Study On The Visual Function Of Myopia After Excimer Laser Corneal Refractive Surgery And The Influence On The Stability Of The Postoperative Eyes With Hypoxia And Vertical Acceleration

In China, the current aeromedical standards for recruiting army pilotcandidates and pilots in service are emmetropia. However, there are somany people with myopia in our country. The incidence of myopia in pilotapplicants is increasing, which has greatly affected the choice to recruitpilots; while the incidence of late-onset myopia in trained pilots is alsoincreasing yearly. Myopia has been the main trouble in our military pilots.In the past20years, corneal refrective surgery (CRS) has been foundto be an effective method for improving vision in foreign air force (AF).The foreign AF gradually approved CRS to reduce dependence ontraditional optical correction with spectacles and contact lenses. Today, ithas become the main technical means to improve vision of military pilots.At present our pilot applicants and trained piolts are not allowed to correctmyopia through the CRS. Yet, in order to improve and keep militancy, thisprogram is gradually being performed.This study is to investigate the effect of excimer laser cornealrefractive surgery on the visual function (contrast sensitivity andstereovision) which greatly affect flying, and to further observe the affectswhich the flight environment (i.e. hypoxia) on visual quality (CS,stereovision, diopter, chromatic vision) and the safety (stability of thecorneal flap, intraocular pressure) after surgery, to evaluate the flightadaptability of CRS. We hope to provide clinical experimental basis to therevision of physical standard for our army pilots. Contrast Sensitivity(CS:22emmetropic pilots (44eyes),33low-to-moderate myopic(64eyes), spherical equivalent were (-3.4±1.3)diopters (D), corrected visual acuity(≥1.0);15postoperative (29eyes),spherical equivalent (SE) of preoperative was between-1.0D and-5.75D,average SE of postoperative were (-0.28±0.29) D, the time after theoperation were (4.47±0.83) years, uncorrected visual acuity(≥1.0). Theywere measured with CSF-1000, under photopic, scotopic andscotopic+glare in the dark environments. There was no significantdifference in the low spatial frequency (3cpd) among three groups(P>0.05). The CS of6,12cpd in pilots was better significantly than thepostoperative (P<0.05), others was no significant difference between them.The contrast sensitivity of pilots at the spatial frequency of6、12、18cpdwas better significantly than of myopic students (P<0.05).Stereo vision:84low-to-moderate myopic, average SE was(-4.17±1.09) D, corrected visual acuity (≥1.0);41high myopia patients,average SE was (-7.71±1.31) D, corrected visual acuity (≥1.0). We usedTitmus stereopsis test card to detect the near stereopsis of the subjectsbefore and after the operation one week,82of the low-to-moderate myopicafter the operation (97.62%) get foveal stereoacuity,73of the preoperative(86.9%.) get foveal stereoacuity, there was significant difference (χ2=5.336,P<0.05);39of the high myopia after the operation (95.12%) get fovealstereoacuity, and73cases accounted for86.9%of the preoperativecomparison was not statistically significant (χ2=0.625, P>0.05).The effects of hypoxia exposure on visual related function inpostoperative:20(aged23.8±1.2years) male volunteers after CRS wereexposed in hypobaric Chamber. Eligibility requirements included visualacuity (≥1.0), without operative complication, average SE of (-0.95±0.62)D. The refractive state, intraocular pressure, near stereovision, color visionand CS were measured during hypobaric hypoxia exposure at ground and5000m (exposed to10minutes), at the same time, corneal stability was observed with slit lamp. During the process of test subjects were not givenoxygen to ensure hypoxic effects, while the saturation of blood oxygen wasmonitored during hypobaric hypoxia exposure. There were no significantdifference between at ground and5000m in refractive state and intraocularpressure (P>0.05), the near stereopsis and coler vision was decrease(P<0.05), CS was depressed only at18cycles/degree in scotopic+glareenvironments (P<0.05). Slit lamp examination showed no morphologicalchanges of the cornea.Effects of vertical acceleration on the stability of corneal flap afterLASIK (laser assisted in situ keratomileusis) in rabbits： It was anexperimental study.24eyes (12Japanese white rabbits) with one weekpostoperative LASIK were randomly divided into2groups, the controlgroup without any simulator, the vertical accelerated group whichunderwent a controlled rapid-sequence ejection at+7Gz, in a cockpitejection seat simulator. The stability of corneal flap was observed withoptical microscope and transmission electron microscope (TEM).Comparision of the group of the stability of corneal flap. The differencesbetween the two groups was insignificant (P>0.05）.Based on this investigation, we conclude that the CS of thepost-operative myopia can achieve the level of emmetropic pilots. Afterrefractive surgery, stereopsis of the low-to-moderate myopia can recoverwell in the early post-operative period, but of high myopic patients can notobviously be improved. Hypoxia has little effect on interocular pressure,diopter, and CS except18cycles/degree in scotopic+glare environmentsafter surgery. Near stereopsis, color vision and CS of18cycles/degree inscotopic+glare environments can be reduced. Corneal flap is stable. Thevisual quality of the low-to-moderate myopia after excimer laser cornealrefractive surgery recover well, can meet applicable vision standards and beeligible for military medical benefits. Corneal flaps after LASIK in rabbitmodel subjected to vertical acceleration are stable.