|Year : 2016 | Volume
| Issue : 1 | Page : 18-23
A comparison between the diagnostic results of short wavelength automated perimetry and standard automated perimetry in glaucoma patients
Ahmed H Mohamed
Department of Ophthalmology, Qena Faculty of Medicine, South Valley University, Qena, Egypt
|Date of Submission||01-Apr-2015|
|Date of Acceptance||05-Aug-2015|
|Date of Web Publication||16-Mar-2016|
Ahmed H Mohamed
Department of Ophthalmology, Qena Faculty of Medicine, South Valley University, Qena 83511
Source of Support: None, Conflict of Interest: None
The aim of this study was to compare the diagnostic results of short wavelength automated perimetry (SWAP) and standard automated perimetry (SAP) in glaucoma patients.
Patients and methods
This study was held in Qena University Hospital from March 2012 to December 2012 and included 60 individuals who underwent full ophthalmological examination by means of slit-lamp biomicroscopy, gonioscopy, best-corrected visual acuity testing on Landolt's chart, fundus and optic nerve head examination using a +90 D lens, intraocular pressure (IOP) measurement by means of applanation tonometry, and finally optic nerve head photography using a Zeiss Visucam 500 fundus camera. The participants were divided into three groups: a normal age-matched control group (group A); a group with primary open-angle glaucoma POAG (group B); and a group with ocular hypertension OHT and glaucoma suspects (group C). Informed consent was obtained from all controls and patients after the nature and possible consequences of the procedure had been fully explained to them. All statistical analyses were performed by using IBM SPSS statistics.
Thirty randomly selected eyes of 30 volunteers made up group A, 20 eyes of 20 POAG patients comprised group B, and 10 eyes of 10 ocular hypertension patients and glaucoma suspects comprised group C. The mean age of the 60 individuals included in the present study was 70.18 years (range: 60-82 years, SD: ±8.068); 29 were female and 31 were male. The prevalence of SWAP and SAP in glaucoma patients showed deficits in groups B and C, as defined by the presence of a glaucoma hemifield test 'outside normal limits'. According to this criterion, three of 10 (33.3%) group C eyes demonstrated a SWAP deficit at the second visit, whereas no (0%) eyes showed a deficit in SAP at the same time point. All 20 patients of group B manifested abnormal SWAP. The level of agreement in terms of the severity of field loss between SWAP and SAP for groups B and C, based on the pattern SD, was studied. In the present study we found that visual field loss was greater and more diffuse in SWAP than in SAP, but no patient exhibited new scotomata.
SWAP is superior to SAP in identifying patients with early glaucoma, ocular hypertension, glaucoma suspects, and patients with progressive optic disc cupping and may therefore be quite useful for determining early and progressive changes in glaucoma.
Keywords: glaucoma suspect, primary open-angle glaucoma, standard automated perimetry, short wavelength automated perimetry
|How to cite this article:|
Mohamed AH. A comparison between the diagnostic results of short wavelength automated perimetry and standard automated perimetry in glaucoma patients. Delta J Ophthalmol 2016;17:18-23
|How to cite this URL:|
Mohamed AH. A comparison between the diagnostic results of short wavelength automated perimetry and standard automated perimetry in glaucoma patients. Delta J Ophthalmol [serial online] 2016 [cited 2020 May 31];17:18-23. Available from: http://www.djo.eg.net/text.asp?2016/17/1/18/178763
| Introduction|| |
Visual field testing is an essential component of glaucoma assessment in terms of detection as well as in monitoring the progression of the disease .
Standard automated white-on-white (W-W) perimetry (SAP), frequency-doubling technology perimetry, and short wavelength automated perimetry (SWAP) are three prevailing visual field testing technologies used in clinical practice .
Visual field testing, usually performed with SAP with a uniform white target projected on a homogenous white background, detects glaucomatous changes only after extensive optic disc damage. This may occur because the W-W stimulus has broadband characteristics that activate the spectrum o`f retinal ganglion cells within the tested retina .
Because the large overlap in the ganglion cell network results in considerable redundancy, glaucomatous losses may be masked if all types of ganglion cells are stimulated. In addition, it is very difficult to distinguish true progression of field loss on SAP from long-term variability. Therefore, there is a general agreement on the need to improve early diagnosis of visual loss in patients suspected to have glaucoma and to improve the sensitivity of SAP to detect the progression of glaucomatous optic neuropathy .
It is well accepted that there are similar limitations of SAP in the early detection of onset as well as progression of GON .
In recent years, SWAP has generated considerable interest as a potential means for detecting the presence of visual field loss before that identified by conventional W-W perimetry and also for detecting progressive field loss in advance of W-W perimetry. SWAP has been studied in a variety of conditions, including glaucoma, diabetic macular edema, and neuro-ophthalmic disorders. SWAP is currently commercially available on the Humphrey Field Analyzer (HFA) models 740 and 750, on the Octopus 101 and 311 perimeters and as an option on the Octopus 301 perimeter. Normative databases are available with HFA programs 30-2 and 24-2 for the full threshold and the FASTPAC algorithms and with Octopus programs such as G1, G2, 32, and M2 for the normal, dynamic, and TOP strategies ,,,.
SWAP utilizes a blue stimulus to preferentially stimulate the blue cones and a high luminance yellow background to adapt the green and red cones and to saturate, simultaneously, the activity of the rods. Compared with W-W perimetry, SWAP is limited clinically by the following: greater variability associated with the estimation of threshold; ocular media absorption; increased examination duration; and an additional learning effect. SWAP is almost certainly able to identify glaucomatous visual field loss in advance of that by W-W perimetry. SWAP appears to be beneficial in the detection of diabetic macular edema and possibly in some neuro-ophthalmic disorders ,,,.
| Patients and methods|| |
This study was conducted in Qena University Hospital from March 2012 to December 2012 and included 60 individuals who were enrolled from the Outpatient Clinic of Qena University Hospital. This study was approved from the ethical committee of Qena faculty of medicine at South Valley University.
This study included eyes from 60 controls and patients who were divided into three groups: a normal age-matched control group (group A); a group with POAG (group B); and a group with OHT and glaucoma suspects (group C).
Informed consent was obtained from all controls and patients after the nature and possible consequences of the procedure had been fully explained to them.
Each participant underwent full ophthalmological examination by means of slit-lamp biomicroscopy, gonioscopy, best-corrected visual acuity (BCVA) testing on Landolt's chart, fundus and optic nerve head examination using a +90 D lens, IOP measurement by means of applanation tonometry, and finally fundus photography using a Zeiss Visucam 500 fundus camera (Carl Zeiss Meditec AG, Goschwitzer Strasse, Germany).
Each participant underwent at least two reliable 24-2 SAPs: central threshold test, Goldmann size III (4 mm 2 , white color, stimulus duration: 0.2 s, background: 31.5 apostilbs); and two reliable 24-2 SITA-SWAPs: Goldmann size V narrow band blue stimulus with a peak transmission of 440 nm (27 nm half-peak width). The blue stimulus is presented for 200 ms on a 100 cd/m 2 yellow background that transmits wavelengths longer than ∼530 nm. This accepted combination of stimulus size and wavelength and of background luminance and wavelength ensures that the degree of SWS pathway isolation for the HFA is ∼1.3 log units (13 dB) at fixation. Statistical package (STATPAC, New York, USA), Zeiss HFA model 745i (Humphrey Systems; Carl Zeiss Meditec Inc., Dublin, California, USA), was used for all patients for both SAP and SWAP. Appropriate refractive correction was used for the viewing distance of the perimeter bowl. Fixation losses were less than 20%, and false-negative and false-positive responses were less than 33% for all participants. Extensive rest periods were given within and between tests to minimize fatigue effects, and no single visit lasted more than 60 min.
SAPs and SWAPs were evaluated by examining the average sensitivity within the 10 glaucoma hemifield test (GHT) zones. For both SAP and SWAP, a visual field was considered to be abnormal if the GHT was 'outside normal limits'. A designation of 'outside normal limits' for the GHT occurs if:
- There is an asymmetry of sensitivity across the horizontal midline for any of the five pairs of GHT clusters that are worse than the normal 1% level or
- Both the superior and inferior clusters of a pair have sensitivities that are worse than the normal 0.5% level .
Inclusion criteria were as follows: refractive error of less than 5.00-D spherical error and 3.00-D cylindrical error; BCVA of 6/9 or better; no history of congenital color vision defect; no systemic medication known to influence the visual field; no ocular surgery or trauma; and no history of diabetes mellitus.
Normal age-matched control group (group A)
The normal control group was composed of 30 randomly recruited, age-matched normal individuals whose ages spanned two decades (age range: 60-82 years, mean: 70.4 years, SD: ±8.13). Eyes of the 30 normal controls were used to establish normative data for SWAP and SAP. The mean IOP on presentation at the hospital was 15.2 mmHg (SD: ±2.7).
Group with primary open-angle glaucoma (group B)
The POAG sample consisted of 20 patients. The mean age of the sample was 69.95 years (range: 60-81 years, SD: ±8.19). Patients of group B exhibited characteristic optic nerve head abnormalities, IOP more than 21 mmHg, and characteristic SAP loss. The mean IOP on presentation at the hospital was 28.65 mmHg (SD: ±2.7).
Group with ocular hypertension and glaucoma suspects (group C)
The OHT and glaucoma suspects' sample consisted of 10 patients. The mean age of the sample was 69.9 years (age range: 61-82 years, SD: ±8.5). The mean IOP on presentation at the hospital was 24.0 mmHg (SD: ±1.7).
Ocular hypertension was defined as BCVA of 6/9 or higher in each eye, intraocular pressure more than 21 mmHg on at least two occasions, refractive error of less than 5-D spherical error and 3.00-D cylindrical error, normal result on SAP examination, and normal appearance of the optic nerve head.
Glaucoma suspect was defined as the presence of an open angle on gonioscopy and one of the following in at least one eye:
- IOP consistently more than 21 mmHg on at least two occasions.
- Appearance of the optic disc or retinal nerve fiber layer suggestive of glaucomatous damage.
- Diffuse or focal narrowing or sloping of the disc rim.
- Diffuse or localized abnormalities of the nerve fiber layer, especially at the superior and inferior poles.
- Disc hemorrhage.
- Asymmetric appearance of the disc or rim between fellow eyes (e.g. cup-to-disc ratio difference>0.2), suggesting loss of neural tissue.
- SAP examination suspicious for early glaucomatous damage.
All participants of group C conformed to the inclusion criteria identical to those of group A except for the criteria for IOP, optic nerve head appearance, visual field, and family history of glaucoma.
One eye of each participant was examined. For group B, the eye with the least field loss was selected, whereas for group C the eye with the highest IOP was examined.
All statistical analyses were performed using IBM SPSS statistics (version 20.0, SPSS Inc., Chicago, Illinois, USA).
| Results|| |
[Figure 1] presents the clinical characteristics of the study population. Sixty eyes of 60 individuals were enrolled in this study. Participants were classified into three groups (A, B, and C).
Thirty randomly selected eyes of 30 volunteers made up group A, 20 eyes of 20 POAG patients comprised group B, and 10 eyes of 10 ocular hypertension patients and glaucoma suspects comprised group C.
The mean age of the 60 participants was 70.18 years (range: 60-82 years, SD: ±8.068); 29 were female and 31 were male [Table 1].
IOP was measured using the Goldmann applanation tonometer, a method that has been considered the clinical gold standard in IOP measurement for the past 50 years. [Table 2] shows IOP descriptive data for the three groups that comprise our study population.
The prevalence of SAP and SWAP deficits in groups B and C, as defined by the presence of a GHT 'outside normal limits', is presented in [Figure 2]. According to these criteria, three of 10 (33.3%) group C eyes demonstrated a SWAP deficit at the second visit, whereas no (0%) eyes showed a deficit in SAP at the same point in time. All 20 patients of group B manifested abnormal SWAP.
|Figure 2: The prevalence of standard automated perimetry (SAP) and short wavelength automated perimetry (SWAP) defi cits in groups B and C.|
Click here to view
The level of agreement in terms of the severity of field loss between SWAP and SAP for groups B and C, based on the pattern SD, is summarized in [Figure 3]. In the present study we found that visual field loss was greater and more diffuse in SWAP than in SAP, but no patient exhibited new scotomata.
|Figure 3: The severity of fi eld loss in short wavelength automated perimetry (SWAP) and standard automated perimetry (SAP) for groups B and C, based on the pattern SD (PSD).|
Click here to view
[Figure 4] shows the pattern deviation and global indices of left eye SAP in a 62-year-old woman who presented at the Qena University Hospital outpatient clinic on 23 June 2012. Her BCVA was 6/12, refraction was 0.0/−0.5 × 180°, IOP was 18 mmHg, and vertical C/D ratio was 0.7. She had no media opacities, no history of congenital color vision defect, no systemic medications known to influence the visual field, and no previous ocular surgery or trauma; she was not diabetic either. The patient met the inclusion criteria for our study, and hence her GHT was within normal limits, as shown in [Figure 4]. She was diagnosed as a glaucoma suspect and was classified a group C patient.
|Figure 4: Normal standard automated perimetry (SAP) in one of the study patients. GHT, glaucoma hemifi eld test; PSD, pattern SD.|
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When the patient underwent SWAP, her pattern deviation plot showed glaucoma changes, and her GHT was outside the normal limits, as shown in [Figure 5].
|Figure 5: Short wavelength automated perimetry (SWAP) of the same patient. GHT, glaucoma hemifi eld test; PSD, pattern SD.|
Click here to view
| Discussion|| |
The starting point of any diagnostic process is when a patient presents with a constellation of signs and symptoms. Ancillary glaucoma tests are designed to provide additional data to supplement clinical evaluation and are helpful for making diagnostic and therapeutic decisions .
There are several glaucoma suspect and ocular hypertension patients with an optic disc appearance or retinal nerve fiber layer defect compatible with glaucoma or with IOP more than 21 mmHg, but without functional loss in SAP, with differing risk levels. Therefore, individual-based decisions are better supported with additional data that help to discriminate early glaucoma damage from ocular hypertension and normal eyes. Careful follow-up of these patients can provide information to modify the results of their basal status and to make therapeutic decisions based on the changes observed .
All individuals included in the present study except group B had normal SAP and no signs of structural glaucomatous damage.
IOP was measured in all participants. IOP was higher in group B and ocular hypertensive patients of group C than in group A. Glaucoma was recently defined as an optic nerve head neuropathy, and elevated IOP is not included in this definition. Increased IOP is considered a risk factor only for developing glaucoma , and thus IOP was not used to further stratify the participants of our study.
Cup/disc ratio evaluation with stereophotographs might not be accurate in the diagnosis of early glaucoma as it might be influenced by the disc area dimensions: when the disc area is larger, the cup size might appear greater. The optic nerve head can be more accurately examined in cases with a large vertical cup/disc ratio, and fortunately this ratio has proved to be one of the most reliable predictors for detecting early glaucoma, but still cannot be used alone in diagnosis .
Abundant evidence exists that SWAP has a higher sensitivity to detect early functional loss in glaucoma compared with SAP ,. In our study, SWAP showed glaucomatous defects in at least one-third of the patients of group C. For both SAP and SWAP, a visual field was considered abnormal if the GHT was 'outside normal limits'. GHT 'outside normal limits' showed the best sensitivity and specificity balance .
The longitudinal studies that were published by Demirel and Johnson , Sample et al. , and Johnson et al.  have confirmed the earlier findings about the sensitivity of SWAP. Patients were followed up longitudinally with both SWAP and SAP. SWAP results were corrected for artifacts caused by early nuclear sclerotic lens changes with lens transmission measurements. A robust definition of abnormality was adopted to reduce the number of false-positive tests.
In the study by Demirel and Johnson  the prevalence of SWAP defects at the beginning of the study was 9.4% compared with 1.4% of patients with SAP defects. Eighty percent of SWAP defects remained abnormal, whereas only 45% of the abnormal SAP visual fields remained normal on subsequent testing. The incidence rates of field loss for SWAP and SAP were virtually identical at 1.2%. The incidence rates reflect the progression of disease and indicate that both tests show worsened disease states at similar rates, even though SWAP defects are manifest at an earlier stage of the disease. This may be true only in the early stages of disease that were evaluated in this study; this relationship may not hold linear for more advanced stages of the disease.
Girkin et al.  have published a longitudinal study that included 47 glaucoma patients with a mean follow-up time of 4.1 years (range: 2.0-8.9 years). The study concluded that SWAP identified more patients than SAP as having progressive glaucomatous changes of the optic disc. Compared with SAP, SWAP may improve the detection of progressive glaucoma.
The limitations of SWAP include false-positive results , media opacities that may influence the performance of the patients , the length of examination time, and the associated problem of the fatigue effect .
In the current study, patients with media opacities - for example, a mild cataract that may influence the performance in SWAP - were excluded from the study, but in clinical practice these patients must also be evaluated. SWAP requires transparent media, but defects on pattern deviation plots might bypass this limitation.
In the current study, group A and most of group C patients had no previous VF testing experience, although most group B patients had undergone SAP tests. All participants underwent at least two reliable SAPs and two reliable SWAPs to minimize the influence of the learning effect .
Extensive rest periods were given within and between tests to minimize fatigue effects, and no single visit lasted more than 60 min.
In our study we preferred the new threshold SITA standard 24-2 strategy for both SAP and SWAP that significantly minimizes test time without significant reduction in data quality ,,.
| Conclusion|| |
SWAP is superior to SAP for identifying patients with early glaucoma, ocular hypertension, glaucoma suspects, and patients with progressive optic disc cupping and may therefore be quite useful for determining early and progressive changes in glaucoma. Longitudinal follow-up studies will elucidate which patients with abnormal SWAP results will eventually exhibit VF losses in SAP, and also whether individuals without previous defects in SWAP will develop glaucomatous defects in SAP.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]