August 2010
Volume 51, Issue 8
Free
Visual Psychophysics and Physiological Optics  |   August 2010
Fixation Stability: A Comparison between the Nidek MP-1 and the Rodenstock Scanning Laser Ophthalmoscope in Persons with and without Diabetic Maculopathy
Author Affiliations & Notes
  • Hannah M. P. Dunbar
    From the Institute of Ophthalmology, London, United Kingdom; and
  • Michael D. Crossland
    From the Institute of Ophthalmology, London, United Kingdom; and
    the NIHR Biomedical Research Centre for Ophthalmology, London, United Kingdom.
  • Gary S. Rubin
    From the Institute of Ophthalmology, London, United Kingdom; and
    the NIHR Biomedical Research Centre for Ophthalmology, London, United Kingdom.
  • Corresponding author: Hannah M. P. Dunbar, Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, United Kingdom; h.dunbar@ucl.ac.uk
Investigative Ophthalmology & Visual Science August 2010, Vol.51, 4346-4350. doi:10.1167/iovs.09-4556
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to Subscribers Only
      Sign In or Create an Account ×
    • Get Citation

      Hannah M. P. Dunbar, Michael D. Crossland, Gary S. Rubin; Fixation Stability: A Comparison between the Nidek MP-1 and the Rodenstock Scanning Laser Ophthalmoscope in Persons with and without Diabetic Maculopathy. Invest. Ophthalmol. Vis. Sci. 2010;51(8):4346-4350. doi: 10.1167/iovs.09-4556.

      Download citation file:


      © 2017 Association for Research in Vision and Ophthalmology.

      ×
  • Supplements
Abstract

Purpose.: Impaired fixation stability is associated with reduced reading speed. In previous research, fixation stability has been assessed using an infrared eye tracker or a confocal scanning laser ophthalmoscope. The new MP-1 microperimeter from Nidek Technologies (Padova, Italy) provides another option for the assessment of fixation. Here the authors compare fixation stability values measured using the MP-1 microperimeter and the Rodenstock scanning laser ophthalmoscope (SLO; Rodenstock GmbH, Munich, Germany) in persons with and without diabetic maculopathy.

Methods.: Sixteen normally sighted volunteers and 21 patients with diabetic maculopathy were recruited. Fixation stability was recorded monocularly on the SLO and the MP-1 in counterbalanced order while participants fixated a red 1° cross. Fixation data collected from each instrument were used to calculate a bivariate contour ellipse area (BCEA) that encompassed 68% of fixation points.

Results.: For control subjects, MP-1 BCEA values were larger than SLO by 0.25 log min arc2, though the difference was small (10%) and of borderline significance (MP-1, 2.51 log min arc2; SLO, 2.26 log min arc2; P = 0.06). In patients with diabetic maculopathy there was no significant difference between MP-1 and SLO values (MP-1, 2.94 log min arc2; SLO, 2.90 log min arc2; P = 0.88).

Conclusions.: No significant difference was found in BCEA values from the SLO and MP-1 in control subjects and patients with diabetic maculopathy. The authors suggest that the similarity between BCEA values, together with the consistent and reliable operation of the MP-1, make it a useful and viable alternative to the SLO in the assessment of fixation.

In normal vision, an eye fixating a static target does not remain stationary 1 ; it constantly makes small involuntary eye movements such as microsaccades, drifts, and tremors. 2 Elimination of such movements would cause our perception of a stationary target to fade completely 36 . However, excessive instability degrades visual resolution 7 and may interfere with the performance of everyday tasks such as reading. 8 Eye conditions affecting central vision are known to impair fixation. 914 Therefore, awareness of a patient's ability to fixate is important when considering functional vision. 
Although it is no longer commercially available, one well-established instrument in the assessment of fixation is the Rodenstock scanning laser ophthalmoscope (SLO; Rodenstock GmbH, Munich, Germany). Since its introduction in the early 1980s it has been used in numerous studies of fixation 911,1418 and has proven to be particularly useful for the examination of fixation in those with eye disease. 9,11,1317,19 The instrument was not specifically designed to measure fixation, but different methods have been described that allow its quantification. 11,14,15,19 One established method follows that first described by Steinman, whereby the position of each fixation point is plotted on Cartesian axes and the elliptical area encompassing a given percentage of points is calculated. 20 This bivariate contour ellipse area (BCEA) presents a value of fixation stability, with smaller values indicating more stable fixation. 
A new instrument, the Nidek MP-1 microperimeter (Nidek Technologies, Padova, Italy), has been designed with fixation stability assessment capability. It allows fixation to be assessed during a microperimetric examination or as an isolated assessment. The MP-1 offers classification of fixation stability based on the system described by Fujii et al., 21 whereby fixation is termed stable if >75% of fixation points fall within a 2° diameter circle centered on the gravitational center of all fixation points, relatively unstable if <75% of fixation points fall within a 2° circle but >75% are located within a 4° diameter circle, and unstable if <75% of all fixation points fall within a 4° diameter circle. 21 The lack of scientific foundation to this classification has been criticized in the literature. 22 However, it is possible to extract raw fixation data from the MP-1, thus allowing fixation points to be plotted and characterized by a BCEA value, as described. Recently we published data showing a lack of correlation between reading speed and fixation stability as classified by the inbuilt MP-1 strategy but a stronger correlation between reading performance and fixation quantified by calculating a BCEA. 23  
Because both the SLO and the MP-1 are used in the evaluation of fixation, an understanding of their comparability is vital. Different methods of assessment are known to produce different BCEA values; for example, in healthy young persons, SLO BCEA values are up to 2.25 times smaller than those from a head-mounted eye tracker system. 24 Given that the factors influencing measurement differ between those with steady fixation and those with poor fixation, we feel it important to compare fixation measurements not only in healthy young subjects but also in patients with poorer fixation. 
Diabetic eye disease is the leading cause of blindness in the working-age population of the United Kingdom, and the incidence of diabetes mellitus continues to rise in many developed countries. 2527 Although fixation behavior has been widely studied in macular disease, 9,1113,19,22,23,28 the impact of diabetic maculopathy on fixation stability is less well understood. 1417,29,30 A better understanding of fixation in the presence of diabetic maculopathy and its impact on visual function is necessary for clinicians involved in the visual rehabilitation of patients and for those responsible for the strategic planning of such services. 
Here we evaluated fixation stability in persons with and without diabetic maculopathy using two different instruments, the Rodenstock confocal SLO and the Nidek MP-1 microperimeter. 
Methods
Participants were recruited into two groups, patients with diabetic maculopathy and normally sighted volunteers. Patients were recruited from medical retina clinics at Moorfields Eye Hospital in London. All had diagnoses of type 1 or type 2 diabetes mellitus for at least 1 year and had recently diagnosed diabetic maculopathy of at least grade M1 according to the National Grading Protocol for England and Wales. This grade is defined as having one or more of the following features: exudates within 1 disc diameter (DD) of the center of the fovea; circinate or group of exudates within the macula; retinal thickening within 1 DD of the center of the fovea; and any microaneurysm or hemorrhage within 1 DD of the center of the fovea, only if associated with a best visual acuity of ≤6/12. 31 All normally sighted volunteers were hospital staff. 
Written informed consent was obtained from all participants once an explanation of the nature and possible consequences of the study had been explained. The research was approved by the Moorfields and Whittington Research Ethics Committee and conformed to the Declaration of Helsinki. 
Measurement of Fixation Stability
Fixation stability was recorded for each participant on both instruments in a counterbalanced order. All measurements were taken from the better eye, with the fellow eye occluded while the head was stabilized between a chin and forehead rest. The same researcher (HD) operated both instruments. 
Scanning Laser Ophthalmoscope
We used a scanning laser ophthalmoscope (SLO-101; Rodenstock GmbH) consisting of a helium-neon laser of wavelength 632.8 nm that produces the stimuli and an infrared laser of 780 nm that simultaneously images the fundus according to a confocal principle. 32 Images were captured on a professional digital video recorder at a resolution of 768 × 576 pixels (model BR-DV600E; JVC, Yokohama, Japan) and a frequency of 12.5 Hz. 
Software provided with the SLO (scotometry module) was used to produce a 1° red cross fixation target. Subjects were asked to view the center of the cross until 10 seconds of relatively blink free data were obtained. The digital video recorder simultaneously recorded fundus images throughout. 
Video images were digitized using a frame grabber (Orion Frame Grabber; Matrox, Montreal, Canada) and retinal position was retrospectively analyzed using software developed in house. The software automatically tracked fundus features within a delineated square of predetermined location on the retinal image at 12.5 Hz, producing x and y coordinates of its position in pixels. If tracking was lost, the square jumped to the extremity of the image, and the related coordinates had unrealistic values. Any such coordinates were manually deleted; complete trials were discarded if >20% of coordinates were deleted for this reason. 
The SLO was calibrated to quantify the amount of retinal movement shown in the captured fundus image. A semi-silvered mirror was placed in front of the SLO, allowing external targets to be viewed on the same visual axis as the SLO. Two cross fixation targets of known horizontal separation were placed on the wall parallel to the observer's line of sight. The distance between the targets and the semi-silvered mirror was recorded, and, therefore, the angular separation of the crosses could be calculated. The observer was instructed to look steadily at one target for 10 seconds and then switch to the second target for another 10 seconds. Fundus images were simultaneously recorded. The position of a retinal landmark was tracked at a frequency of 12.5 Hz, recording eye position in two-dimensional pixel coordinates. The horizontal movement of the retinal image between the two positions in image pixels was determined and used in a simple transformation, with the angular separation of the two crosses to describe the retinal motion seen on SLO recording in terms of visual angle. The resultant conversion factor, 1 pixel:2.6 min arc, was used in all SLO BCEA calculations. Because pixels within the central 5° of the SLO screen have been shown to be square with respect to the retina, 33 this conversion factor is applicable in both the horizontal and the vertical planes. 
MP-1 Microperimeter
The MP-1 microperimeter (Nidek Technologies) was used. This instrument comprises an infrared fundus camera and a liquid crystal display (LCD) that presents stimuli to the observer. 
A 1° red cross was displayed on the center of the LCD screen, and subjects were asked to view the center of the cross. Standard fixation measurement was performed using the techniques recommended by Nidek. First, a reference image of the fundus was captured, and a reference area of high-contrast retinal features was selected. During the examination, inbuilt software (MP-1 SW 1.7) tracked this reference area, calculating any shift in its position between the reference image and subsequent frames within the image at a frequency of 25 Hz, producing x and y coordinates of retinal position in degrees of visual angle. If tracking of the real-time image failed, coordinates were not generated until tracking was resumed. Nidek calculates the degree/pixel ratio of each individual instrument, found to be 1:15.714 when recently serviced. The MP-1 reports the total time of a fixation trial and the tracked time; therefore, the amount of time during which tracking fails is known. Ten seconds of tracked data were collected and exported for offline analysis. 
BCEA Calculation
The BCEA encompassing 68% of fixations was calculated using the formula   where σH and σV are the standard deviations of fixation position in the horizontal and vertical meridia, respectively, and ρ is the product moment correlation of these two components. 20 BCEA values in minutes of arc squared were normalized with a log transform. In addition to correlation, agreement between values from each instrument was assessed using the techniques described by Bland and Altman, 34 whereby the difference between the two measurements is plotted against their mean. This also reveals the magnitude of any difference. 
Results
Thirty-seven participants were recruited. The 16 normally sighted volunteers (6 men, 10 women; age range, 21–41 years) had visual acuity of 0.0 logMAR (6/6, 20/20) or better. The 21 (14 men, 7 women; age range, 24–77 years) patients with diabetic maculopathy had visual acuity between 0.8 and 0.0 logMAR (6/38, 20/125 to 6/6, 20/20). All participants had refractive error of between −6 and +4 DS spherical equivalent. 
Complete data were obtained from 28 subjects (14 in each group). The nine instances of incomplete data—four instances of He-Ne laser failure and five instances during which tracking software failed to track recorded images accurately—all arose from technical problems with the SLO. Analysis was conducted on complete data only. 
Normally Sighted Volunteers
Median BCEA value for SLO was 201 min arc2 (inter quartile range 80–415) and for MP-1 was 303 min arc2 (173–541). Mean log BCEA value for SLO was 2.26 log min arc2 (range, 1.51–2.91; SD, 0.44), and for MP-1 it was 2.51 log min arc2 (2.05–3.21; SD, 0.30). Figure 1 shows SLO versus MP-1 log BCEA values. A weak linear correlation was found (r = 0.33), but this was not significant (P = 0.24). 
Figure 1.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with normal vision. All values are in log minutes of arc squared.
Figure 1.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with normal vision. All values are in log minutes of arc squared.
On average, SLO log BCEA values were smaller than their MP-1 counterparts by 0.25 log min arc2; the difference failed to reach significance (matched pairs; P = 0.06). This is shown in Figure 2, with the difference between values from both instruments plotted against their mean. The solid horizontal line represents the mean difference, and the dashed lines represent ±1.96 SD around the mean. 
Figure 2.
 
Differences between SLO and MP-1 BCEA values are plotted against the mean of the two values for subjects with normal vision. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
Figure 2.
 
Differences between SLO and MP-1 BCEA values are plotted against the mean of the two values for subjects with normal vision. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
Subjects with Diabetic Maculopathy
The median BCEA value for SLO was 453 min arc2 (359–2770), and for MP-1 it was 615 min arc2 (209–2350). Mean log BCEA value for SLO was 2.90 log min arc2 (range, 2.03–4.05; SD, 0.60), whereas for the MP-1 it was 2.94 log min arc2 (1.90–5.44; SD, 0.88). A slightly stronger linear correlation was seen between the two sets of values (r = 0.42), as shown in Figure 3, but again this did not reach significance (P = 0.13). 
Figure 3.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with diabetic maculopathy. All values are in log minutes of arc squared.
Figure 3.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with diabetic maculopathy. All values are in log minutes of arc squared.
On average MP-1 and SLO log BCEA values were similar. SLO values were smaller by only 0.03 log min arc2. This small difference was not significant (matched pairs; P = 0.88), as shown in Figure 4
Figure 4.
 
Differences between SLO and MP-1 BCEA values plotted against the mean of the two values for subjects with diabetic maculopathy. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
Figure 4.
 
Differences between SLO and MP-1 BCEA values plotted against the mean of the two values for subjects with diabetic maculopathy. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
Discussion
On average, no significant difference in BCEA values between the SLO and the MP-1 was observed in subjects with normal vision and patients with diabetic maculopathy. Somewhat surprisingly, the correlation between BCEA values from the two instruments was weak in both study groups but was slightly stronger over the larger range of BCEA values recorded in patients with diabetic maculopathy. 
A previous study reported moderate agreement between SLO and MP-1 fixation assessments in eyes with retinal disease, but the means of quantifying fixation differed significantly from our method. Fixation was classified according to the MP-1 classification system described 21 and was compared for agreement using Cohen's κ coefficient. In the case of the SLO data, fixation was stable if the SD of fixation points around the mean fixation point was less then 0.6°, relatively unstable if the SD was between 0.6° and 1.2°, and unstable if the SD was greater than 1.2°. 35 Additionally, fixation was assessed during microperimetric examination compared with our isolated fixation task. Earlier work by the same author noted steadier fixation during an isolated task than during microperimetry. 15  
In contrast to our results, a significant correlation between MP-1 and SLO fixation assessment in patients with macular disorders has been observed; however, the method of quantification differed considerably between each instrument. MP-1 fixation was quantified by mean extent, which is double the square root of the product of the x and y degree positions of fixation points, whereas SLO fixation was calculated as the percentage of fixation points within the central 2° on SLO measurement. 28 Because of notable differences in study design, the findings from these studies cannot be directly compared with our results. 
To make direct comparisons between our BCEA measurements and other published values, we examined the standard deviations of fixation points along the horizontal and vertical axes. In normal vision, while fixating a stationary target, fixation points tend to spread out horizontally more than vertically. 10,11,22,36,37 The mean horizontal and vertical SDs of our SLO and MP-1 data from subjects with normal vision conformed to this description, with average horizontal and vertical SDs of 8 min arc and 6 min arc, respectively, on SLO and 9 min arc and 7 min arc, respectively, on MP-1. Our SLO standard deviations fall within the narrow range cited by Culham (4–8 min arc horizontally and 3–7 min arc vertically) 10 and toward the lower ranges quoted by Rohrschneider 11 (8–88 min arc horizontally and 6–65 min arc vertically) and Timberlake 37 (4–38 min arc horizontally and 4–18 min arc vertically). Data published in 2008 reported horizontal and vertical ranges of 4 to 9 min arc and 3 to 6 min arc, respectively, on the MP-1 for 10 experienced observers with normal vision. 22 Although our mean values fall slightly above these top limits, we suggest this to be a consequence of the relative inexperience of our observers. 
In those with diabetic maculopathy, the mean horizontal and vertical standard deviations were 29 min arc and 22 min arc, respectively, on SLO and 34 min arc and 59 min arc, respectively, on MP-1. We do not know of any previous studies that have quantified fixation in patients with diabetic maculopathy in terms of BCEA or horizontal and vertical SDs. Our findings agree with the value of 45 min arc given for a standard deviation around a mean fixation point in eyes with clinically significant diabetic macular edema. 15 Fixation characteristics in this patient group are not well defined. One recent study looking at fixation in this population using the MP-1 found stable fixation in more than 70% of eyes, 29 whereas another observed found unstable fixation in most (60%) eyes. 30  
To discover whether the different sampling rates of the two instruments, 12.5 Hz on SLO and 25 Hz on MP-1, should influence the size of the BCEA, we under sampled three MP-1 data files. Every second frame was removed, thereby simulating a sampling rate of 12.5 Hz, equal to that of the SLO. Because nearly equivalent values were found in each case (full data sets: 212, 80 and 514 min arc2; half data sets: 213, 80 and 528 min arc2), it is unlikely to be a source of error. 
We chose fixation durations of 10 seconds because longer durations of blink-free data are difficult to record. Because previous work revealed no systematic variation over time in BCEAs calculated from the first 10 seconds of each of 8 consecutive minutes of fixation, we believe 10-second fixation trials to be of adequate length for BCEA calculation. 38  
It has been reported that the SLO raster is distorted in a trapezoidal manner such that the raster is 10% larger at the bottom than the top. 39 Misalignment between the infrared imaging system and the LCD screen of the MP-1 has also been described. Spatial alignment errors of 0.5° have been observed between recorded retinal position and the true retinal location stimulated (Woods RL, et al. IOVS 2007;48:ARVO E-Abstract 144). Because our subjects viewed a single fixation target in a fixed central position, these distortions are unlikely to meaningfully influence our findings. 
In summary, fixation stability values measured using the SLO and the MP-1 did not differ significantly on average. Because fixation stability is of more clinical interest in patients with macular disease, we were encouraged to find such small differences in the values of patients with diabetic maculopathy. As described earlier, the collection of complete data was hampered by persistent technical problems with the SLO. In contrast, the MP-1 was operational throughout. The Rodenstock is no longer commercially available, difficult to maintain, and expensive to service. The MP-1 is backed up by technical and maintenance support from Nidek distributors. We suggest that the similarity found in BCEA values and the consistent and reliable operation of the MP-1 make it a useful and viable alternative to the SLO in the assessment of fixation. 
Footnotes
 Supported by Fight for Sight Clinical Fellowship Grant 1775/76.
Footnotes
 Disclosure: H.M.P. Dunbar, None; M.D. Crossland, None; G.S. Rubin, None
The authors thank William Seiple (Lighthouse International) for his assistance with validation of the BCEA calculation. 
References
Barlow HB . Eye movements during fixation. J Physiol. 1952;116(3):290–306. [CrossRef] [PubMed]
Ditchburn RW . Kinematic Description of Small Eye Movements. Oxford: Claredon Press; 1973.
Ditchburn RW Ginsborg BL . Involuntary eye movements during fixation. J Physiol. 1953;119(1):1–17. [CrossRef] [PubMed]
Riggs LA Ratliff F Cornsweet JC Cornsweet TN . The disappearance of steadily fixated visual test objects. J Opt Soc Am. 1953;43(6):495–501. [CrossRef] [PubMed]
Yarbus AL . Eye Movements during Fixation on Stationary Objects. New York: Plenum Press; 1967.
Martinez-Conde S Macknik SL Troncoso XG Dyar TA . Microsaccades counteract visual fading during fixation. Neuron. 2006;49(2):297–305. [CrossRef] [PubMed]
Macedo AF Crossland MD Rubin GS . The effect of retinal image slip on peripheral visual acuity. J Vis. 2008;8(14):16.1–16.11. [CrossRef]
Rubin G Feely M . The role of eye movements during reading in patients with age-related macular degeneration (AMD). Neuro-Ophthalmology. 2009;33(3):120–126. [CrossRef]
Timberlake GT Mainster MA Peli E Augliere RA Essock EA Arend LE . Reading with a macular scotoma, I: retinal location of scotoma and fixation area. Invest Ophthalmol Vis Sci. 1986;27(7):1137–1147. [PubMed]
Culham LE Fitzke FW Timberlake GT Marshall J . Assessment of fixation stability in normal subjects and patients using a scanning laser ophthalmoscope. Clin Vision Sci. 1993;8(6):551–561.
Rohrschneider K Becker M Kruse FE Fendrich T Volcker HE . Stability of fixation: results of fundus-controlled examination using the scanning laser ophthalmoscope. Ger J Ophthalmol. 1995;4(4):197–202. [PubMed]
Bellmann C Feely M Crossland MD Kabanarou SA Rubin GS . Fixation stability using central and pericentral fixation targets in patients with age-related macular degeneration. Ophthalmology. 2004;111(12):2265–2270. [CrossRef] [PubMed]
Crossland MD Culham LE Rubin GS . Fixation stability and reading speed in patients with newly developed macular disease. Ophthalmic Physiol Opt. 2004;24(4):327–333. [CrossRef] [PubMed]
Kube T Schmidt S Toonen F Kirchhof B Wolf S . Fixation stability and macular light sensitivity in patients with diabetic maculopathy: a microperimetric study with a scanning laser ophthalmoscope. Ophthalmologica. 2005;219(1):16–20. [CrossRef] [PubMed]
Rohrschneider K Bultmann S Gluck R Kruse FE Fendrich T Volcker HE . Scanning laser ophthalmoscope fundus perimetry before and after laser photocoagulation for clinically significant diabetic macular edema. Am J Ophthalmol. 2000;129(1):27–32. [CrossRef] [PubMed]
Mori F Ishiko S Kitaya N . Use of scanning laser ophthalmoscope microperimetry in clinically significant macular edema in type 2 diabetes mellitus. Jpn J Ophthalmol. 2002;46(6):650–655. [CrossRef] [PubMed]
Moller F Bek T . Lack of correlation between visual acuity and fixation stability after photocoagulation for diabetic maculopathy. Graefes Arch Clin Exp Ophthalmol. 2000;238(7):566–570. [CrossRef] [PubMed]
Rohrschneider K Becker M Schumacher N Fendrich T Volcker HE . Normal values for fundus perimetry with the scanning laser ophthalmoscope. Am J Ophthalmol. 1998;126(1):52–58. [CrossRef] [PubMed]
Reinhard J Messias A Dietz K . Quantifying fixation in patients with Stargardt disease. Vision Res. 2007;47(15):2076–2085. [CrossRef] [PubMed]
Steinman RM . Effect of target size luminance and color on monocular fixation. J Opt Soc Am. 1965;55(9):1158. [CrossRef]
Fujii GY de Juan EJr Sunness J Humayun MS Pieramici DJ Chang TS . Patient selection for macular translocation surgery using the scanning laser ophthalmoscope. Ophthalmology. 2002;109(9):1737–1744. [CrossRef] [PubMed]
Tarita-Nistor L Gonzalez EG Markowitz SN Steinbach MJ . Fixation characteristics of patients with macular degeneration recorded with the mp-1 microperimeter. Retina. 2008;28(1):125–133. [CrossRef] [PubMed]
Crossland MD Dunbar HM Rubin GS . Fixation stability measurement using the MP1 microperimeter. Retina. 2009;29(5):651–656. [CrossRef] [PubMed]
Crossland MD Rubin GS . The use of an infrared eye tracker to measure fixation stability. Optom Vis Sci. 2002;79(11):735–739. [CrossRef] [PubMed]
Bunce C Wormald R . Causes of blind certifications in England and Wales: April 1999-March 2000. Eye. 2008;22(7):905–911. [CrossRef] [PubMed]
Patterson CC Dahlquist GG Gyurus E Green A Soltesz G . Incidence trends for childhood type 1 diabetes in Europe during 1989–2003 and predicted new cases 2005–20: a multicentre prospective registration study. Lancet. 2009;373(9680):2027–2033. [CrossRef] [PubMed]
Masso-Gonzalez EL Johansson S Wallander MA Garcia-Rodriguez LA . Trends in the prevalence and incidence of diabetes in the UK—1996 to 2005. J Epidemiol Community Health. 2009;63(10):332–336. [CrossRef] [PubMed]
Sawa M Gomi F Toyoda A Ikuno Y Fujikado T Tano Y . A microperimeter that provides fixation pattern and retinal sensitivity measurement. Jpn J Ophthalmol. 2006;50(2):111–115. [CrossRef] [PubMed]
Vujosevic S Pilotto E Bottega E Benetti E Cavarzeran F Midena E . Retinal fixation impairment in diabetic macular edema. Retina. 2008;28(10):1443–1450. [CrossRef] [PubMed]
Carpineto P Ciancaglini M Di Antonio L Gavalas C Mastropasqua L . Fundus microperimetry patterns of fixation in type 2 diabetic patients with diffuse macular edema. Retina. 2007;27(1):21–29. [CrossRef] [PubMed]
Harding S Greenwood R Aldington S . Grading and disease management in national screening for diabetic retinopathy in England and Wales. Diabet Med. 2003;20(12):965–971. [CrossRef] [PubMed]
Webb RH Hughes GW Delori FC . Confocal scanning laser ophthalmoscope. Appl Opt. 1987;26(8):1492–1499. [CrossRef] [PubMed]
Kambanarou SA . Binocular versus Monocular Viewing in Age-Related Macular Degeneration. London: University College London; 2005.
Bland JM Altman DG . Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1(8476):307–310. [CrossRef] [PubMed]
Rohrschneider K Springer C Bultmann S Volcker HE . Microperimetry—comparison between the micro perimeter 1 and scanning laser ophthalmoscope—fundus perimetry. Am J Ophthalmol. 2005;139(1):125–134. [CrossRef] [PubMed]
Kosnik W Fikre J Sekuler R . Visual fixation stability in older adults. Invest Ophthalmol Vis Sci. 1986;27(12):1720–1725. [PubMed]
Timberlake GT Sharma MK Grose SA Gobert DV Gauch JM Maino JH . Retinal location of the preferred retinal locus relative to the fovea in scanning laser ophthalmoscope images. Optom Vision Sci. 2005;82(3):177–185. [CrossRef]
Crossland MD Morland AB Feely MP von dem Hagen E Rubin GS . The effect of age and fixation instability on retinotopic mapping of primary visual cortex. Invest Ophthalmol Vis Sci. 2008;49(8):3734–3739. [CrossRef] [PubMed]
Timberlake GT Sharma MK Gobert DV Maino JH . Distortion and size calibration of the scanning laser ophthalmoscope (SLO) laser-beam raster. Optom Vis Sci. 2003;80(11):772–777. [CrossRef] [PubMed]
Figure 1.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with normal vision. All values are in log minutes of arc squared.
Figure 1.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with normal vision. All values are in log minutes of arc squared.
Figure 2.
 
Differences between SLO and MP-1 BCEA values are plotted against the mean of the two values for subjects with normal vision. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
Figure 2.
 
Differences between SLO and MP-1 BCEA values are plotted against the mean of the two values for subjects with normal vision. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
Figure 3.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with diabetic maculopathy. All values are in log minutes of arc squared.
Figure 3.
 
SLO BCEA values compared with MP-1 BCEA values for subjects with diabetic maculopathy. All values are in log minutes of arc squared.
Figure 4.
 
Differences between SLO and MP-1 BCEA values plotted against the mean of the two values for subjects with diabetic maculopathy. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
Figure 4.
 
Differences between SLO and MP-1 BCEA values plotted against the mean of the two values for subjects with diabetic maculopathy. Solid line: mean difference between the two values. Dashed lines: ±1.96 SD from the mean. All values are in log minutes of arc squared.
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×