Mean Keratometric Values Research Articles

Análise de nova técnica para o implante do anel de Ferrara no ceratocone

OBJETIVO: Descrever nova técnica para o implante do anel de Ferrara por meio de incisão única e avaliar segurança e eficácia em pacientes com ceratocone. MÉTODOS: Estudo prospectivo em vinte pacientes com ceratocone, submetidos ao implante por meio desta nova técnica. Critérios de exclusão: boa adaptação a lentes de contato, presença de cicatrizes corneanas significativas, ápice do cone com mais de 65 dioptrias, paquimetria inferior a 400 micra no local da incisão e presença de doenças oculares ou sistêmicas que contra-indicassem a cirurgia. Acuidade visual (LogMAR) e medida do ápice corneano pela topografia foram as variáveis analisadas no pré e pós-operatório. Foram registradas possíveis complicações ou queixas relacionadas às cirurgias. Período mínimo de um ano de acompanhamento. RESULTADOS: A acuidade visual média não corrigida melhorou de 1,045 ± 0,478 (mediana de 1,150) no pré-operatório, para 0,586 ± 0,373 (mediana de 0,500) unidades LogMAR, após doze meses de pós-operatório (p<0,0001). A acuidade visual com correção melhorou de 0,714 ± 0,542 (mediana de 0,500) para 0,264 ± 0,162 (mediana de 0,200) unidades LogMAR (p=0,001). A média do ápice corneano pela topografia variou de 55,9 ± 4,4D no pré-operatório, para 51,5 ± 4,8D após doze meses de pós-operatório (p<0,0001). Após o terceiro mês de cirurgia, todos os pacientes evoluíram com estabilização da acuidade visual. Não houve complicações ou queixas durante o período estudado. CONCLUSÃO: O implante do anel de Ferrara, por meio de incisão única, determinou melhora da acuidade visual, sem correção e com correção, e aplanamento corneano significativos no grupo estudado, após doze meses de cirurgia.

Correcting the corneal power measurements for intraocular lens power calculations after myopic laser in situ keratomileusis

Purpose To describe and evaluate a refraction-derived method and a clinically derived method to calculate the correct corneal power for intraocular lens (IOL) power calculations after laser in situ keratomileusis (LASIK) and to compare the results to the commonly used history-derived method. Design Interventional case series. Methods Retrospective analysis of consecutive cases from clinical practice. Two hundred randomly selected eyes from 200 patients were evaluated before and after LASIK surgery. For each patient, we established the pre-LASIK and post-LASIK spectacle refraction, the pre-LASIK (Kpre) and post-LASIK K readings (Kpost). We then calculated for each case the pre- and post-LASIK refraction at the corneal plane and the amount of correction obtained by the refractive surgery (CRc). The cases were divided into two groups. Group I was used to derive the two formulas. The K values were calculated using the history-derived method (Kc.hd) in which Kc.hd = Kpre – CRc. Kc.hd was compared with Kpost. The average difference was 0.23 diopters for every diopter of myopia corrected. This value was used to calculate the corneal power using the refraction-derived method (Kc.rd) where Kc.rd = Kpost –0.23CRc. A regression equation was used to develop a clinically derived method (Kc.cd) where Kc.cd = 1.14Kpost –6.8. The values obtained with the two methods were compared with the Kc.hd values in group II to validate the results. Results Both Kc.rd and Kc.cd values correlated highly with Kc.hd when plotted on a scattergram ( P < .001), and there was no statistically significant difference between the mean keratometric values ( P > .5). Conclusions The corneal power measurements for intraocular lens power calculations after LASIK need to be corrected to avoid hypermetropia after cataract surgery by either the history-derived method, the refraction-derived method, or the clinically derived method.

Central corneal thickness is lower in osteogenesis imperfecta and negatively correlates with the presence of blue sclera

Osteogenesis imperfecta (OI) is a rare, autosomal-inherited, connective tissue disorder characterised by bone fractures, deafness and blue sclera. Additional ocular findings are decreased ocular rigidity, myopia, glaucoma, keratoconus, corneal opacity, small corneal diameter and congenital Bowman's layer agenesis. This cross-sectional, masked, case-control study aimed to assess whether central corneal thickness (CCT) is affected in patients with OI and to focus on the clinical significance of scleral blueness. Twenty-three children with OI (13 boys, 10 girls) and 15 age-, sex- and refraction-matched healthy control subjects (eight boys, seven girls) were assessed for CCT by ultrasound pachymetry. The CCT was compared between two different patient subgroups (type-I OI with blue sclera, n = 12; type-IV OI without blue sclera, n = 11). Mann-Whitney U-test or analysis of variance was used as indicated and only right eyes of each subject were included in statistical analysis. Results were expressed as mean +/- S.D. and statistical significance was taken as p < 0.05. Mean age and sex distribution was similar between the groups (10.1+/-2.5 vs 9.8+/-1.8 years, p > 0.05). Patients with OI had significantly lower CCT (459.5+/-24.6 microm) than in control subjects (543.6+/-21.4 microm; p < 0.001). The CCT was below 500 microm in 22 of 23 children (95.6%) with OI, 15 of which (65.2%) were below 450 microm. In contrast, CCT was over 500 microm in all eyes in the control group. Type-I OI eyes with blue sclera had significantly (p = 0.005) lower CCT readings (446.5+/-16.3 microm) than type-IV OI eyes without blue sclera (473.6+/-25.0 microm). Mean keratometric values were similar between the groups (44.2+/-1.7 vs 43.8+/-1.6 dioptre, p > 0.05). Mean cycloplegic refraction was similar between the groups (-0.32+/-0.5 vs -0.18+/-0.4 dioptre; p > 0.05), although five of 23 OI patients had myopia, and mean intraocular pressure was lower in OI patients than controls (12.7+/-1.8 mmHg vs 15.6+/-1.9 mmHg; p < 0.001). The CCT is thinner and negatively correlated with the blueness of the sclera in patients with OI. The CCT readings may therefore be of utmost importance in the diagnosis of OI. An ophthalmologist should be aware of an artificially low intraocular pressure measurement in such patients. In addition, when considering a keratorefractive treatment, CCT must be evaluated carefully to avoid unexpected results or complications. Sturdy protective spectacles should be prescribed to those who are not bed bound. Possible correlation of low CCT with biochemical changes in scleral collagen or systemic parameters awaits further investigation.

Astigmatism associated with Fuchs' heterochromic iridocyclitis.

To determine whether there is inherent corneal astigmatism in patients with Fuchs' heterochromic iridocyclitis (FHI). A case-controlled study of 48 patients with unilateral FHI was conducted. These patients had no history of previous surgery or previous diagnosis of glaucoma or cataract. The controls were the fellow eyes of the patients, and the cases were the FHI eyes. All eyes were refracted, and the results were analyzed with descriptive and parametric statistics. Twenty-one women and 27 men were studied. The mean age was 39.5 years. The mean keratometric value for the astigmatism in the FHI eye was 2.2 diopters (D) (standard deviation +/-1.19) and 0.96 D (+/- 0.64) in the controls (p= 0.000). Refractive astigmatism was 1.44 D (+/-1.45) in FHI eyes and 0.38 D (+/-0.62) in the controls (p= 0.000). Patients with unilateral FHI have inherent corneal astigmatism in the disease eye.

Comparison of Keratometric Readings as Obtained by Javal Ophthalmometer and Corneal Analysis System (EyeSys)

We examined 92 normal eyes using Javal Ophthalmometer and Corneal Analysis System (EyeSys) intending to compare the keratometric readings obtained by these two instruments. Dioptric power and location at flatter and steeper meridians, keratometric astigmatism values, and average central keratometric power were measured in the central cornea of all eyes. Statistical analysis showed significant differences in flatter meridians' mean power values (mean difference = 0.13 D, P = .008), mean keratometric astigmatism values (mean difference = -0.20 D, P = .001) and steeper meridians' location (mean difference = 7 degrees, P = .0001). There was no significant difference in steeper meridians' mean power values (mean difference = -0.06 D, P = .38), flatter meridian location (mean difference = 5.9 degrees, P = .07), and mean average central keratometric power (mean difference = 0.03 D, P = .471). Clinically meaningful difference was observed only in keratometric astigmatism readings of eyes with keratometric astigmatism higher than 1.50 D (mean difference = -0.84 D). For all the other parameters measured, the differences between the two instruments readings were clinically acceptable.

Ocular Refraction After Penetrating Keratoplasty with Infant Donor Corneas

Five adult patients underwent penetrating keratoplasty in which corneal tissue from donors 3 months old or younger was used. In each case, a large myopic shift in refraction was found after surgery (mean, 9 diopters). The average postoperative spherical equivalent was -7.35 diopters. This resulted from the extremely steep curvature of the infant donor cornea (mean keratometric value, 57.67 diopters). The induced anisometropia and steep corneal topography of the infant donor cornea prevented visual rehabilitation with spectacles or contact lenses in four of five patients. Our findings suggested that corneal tissue from donors 3 months old or younger may be unsuitable for penetrating keratoplasty in emmetropic adults or anisometropic patients undergoing surgery in the more myopic eye.