Key-words:
Libya - normal macular thickness - optical coherence tomography - spectral domain
Introduction
Macular thickness is key to the treatment and follow-up of patients with various ocular diseases.[[1]] Nussenblatt et al. claimed that the thickness of macula and not the occurrence of macular edema is correlated with changes in visual acuity.[[2]]
Optical coherence tomography (OCT) is a valuable technique that measures retinal thickness quantitatively and provides information helping in the diagnosis, management, and follow-up of patients with retinal diseases.[[3]],[[4]],[[5]]
Many studies reported an association between macular thickness and demographic variations such as different races, gender, and age, which should be taken into consideration when diagnosing macular diseases.[[6]],[[7]],[[8]],[[9]] However, there is no data for normal macular thickness for the Libyan population. Our report is the first for the measurement of macular thickness in healthy Libyans' eyes.
Subjects and Methods
The study was conducted at the Ophthalmology Outpatient Department at Alkeish polyclinic, Benghazi, Libya, between January 1 and December 31, 2018. During the study period, the clinic was serving patients from all around Benghazi city as well as the population from the east and some parts of the south of Libya.
This study included 243 healthy eyes of 131 Libyan adults of both genders. The chosen adults were Arab Libyans attending the clinic complaining of dry eye, headache, reading problems, and some volunteering 4th-year medical students. All the participants underwent complete medical and ophthalmic history and examination, including best-corrected visual acuity and assessment of intraocular pressure (by Goldman applanation tonometry). Slit-lamp biomicroscopic evaluation using +90 D lens was performed to exclude any posterior segment pathology.
Exclusion criteria were any history of diabetes mellitus or any other systemic disease that could affect the eye, history of glaucoma, intraocular pressure higher than 21 mmHg, previous intraocular surgery, eyes with media opacity that might obscure OCT view, evidence of vitreoretinal disease, amblyopia, visual acuity <6/9 Snellen, or refractive errors of > +4.00 or [[10]] An average retinal thickness (mean macular thickness) was declared for all the nine regions, along with the total macular volume. Macular thickness was defined as the distance between the vitreoretinal interface and the outer border of the retinal pigment epithelium.
Data were presented as mean ± standard deviation. Statistical analyses were performed using Statistical Package for the Social Sciences (Windows version 23.0; SPSS Inc., Chicago, IL, USA). P < 0.05 was considered statistically significant.
Results
Out of 131 adults (243 healthy eyes) included in this study, 52 adults (40.0%) were male with 101 eyes and 79 adults (60.0%) were females with 142 eyes (when the media was clear, both eyes were chosen, but sometimes, due to media opacity [cataract or corneal opacity], only one eye was chosen). The mean age of the study population was 48.3 ± 16.6 years (range: 21–79 years). The mean ± Sd of retinal thickness by sector is shown in [[Table 1]]. The mean thickness is lower centrally, and then it increases in the internal perifoveal ring and subsequently decreases in the external perifoveal ring. In addition, the thickest quadrant is the internal nasal followed by the internal superior. The thinnest quadrant is the external temporal.
Table 1: Mean retinal thickness and macular volume for the whole study population
[[Table 2]] illustrates the mean normality values by gender. Values of all male eyes are higher than those of female eyes, and most of these values were statistically significant (P < 0.05) (except for the external superior, inferior, and nasal).
Table 2: Results of macular thickness and volume by gender
Discussion
OCT device provides a noninvasive measurement for studying the structure and physiology of the eye with repeatability and reliability.[[5]],[[11]] Many studies demonstrated changes in macular thickness with race and gender,[[1]],[[7]],[[12]],[[13]],[[14]],[[15]] and to our knowledge, this is the first study to be done in Libyan adults.
The present study included 243 healthy eyes of 131 Libyan adults of both genders; as expected, the internal perifoveal ring is the thickest. Similarly, the nasal area was the thickest, whereas the temporal area was the thinnest part of the macular area; this is consistent with many previous studies and is explained well by the normal anatomy of the macula.[[13]],[[16]],[[17]],[[18]]
There are variations in the retinal thickness among different ethnic populations. Grover et al.[[13]] reported a higher central foveal thickness in caucasian compared to Africans. In the present study, the central foveal thickness was 230.3 ± 18.3 μm, which is comparable to the foveal thickness of 229.0 ± 20.5 μm reported by Adhi et al.[[19]] On the other hand, this result was less compared to that reported by many studies (which ranged between 244 and 270 μm)[[1]],[[13]],[[16]],[[17]],[[18]],[[20]],[[21]] and thicker than (221.9 μm) what was reported by Ooto et al.[[22]] The variations in retinal thickness among different races can be explained based on the hypothesis of the “attenuation of incident optical radiation by the increased pigment in the apical portion of the retinal pigment epithelium cells, leading to a decreased signal of posterior retinal segments and concomitant underassessment of retinal thickening in darkly pigmented persons.”[[13]]
The foveola's thickness (CPT) for the total study population in the present study (192 ± 22.4 μm) was thinner than other studies' reports.[[13]],[[16]] Nevertheless, the average thickness in this study was also less than what was described by many studies (range: 275.7–305.6 μm),[[1]],[[16]],[[20]] but thicker than what was reported by Adhi et al. (262.7 ± 13.3 μm).[[19]]
The thickness in all the ETDRS areas, as well as the total volume, was higher in males compared to females, and the thickness values were statistically significant for most of the areas except for the external ring, although this is not consistent with Grover et al.,[[13]] but it goes in agreement with many other studies[[1]],[[7]],[[17]],[[18]] and may be consistent with the observation that women having higher risk of developing macular hole.[[23]],[[24]] The limitations of the study include the lack of evaluation of some of the parameters that may affect the retinal thickness such as age, race, and axial length, which should be taken into considerations in future studies.
Conclusion
This report is a first study for normative data for macular thickness in healthy Libyans. These data should be taken into consideration when diagnosing macular diseases. The report demonstrated that the thickness in the foveola (CPT) is 192 ± 22.4 μm, the central foveal thickness is 230.30 ± 18.26 μm, and the average thickness is 270.1 ± 9.4 μm. It also revealed that males have a thicker macula than females, which indicates that gender must be considered while interpreting macular retinal thickness data.
Authors' contributions
This study was carried out by all the named authors. They have developed their assigned parts of the manuscript and reviewed the other parts. All authors reviewed and agreed the final version of the manuscript.
Compliance with ethical principles
The study was approved by the Research Ethical Committee of the Martyr Sohail Al-Atrash Eye Hospital, and all participants provided informed consent before enrollment in the study.
Reviewers:
Riyad Banayot, (Hebron, Palestine)
Emmanuel Nartey (Durban, South Africa)
Editors:
Salem Beshyah (Abu Dhabi, UAE)
Elmahdi Elkhammas (Columbus OH, USA)
