Responses of Postreceptoral Pathways Elicited by L- and M-Cone Isolating ON- and OFF-Electroretinograms in Glaucoma Patients

PurposeTo compare the electroretinographical (ERG) responses elicited by L- and M-cone isolating ON- and OFF-sawtooth stimuli in normal subjects and glaucoma patients.MethodsTwenty-one normal subjects and 44 primary open-angle glaucoma patients participated in the study. L- and M-cone isolating (18% cone contrast; 284 cd/m²) rapid ON- and rapid OFF-sawtooth (4 Hz) stimuli with two stimulus sizes (full-field (FF) and central 70° diameter) were generated using the triple silent substitution technique. ON- and OFF-response asymmetries were studied by adding the two (to obtain L-add and M-add responses). The initial positive (P) and subsequent late negative (LN) components of the L-add and M-add ERGs were compared between the subject groups and correlated with retinal nerve fiber layer thickness (RNFLT) and pattern ERG responses.ResultsThe responses to L-ON and to M-OFF stimuli and vice versa resembled each other particularly with 70° stimuli. The P_L-add amplitudes were not significantly different between the normal subjects and glaucoma patients, whereas the LN_L-add amplitude was significantly (P < 0.01) smaller in the glaucoma patients. Both P_M-add and LN_M-add were not significantly different between the subject groups. The PERG amplitude with 0.8° check sizes and the 0.8°/16° amplitude ratio (PERG ratio) were significantly (P < 0.05) different between the subject groups. The 70° LN_L-add amplitude and the 0.8° PERG amplitude were significantly correlated with RNFLT.ConclusionsThe ERGs to 70° cone isolating sawtooth stimuli reflect cone opponency. The cone opponent ERG responses were not significantly different between glaucoma patients and normal subjects. Luminance driven L-add responses were significantly different, indicating that central luminance signals are mainly affected in glaucoma.     

电生理测试作为早期青光眼诊断指标的横断面研究

明视负向反应(PhNR)和图形视网膜电图(PERG)的结果作为评估青光眼的诊断指标.10例对照组和15例早期青光眼患者接受了完整的眼科检查,包括视力测量,眼压(IOP)测量,眼底检查和视野检查.同时进行图形视网膜电图和全视野视网膜点图纪录.青光眼组的平均偏差和图形平均标准偏差显著较低(P＜0.001,P＜0.01).PERGN95,PhNR,b波以及PhNR/b波的幅值显著较低(P＜0.001).眼压升高降低了PERG与PhNR的振幅.     

Pattern electroretinogram in glaucoma and ocular hypertension

We recorded the pattern electroretinogram (PERG) to small (0.8°) and very large (15°) check sizes in normal subjects, in patients with early-stage glaucoma, and in patients with ocular hypertension. In glaucoma, the PERG amplitude was reduced. This reduction was more prominent for a check size of 0.8° as compared with 15° stimuli and for high (16/s) as compared with low (7.8/s) reversal rates. Using a discriminant analysis of the amplitudes for two different check sizes, we could distinguish the normal and the glaucoma groups with a specificity of 96% and a sensitivity of 91%. Of the ocular hypertension patients, 43% were classified as pathologic by the discriminant analysis. Thus multivariate analysis of the PERG may increase its diagnostic value.     

The glaucoma suspect: Differentiation of the future glaucoma eye from the non-glaucomatous suspect eye

Visual-field areas to a I_2e stimulus were measured planimetrically using an X-Y digitizer and a computer program. Sampling of normal subjects and patients suspected of having glaucoma was done at two points in time. Calculations of eye-wall stress were done using ultrasonic data and intra-ocular pressure (IOP) measurements from patient records. For those suspected of having glaucoma who developed chronic open-angle glaucoma (COAG), the time of transition was the second point in time. The visual field area was regressed against patient age at the two points in time. No difference in the regression slopes was found for the normal subjects and unchanged patients. The patients who did develop glaucoma were significantly different. The mean annual rate of visual-field change (rate of decay) was calculated and found to be 28.5 mm²/year for the normals, 153.5 mm²/year for the suspects, and 376.4 mm²/year for those patients who developed glaucoma. The rate of visual-field decay only correlated with patient age (P = 0.03) and eye-wall stress (P < 0.01) in the patients who developed glaucoma.     

Color Doppler imaging in ocular hypertension and open-angle glaucoma

Purpose To quantify the retrobulbar hemodynamics of patients with ocular hypertension and open-angle glaucoma and to compare it with that of normal subjects.Methods Nineteen eyes of 19 ocular hypertensive patients, 19 eyes of 19 open-angle glaucoma patients and 19 eyes of 19 normal subjects were recruited from our clinic and underwent color Doppler imaging evaluation of the ophthalmic, posterior ciliary, and central retinal arteries. The peak systolic and end-diastolic blood flow velocities and resistivity indices of all retrobulbar vessels were measured.Results The retrobulbar blood flow velocities were lower and resistivity indices were higher in all retrobulbar vessels in ocular hypertensive patients than in normal subjects. The differences, however, did not reach statistical significance (P>0.05). Glaucoma patients had lower end-diastolic velocities and higher resistivity indices than did normal subjects in the ophthalmic (P=0.003 and P=0.003, respectively), posterior ciliary (P=0.001 and P<0.001, respectively), and central retinal arteries (P=0.03 and P=0.04, respectively). Glaucoma patients had significantly lower end-diastolic velocity and higher resistivity index than did patients with ocular hypertension in the posterior ciliary artery (P=0.04 and P=0.001, respectively).Conclusions This study suggests that ocular hypertensive patients have more normal blood flow than do glaucoma patients, because all retrobulbar homodynamic measurements in ocular hypertension range between glaucoma and normal subjects. On the other hand, glaucoma is associated with blood-flow velocity reduction and resistivity index elevation in all retrobulbar arteries.     

Short-wavelength automated perimetry in patients with migraine

Background The aim was to investigate short-wavelength sensitivity deficits in patients with migraine.Methods Fifteen migraine and 18 age-matched healthy volunteers with normal ophthalmologic examination participated in this study. Migraine characteristics were graded by the Migraine Disability Assessment Questionnaire (MIDAS). All participants underwent SWAP (short wavelength amplitude perimetry) testing using a Humphrey field analyzer; there was a 30-2 presentation pattern.Results Short wavelength amplitude perimetry parameters for mean deviation (MD; p<0.0001) and pattern standard deviation (PSD; p<0.0001) were significantly worse in the migraine group. In the migraine group 53.3%. of eyes had glaucoma hemi-field tests (GHT) outside normal limits and 10 of these had early glaucomatous visual field loss. Statistically significant correlations were found between frequency of migraine attacks and MD (p=0.02; r=0.56) and PSD (p=0.03; r=0.41) and also between the MIDAS score and MD (p=0.03; r=0.49) and PSD (p=0.04; r=0.51). In all migraine cases with early glaucomatous visual field defect a corresponding site of the head was predominantly involved in headache (p=0.03).Conclusion Some patients with severe migraine have earlier defects on SWAP suggesting a common vascular insult of glaucoma and migraine, and all migraine cases with high MIDAS scores should be further evaluated for early glaucomatous visual field defects using SWAP.     

Multifocal Pattern Electroretinogram does not demonstrate localised field defects in glaucoma

Purpose: To determine if a multifocal PERG could be recorded in normals, and to examine changes in the multifocal PERG in glaucoma patients. To compare the ability of multifocal PERG and multifocal VEP responses in the same individuals to identify localised field defects in glaucoma. Methods: Using the VERIS Scientific^TM system multifocal PERGs were recorded from 19 sites of the visual field according to pseudo-random binary m-sequence. Twenty normals and 15 glaucoma subjects were tested. Multifocal pattern VEPs were also recorded in the glaucoma cases using a cortically scaled stimulus. Results: The second order kernel of the PERG shows a consistent signal. The overall PERG amplitude decreases with age in normals. In glaucoma the PERG amplitude was reduced across the field, but reductions did not correspond to the area of the scotoma. The VEP showed localised signal reductions in all 15 cases of glaucoma. Conclusion: A multifocal PERG can be recorded in normals. However it did not reflect localised ganglion cell losses, whereas the multifocal pattern VEP recorded to a very similar stimulus in the same individual did show losses in the scotoma area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pattern electroretinogram association with spectral domain-OCT structural measurements in glaucoma

Purpose

To describe the association between pattern electroretinogram (PERG) amplitude and spectral domain-optical coherence tomography (SD-OCT) macular thickness, retinal nerve fibre layer (RNFL) thickness and optic disc topography measurements.

Subjects and methods

Both eyes (n=132) of 66 glaucoma patients (mean age=67.9 years) enroled in the University of California, San Diego, CA, USA, Diagnostic Innovations in Glaucoma Study (DIGS) were included. Eyes were tested with PERG (Glaid PERGLA, Lace Elettronica, Pisa, Italy), RTVue SD-OCT (Optovue Inc., Fremont, CA, USA) GCC, and NHM4 protocols on the same day. Of the 66 enroled patients, 43 had glaucoma defined by repeated abnormal standard automated perimetry (SAP) results in at least one eye and 23 were glaucoma suspects defined by a glaucomatous-appearing optic disc by physicians'' examination in at least one eye and normal SAP results in both eyes. Associations (R ²) were determined between PERG amplitude (μV) and SD-OCT macular ganglion cell complex (GCC) thickness (μm), macular thickness (μm), macular outer retinal thickness (macular thickness minus GCC thickness) (μm), RNFL thickness (μm), neuroretinal rim area (mm²), and rim volume (mm³).

Results

PERG amplitude was significantly associated with GCC thickness (R ²=0.179, P<0.001), RNFL thickness (R ²=0.174, P<0.001), and macular thickness (R ²=0.095, P<0.001). R ² associations with other parameters were not significant (all P>0.624). Significant associations remained for GCC and average RNFL thickness when age and intraocular pressure at the time of testing were included in multivariate models (both P≤0.030).

Conclusions

PERG amplitude is significantly (but weakly) associated with macular GCC thickness, RNFL thickness, and macular thickness. The lack of association between PERG amplitude and macular outer retinal thickness supports previous results, possibly suggesting that that the PERG is driven primarily by retinal ganglion cell (inner retinal) responses.     

The pattern ERG in glaucoma: effect of pattern reversal time

Pattern reversals with a ramp-like temporal course evoke transient pattern electroretinograms (PERG) that are delayed and attenuated in comparison with responses evoked by a step-like course (abrupt pattern reversals). This delay depends on the reversal time and probably represents a measure for temporal characteristics of the activated retinal structures. A pattern reversal stimulator with adjustable reversa) periods (matrix of 8X14 rectangular red light emitting diodes, element size 2° X 1°, stimulus area 16° X 14°) was used to record transient PERGs from 20 glaucomatous eyes with early or moderate visual field damages (measured with computer perimetry). The q-wave (P1) amplitude difference between the glaucoma group and normal subjects with step-like reversal stimulation was not significantP=0.23). On the other hand, a highly significant separation (P< 0.0001) between both groups was possible using the P1 latency at ramp-like stimulation or the response latency shift between step and ramp-like stimulation (Pattern reversal time, 30 ms).     

孔源性视网膜脱离并发脉络膜脱离患者的角膜内皮形态学参数

目的：探讨孔源性视网膜脱离并发脉络膜脱离(RRD-CHD)患者的角膜内皮细胞形态学参数变化。

方法：连续收集RRD-CHD患者70例70眼,分为无高度近视组(A组)38眼38眼、高度近视组(B组)32例32眼,另收集正常组(C组)36例36眼。使用角膜内皮镜检测各组角膜内皮细胞最小面积(S_min)、最大面积(S_max)、平均面积、平均密度(CD)、细胞面积标准差(SD)、变异系数(CV)及六角形细胞比例(HG)。

结果：RRD-CHD患者和正常组的角膜内皮细胞CD、HG均有差异(P<0.001)。A组的CD与B组、C组均有差异(P<0.05),B组与C组有差异(P<0.001)。在A组中,SD、CV与眼轴(r_s=-0.426、0.494, 均P<0.01),CD与眼压、眼轴(r_s=-0.025、0.368, 均P<0.05),HG与病程(r_s=0.552, P<0.05)均相关。在RRD-CHD患者中,SD、CV与眼轴(r_s=0.236、0.159, 均P<0.05),HG与病程(r_s=0.142, P<0.05),S_max与眼压(r_s=-0.314, P<0.01)均相关。

结论：RRD-CHD患者持续低眼压状态下角膜内皮细胞的HG和CD均明显降低,眼轴、病程和眼压可影响角膜内皮的形态学参数。     

Association of n3 and n6 polyunsaturated fatty acids in red blood cell membrane and plasma with severity of normal tension glaucoma

AIM:To determine whether red blood cell (RBC) membrane and plasma lipids, particularly long-chain polyunsaturated fatty acids such as eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), arachidonic acid (AA) are significantly correlated with severity of normal tension glaucoma (NTG).METHODS:This study included 35 patients with NTG and 12 healthy normal control subjects, matched for age and sex with the study group. The stage of glaucoma was determined according to the Hodapp-Parrish-Anderson classification. Lipids were extracted from RBC membranes and plasma, and fatty acid methyl esters prepared and analyzed by gas chromatography-mass spectrometry (GC-MS).RESULTS:When RBC lipids were analyzed, the levels of EPA, the levels of DHA and the ratio of n3 to n6 were positively associated with the Humphrey Perimetry mean deviation (MD) score (r=0.617, P<0.001; r=0.727, P<0.001 and r=0.720, P<0.001, respectively), while the level of AA was negatively associated with the MD score (r=-0.427, P=0.001). When plasma lipids were analyzed, there was a significant positive relationship between the levels of EPA and the MD score (r=0.648, P<0.001), and the levels of AA were inversely correlated with the MD score (r=-0.638, P<0.001).CONCLUSION:The levels of n3 and n6 polyunsaturated fatty acids in RBC membrane and plasma lipids were associated with severity of NTG.     

应用MAIA微视野计评估青光眼黄斑部功能改变

目的:观察青光眼患者微视野特征,探讨微视野检测值与最佳矫正视力(BCVA)、标准自动视野检测指标和光学相干断层扫描(OCT)检测指标的相关性。方法:病例对照研究。纳入青光眼患者45例76眼,其中原发开角型青光眼15例25眼,慢性闭角型青光眼30例51眼;正常对照组40例76眼。所有受检眼进行了MAIA微视野、Humphrey视野、BCVA检测,并与OCT测量的结构指标进行相关性分析。结果:青光眼患者与正常人群相比,微视野测出的黄斑平均光敏感度(MS)、OCT测出的神经节细胞复合体(GCC)、神经纤维层(RNFL)厚度低于正常对照组,Humphrey视野计10-2程序测出的视野平均缺损(MD)、GCC局部丢失体积(FLV)、GCC整体丢失体积(GLV)、63%双曲线椭圆面积(BCEA)高于正常对照组。青光眼组MS与MD、FLV、GLV、BCVA(LogMAR)呈负相关(r_s=-0.839、-0.665、-0.530、-0.424,均P<0.01)。青光眼组MS与GCC、RNFL呈正相关(r_s=0.437、0.500,均P<0.01)...     

The pattern-elicited electroretinogram. I. A tool in the early detection of glaucoma?

The pattern-elicited electroretinogram (PERG) was recorded in 75 patients known with glaucoma, each one of them having a normal visual acuity, and compared with the results in normal test subjects. Although there is a great overlap between normal and glaucomatous eyes, a lower average amplitude and a delay in latency is recorded in the case of glaucoma. A correlation was sought between the PERG outcome on the one hand and different glaucomatous parameters (visual field loss, intraocular pressure, cup disc/ratio) on the other; this could only be confirmed for the cup/disc ratio. In beginning glaucoma the PERG is more often disturbed than the VECP.     

The response of blood flow velocity in the ophthalmic artery and blood flow of the finger to warm and cold stimuli in glaucomatous patients

Vasospasm appears to be a probable risk factor in the development of glaucoma. Transcranial Doppler (TCD) can detect vasospasm in cerebral vessels. It gives reproducible readings for ophthalmic artery blood velocity measurements. We used the TCD to measure peak flow velocity, mean flow velocity, and end-diastolic flow velocity in the ophthalmic artery and a laser Doppler flow meter to measure blood flow in the fingers of 17 patients with chronic open-angle glaucoma (COAG), 13 patients with normal tension glaucoma (NTG), and 8 nonglaucomatous subjects with normal eyes (normals). The opposite hand to that in which the measurements were made was challenged with warm (40°) and cold (4°) water. Five measurements of the ophthalmic artery velocity and finger flow were recorded: the first at baseline, the second during warming of the hand, the third after warming of the hand, the fourth when the hand was immersed in iced water, and the fifth after the hand was removed from the cold water. There was no detectable change in the ophthalmic artery blood velocities but significant decreases in the finger flow measurements when the opposite hand was immersed in cold water. These changes were present in all three diagnostic groups (P<0.001 for COAG;P<0.005 for NTG;P<0.05 for normals). The findings suggest a reflex vasospasm to cold in the finger circulation of most persons but no measurable changes in the ophthalmic artery.     

Pattern electroretinogram as a function of spatial frequency in ocular hypertension and early glaucoma

Pattern electroretinograms (PERGs) in response to 8.3 Hz alternating gratings (16.6 rev/sec) of different spatial frequencies were recorded in normal subjects as well as in patients affected by early glaucoma and ocular hypertension. In normal subjects the PERG response is spatially tuned, with a maximum at about 1.5 cycles/deg and attenuation at higher and lower spatial frequencies. In all cases of early glaucoma and in the great majority of cases of ocular hypertension the PERG was reduced, as compared with that of normal subjects, mainly in the medium range of spatial frequencies (at which the PERG has its maximal amplitude).     

Central corneal thickness in low-tension glaucoma

BACKGROUND: It is possible that the intraocular pressure (IOP) is underestimated in eyes whose central cornea is thinner than normal. The objective of this study was to determine and establish the significance of central corneal thickness in patients with low-tension (normal-tension) glaucoma compared with those with chronic open-angle glaucoma (COAG) or ocular hypertension and healthy eyes. METHODS: The study was carried out from February 1998 to May 1999. Central corneal thickness was measured by ultrasonic pachymetry and IOP was measured by Goldmann applanation tonometry in 25 patients with low-tension glaucoma (untreated IOP less than 21 mm Hg with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 80 patients with COAG (untreated IOP 21 mm Hg or greater with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 16 patients with ocular hypertension (untreated IOP 21 mm Hg or greater, with normal optic nerve head and no history of glaucoma or elevated IOP, and normal visual field on automated perimetry) and 50 control subjects (untreated IOP less than 21 mm Hg with normal optic nerve head and no history of glaucoma or elevated IOP). Analysis with Pearson's product-moment correlation was performed to determine the correlation of IOP and central corneal thickness, and one-way analysis of variance was used to compare corneal thickness between groups. RESULTS: The central cornea was significantly thinner in the low-tension glaucoma group (mean 513.2 mu [standard deviation (SD) 26.1 mu]) than in the COAG group (mean 548.2 mu [SD 35.0 mu]) and the control group (mean 556.7 mu [SD 35.9 mu]) (p < 0.001). No significant difference in corneal thickness was found between the COAG and control groups. The ocular hypertension group had significantly thicker corneas (mean 597.5 mu [SD 23.6 mu]) than the three other groups (p < 0.001). INTERPRETATION: Patients with low-tension glaucoma may have thinner corneas than patients with COAG and healthy subjects. This results in underestimation of their IOP. Corneal thickness should be taken into account when managing these patients to avoid undertreatment.     

The pattern electroretinogram and visual-evoked potential in glaucoma

The pattern electroretinogram (PERG) may reflect ganglion cell or inner retinal layer activity. The most sensitive spatial and temporal variables for testing patients with glaucoma have not yet been identified. Fifty-two glaucoma suspects, 51 glaucoma patients, and 28 normal subjects were studied with the PERG and VEP, using three repetition rates and three spatial frequencies. Fast Fourier transforms were calculated at each spatial frequency and reversal rate. An analysis of variance revealed that normals could be differentiated from ocular hypertension and glaucoma patients using the amplitude of the PERG (second and fourth harmonic). Abnormalities in phase of the PERG between groups were also detected. A discriminant analysis of all amplitude and phase data revealed that the phase shift of the response of the second harmonic at 11 alternations/s (15-min checks) and at 5.5 alternations/s (15-min checks) correctly identified 81% of the normal and 75% of the glaucoma patients. The phase shift determinations of the VEP revealed significant abnormalities using 2 and 1/2 standard deviation confidence limits. There was significant overlap in the pattern ERG amplitude and phase shift in all three groups.     

Pattern electroretinograms for the detection of neural loss in patients with permanent temporal visual field defect from chiasmal compression

Purpose To evaluate the ability of full-field and hemifield pattern electroretinogram (PERG) parameters to differentiate between healthy eyes and eyes with band atrophy (BA) of the optic nerve. Methods Twenty-six eyes from 26 consecutive patients with permanent temporal hemianopic visual field defects and BA of the optic nerve from previous chiasmal compression and 26 healthy subjects were studied prospectively. All patients were submitted to an ophthalmic examination including Humphrey 24-2 SITA Standard automated perimetry. Full-field and hemifield (nasal and temporal) stimulation transient pattern electroretinograms (PERG) were recorded using checkerboard screens. Amplitudes and peak times for the P50 and N95 as well as the overall P50+N95 amplitude were measured. The intraocular N95:P50 amplitude ratio was calculated. Comparisons were made using Student’s t-test. Receiver operating characteristic (ROC) curves were used to describe the ability of PERG parameters to discriminate the groups. Results Full-field P50, N95, and P50+N95 amplitude values were significantly smaller in eyes with BA than in control eyes (P < 0.001). Nasal and temporal hemifield PERG studies revealed significant differences in N95 and P50+N95 amplitudes measurements. No significant difference was observed regarding peak times or N95:P50 amplitude ratios. Nasal and temporal hemifield PERG values did not differ significantly in eyes with BA or in controls. Using the 10th percentile of normals as the lower limit of normal, 16 of 26 eyes were considered abnormal according to the best discriminating parameters. Conclusions Transient PERG amplitude measurements were efficient at differentiating eyes with BA and permanent visual field defects from normal controls. Hemifield stimulation PERG parameters were unable to detect asymmetric hemifield neural loss, but further studies are required to clarify this issue. Study registered on ClinicalTrial.gov number: NCT00553761     

The relationship between macular cell layer thickness and visual function in different stages of glaucoma

Purpose

To determine whether there were differences in the structure–function relationship between early and advanced glaucoma, and study the association between thickness of discrete macular cell layers, the thickness of the retinal nerve fiber layer, and visual field sensitivity.

Methods

In all, 71 eyes of 50 subjects (28 glaucoma patients and 22 normal control subjects) were included. Thickness of macular retinal nerve fiber layer (mRNFL), macular inner retinal layer (mIRL), and macular outer retinal layer (mORL) were measured from Stratus optical coherence tomography macular scans, using our previously published segmentation algorithm. Visual sensitivity loss was determined by mean deviation (MD) using Humphrey Visual Field Analyzer. The mean thickness for each layer from the normal control subjects, early, and advanced glaucoma groups was compared. In addition, a mixed model analysis was used to explore the relationship between structure–function, allowing for possible interaction with glaucoma stage.

Results

The mean mRNFL thickness in early and advanced glaucoma patients was significantly less than measurements in normal subjects (P<0.01). The mean mIRL thickness in advanced glaucoma was significantly less than normal subjects (P=0.04). The mean mORL thickness in early and advanced glaucoma was not statistically significant different from that of normal subjects (P>0.8). There was no statistically significant difference in macular structure–function relationship between the two glaucoma groups (P>0.05). Mean mIRL thickness was significantly associated with MD (P=0.04).

Conclusion

There was no significant difference in macular structure–function relationship between early and advanced glaucoma groups. Combined data from both glaucoma groups indicated that mIRL thickness was associated with visual sensitivity loss.     

Little correlation of the pattern electroretinogram (PERG) and visual field measures in early glaucoma

Pattern-electroretinograms (PERG) to checkerboard reversal at 16/s. 0.8° and 15° check size and visual fields (Octopus G1) were retrospectively analyzed in 40 eyes of 30 patients with early glaucoma. The mean visual field defect was calculated separately for the central 26°×34° covered by the PERG stimulus (MDc) and the more peripheral area (MDp) surrounding the stimulus. Deeper field loss was correlated with a reduced pattern electroretinogram amplitude (p<0.01 for both MDp and MDc), indicating that the pattern electroretinogram deteriorates as glaucoma advances. If the analysis was confined to those 18 eyes (16 patients) that had no field defect within the area covered by the PERG stimulus (normal MDc but abnormal MDp), 13 of these had an abnormal PERG amplitude (p<0.001). The results suggest that the PERG can reveal impairment of ganglion cell function that is not detected by conventional perimetry.