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  5. FP1311 : The Outer Nuclear Layer Normative Data from Population Based Study in Central India

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Dr. Sameeksha Agrawal, S20207, Dr. Nangia Vinay Kumar B, Dr. Sarang Lambat, Dr.Hemangi Rathi

 

Introduction. The outer nuclear layer  (ONL)  constitutes a significant part of the retinal thickness and its involvement is well known in diabetic maculopathy (DM)   and many retinal conditions. The ONL is also involved in   increasing  the thickness  of the retinal as a whole  in diabetic macular oedema.  It often manifests the presence of cystic accumulations of fluid.  It is also known to be increased in thickness in several other retinal pathologies.  While in patients with atrophic  diseases,  it may also reduce in thickness.  In order to determine the exact role and the contribution to retinal thickness in normal and  pathologic states, it is important  that normative data should be available from a population based study.    Normative Data for the thickness characteristics of  the ONL for Central India were not available. It was the purpose to determine the normative values in a population based study in Rural Central India to give perspective to changes in thickness in various conditions.

Methods:  200 subjects  aged 40+ years were  selected randomly from 550 subjects that were studied  from two villages in rural Central India. Subjects were brought to the hospital for undergoing  the interview and examination. All subjects underwent a sociodemographic assessment, followed by an  ophthalmic evaluation  along with post meal blood sugar and recording of the  blood pressure.  The ophthalmic evaluation included,  Vision with ETDRS,  refraction, slit lamp biomicroscopy, applanation tonometer, gonioscopy,  dilatation, fundus evaluation, followed by colour photography and spectral domain OCT for retinal layers and for the retinal nerve fiber layer.  Segmentation was performed using the Spectralis software ( V) . Where necessary manual segmentation was done if the automated segmentation was  considered inaccurate. Only the right eyes were included for analysis for this study.  Subjects with  history of glaucoma or with intraocular pressure of more than 22mm.Hg,  history of anti glaucoma medications, any previous  intraocular surgery,  history of  diabetes or with  post meal blood sugar of more than 200 mg%, and history of hypertension or with systolic BP of > 140mmHg or diastolic BP of >90 mmHg.  were excluded, as were subjects with a VA of <0.32 DU. Eventually 134 subjects were included, (75 females).  The mean age was 53.34+10.57 yrs. Mean sph. equ was 0.17+1.8 D. Mean VA in DU was 0.78+0.24.  The mean axial length was  22.67+-0.78 mm.  The mean IOP was 12.46+2.91 mmHg.

Results:

The mean value of the total retinal thickness in 1mm circle was  262.68+-47.58u.

The mean values for outer nuclear layer thickness  were as follows:

Global 96.91+12.41u, average thickness in 1mm circle 84.14+-11.04u.  ONL Values for ETDRS  3 mm circle  quadrants were, nasal 71.66+-11.46 u, superior 66.15+-11.80u, temporal 69.72+-9.23u, and inferior 63.19+-10.19u. Values for the 6 mm circle quadrants were, nasal 54.71+-7.80u, superior 57.25.66+-7.05u, temporal 54.33+-6.53u, and inferior 49.91+-7.80u.  The percentage ratio of thickness occupied by ONL vs retinal thickness was 32.42+-4.38 in the inner 1mm. ETDRS circle.   Table 1.  Figure. 1.  There was a significant reduction in thickness  at distances away from the fovea.

Discussion: ONL values were determined for the first time in a population based study in Central India.   The  ONL is part of the photoreceptor complex and  contains the nuclei of the cone and rod photoreceptors. (1)   Swelling of this layer or atrophy of this layer would therefore affect the visual function of the retina.  and the Normative values have been determined for the ONL which occupies a significant percentage of the central retinal thickness in the foveal region. It may be mentioned that  Henles layer is also often included in the measurements of the ONL when measured using the automated segmented techniques. (2)  In DM the ONL is specially important since a number of pathologies manifest here.  Normal values would also enhance the ability to diagnose perhaps early disease, which may affect the photoreceptors.  ONL thickness alterations have been reported in various conditions including outer retinal atrophy, geographic atrophy and ABCA4 mutations.(3,4,5)    Changes in ONL thickness have been found also in normal ageing.(6,7)  The thickness of the ONL which occupies a substantial part of the retinal thickness specially  in and around the fovea  would be expected to be involved at an early stage. This may also lend   a particular condition to early diagnosis,  in asymmetric early stage involvement.  Normative data may provide a reference value and  comparative clues in determining  early involvement  of the ONL in diabetic maculopathy and other retinal conditions

References:

  1. Hogan, MJ.; Alvarado, J.; Weddell, J. Histology of the Human Eye. Philadelphia, PA: W.B. Saunders; 1971. p. 444-57.
  2. Lujan, J B Roorda A, Croskrey J et. al. Directional Optical Coherence Tomography ProvidesAccurae Outer Nuclear Layer and Henle Fiber Layer measurements. Retina, 2015 August; 35(8):1511-1520.
  3. Spaide RF. Outer retinal atrophy after regression of subretinaldrusenoid deposits as a newly recognized form of late age-related macular degeneration. Retina. 2013; 33(9):1800–8. [PubMed: 23764969]
  4. Savastano MC, Minnella AM, Tamburrino A, et al. Differential vulnerability of retinal layers to early age-related macular degeneration: evidence by SD-OCT segmentation analysis. Invest Ophthalmol Vis Sci. 2014; 55(1):560–6. [PubMed: 24408984]
  5. Huang WC, Cideciyan AV, Roman AJ, et al. Inner and outer retinal changes in retinal degenerations associated with ABCA4 mutations. Invest Ophthalmol Vis Sci. 2014; 55(3):1810– 22. [PubMed: 24550365]
  6. Eliasieh K, Liets LC, Chalupa LM. Cellular reorganization in the human retina during normal aging. Invest Ophthalmol Vis Sci. 2007; 48(6):2824–30. [PubMed: 17525218]
  7. Gartner S, Henkind P. Aging and degeneration of the human macula. 1. Outer nuclear layer and photoreceptors. Br J Ophthalmol. 1981; 65(1):23–8. [PubMed: 7448155]

Table 1.   Systemic and  Ocular Characteristics.

Mean and SD
Age. yrs. 53.34+10.57
Height. cms. 156.78+-9.14
Weight. Kg. 50.01+-10.81
Blood Pressure Sys. mm.Hg. 125.62+-22.52
Blood Pressure Diastolic. mm.Hg. 75.41+-14.22
Sph. Equi. Dioptres 0.17+1.8
BCVA. DU 0.78+0.24
Axial length 22.67+-0.78
IOP. mm.Hg. 12.46+2.91

 

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