The Effect Of Optical Amplification On The Measurement Of Retinal Nerve Fiber Layer Thickness With Frequency Domain OCT In Different Degree Myopia

Background and ObjectiveMyopia is one of the most common diseases in ophthalmology,The incidence of myopia is increasing,which endangers human health,especially HM.HM is a serious refractive error,often accompanied by fundus diseases,such as macular degeneration,glaucoma,retinal detachment and posterior scleral staphyloma,etc,which seriously affect the vision of patients and even lead to blindness.POAG is the main type of glaucoma associated with myopia,which may be related to the long axis,wide angle and deep anterior chamber of myopia.There is a great relationship between myopia and POAG.The moderate and high myopia make the optic disc more prone to depression and reduce the tolerance to damage.The increase of intraocular pressure can change the refractive state of the eye and further aggravate the degree of myopia.Therefore,accurate discriminate of myopia,POAG and myopia combined withPOAG are of great clinical significance.HD-OCT is often used to measure RNFL thickness in clinic,but the area of human optic disc varies greatly.the larger the area of the optic disc,the larger the area of the rim.The conventional HD-OCT measurement of RNFL thickness at the ring with 3.4 mm scanning diameter can produce larger errors.At the same time,the growth of eye axis is different in different degree of myopia.But HD-OCT system uses fixed eye axis length to scan.With the increase of eye axis,the scanning range increases,resulting in optical amplification effect,which results in errors in measurement results.In view of the above situation,Littmann formula can be used clinically to eliminate optical amplification effect and make the measurement results more accurate.In this study,we collected myopic patients of different degrees and normal persons.After HD-OCT examination,all patients used Littmann formula to eliminate optical amplification effect,and observed RNFL thickness of myopic patients of different degrees,so as to provide more evidence for clinical practice.Materials and MethodsA total of 85 myopic patients who were scheduled to undergo myopia correction,healthy persons in the ophthalmology department of the Second Affiliated Hospital of Zhengzhou University from September 2017 to March 2018 were selected.One eye of each case was randomly selected for study.All subjects were divided into emmetropic group 20 cases,low myopia group 21 cases,moderate myopia 20 cases,high myopia group 24 cases.All subjects underwent best corrected visual acuity,intraocular pressure,diopter measurement,axial measurement,HD-OCT examination and visual field examination.Before and after correction of optical amplification effect,the difference of RNFL thickness between each group and quadrants,and the correlation with the length of eye axis and diopter were observed in the emmetropic group,low,moderate and high myopia groups.Results1.There were no significant differences in gender and age(P>0.05)between subjects with emmetropia,low myopia,moderate myopia,high myopia group.There were significant differences in axial length and diopter(P<0.05)between subjects with four groups.2.In the emmetropic,low myopia,moderate myopia and high myopia,the thickness of average RNFL,upper,lower and nasal quadrants before correction were negatively correlated with the length of ocular axis,positively correlated with refraction(P<0.05),Temporal quadrant thickness was positively correlated with axial length,but negatively correlated with diopter(P<0.05)The average RNFL,upper,lower and nasal quadrant thickness after correction were not correlated with axial length and diopter(P>0.05),while temporal quadrant was positively correlated with axial length and negatively correlated with diopter(P<0.05).3.Among the four groups of emmetropic,low,moderate and high myopia,the average RNFL,upper,lower and nasal quadrants of the emmetropic group before correction of optical magnification effect were significantly thicker than those of the other three groups(P<0.05).There was little difference between low and moderate myopia(P>0.05).The average RNFL,upper,lower and nasal quadrants of the high myopia group were significantly thinner than those of the other three groups(P<0.05).The temporal quadrant thickness of visual acuity was significantly thicker than that of the other three groups(P<0.05).The difference between low and moderate myopia groups was small(P>0.05).The temporal quadrant thickness of emmetropic group was significantly thinner than that of the other three groups(P<0.05).4.In the emmetropic,low myopia,moderate myopia and high myopia,therewere no significant difference in the mean RNFL,upper,lower and nasal quadrant thickness between the four groups after correction of optical magnification(P>0.05),but there was still significant difference in the temporal quadrant thickness between the four groups after correction of optical magnification(P<0.05).The temporal quadrant thickness in the emmetropic group was thinner than those in the other three groups,and that in the high myopia group was significantly thicker than those in the other three groups(P<0.05).Conclusions1.With the increase of myopia degree before correction of optical magnification effect,the thickness of retinal nerve fiber layer in the upper,lower and nasal quadrants decreased,while that in the temporal quadrant increased.After correction of optical method effect,the thickness of temporal quadrant was different with the increase of myopia degree,but there was no difference in other phenomena.2.Littmann formula can effectively correct the optical amplification effect and reduce the error of measurement results.