The Foundational And Clinical Research Of Corneal Traumatic Astigmatism

BackgroundOcular trauma is common clinically. After cornea wound healing, astigmatismemerged and disturbed visual function as scar formed. Sometimes the astigmatism isdifficult to be corrected by spectacles or excimer laser. Oculists have been striving toexplore and improve operation methods to correct corneal astigmatism for a century.These operations are effective in astimagtism treatment, but there are also manydefects and restricts in practice. Up to now, correcting traumatic corneal astimagtismby operation hasn't been reported. Based on the anatomical and physiologicalchataracters of cornea and the pathophysiology procedure of corneal wound healing,this research explored the prevention and treatment measures about traumatic cornealastigmatism from foundational and clinical aspects. The foundational part studieddrugs effects on lessening corneal scars forming in the early healing period of cornealwounds. In the clinical part, operations were designed and performed to correcttraumatic corneal astigmatism 3 months after cornea wounds suture, meanwhileoperations effects were investgated. The results confirmed that the traumatic cornealastagmatism can be corrected effectively by drugs and operations. On the basis of thetreatments mentioned above, spectacles and excimer laser proved practical.Partâ… The influence of TGF-β₂ASON to the corneal injuries rehabilitionObjectiveResearchs have proved that TGF-βplays an important role in organism wound healing. Among them,TGF-β₂ is the initiator of corneal wounds repair and it isfeasible to controll the repair procedure by regulating the actaviting of TGF-β₂In this study, rabbit models of corneal perforating injuries were made andTGF-β₂ ASON were designed and applied to transfect the scars tissue of post-suturecorneal perforation. To reveal the influence of TGF-β₂ ASON to TGF-β₂ actaviting incorneal injuries rehabilition, the changes in morphous, histio-structure,cell proteinquantities and gene expression were observed and analysised by slitlamp observation,HE staining,immunohistochemistory and real-time PCR. The results provided atheoretical ground for the presumption of reducing corneal scars forming by drugs.Methods1. The preparation of TGF-β₂ anti-sense oligodeoxynucleotide (TGF-β₂ASON)Reference to the sequence of TGF-β₂ mRNA (Gene bank AY429466),ShanghaiSangon Biotechnology co. synthesized a piece of ASON that is 21 bp.Its sequence is5'-AGAAGTTGGCATTATACCCTT-3'. as a control, a piece of missense oligodeoxy-nucleotide(MSON) were synthesized.2.A total of 24 clearing, healthy Newzealand rabbits which are three monthsold were used.Randomization: Experiment group were sixteen, all whose corneas were madecornea perforating injuries and then sutured. After surgery the TGF-β₂ ASON wasgiven to their left eyes as TGF-β₂ ASON group and the normal saline(N.S) was givento their right eyes as N.S group. Eight rabbits were in control group and did notreceive operation. Samely TGF-β₂ ASON was given to their left eyes as TGF-β₂ASON group and the N.S to their right eyes as N.S group. We took out of theircorneas on the 4th,7th,14th and 28th day after operation. Six rabbits were executed oncetime.Observation index: observing the morphologic changes of cornea scars with slitlamp, detecting theα-SMA staining of fibroblasts and FN with immunohisto-chemistry, analyzing the mRNA expression of TGF-β₂ with real time fluorescencequantitative RT-PCR. Thenevaluating the TGF-β₂ toxicant effect and the influence to the cornea rehabilition.Results1.Slitlamp observationTGF-β₂ ASON group: Bulbar conjunctiva hyperemia slightly, the cornea edmaaroud the suture, aqueous flare (0～+), iris clear, the pupil round, IOP normal. Theinflammation released gradually and eliminated utterly 1 week after operation NSgroup: The cornea edema apparently, aqueous flare (+～++),iris blurred, the pupilirregular, IOP normal. There are lots of new vessels near limbus. The inflammationreleased gradually and eliminated utterly 2 weeks after operation, but the new vesslesaren't vanished.2.Histopathology resultsThe TGF-β₂ ASON group: Epithelial cells grew 1～2 layers on the 4th day afteroperation and fibroblasts increased to 9/HP in the stroma, whose bodies became largeand applanatus. On the 7th day, epithelial cells grew 4～5 layers, arrangingirregularly,and fibroblasts in the stroma increased to 12/HP. On 14th day, epitheliumalmost became integrity, fibroblasts reduced and collogen fibril arranged loosely.The N.S group: epithelial cells grew 4～6 layers on the 4th day after operation andfibroblast increased to 21/HE On the 7th day, epithelial cells grew 4～5 layers,arranging irregularly, and fibroblasts in the stroma increased to 18/HP. On the 14thday,epithelium arrange irregularly little, fibroblasts increased persistently andcollogen fibril arranged closely.In the control group, the appearance of the TGF-β₂ ASON group were similar tothe N.S group under the high power lens, which proved TGF-β₂ ASON was safe.3.Immunohistochemistry resultsThe TGF-β₂ ASON group: positive fibroblasts ofα-SMA staining rised to peakon the 7th day after operation and returned to the basic line on the 14th day. The N.Sgroup: positive fibrobiasts ofα-SMA staining rised to peak on the 4th day afteroperation and reduced gradually, but on the 14th day, there were still a few positivefibroblasts. On the 4th and 7th days after operation,positive fibroblasts in the TGF-β₂ASON group were fewer than that in the N.S group and the difference is significant statistically (P＜0.05).Fibronectin: fibronectin stained in the TGF-β₂ ASON group was fewer than inthe N.S group and loosely distributed in the stroma layer aroud the cornea wound,butin the N.S group fibronectin distributed thickly.4.The results of the real time RT-PCRThe TGF-β₂ ASON group: the mRNA of TGF-β₂ expression in 4d, 7d, 14d, 28dis respectively 0.0851±0.0034, 0.1371±0.0086, 0.0756±0.0031, 0.0660±0.0008. theN.S group is 0.1921±0.0103,0.1892±0.0109, 0.1622±0.0110, 0.1280±0.0135. In thesame periods, the difference of TGF-β₂ mRNA expression is significantstatistically(p＜0.05).Conclusions1.TGF-β₂ ASON can specificly block the transcription and translation of TGF—β₂ and restrain the synthesis of TGF-β₂ mRNA, so to regulate the healing process ofcornea injuries. In the process, TGF-β₂ reduce scar forming by restrained fibroblasticactivation and accumulation of collagen and fibronectin.2.After suture of injured cornea the most activating period of fibroblast migrationand proliferation is 4d～7d after operation. The evident restraining effect ofTGF-β₂ ASON to positiveα-SMA fibroblast is within 14 days after operation, thusregulating corneal rehabilation in the early period is the key of reducing scarsforming.3. Real time fluorescence quantitative RT-PCR is feasible technique to examinethe microamount gene expression of rabbit cornea. It is high specific, quantitateaccurately, and reliable.Partâ…¡The regularity study of traumatic corneal astigmatism and the operationexplore of correcting corneal astigmatismObjectiveThis research was divided into two parts.The first part was to explore the relationship andregularity between traumatic corneal scars and astimagtism.The second part systematicallyelucidated the operation methods and provided theory ground for astigmatism correction operation Chapterâ… The regularity study of traumatic corneal astigmatismMethods30 cases(30 eyes) of suffering from corneal perforation injuries and consistingof screening standard were collected in the study and accepted examinations ofcorneal topography,computer and retinoscopy optometry(＜35y applying forcycloplegica) and took photographs under slitlamp.The following items wereprecisely surveyed and recorded: the shape, length and location of corneal scars, theastigmatism power and axial direction. In order to explore the relationships betweencorneal scars and the power of corneal astigmatism, these datas were entered into thetable and made correlation analysis and regression analysis.Results1. The correlation analysis showed that the correlation coefficient between thelength of corneal scars and the astigmatism power is 0.563(p＜0.01), which provedcorrelation between the scars length and astigmatism. The regression equation is thefollowing: Y=1.703+0.478X. Hypothesis test of the equation model indicated F=13.023,P=0.001,which proved to be positive correlation between them, I.e.the scars lengthincrease 1 mm,the power of astigmatism will increase 0.478D correspondingly2. The relations among the shape, length, and location of corneal scars and thetype of astigmatism and the astigmatism power are the following:â‘ the scarsparallelling to the corneal limbus resulted in myopic astigmastism as the suture madethe meridian perpendicular to the scar steepâ‘¡the scars perpendicular to the corneallimbus resulted in hypermetropic astigmastism as the suture made the meridianperpendicular to the scar flat.Chapterâ…¡The study of correcting corneal astigmatism by operationMethods22 patients(22 eyes) of traumatic corneal astigmism were collected randomlywhich were 3 months after the corneal suture operation and whose types ofastigmatism are variant. The astigmatism power of all the cases exceeded 2.5D,the length of corneal scars exceeded 4mm.1.preoperative examinationIncluding slitlamp examination, fundus examination, IOP measurement,measuring the scars length precisely,recording the shape and position of scars,computer and retinoscopy optometry: recording naked vision,corrected vision,theastigmatism power and axial direction, corneal topography examination(TMS,AMOOBSCANâ…¡): recording the astigmatism power and axial direction and analyzingcorneal steep and flat meridian, examinations of contrast sensitivity, stereoscopicvision and wavefront diffrence.2. The design and principle of operation(1)the shape and location of incision: to remain apparent cornea utmostly,theincisions were designed to locate in flat meridian behind corneal limbus0.5～1.0mm,which are a pair of symmetrical bracket-shaped incisions parallelling tocorneal limbus. The length of incisions are 90°radian and the depth is 3/4 sclera'sthickness. Then we wedge excised little tissue of sclera and sutured the incision, sothe flat meridian became steep after the operation,meanwhile the steep meridianbecame flat due to "the couple effect", so the myopic astigmatism was corrected.(2)The width calculation of wedge excision: According to Gullstrand'sschematic ocular,a calculating formula was deduced as following: D_V=(n′-n)/(r-x/Ï€)-D_AD_V represents the corrected power of astigmatism, x represents the width of wedgeexcision. Such as, when x is 0.1mm, the Dv is 0.73. Due to the "coupling effect", theactual corrected power of astigmatism is: 0.73×(1+1/2)=1.1D, which is similar withTroutman's test value. However, when x is 0.2ram, the actual corrected power ofastigmatism is 1.4D, and when x is 0.3mm the corrected value is 1.7D. Similarily we cancalculate the the width of wedge excision according to the preoperative astigmatismpower.(3)The calculation of corrected astigmatism power: the corrected astigmatism power must be considered preoperatively according to "the laws of cornea flexiblehemisphere" and "the couple effect". According to Troutman's theories, for example,when wedge excision and stretching suture were done on the flat 90°meridian,themeridian will become steep, meanwhile the 180 meridian will become flat. Theproportion of refractive power change is 2:1.3. Operation methodA pair of incisions on the corneal fiat meridian behind corneal limbus 0.5-1ramwere made symmetrically.The length of incisions is 90°radian and the depth is 3/4sclera's thickness. The width of incision is the calculation according to the formulathat had been deduced, then we sutured the incisions with 10-0 polypropylene stitchand adjusted the tensity with the Placidou ophthalmometer and buried the knot.Results1.The change of postoperative dioptric stateThe preoperative power of corneal astigmatism was averagely 5.13±0.85D andthe postoperative power of corneal astigmatism was 1.42+0.22D, reduced 3.71Daveragely. The remain power of astigmatism didn't exceed 2.0D and the axialdirection of astigmatism changed within 5°～10°. The astigmatism powerfluctuated within 0.5～1.0D 3 months after operation.2.The change of visual function(1)The postoperatative visual: the preoperative average uncorrected vision was0.23±0.12 and the postoperative vision improved to 0.62±0.26. The preoperativeaverage corrected vision was 0.8±0.25 and the postoperative corrected vision was0.94±0.18. The difference is significant statistically (P＜0.01)(2) The postoperatative OrbScan-â…¡examination: the preoperative value ofSimK was 45.03±2.16D and the postoperative value was 43.75±1.98D,which wasapproximate to normal value of 43.05±1.20D. The postoperative corneal topographyimproved apparently(3) Postoperative CS test: There are no significant difference betweenpreoperation and 1 month after operation, but the CS between preoperation and 3months after operation showed significant difference (P＜0.01). (4)Postoperative stereoacuity test: comparing to 17 (77.3ï¼…) patients included inthe 400"～200" group preoperatively, only 8(36.4ï¼…) patients were remained 3months after operation. Datas showed that more than 60ï¼…had the stereoacuitywithin 100" 3 months after operation.(5)The test of postoperative wavefront aberrations: the majority could not beensurveied as severe aberration made by corneal scars, so the datas had not been dealwith statistically.Conclusions1. Among the patients of traumatic corneal astigmatism, the scars parallelling tocorneal limbus formed myopic astigmatism, and the scars perpendicular to corneallimbus formed hypermetropia astigmatism.2. On the paracentral, peripheral and limbal zone of cornea, the length of linear scarsand the astigmatism power is positive correlation, the linear regression equation is:Y=1.703+0.478X. I.e.the scars length increase 1ram, the power of astigmatism willincrease 0.478D correspondingly3. Paired wedge shape excision combined stretching suture behind limbus is asafe and effective surgical operation for correcting astigmatism. It can correct thesimple or compound hypermetropic astigmatism between +2.50D～+4.00D and themyopia astigmatism which lower than -2.00D.4.According to Gullstrand's schematic ocular,a calaculating formula was deduced.Caculating and analyzing indicated: it is nonlinear correlation between the width of thewedge shape excision and corrected astigmatism power. But the accurate details andthe applied perspective need more investigation and verification.