the threshold fluence of 1,528 J/cm2 was not affected by compression. Histopathologic studies showed transretinal damage at the lowest levels necessary to achieve angiographic evidence of a treatment lesion or a barely visible funduscopic lesion at the time of treatment.

CONCLUSIONS

Nonpigmented rabbits required more than a 12-fold increase in total TTT fluence compared with pigmented rabbits with the 2-mm spot size and a ninefold increase with the 3-mm spot size. Inner and outer retinal damage was seen histopathologically at these levels.

Transpupillary thermotherapy threshold parameters: effect of indocyanine green pretreatment

PURPOSE

To evaluate the effect of combined treatment with systemic indocyanine green (ICG) on threshold fluence levels of transpupillary thermotherapy (TTT) in rabbits.

METHODS

Four pigmented rabbits and 13 nonpigmented rabbits were studied. TTT was performed on normal rabbit choriocapillaris using an 810-nm diode laser via slit-lamp biomicroscope delivery through a Goldmann macular lens. Laser spot size, power, and duration of laser exposure were varied to achieve a range of TTT fluences for threshold testing in both albino and pigmented rabbit fundi. Intravenous ICG pretreatment at doses of 0.41 to 10 mg/kg was initiated at varying times before TTT treatment. After the experiment, the eyes were enucleated under deep anesthesia, the animals were killed, and the eyes were prepared for light microscopy.

RESULTS

When intravenous ICG pretreatment was employed, there was a dose-dependent decrease in the TTT fluence threshold as compared with known threshold values. At threshold fluences, histopathologic sections revealed damage to all layers of the retina in addition to choriocapillaris damage.

CONCLUSION

Intravenous ICG pretreatment can be used to lower the TTT threshold fluence and irradiance required to create angiographically visible lesions in the normal rabbit choriocapillaris. Damage was seen in all layers of the retina and choriocapillaris at threshold levels when TTT was used alone or in combination with ICG pretreatment.

Retinal oxygen saturation levels in patients with central retinal vein occlusion

PURPOSE

To validate the efficacy of Fourier transform-based spectral retinal imaging (SRI) in quantifying retinal ischemia.

DESIGN

Prospective, observational case series.

PATIENTS AND METHODS

Eleven eyes of 10 patients with central retinal vein occlusion (CRVO) and 4 fellow unaffected eyes of selected patients were examined by both fluorescein angiography and SRI. The fluorescein angiograms were correlated with oxygen saturation maps that were calculated from the SRI.

RESULTS

Oxygen saturation levels in the fundus were shown as color grading in 35 degrees fundus images processed by SRI. This grading correlated well with the severity of CRVO, as estimated by fluorescein angiography.

CONCLUSIONS

The severity of circulatory disturbances in CRVO may be graded by applying SRI.

The ultra-late phase of indocyanine green angiography for healthy subjects and patients with age-related macular degeneration

PURPOSE

To compare the characteristics of residual fundus fluorescence observed in the ultra-late phase of indocyanine green (ICG) angiography, in normal subjects and in patients with age-related macular degeneration (ARMD).

METHODS

ICG angiography was performed on 38 patients, 21 had ARMD, 9 were normal subjects aged >62, and 8 were normal subjects aged <36. The intensity and pattern of fluorescence from angiograms obtained in the ultra-late phase, 24 hours after dye injection, was also recorded and analyzed.

RESULTS

In the ultra-late phase, 95% of ARMD eyes with CNV showed geographic hypofluorescent lesions. All of the CNV that could be delineated with fluorescein and/or ICG angiography were located in these geographic lesions. In 73% of ARMD eyes without CNV, these hypofluorescent lesions occurred, while age-matched normal subjects had no hypofluorescent lesions. The mean intensity of fluorescence in the normal older subject group was significantly higher than that seen in the normal young subject group.

CONCLUSIONS

Increased fluorescence, associated with older subjects, in the ultra-late phase of ICG angiography may reflect aging changes in the chorioretinal complex. Geographic hypofluorescent areas, demonstrated only in the ultra-late phase, associate with ARMD and may represent areas predisposed to CNV development.

Fish oil (polyunsaturated fatty acid) prevents ischemic-induced injury in the mammalian retina

The long-chain polyunsaturated omega-3 fatty acid docosahexaenoic (22:6n-3) acid (DHA) accumulates in rod outer segment disks and synaptic terminals. It has been thought to play an important role in disordering disk membranes and in providing an adequate environment for conformational rhodopsin changes and in modifying the activity of retinal enzymes. The decrease of DHA content in the retina has been shown to affect visual function in monkey. In rat retina, prolonged light exposure has produced reduction of DHA content in rod outer segments. The authors found that when DHA was administered before ischemia, it diminished pressure-induced retinal damage. The recovery of electroretinographic amplitudes in DHA-pretreated eyes was significantly greater than those in the control eyes after 4 hr of reperfusion. The histopathologic study of control eyes showed cell swelling and cell nuclei pyknosis in the inner nuclear layer after 4 hr of reperfusion and in TUNEL-positive cells in the inner and outer nuclear layers after 24-72 hr of reperfusion. The DHA pre-treated eyes had fewer pyknotic nuclei and vacuolated spaces in the inner nuclear layer and no TUNEL-positive cells for up to 72 hr of reperfusion. The precise role of the polyunsaturated n-3 fatty acid has not been identified in the retina and other tissues. Our findings showed that DHA probably prevented sensory retina from ischemic-reperfusion cell damage not only by inhibiting the formation of hydroxyl radicals, but also by reducing the non-NMDA responses or the inflammatory responses.

[Quantitative analysis of indocyanine green angiography in multifocal posterior pigment epitheliopathy and its related diseases]

PURPOSE

To clarify the indocyanine green(ICG) angiographic features in multifocal posterior pigment epitheliopathy(MPPE), we measured the maximum diameter of the choroidal vein and mean fluorescence intensity within the vascular arcade.

METHODS

ICG angiography was performed in 40 eyes of 20 patients with MPPE and 10 age-matched normal controls, and quantified by IMAGEnet.

RESULTS

The mean maximum choroidal venous diameter was 544 +/- 162(mean +/- standard deviation) microns in eyes with MPPE and 278 +/- 55 microns in healthy age-matched control eyes. The mean fluorescence intensity was 106.9 +/- 52.5 and 86.5 +/- 32.5, respectively. Both the mean maximum choroidal venous diameter and the mean fluorescence intensity showed statistical difference between the two groups. In contrast, there was no statistically significant difference between the eyes with serous retinal detachment and without detachment in the MPPE group.

CONCLUSIONS

These results show that choroidal venous dilation and choroidal hyperfluorescence in MPPE are clearly distinguished from choroidal aging changes. Additionally, these pathological angiographic changes seemingly do not delineate the activity of MPPE, but demonstrate the background factor of the pathogenesis of MPPE.

[Retinal thickness and changes with age]

PURPOSE

We studied the morphological changes occurring with aging in the macula using optical coherence tomography(OCT).

METHODS

Forty-seven eyes from 47 normal volunteers were studied. The subjects ranged in age from 21 to 79 years and their refractive errors were within +/- 3.00 diopters. The measurement of the retinal thickness was done by OCT. The retinal thickness was evaluated at five points: the foveola, and 1 mm superior, inferior, nasal, and temporal to the foveola. The axial length of the eye and the refraction were also measured in all subjects.

RESULTS

The retinal thickness was 142 +/- 15 microns at the foveola, 257 +/- 18 microns at the superior point, 255 +/- 18 microns at the inferior point, 246 +/- 20 microns at the temporal point, and 261 +/- 21 microns at the nasal point (mean +/- standard deviation). All points except the foveola showed reduced retinal thickness with age. Thus, attenuation of the retinal thickness in the parafoveal area was correlated significantly with age. However, no change in the retinal thickness at the foveola was observed with increasing age. Neither axial length nor refractive error biased this result.

CONCLUSION

Our results demonstrated that the macular thickness changes with aging, but no obvious change could be detected in the foveola.

Photodynamic therapy of experimental choroidal neovascularization with a hydrophilic photosensitizer: mono-L-aspartyl chlorin e6

PURPOSE

To demonstrate the selective localization of the hydrophilic photosensitizer mono-L-aspartyl chlorin e6 (NPe6) in experimental choroidal neovascularization in nonhuman primate eyes.

METHODS

Sixty-seven experimental choroidal neovascular lesions (CNV) were created in the fundi of Macaca monkeys using the modified Ryan's model and documented by fluorescein and indocyanine green angiography. To determine the biodistribution of NPe6 and the optimal timing of laser irradiation after dye administration, NPe6 angiography and fluorescence microscopy with NPe6 were performed. Photodynamic therapy (PDT) was performed at various dye doses (0.5-10.0 mg/kg) and laser fluences (7.5-225.0 J/cm2) on the CNV and on 10 areas of normal retina and choroid. Treatment outcomes were assessed by fluorescein and indocyanine green angiography and confirmed by light and electron microscopy.

RESULTS

NPe6 fluorescence microscopy demonstrated intense fluorescence of CNV and retinal pigment epithelial cells. Choroidal vessel walls and outer retina adjacent to CNV fluoresced moderately; retinal vessel walls and microcapillaries had trace fluorescence. The fluorescence of CNV lesions on fluorescein angiography became stronger than that of retinal vessels 20-60 minutes after dye injection. Choroidal neovascular lesion closure was achieved with NPe6 PDT without significant damage to the sensory retina. Histology demonstrated necrosis of CNV endothelial cells with minimal damage to surrounding tissues.

CONCLUSIONS

NPe6 PDT selectively localizes to experimental CNV in nonhuman primates, resulting in occlusion of CNV with sparing of the neurosensory retina.

Retreatment effect of NPe6 photodynamic therapy on the normal primate macula

PURPOSE

To evaluate the safety and efficacy of repeated photodynamic therapy (PDT) with mono-L-aspartyl chlorin e6 (NPe6) on normal primate fovea and choroid.

METHODS

Macaca fuscata monkeys were used as experimental subjects. Mono-L-aspartyl chlorin e6 at a dose of 2 mg/kg was administered by intravenous infusion. Laser irradiation was applied within 5 minutes using a 664-nm diode laser at a power output of 5.9 mW (750 mW/cm2), spot size of 1,000 microm, and time of 10 seconds. This resulted in a fluence of 7.5 J/cm2. Three consecutive PDT treatments at 2-week intervals were applied over the center of the fovea and posterior fundus near the arcade vessels of each eye. The animals were killed and the eyes were enucleated for histologic study 2 weeks after the last treatment.

RESULTS

Limited changes could be observed in the sensory retina under light microscopy. Photoreceptor cells and outer segments were not damaged, even after repeated PDT. Proliferation and duplication of the retinal pigment epithelial cells were common findings. A plaque of fibrous tissue was present, interwoven with retinal pigment epithelial cells in eyes that received repeated PDT. The retinal vessels remained patent even after three sessions of PDT. However, occlusion of the choriocapillaris and the large choroidal vessels was observed after repeated PDT treatment.

CONCLUSION

Repeated PDT of healthy nonhuman primate fundi using a hydrophilic photosensitizer (NPe6) shows preservation of the neurosensory retina components and architecture with damage confined to the retinal pigment epithelium and choriocapillaris.

[Clinical dose finding study of indocyanine green to detect choroidal neovascularization in patients with exudative age-related macular degeneration]

PURPOSE

To evaluate the proper clinical dosage of indocyanine green(ICG) in angiography for detecting choroidal neovascularization(CNV) of exudative age-related macular degeneration(AMD).

SUBJECTS AND METHODS

Indocyanine green angiography (IA) was performed using a randomized crossover method with two different doses on two occasions. Ease of detection, side effects and clinical serum data were also evaluated.

RESULTS

Among the 39 eyes, detection of CNV using 12.5 mg and 25 mg was most effective in 21 and 31 eyes respectively, showing a statistically significant difference. Slight vomiting was observed temporarily in one patient who had taken 25 mg.

CONCLUSION

A dose of 25 mg is appropriate for detection of CNV of exudative AMD and this dosage raises no safety concerns.

Aging changes of the choroidal dye filling pattern in indocyanine green angiography of normal subjects

PURPOSE

To study the aging changes in the choroid of healthy volunteers with indocyanine green (ICG) angiography.

METHODS

Video ICG angiography with adjunctive computer-assisted image analysis was performed on 35 eyes of 30 healthy volunteers (age range, 21-81 years; mean +/- standard deviation, 50.5 +/- 16.2 years) to observe the aging changes of the choroid.

RESULTS

In patients in the second and third decades of life, the subfoveal choroidal arterioles fluoresced initially with subsequent rapid filling of the feeding arterioles and choriocapillaris. The watershed zone was clearly observed. In patients older than age 50, the choroidal vasculature filled more slowly. Eventually, the margin of the watershed zone became blurred. The quantitative analysis showed that the number of choroidal arterioles and the fluorescent intensity in the macular region were reduced with age (P < 0.005). In the early venous phase, hypofluorescent patches seen in all ages increased in size and number and remained with aging. The mean fluorescence intensity was not correlated statistically with age.

CONCLUSIONS

The features of normal aging patterns of the choroid that we investigated are essential to the interpretation of ICG angiography and may help in understanding the physiologic and pathologic conditions of the choroidal circulations and the choroid and retina themselves.

Toxicity of the photosensitizer NPe6 following intravitreal injection

BACKGROUND AND OBJECTIVE

To determine the retinal toxicity of mono-L-aspartyl chlorin e6 (NPe6) following intravitreal injection.

METHODS

Twelve Dutch-belted rabbits divided into 5 experimental groups (n=2 each) were injected intravitreally with 6.25, 12.5, 25, 50, or 100 microg of NPe6; one control group (n=2) was injected with intravitreal normal saline. One eye in each rabbit was sutured shut to test the effect of light exposure. Fundus photography and electroretinograms were performed before treatment and 2 days, 1 week, and 2 weeks after injection. Animals were euthanized and the eyes enucleated for histopathologic analysis.

RESULTS

After 1 week, 4 uncovered eyes given 50 and 100 microg had central retinal vein occlusion and varying degrees of retinal hemorrhage. RPE proliferation was seen in the covered eyes given 50 or 100 microg. Electroretinograms revealed absent retinal response at 100 microg and mild toxicity at 50 microg, but no change from normal at doses of < or = 25 microg of NPe6.

CONCLUSIONS

Intravitreal doses of < or = 25 microg NPe6 caused little or no apparent toxicity; however, toxicity was significant at doses of 50 microg and 100 microg.

Quantitative Analysis of Indocyanine Green Angiographic Image in Central Serous Chorioretinopathy

Purpose: To disclose the possible involvement of choroidal vascular change in developement of central serous chorioretinopathy (CSC).Methods: Indocyanine green (ICG) angiography was performed in 31 eyes with acute CSC, and 21 eyes from normal subjects. The maximum diameter of the choroidal veins and intensity of background fluorescence in the posterior fundus with ICG video images were measured for further analysis using IMAGEnet((R)) (Topcon). Then the results from CSC affected eyes, their fellow eyes, and normal eyes were compared. Aging factors were taken into consideration when we analyzed the data.Result: The maximum diameters of the choroidal veins were larger in both affected and fellow eyes than in the normal eyes (P <.001), and had a positive correlation with aging particularly in fellow eyes (r = 36). Both in the affected and fellow eyes, the background fluorescein intensity in the posterior pole of the late phase images was lower than in the normal eyes (P <.001), and was correlated with aging (r = 0.28, r = 0.43).Conclusion: This quantitative study showed that choroidal venous dilatation and the residual background fluorescence in the posterior fundus might be positive findings reflecting the pathogenesis of CSC.

Thickness of Retinal Nerve Fiber Layer Decreases after Vitreous Surgery for Idiopathic Macular Hole

Purpose: The alteration of the retinal nerve fiber thickness (NFLT) before and after vitreous surgery for a macular hole in cases with or without visual field defects was investigated.Methods: The NFLT of 23 eyes with idiopathic macular hole was measured with scanning laser polarimeter up to 12 months after surgery. The NFLT was divided into superior, inferior, nasal, and temporal quadrants. The mean NFLT of each quadrant was analyzed statistically and compared to the results of visual field tests.Results: In all cases, the NFLT decreased significantly up to 3 months after surgery, but increased gradually up to 12 months. In cases with visual field loss, the thickness of the nerve fiber layer that corresponds to the visual field defect diminished strongly, in contrast with other quadrants. Even in cases without visual field loss, the NFLT decreased significantly a month after surgery, especially in the nasal and inferior quadrants.Conclusion: This study demonstrates that the thickness of retinal nerve fiber layer decreases at least one month after surgery, even in cases without visual field defect. This may suggest the existence of a subclinical complication of vitreous surgery.

[Quantitative analysis of indocyanine green angiographic image in central serous chorioretinopathy]

PURPOSE

To disclose the possible involvement of choroidal vascular change in development of central serous chorioretinopathy (CSC).

METHODS

Indocyanine green (ICG) angiography was performed in 31 eyes with acute CSC, and 21 eyes from normal subjects. The maximum diameter of the choroidal veins and intensity of background fluorescence in the posterior fundus with ICG video images were measured for further analysis using IMAGEnet (Topcon). Then the results from CSC affected eyes, their fellow eyes, and normal eyes were compared. Aging factors were taken into consideration when we analyzed the data.

RESULT

The maximum diameters of the choroidal veins were larger in both affected and fellow eyes than in the normal eyes (p < 0.001), and had a positive correlation with aging particularly in fellow eyes (r = 0.36). Both in the affected and fellow eyes, the background fluorescein intensity in the posterior pole of the late phase images was lower than in the normal eyes (p < 0.001), and was correlated with aging (r = 0.28, r = 0.43).

CONCLUSION

This quantitative study showed that choroidal venous dilatation and the residual background fluorescence in the posterior fundus might be positive findings reflecting the pathogenesis of CSC.

Threshold and retreatment parameters of NPe6 photodynamic therapy in retinal and choroidal vessels

BACKGROUND AND OBJECTIVE

To determine the threshold fluence for producing choroidal and retinal vascular occlusion with mono-L-aspartyl chlorin e6 (NPe6) photodynamic therapy (PDT) during primary treatment and the effect of retreatment.

METHODS

Primary treatment: Rats, rabbits, and monkeys underwent NPe6 PDT to determine the threshold fluences for choroidal and retinal vessel occlusion. The threshold was determined by analyzing fluorescein angiograms for areas of nonperfusion. Retreatment: Dutch-belted rabbits underwent NPe6 PDT followed by fluorescein angiography. Rabbits were retreated one week later at the same parameters.

RESULTS

Fluence levels and vascular damage thresholds were always higher for retinal than for choroidal vascular occlusion. Retreatment caused choroidal vessel closure at all tested fluences but retinal capillaries closed only at a fluence > 17.7 J/cm2.

CONCLUSION

NPe6 PDT has a lower threshold to occlude choroidal vessels than retinal vessels. The cumulative effect of retreatment does not damage retinal vessels unless the threshold is exceeded during a single retreatment session.

Dome-shaped detachment of premacular vitreous cortex in macular hole development

PURPOSE

To clarify the role of the posterior vitreous cortex in macular hole development, we evaluated the follow-up findings of clinical observations and optical coherence tomography (OCT) images of macular holes in early stage.

METHODS

The vitreoretinal tomography was examined and followed in eyes with stage 1 and 2 macular holes with OCT.

RESULTS

The posterior cortical vitreous was identified in 12 of 17 eyes with early-stage macular holes by OCT (71%). In these eyes, the detached posterior vitreous appeared to be merged to the fovea and the disc. The vitreoretinal separations showed typically dome-shaped. A long scan along the papillomacular axis also delineated the posterior vitreous face as dome-shaped perifoveal vitreous detachment with adhesion to the fovea and disc. Repetitive OCT examinations clearly demonstrated the course of development of the macular hole.

CONCLUSIONS

The dome-shaped vitreoretinal separation seen with OCT gives rise to an idea that the posterior vitreous cortex may not be taut but slack, and would not cause a continuous tractional force even in early-stage macular holes. This finding brings us an idea that the tangential traction at the fovea may be generated by fluid movements, rather than by contraction of the cortical vitreous.

Threshold power levels for NPe6 photodynamic therapy

OBJECTIVE

To determine the threshold power levels for producing retinal and choroidal vascular occlusion using mono-L-aspartyl chlorin e6 (NPe6) photodynamic therapy; to evaluate its efficacy with longer intervals between photosensitizer injection and laser application; to determine the elapsed time between light application and appearance of angiographic changes.

METHODS

Pigmented and nonpigmented rabbits were injected intravenously with 2 mg/kg of NPe6 before laser irradiation of the retina-choroid. Group 1 was treated at increasing power levels; fluorescein angiograms were obtained at each fluence. Group 2 animals were exposed to laser irradiation at 5 minutes, and 1 and 3 hours postinjection to determine (by fluorescein angiography 24 hours post-treatment) if increasing the interval affected outcome. Group 3 animals underwent fluorescein angiography at 30 minutes, 1 hour, 2 hours, and 24 hours posttreatment to document the time between laser application and subsequent vessel closure.

RESULTS

Choroidal vessel occlusion was angiographically evident in all lesions at fluences of > or = 2.65 J/cm2 in pigmented rabbits and at > or = 0.88 J/cm2 in nonpigmented rabbits. Lesion diameter decreased as the time between injection and treatment increased. Vessel occlusion was documented at least 2 hours after treatment.

CONCLUSION

Choroidal vessel occlusion can occur at very low fluence.

[Thickness of retinal nerve fiber layer decreases after vitreous surgery for idiopathic macular hole]

PURPOSE

To investigate the alteration of the retinal nerve fiber thickness (NFLT) before and after vitreous surgery for a macular hole in cases with or without visual field defects.

METHODS

The NFLT of 23 eyes with idiopathic macular hole was measured with scanning laser polarimeter upto 12 months after surgery. The NFLT was divided into superior, inferior, nasal, and temporal quadrants. The mean NFLT of each quadrant was analyzed statistically and compared to the results of visual field tests.

RESULTS

In all cases, the NFLT decreased significantly upto 3 months after surgery, but increased gradually upto 12 months. In cases with visual field loss, the thickness of the nerve fiber layer that corresponds to the visual field defect diminished strongly, in contrast with other quadrants. Even in cases without visual field loss, the NFLT decreased significantly a month after surgery, especially in the nasal and inferior quadrants.

CONCLUSION

This study demonstrates that the thickness of retinal nerve fiber layer decreases at least one month after surgery, even in cases without visual field defect. This fact may suggest the existence of a subclinical complication of vitreous surgery.