The retinal ganglion cell density and nerve fiber layer thickness in the human myopic eye

Abstract

Purpose: The myopic eye is usually longer than an emmnetropic eye. Does this increase in size come predominantly from new growth of ocular tissue or from the "stretching" of existing tissues? One way to evaluate this is to investigate the distribution of retinal cells. It is speculated that in the case of stretching', the density of neural cells in the retina would be lower in the highly myopic eye when compared to an emmetropic eye. This stretching may affect the resolution acuity. Another approach is to investigate the thickness of the retinal nerve fiber layer. It is speculated that in a highly myopic eye, the retinal nerve fiber layer would be thinner when compared to an emmetropic eye. Methods: Sixty healthy Chinese subjects (35 males and 25 females; age range 20-29 years) were recruited from the student population of The Hong Kong Polytechnic University. Subjects were divided into two groups according to their refractive status: Low myopia, -0.50D to -3.50D (n=30) and high myopia, -6.00D to -15.00D (n=30). Using a psychophysical approach, the calculated retinal sampling density was evaluated in subjects with different levels of myopia using a custom-designed retinal acuity perimeter. A two alternative forced-choice staircase technique was used to determine the Nyquist frequency in 60 normal subjects. Using a clinical instrument, the Nerve Fiber Analyser (NFA)-GDx, the retinal nerve fiber layer (RNFL) thickness was measured in low and high myopic eyes. The average of three RNFL thickness maps was used for analysis. Results: We found that the retinal sampling density was significantly reduced with increasing myopia in both the central and peripheral retina. We also found that the RNFL thickness was significantly lower in highly myopic eyes when compared to low myopic eyes. Conclusion: We conclude that in high myopia, the enlargement of the globe is more likely to be achieved by tissue stretching than tissue growth, since the retinal sampling density and RNFL were reduced.