AIOS – Ophthalmic Education , Epidemiology & Prevention of Blindness Award
Dr. Punita Kumari Sodhi, S06682, Dr.Vidula, Dr. Goyal J L, Dr. Jugal Kishore
Ophthalmic Education, Epidemiology & Prevention of Blindness
PUNITA KUMARI SODHI,* DR. VIDULA RAO,* DR. J L GOYAL,* DR. JUGAL KISHORE**
Department of Ophthalmology, Guru Nanak Eye Centre &Maulana Azad Medical College, New Delhi & Department of Community Medicine, VardhmanMahavir Medical College &Safdarjung Hospital, New Delhi
ABSTRACT
Purpose-
To find diagnostic value of optical coherence tomography (OCT) and electroretinography (ERG) parameters in primary open angle glaucoma (POAG).
Materials and Methods-
The OCT and ERG parameters of 71 POAG eyes were compared with cup-disc ratio and visual field mean and pattern standard deviation (MD & PSD).
Results- Keeping cup-disc ratio, MD and PSD respectively as standard, highest sensitivity was found in focal loss of volume (FLV) (83.33% w.r.t. cup-disc ratio; 93.61% w.r.t. MD; 94.28% w.r.t. PSD), vertical cup-disc ratio (VCDR) (95.45%; 95.74%; 94.28%), infero-temporal quadrant (IT) (90.90%; 93.61%; 94.28%) and N95 amplitude (N95A) (96.96%; 95.74%; 94.28%) and highest specificity was found in average count (AvC) (60%; 70.83%; 77.77%), disc area (DA) (40%; 41.66%; 50%), nasal-upper quadrant (NU) (40%; 41.66%; 38.88%) and N95 latency (N95L) (60%; 66.66%; 52.77%).
Conclusion-
FLV, VCDR, IT and N95A are good screening tests and AvC, DA, NU and N95L have good diagnostic value.
INTRODUCTION
In glaucoma, retinal ganglion cell (RGC) death can be caused both by pressure-dependent damaging factors and pressure-independent damaging factors.1 RGC death is permanent since mammalian nerves do not regenerate. Thus in glaucoma, retinal ganglion cell survival can be enhanced by lowering down intraocular pressure (IOP), normalizing altered blood flow1 and by use of neurotrophic factors.1
Raised IOP results in an alteration of the blood supply to the optic nerve head to affect normal RGC function,2but it is the risk factor which is quite amenable to correction. Thus the primary aim of glaucoma treatment involves lowering of IOP.
Among the methods used to assess RGC function, electrophysiological tests (EPT) and automated perimetry, studies the functional aspects while optical coherence tomography (OCT) studies the structural aspects.2,3,4 It has been found that functional loss precede structural loss and a good correlation has been noted between the two as well as anatomical changes induced in optic nerve head due to glaucoma.4
The pattern electroretinogram (PERG) has been shown to be potentially useful as a measure of detecting early glaucomatous changes.5,6 Full-field flash ERG has been well established as a measure of photoreceptor and bipolar activity.However a response has been newly identified called photopic negative response (PhNR), has been found to be dependent on RGC activity.7 OCT measures the relative time-of-flight delay of a typically near infrared source after it is reflected by structures at different depths within tissue sample,3 thus it measures retinal nerve fibre layer (RNFL) changes and optic nerve head (ONH) parameters. These tests have been claimed to diagnose glaucomatous changes even before perimetric defects occur, so utilized for pre-perimetric diagnosis.
In this study, we evaluated the OCT and EPT parameters, before and after treatment of open angle glaucoma (OAG), attained by lowering IOP and compared these with normal values of Indian population. The studies investigating these testing techniques useful in detection of glaucoma have been limited5-31and none has studied their diagnostic value. In this study we have aimed to find the diagnostic values of various parameters which would tell about the sensitivity and specificity values of these parameters.
MATERIALSAND METHODS
A total of 71 eyes of newly diagnosed primary open angle glaucoma patients in the age group of 20–60 years were included in a nonrandomized interventional study without control group. This study was conducted in the Department of Ophthalmology, Guru Nanak Eye Centre, New Delhi from November 2014 to March 2016.
According to the available literatures, it is found (Niyadurupolaet al33) that lowering of IOP increased the amplitude of PERG by 54%. To find this difference whether significant or not at 95% confidence level, with 80% power, the sample size would be 82 eyes. Considering the attrition rate a total of 40 eyes were planned for this study. However, 71 eyes were included in the study.
The inclusion criteria were subjects of open angle glaucoma, in age group of 20-60 years and those who could attain best corrected distance visual acuity of at least 6/60 separately in each eye. The subjects who had undergone previous glaucoma surgery, subjects having retinal diseases, central nervous system disease or systemic disease like diabetes, hypertension, etc. which can influence the retinal ganglion cell function and confound results; subjects having any media opacity like corneal opacity, significant cataract, vitreous hemorrhage, etc.; and subjects with unreliable standard automated perimetry (SAP) results, were excluded from the study.
A detailed personal and family history to rule out significant ocular disease, retinal disease, central nervous system disease or systemic diseases like diabetes, hypertension, etc. was taken.
The subjects underwent detailed ocular examination including visual acuity, refraction for best corrected visual acuity (BCVA) for both distance and near (N6 in both eyes separately), IOP measurement by Goldmannapplanation tonometry, slit lamp examination to rule out any anterior or posterior segment abnormality and stereoscopic fundus examination on slit lamp using 90.0 D lens. For gonioscopy,Goldmann single mirror indirect gonioscope and a slit lamp viewing system was used to visualize angle. After cleaning the gonioscope and anesthetizing the cornea of patient, gonioscope was carefully placed over the cornea using coupling jelly. A 1 mm light beam was reduced to a very narrow slit and care was taken to avoid light falling on the pupil and to avoid accidental indentation during examination. The angle in each quadrant was graded using Shaffer’s grading. Stereoscopic optic disc photographs – both colourand red-free for retinal nerve fiber layer were taken on the Fundus camera after dilating the pupils. Central corneal thickness (CCT) was performed by A scan ultrasonography using SonomedPacScan 300AP.
Subjects underwent standard automated perimetry on the Humphrey’s Field Analyzer using the 24-2 testing protocol by SITA-Standard strategy.
Before initiation of treatment, a baseline examination with Humphrey’s Field Analyzer 24-2 testing, spectral domain OCT (Optovue version 4.0), flash ERG and PERG was done and parameters were recorded.
These were compared with normative data for our population group to find the sensitivity and specificity values.
OBSERVATIONS ANDRESULTS
The present study is nonrandomized interventional study without control group conducted in the Department of Ophthalmology, Guru Nanak Eye Centre, New Delhi. A total of 71 eyes of newly diagnosed primary open angle glaucoma patients in the age group of 20 – 60 years were included in study.
The mean age of our subjects was 52.20 ± 15.87 years and range being 20-60 years, with standard deviation of 11.47 yrs.The number of eyes of male subjects was 48 (66.6%) and female subjects was 23 (32.4%). (There was systemic disease in 19 (26.8%) and 52 (73.2%) did not have any systemic disease) (how many cases, eyes are 71 but no of patients?). Three (4.2%) had family history and 68 (95.8%) did not have any systemic disease (need correction). The number of eyes which received medical treatment was 60 (84.5%), surgical treatment was 10 (14.1%) and both was 1 (1.4%).The topical drops used for treatment included latanoprost, timolol, brimonidine, bimatoprost and travaprost. Target IOP was achieved in all the eyes.
The mean OCT “GCC average” before treatment was 80.53±12.91 and after treatment was 81.45 ±13.00 (mean difference being -0.92; 1.14% change; p=0.29, NS); mean OCT “GCC superior” before treatment was 82.57±12.39 and after treatment was 82.85 ±13.41 (mean difference being -0.28; 0.34% change; p=0.74, NS); mean OCT “GCC inferior” before treatment was 79.06±15.03 and after treatment was 80.79 ±14.74 (mean difference being -1.73; 2.19% change; p=0.11, NS); mean OCT “GCC S minus I” before treatment was 3.48±8.40 and after treatment was 2.94 ±9.89 (mean difference being 0.54; 15.52% change; p=0.60, NS); mean OCT “GCC FLV” before treatment was 7.15±5.09 and after treatment was 7.07 ±5.18 (mean difference being 0.09; 1.13% change; p=0.78, NS); and mean OCT “GCC GLV” before treatment was 18.19±10.94 and after treatment was 18.21 ±10.62 (mean difference being -0.01; 0.11% change; p=0.99, NS). There was no SS change in any of OCT GCC parameter induced by treatment of glaucoma.
The mean OCT ONH “Disc Area” before treatment was 2.10±0.14 and after treatment was 2.15 ±0.35 (mean difference being -0.05; increased by 2.38%; p=0.09, NS);mean OCT ONH “Cup Area” before treatment was 1.42±0.58 and after treatment was 1.34 ±0.60 (mean difference being 0.07; reduced by 5.63%; p=0.09, NS);mean OCT ONH “Rim Area” before treatment was 0.78±0.56 and after treatment was 0.87 ±0.57 (mean difference being -0.09; increased by 11.54%; p=0.09, NS); mean OCT ONH “Rim volume” before treatment was 0.08±0.12 and after treatment was 0.12 ±0.21 (mean difference being -0.04; increased by 42.86%; p=0.72, NS);mean OCT ONH “NH Volume” before treatment was 0.23±0.30 and after treatment was 0.26 ±0.32 (mean difference being -0.03; increased by 15.72%; p=0.19, NS); mean OCT ONH “Cup Volume” before treatment was 0.44±0.36 and after treatment was 0.39 ±0.37 (mean difference being 0.05; reduced by 10.91%; p=0.04, SS); mean OCT ONH “CD Ratio” before treatment was 0.68±0.21 and after treatment was 0.61 ±0.24 (mean difference being 0.07; reduced by 10.00%; p=0.01, SS); mean OCT ONH “HCD Ratio” before treatment was 0.85±0.15 and after treatment was 0.76 ±0.22 (mean difference being 0.09; reduced by 10.59%; p=0.003, SS); mean OCT ONH “VCD Ratio” before treatment was 2.24±12.19 and after treatment was 0.76 ±0.19 (mean difference being 1.48; reduced by 66.03%; p=0.31, NS); mean OCT ONH “RNFL average” before treatment was 86.59±18.37 and after treatment was 84.96 ±17.86 (mean difference being 1.63; reduced by 1.88%; p=0.16, NS); mean OCT ONH “RNFL Superior” before treatment was 88.28±20.64 and after treatment was 86.33 ±19.74 (mean difference being 1.95; reduced by 2.21%; p=0.28, NS); and mean OCT ONH “RNFL Inferior” before treatment was 85.21±20.65 and after treatment was 83.83 ±19.46 (mean difference being 1.37; reduced by 1.62%; p=0.26, NS). Among OCT ONH parameters, there was statistically significant change in OCT ONH Cup volume, CD Ratio and HCD ratio following treatment while rest of parameters did not get SS change after treatment.
The mean OCT RNFL (parapapillary) “SN” before treatment was 93.13±31.76 and after treatment was 92.56 ±31.26 (mean difference being 0.56; reduced by 0.61%; p=0.86, NS);mean OCT RNFL (parapapillary) “NU” before treatment was 62.18±23.04 and after treatment was 63.90 ±31.26 (mean difference being 0.56; increased by 2.77%; p=0.86, NS);mean OCT RNFL (parapapillary) “NL” before treatment was 59.24±19.60 and after treatment was 58.97 ±20.44 (mean difference being 0.27; reduced by 2.46%; p=0.85, NS);mean OCT RNFL (parapapillary) “IN” before treatment was 92.21±27.93 and after treatment was 92.65 ±27.80 (mean difference being -0.44; increased by 0.48%; p=0.87, NS);mean OCT RNFL (parapapillary) “IT” before treatment was 92.86±30.82 and after treatment was 93.61 ±31.89 (mean difference being -0.75; increased by 0.81%; p=0.82, NS);mean OCT RNFL (parapapillary) “TL” before treatment was 57.37±15.17 and after treatment was 64.80 ±61.36 (mean difference being -7.44; increased by 12.95%; p=0.31, NS);mean OCT RNFL (parapapillary) “TU” before treatment was 63.91±20.19 and after treatment was 62.03 ±21.05 (mean difference being 1.94; reduced by 2.94%; p=0.35, NS);mean OCT RNFL (parapapillary) “ST” before treatment was 98.32±28.80 and after treatment was 96.66 ±29.02 (mean difference being 1.66; reduced by 1.69%; p=0.68, NS);mean OCT RNFL (parapapillary) “average” before treatment was 79.86±18.42 and after treatment was 84.95 ±17.87 (mean difference being 5.09; increased by 6.37%; p=0.006, SS);mean OCT RNFL (parapapillary) “superior” before treatment was 80.86±21.15 and after treatment was 81.48 ±20.30 (mean difference being 0.62; increased by 0.77%; p=0.79, NS);and mean OCT RNFL (parapapillary) “inferior” before treatment was 78.93±18.42 and after treatment was 79.15 ±19.09 (mean difference being 0.22; increased by 0.28%; p=0.91, NS).Among OCT RNFL parameters, there was statistically significant change in OCT RNFL (parapapillary) “average” only due to effect of treatment while rest of parameters did not get SS change after treatment.
The mean PERG N35 latency before treatment was 35.73±6.91 and after treatment was 31.64 ±8.43 (mean difference being 4.09; reduced by 11.45%; p=0.00, SS);mean PERG P50 latency before treatment was 56.23±9.50 and after treatment was 54.50 ±10.18 (mean difference being 1.73; reduced by 3.08%; p=0.26, NS); mean PERG N95 latency before treatment was 96.01±15.52 and after treatment was 92.05 ±10.98 (mean difference being 3.95; reduced by 4.12%; p=0.08, NS);mean PERG P50 amplitude before treatment was 1.85±2.08 and after treatment was 2.49 ±2.38 (mean difference being -0.63; increased by 34.59%; p=0.03, SS);mean PERG N95 amplitude before treatment was 3.02±2.53 and after treatment was 3.29 ±2.89 (mean difference being -0.26; increased by 8.94%; p=0.48, NS);and mean PERG N95/P50 (amplitude) ratio before treatment was -2.79±9.17 and after treatment was -0.15 ±3.65 (mean difference being -2.63; increased by -94.62%; p=0.02, SS). Among PERG parameters, following treatment, there was statistically significant change in N35 latency, P50 amplitude and N95/P50 ratio while rest of parameters did not get significant change after treatment.
In order to find the diagnostic value, the pretreatment values of various diagnostic parameters were used to find the sensitivity and specificity values and is mentioned in the tables below.
| S. No. | Parameters | Sensitivity (%) | Specificity (%) |
| 1. | Cup disc ratio >4 =disease
GCC average (µm) GCC Superior (µm) GCC inferior (µm) GCC FLV% (µm) GCC GLV% (µm)
Optic nerve head Disc area Vertical Cup : Disc Cup area Rim area Average RNFL thickness
RNFL average (parapapillary)(µm) RNFL superior (µm) RNFL inferior(µm) TL(µm) TU(µm) ST(µm) SN(µm) NU(µm) NL(µm) IN(µm) IT(µm)
Pattern ERG P50 latency Pattern ERG N95 latency Pattern ERG P50 amplitude Pattern ERG N95 amplitude
A latency B latency A amplitude B amplitude PhNR amplitude
Visual Field Analysis MD Visual Field Analysis PSD |
16.66 77.27 80.30 83.33 81.81
43.93 95.45 92.42 84.84 86.36
86.36 81.81 86.36 84.84 77.27 89.39 83.33 72.72 77.27 83.33 90.90
83.33 50 95.45 96.96
89.23 80.00 27.66 43.08 83.08
68.18 50 |
60 40 40 20 40
40 20 40 20 20
20 20 20 40 0 40 40 40 0 0 20
20 60 40 0
28.57 42.86 88.00 57.14 57.14
60 60 |
Table 1- showing sensitivity and specificity of each testing technique w.r.t diagnostics of cup to disc ratio in fundus
| S. No. | Parameters | Sensitivity (%) | Specificity (%) |
| Visual Field Analysis MD >6 =disease
GCC average (µm) GCC Superior (µm) GCC inferior (µm) GCC FLV% (µm) GCC GLV% (µm)
Optic nerve head Disc area Vertical Cup : Disc Cup area Rim area Average RNFL thickness
RNFL average (parapapillary)(µm) RNFL superior (µm) RNFL inferior(µm) TL(µm) TU(µm) ST(µm) SN(µm) NU(µm) NL(µm) IN(µm) IT(µm)
Pattern ERG P50 latency Pattern ERG N95 latency Pattern ERG P50 amplitude Pattern ERG N95 amplitude
A latency B latency A amplitude B amplitude PhNR amplitude
Visual Field Analysis PSD |
12.76 78.72 87.23 93.61 85.10
38.29 95.74 89.36 87.23 87.23
91.48
91.48 91.48 89.36 80.85 93.61 87.23 78.72 85.10 87.23 93.61
91.48 57.44 91.48 95.74
91.49 85.11 23.08 53.19 87.23
72.34 |
70.83 29.16 37.50 37.50 29.16
41.66 8.33 8.33 20.83 16.66
20.83
31.03 25 29.16 25 25 29.16 41.66 33.33 20.83 16.66
33.33 66.66 4.16 0
20.00 36.00 85.71 76.00 36.00
95.83 |
Table 2 showing sensitivity and specificity of each testing technique w.r.t diagnostics of Visual Field Analysis MD values
| S. No. | Parameters | Sensitivity | Specificity |
| Visual Field Analysis PSD >6 =disease
GCC average (µm) GCC Superior (µm) GCC inferior (µm) GCC FLV% (µm) GCC GLV% (µm)
Optic nerve head Disc area Vertical Cup : Disc Cup area Rim area Average RNFL thickness
RNFL average (parapapillary)(µm) RNFL superior (µm) RNFL inferior(µm) TL(µm) TU(µm) ST(µm) SN(µm) NU(µm) NL(µm) IN(µm) IT(µm)
Pattern ERG P50 latency Pattern ERG N95 latency Pattern ERG P50 amplitude Pattern ERG N95 amplitude
A latency B latency A amplitude B amplitude PhNR amplitude
Visual Field Analysis MD |
14.28 80 85.71 94.28 82.85
40 94.28 88.57 88.57 85.71
91.42 88.57 88.57 91.42 94.28 94.28 88.57 82.85 88.57 88.57 94.28
91.42 51.42 88.57 94.28
91.43 80.00 28.57 48.57 88.57
97.14 |
77.77 27.77 27.77 27.77 22.22
50 5.55 8.33 19.44 13.88
16.66 25 16.66 25 36.11 19.44 25 38.88 30.55 19.44 13.88
25 52.77 2.77 0
16.22 24.32 83.78 62.16 29.73
63.88 |
Table 3 showing sensitivity and specificity of each testing technique w.r.t diagnostics of Visual Field Analysis PSD values
DISCUSSION
The present study is nonrandomized interventional study without control group conducted in the Department of Ophthalmology, Guru Nanak Eye Centre, New Delhi. A total of 71 eyes of newly diagnosed primary open angle glaucoma patients in the age group of 20 – 60 years were included in study to find outcome of glaucoma treatment on these eyes with use of OCT and electrophysiological tests (need to remove as already mentioned in result).
The number of eyes enrolled by various authors in their study varied from 11 eyes to 95 eyes of OAG.5,12,13,15,18,19. In this study a total of 71 eyes of newly diagnosed primary open angle glaucoma patients in the age group of 20 – 60 years were included
While Aydin et al,15Chang,16 Rebolleda,17 Sogano,18 Shirakashi,20 and Raitta,21 studied RNFL changes; Kotecha,14Lesk, Topouzis,22 and Irak19 studied ONH changes; Fortune et al3 and Raghu et al13 studied both RNFL and ONH changes with treatment; we however studied all three available parameters i.e. OCT GCC, OCT RNFL and OCT ONH parameters and found the effect on these following treatment. While Fortune et al3 and Wittstorm12 compared OCT RNFL changes with multifocal ERG, we compared OCT changes with both pattern and flash ERG.
Ventura and Porciatti stated that reduction in IOP yielded improvement in PERG amplitude.10Investigations of patients with early glaucoma by PERG have demonstrated a strong correlation between reduction in PERG amplitude and prolongation of PERG latency with loss of ganglion cells.32,33,34Van Toi et al found reported electrophysiological changes in response to changes in IOP. Tytla et al reported a subset of ocular hypertensive eye with an initial flicker sensitivity loss that (loss) disappeared after pharmacological reduction of IOP using timolol 0.5%.35Other studies suggest that increased IOP is associated with decreased counterphase flicker sensitivity in normal subjects.36We found a decrease in latency of N35, P50 and N95 waves and an increase in amplitude of P50 and N95 waves. The ratio of N95/P50 also reduced numerically.
While various authors found variable changes in OCT and PERG parameters, however they have not evaluated sensitivity and specificity values of OCT and PERG parameters by comparing these with gold standards i.e. Fundus and Field changes for diagnosing open angle glaucoma. Additionally normative data for relevant population groups were absent for these authors to find sensitivity and specificity values of diagnostic parameters of OCT and PERG.
We have already found the normative data for OCT parameters and PERG parameters in Indian population group.37,38We compared the values of the OCT and PERG diagnostic parameters and compared these values with values of fundus and field changes which are considered gold standards for diagnosing primary open angle glaucoma.
Keeping cup-disc ratio, MD and PSD respectively as standard, highest sensitivity was found by us in focal loss of volume (FLV) (83.33% w.r.t. cup-disc ratio; 93.61% w.r.t. MD; 94.28% w.r.t. PSD); vertical cup-disc ratio (VCDR) (95.45%w.r.t. cup-disc ratio; 95.74%w.r.t. MD; 94.28%w.r.t. PSD), infero-temporal quadrant (IT) (90.90%w.r.t. cup-disc ratio; 93.61%w.r.t. MD; 94.28%w.r.t. PSD) and N95 amplitude (N95A) (96.96%w.r.t. cup-disc ratio; 95.74%w.r.t. MD; 94.28%w.r.t. PSD) and highest specificity was found in average count (AvC) (60%w.r.t. cup-disc ratio; 70.83%w.r.t. MD; 77.77%w.r.t. PSD), disc area (DA) (40%w.r.t. cup-disc ratio; 41.66%w.r.t. MD; 50%w.r.t. PSD), nasal-upper quadrant (NU) (40%w.r.t. cup-disc ratio; 41.66%w.r.t. MD; 38.88%w.r.t. PSD) and N95 latency (N95L) (60%w.r.t. cup-disc ratio; 66.66%w.r.t. MD; 52.77%w.r.t. PSD).
CONCLUSION
Focal loss of volume (FLV), vertical cup-disc ratio (VCDR), RNFL infero-temporal quadrant (IT) and N95 wave amplitude (N95A) are good screening tests and GCC Average count (AvC), OCT Disc area (DA), RNFL nasal upper (NU) and N95 wave latency (N95L) have good diagnostic value.
REFERENCES
1. Araie M. [Basic and clinical studies of pressure-independent damaging factors of open angle glaucoma].Nihon Ganka Gakkai Zasshi. 2011;115(3):213-36.
2. Banitt MR, Ventura LM, Feuer WJ, Savatovsky E, Luna G, Shif O, et al. Progressive loss of retinal ganglion cell function precedes structural loss by several Years in glaucoma suspects. Invest Ophthalmol Vis Sci. 2013;54(3):2346-52.
3. Fortune B, Burgoyne CF, Cull GA, Reynaud J, Wang L. Structural and functional abnormalities of retinal ganglion cells measured in vivo at the onset of optic nerve head surface change in experimental glaucoma. Invest Ophthalmol Vis Sci. 2012;53(7):3939-50.
4.resciani-Battilana E,Teixeira IC, Barbosa DT, Caixeta-Umbelino C, Paolera MD, Kasahara N. Correlation between the ganglion cell complex and structural measures of the optic disc and retinal nerve fiber layer in glaucoma. 2015;35(5):645-50.
5.Sehi M, Grewal DS, Goodkin ML, Greenfield DS. Reversal of retinal ganglion cell dysfunction after surgical reduction of intraocular pressure. Ophthalmology. 2010;117(12):2329-36.
6.Ventura LM, Porciatti V. Restoration of retinal ganglion cell function in early glaucoma after intraocular pressure reduction: a pilot study. Ophthalmology. 2005;112(1):20-7.
7.Li B, Barnes GE, Holt WF. The decline of the photopic negative response (PhNR) in the rat after optic nerve transaction. DocumentaOphthalmologica. 2005;111:23-31.
8.Schlottmann PG, De Cilla S, Green field DS,Cprioli J, Garway Heath DF. Relationship between visual field sensitivity and retinal nerve fibre layer thickness as measured by scanning laser polarimetry. Invest Ophthalmol Vis Sci. 2004;45(6):1823-9.
9.Sehi M, Pinzon-Plazas M, Feuer WJ, Greenfield DS. Relationship between pattern electroretinogram, standard automated perimetry, and optic nerve structural assessments. J Glaucoma.2009;18:608-17.
10.Ventura LM, Porciatti V. Pattern electroretinogram in glaucoma. CurrOpinOphthalmol. 2006;17(2):196-202.
11.Tytla ME, Trope GE, Buncic JR. Flicker sensitivity in treated ocular hypertension. Ophthalmology. 1990;97(1):36-43.
12.Wittstrom E, Schatz P, Lovestam-Adrian M, Ponjavic V, Bergstrom A, Andreasson S. Improved retinal function after trabeculectomy in glaucoma patients. Graefes Arch ClinExpOphthalmol. 2010;248(4):485-95.
13.Raghu N,Pandav SS, Kaushik S, Ichhpujani P, Gupta A. Effect of trabeculectomy on RNFL thickness and optic disc parameters using optical coherence tomography. Eye (Lond). 2012;26(8):1131-7.
14.Kotecha A, Siriwardena D, Fitzke FW, Hitchings RA, Khaw PT. Optic disc changes following trabeculectomy: longitudinal and localization of change. Br J Ophthalmol. 2001;85(8):956-61.
15.Aydin A, Wollstein G, Price LL, Fujimoto JG, Schuman JS. Optical coherence tomography assessment of retinal nerve fibre layer thickness changes after glaucoma surgery. Ophthalmology. 2003;110(8):1506-11.
16.Chang PT, Sekhon N, Budenz DL, Feuer WJ, Park PW, Anderson DR. Effect of lowering IOP on OCT measurement of peripapillary RNFL thickness. Ophthalmology. 2007;114(12):2252-8.
17.Rebolleda G, Munoz-Negrete F, Noval S. Evaluation of changes in peripapillary nerve fiber layer thickness after deep sclerectomy with optical coherence tomography. Ophthalmology. 2007;114(3):488-93.
18.Sogano S, Tomita G, Kitazawa Y. Changes in retinal nerve fibre layer thickness after reduction of intraocular pressure in chronic open angle glaucoma. Ophthalmology. 1993;100(8):1253-8.
19.Irak I, Zangwill L, Garden V, Shakiba S, Weinreb RN. Change in optic disc topography after trabeculectomy. Am J Ophthalmol. 1996;122(5):690-5.
20.Shirakashi M, Nanba K, Iwata K. Reversal of cupping in experimental glaucoma. Ophthalmologica. 1991;202(4):194-201.
21.Raitta C, Tomita G, Vesti E, Harju M, Nakao H. Optic disc topography before and after trabeculectomy in advanced glaucoma. Ophthalmic Surg Lasers. 1996;27(5):349-54.
22.Topouzis F, Peng F, Kotas-Neuman R, Garcia R, Sanguinet J, Yu F, et al. Longitudnal changes in optic disc topography of adult patients after trabeculectomy. Ophthalmology. 1999;106(6):1147-51.
23.Viswanathan S, Frishman LJ, Robson JG. The uniform field and pattern ERG in macaques with experimental glaucoma: removal of spiking activity. Invest Ophthalmol Vis Sci. 2000;41(9):2797-810.
24.Tsai CS, Shin DH, Wan JY, Zeiter JH. Visual field global induces in patients with reversal of glaucomatous cupping after intraocular pressure reduction. Ophthalmology. 1991;98(9):1412-9.
25.Aydin A, Wollstein G, Price LL, Fujimoto JG, Schuman JS. Optical coherence tomography assessment of retinal nerve fiber layer thickness changes after glaucoma surgery. Ophthalmology.2003;110(8):1506-11.
26.Gandolfi SA. Improvement of visual field indices after surgical reduction of intraocular pressure. Ophthalmic Surg. 1995;26(2):121-6.
27.Gandolfi SA, Cimino L, Sangermani C, Ungaro N, Mora P, Tardini MG. Improvement of spatial contrast sensitivity threshold after surgical reduction of IOP in unilateral high-tension glaucoma. Invest Ophthalmol Vis Sci. 2005;46(1):197-201.
28.Holmin C, Thorburn W, Krakau CE. Treatment versus no treatment in chronic OAG. ActaOphthalmol. 1988;66(2):170-3.
29.Tavares IM, Melo LA, Prata JA, Galhardo R, Paranhos A, Mello PA. No changes in anatomical and functional glaucoma evaluation after trabeculectomy. Graefes Arch ClinExpOphthalmol. 2006;244(5):545-50.
30.Niyadurupola N,Luu CD, Nguyen DQ, Geddes K, Tan GX, Wong CC, et al. Intraocular pressure lowering is associated with an increase in the photopic negative response (PhNR) amplitude in glaucoma and ocular hypertensive eyes. Invest Ophthalmol Vis Sci. 2013;54(3):1913-9.
31.Vishwanathan S, Frishman LJ, Robson JG, Walter JW. The photopic negative response of the flash ERG in primary open angle glaucoma. Invest Ophthalmol Vis Sci. 2001;42(2):514-22.
32.Hood DC, Xu L, Thienprasiddhi P,Greenstein VC, Odel JG, Grippo TM, et al. The pattern ERG in glaucoma patients with confirmed visual field deficits. Invest OphthalmolVis Sci.2005;46(7):2411-8.
33.Ventura LM. Porciatti V. Restoration of retinal ganglion cell function in early glaucoma after IOP reduction: a pilot study. Ophthalmology. 2005;112(1):20-7.
34.Ventura LM, Porciatti V, Ishida K, Feuer WJ, Parrish RK. Pattern electroretinogram abnormality and glaucoma. Ophthalmology. 2005;112(1):10-9.
35.Price MJ, Drance SM, Price M, Schulzer M, Douglas GR, Tansley B. The pattern electroretinogram and visual-evoked potential in glaucoma. Graefes Arch ClinExpOphthalmol. 1988;226(6):542-7.
36.Tyler CW, Ryu S, Stamper R. The relation between visual sensitivity and intraocular pressure in normal eyes. Invest Ophthalmol Vis Sci. 1984;25(1):103-5.
37.Yadava U, Goel A, Mutreja A, Soren AJ. Study of macula ganglion cell complex by spectral domain OCT in glaucoma. Presented in American Academy of Ophthalmology Meeting 2015, Las Vegas.
38.Goyal JL, Karothia B, Arora R, Ghosh B. Evaluation of PERG, PhNR, Ops and 30 Hz in diabetic retinopathy. Presented in All India Ophthalmological Conference, 2012, Cochin.