Measuring Refractive Components In Adolescent With Pentacam

[Background]:The exact measurement of keratometry and anterior chamber depth are of major importance for the implantation of intraocular lens(IOL)in refractive surgery and the research of refractive errors.IOLMaster is a noncontact device which employs partial coherence interferometry and has been proved good in accuracy and repeatability.IOLMaster presents more accurate and convenient results over traditional ultrasound methods in measuring optical components.Pentacam is a novel imaging device that uses a rotating Scheimpflug camera to image the anterior segment of the eye.It is a noncontact instrument,which conveniently provides maps of the cornea,anterior chamber,iris,lens and make a new choice to the anterior segment measurement.Due to short period use,there are fewer researches in comparison to IOLMaster.So it is necessary to evaluate its accuracy.[Objective]:To compare the difference of measurements of keratometry and anterior chamber depth(ACD)obtained with Pentacam and IOLMaster and evaluate the agreement of two instruments.[Methods]:169 young healthy volunteers(aged 20.80±1.29y/o)from Advanced Medical Specialized School Of Shandong Province were recruited.Both eyes refracted using auto-refractomer and manifestation refraction.Recruit criterior: Best corrected vision for both eyes≥1.0,no ocular diseases or history of contact lens wearing during the previous 24 hours.Pentacam and IOLMaster were used to examine keratometry and anterior chamber depth on both eyes.Left eye of each subject was investigated.The mean spherical equivalent was(-3.44±2.04)D. Difference in measurements of mean keratometry(K)[K=(K₁+K₂)/2]and ACD between two methods were assessed using Paired t test.Bland-Altman method was used to evaluate the agreement of two methods.[Results]:The mean K values were(43.35±1.49)D for Pentacam and (43.84±1.54)D for IOLMaster and the difference was significant(P＜0.01).The ACD were(3.65±0.21)mm for Pentacam and(3.70±0.22)mm for IOLMaster and the difference was significant(P＜0.01).The difference of K values and ACD values are respective used the Bland-Altmann method for analysis.The mean difference of K values((?))was 0.49D, the standard deviation(SD)of difference(S_d)was 0.29D with a probability of 95%, difference in K values did not exceed -0.09～1.06D and the maximum was 1.035D. The mean difference of ACD values((?))was 0.05mm,while the SD of difference(S_d) was 0.09mm with a probability of 95%.The difference in K values did not exceed -0.14～0.23mm and the maximum was 0.2mm.For clinical consideration,these two modalities showed incomparable results for K values and comparable results for ACD.[Conclusion]:Pentacam and IOLMaster can not be considered as interchangeable on measurement of keratometry,but can be interchangeable on measurement of ACD,especially for IOL calculation. [Background]:Cornea is the major optical element of eye and accounts for 2/3～3/4 of the whole refractive power.Asphericity of the normal anterior corneal surface coordinating with other refractive components can guarantee the quality of the image formed on the retina.The standard corneal refractive surgery,which based on the change in corneal curvature to compensate for refractive error,can change the corneal asphericity,so that the quality of postoperative vision deteriorated significantly.In order to enhance the quality of vision,the Q-factor guided corneal ablation has generated.The majority of myopic patients who performed excimer laser photorefractive keratectomy in our country is adolescent.There are a few reports about the distribution and related factors of Q-factor in adolescent.So the present study was conducted to observe the corneal asphericity and its related factors in adolescent.[Objective]:To assess the distribution of comeal Q-value in adolescent and the relationship between Q-value and other related parameters in order to supply the basis for customized ablation.[Methods]:203 young healthy volunteers(aged 21.13±1.39 y/o)from Advanced Medical Specialized School Of Shandong Province were recruited.Both eyes refracted using auto-refractomer and manifestation refraction.Recruit criterior: Best corrected vision for both eyes≥1.0,no ocular diseases or history of contact lens wearing during the previous 24 hours.IOLMaster was used to examine(AL)and the Pentacam was used to measure the smallest keratometry(K₁),the largest keratometry (K₂),anterior chamber depth(ACD),central corneal thickness(CCT)and Q-value. Q-value of four regions in cornea divided by the steepest and the flattest meridians were also measured using Pentacam.The mean keratometry(K)and spherical Equivalent(SE)were calculated according to the equation of K=(K₁+K₂)/2 and SE=S+C/2.369 eyes(203 cases)were categorized into four groups according to SE: emmetropia group,mild myopia group,moderate myopia group,high myopia group. Astigmatism was below 1.50D.The correlation between Q-value and other parameters were analyzed.[Results]:The Q-value was -0.249±0.134 with normal distribution and corneal curvature of majority become flatter from center to periphery(Q＜0).Q-value for the superior region was significantly different with the inferior region(P=0.000),same thing for the nasal region with the temporal region.Q-value was -0.230±0.143 for male and -0.252±0.132 for female without statistically difference between genders. The average Q-value for 58 eyes of emmetropia group was -0.249±0.164 and -0.249±0.128 for 311 eyes of myopia without statistically difference between them. The average Q-value of mild myopia group was -0.254±0.137;the average Q-value of moderate myopia group was -0.249±0.110;the average Q-value of high myopia was -0.226±0.144.There was no significant difference among these subgroups.The comeal Q-value was not related with refractive degree,the mean keratometry,central comeal thickness,and anterior chamber depth or axis ocular length.[Conclusion]:In emmetropic and myopic adolescent,corneal curvature of majority become flatter from center to periphery(Q＜0),minority become steeper from center to periphery(Q＞0).Q-value of differ regions in one cornea are different.The corneal Q-value has no relationship with gender,the refractive degree,the mean keratometry,central corneal thickness,anterior chamber depth and axis ocular length.