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 Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 108  |  Issue : 3  |  Page : 153-155

Contrast sensitivity in β-thalassemic patients


Lecturer of Ophthalmology, Assistant Professor of Medicine, Ain Shams University, Cairo, Egypt

Date of Submission11-May-2015
Date of Acceptance15-May-2015
Date of Web Publication30-Oct-2015

Correspondence Address:
Tamer H El-Sersy
11 Montazah St., Heliopolis, 11311 Cairo
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2090-0686.168723

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  Abstract 

Aim of work
This work aimed to diagnose any abnormalities in contrast sensitivity and retinal functions in β-thalassemic patients.
Patients and methods
Thirty patients diagnosed with b-thalassemia were included in this study. Detailed assessment of history and full ophthalmological examination were performed for all our cases. Contrast sensitivity and electroretinogram were performed for all our cases.
Results
Thirty β-thalassemic patients were included in this study. The mean age of the patients was 37 years; most of our patients were women. The main presenting symptoms were discomfort in night vision. Contrast sensitivity was significantly low in all our cases and electroretinogram showed low scotopic visual sensitivity in 23 cases.
Conclusion
Ophthalmic follow-up in β-thalassemic patients is mandatory.

Keywords: B-thalassemia, contrast sensitivity, electroretinogram, visual evoked potential


How to cite this article:
El-Sersy TH, El-Saed HW. Contrast sensitivity in β-thalassemic patients. J Egypt Ophthalmol Soc 2015;108:153-5

How to cite this URL:
El-Sersy TH, El-Saed HW. Contrast sensitivity in β-thalassemic patients. J Egypt Ophthalmol Soc [serial online] 2015 [cited 2022 Sep 28];108:153-5. Available from: http://www.jeos.eg.net/text.asp?2015/108/3/153/168723


  Introduction Top


Over the years, several reports have shown the involvement of the neuro-ophthalmological system in β-thalassemic patients.

Neuro-ophthalmological complications have been attributed to various factors such as chronic hypoxia, bone marrow expansion, iron overload, and deferoxamine neurotoxicity [1].

An acquired diffuse elastic tissue defect that resembles inherited pseudoxanthoma elasticum has been observed with a significant age-related frequency in hemoglobin disorders, especially β-thalassemia, and has been held responsible for a number of complications observed in these cases, some of which are quite severe [2].


  Patients and methods Top


Thirty β-thalassemic patients were selected randomly from Ain-Shams University Hospitals and included in this study. All the patients were subjected to a detailed assessment of history and a full ophthalmological examination. The examination included best-corrected visual acuity, slit-lamp examination of the anterior segment, fundus examination using an indirect ophthalmoscope, and measurement of intraocular pressure using applanation tonometry.

Electroretinogram, visual evoked potential, and contrast sensitivity measurement were performed for all our cases.

The measurement of contrast sensitivity involves the recognition of light and dark stripes or gratings that reflect light in a sine wave pattern and are displayed at variable spatial frequencies and contrast values. The spatial frequency of the stripes increases along the horizontal axis from left to right and the contrast decreases on moving up the vertical axis. As the frequency of the stripes increases to the minimum resolvable acuity (30-40 cycles per second or 1-0.5 min of arc), contrast between the stripes decreases and the highest resolvable frequencies can only be seen with high contrast; beyond this point, the grating appears as uniform grayness. As the spatial frequency reduces, there is insufficient contrast to distinguish the stripes from the background illumination. It is thus possible for patients to retain a good Snellen acuity, but have a reduced threshold at lower levels of contrast sensitivity.

Electroretinographic a-wave and b-wave responses and dark adapted visual thresholds were obtained from all our patients. A quantitative model of the activation of phototransduction was fitted to the a-waves to estimate the gain of the transduction processes and the saturated amplitude of the rod photoresponse. From b-wave stimulus/response functions, the saturated b-wave amplitude and an index of b-wave sensitivity (log sigma) were calculated.


  Results Top


Thirty patients previously diagnosed with β-thalassemia were included in this study. The mean age of the patients was 37 years; the age of the patients ranged from 24 to 53 years in our study. Most of our patients were women (80%), with no significant change in the visual abnormalities in terms of sex.

Ophthalmic examinations of all our cases bilaterally showed slowly progressive bilateral visual loss (best-corrected visual acuity ranged from 6/36 to hand movement).

In our study, measurements of contrast sensitivity at four spatial frequencies were performed for all our cases. Contrast sensitivity function was significantly low for all spatial frequencies tested in all our cases, with no significant correlation with age.

In the electroretinogram for all patients, both the gain and the saturated amplitude of the rod response were normal. In 22 patients, log sigma was below the 99% prediction interval for the normal standard. Twenty-seven patients had low scotopic visual sensitivity.


  Discussion Top


International collaboration is needed to establish the risk factors for central nervous system sequelae in patients with β-thalassemia, leading to evidence-based prevention [3].

In this study, 30 β-thalassemic patients were selected randomly from Ain-Shams University Hospitals. All cases were subjected to a detailed assessment of history and full ophthalmological examinations. Contrast sensitivity and electroretinogram were measured in all our cases.

The mean age of the patients in our study was 37 years; most of our patients were women. The main presentations were detective night vision.

Low scotopic visual sensitivity in electroretinography was detected in 27 of our patients.

Jiang et al. [4] reported that scotopic retinal function is altered in thalassemics.

Abnormal findings in the visual, auditory, and somatosensory evoked potential recordings can be mainly attributed to iron chelation therapy (deferoxamine) neurotoxicity. However, nerve conduction velocity abnormalities are associated either with chronic hypoxia and older age or with hemosiderosis, whether by means of pancreas involvement or not (Zafeririou et al., 2006) [1].

To our knowledge, no other authors have reported any findings on electroretinograms or contrast sensitivity changes in β-thalassemic patients.

Thus, monitoring of the retinal function in thalassemic patients is recommended, especially those receiving blood transfusion or chelation therapy. Early detection of the neuro-ophthalmic pathway impairment is important for appropriate management to achieve better quality of life in thalassemic patients [Figure 1],[Figure 2],[Figure 3],[Figure 4],[Figure 5] and [Figure 6].
Figure 1: Graph showing the age distribution of the patients in our study.

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Figure 2: The lines of this clinical test chart show contrast sensitivity. They are most visible near the center of the chart, but disappear on either side.

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Figure 3: Decrease in contrast sensitivity at different freque ncies.

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Figure 4: The Vistech contrast sensitivity test for distance VCTS 6500.

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Figure 5: Marked reduction of scotopic b-wave amplitudes noted at different intens ities.

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Figure 6: Scotopic electroretinographics (ERGs) obtained with the highest flash intensity stimulation (delayed a-wave and b-wave implicit times and reduced b-wave amplitude).

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  Acknowledgements Top


Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Zafeiriou DI, Economou M, Athanasiou-Metaxa M. Neurological complications in beta-thalassemia. Brain Dev 2006; 28 :477-481.   Back to cited text no. 1
    
2.
Aessopos A, Floudas CS, Kati M, Tsironi M, Giakoumi X, Livir-Rallatos C, Farmakis D. Loss of vision associated with angioid streaks in beta-thalassemia intermedia. Int J Hematol 2008; 87 :35-38.   Back to cited text no. 2
    
3.
Zafeiriou DI, Prengler M, Gombakis N, Kouskouras K, Economou M, Kardoulas A, et al. Central nervous system abnormalities in asymptomatic young patients with Sbeta-thalassemia. Ann Neurol 2004; 55 :835-839.  Back to cited text no. 3
    
4.
Jiang C, Hansen RM, Gee BE, Kurth SS, Fulton AB. Rod and rod mediated function in patients with beta-thalassemia major. Doc Ophthalmol 1998; 96 :333-345.  Back to cited text no. 4
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]


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Abstract
Introduction
Patients and methods
Results
Discussion
Acknowledgements
References
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