To compare the measurements of contrast sensitivity at a distance in patients submitted to penetrating keratoplasty versus patients submitted to deep anterior lamellar keratoplasty for keratoconus treatment.
METHODSContrast sensitivity of 15 subjects submitted to penetrating keratoplasty and 15 subjects submitted to deep anterior lamellar keratoplasty have been analyzed through the Functional Acuity Contrast Test (F.A.C.T®) 301.
RESULTSThere was no statistically significant difference between the measurements for penetrating keratoplasty and deep anterior lamellar keratoplasty.
CONCLUSIONContrast sensitivity was similar among the subjects submitted to penetrating keratoplasty and to deep anterior lamellar keratoplasty for keratoconus treatment.
Comparar as medidas de sensibilidade ao contraste à distância entre pacientes submetidos à ceratoplastia penetrante e pacientes submetidos à ceratoplastia lamelar anterior profunda para tratamento do ceratocone.
MÉTODOSSensibilidades ao contraste de 15 pacientes submetidos à ceratoplastia penetrante e de 15 pacientes submetidos à ceratoplastia lamelar anterior profunda foram analisadas através do Functional Acuity Contrast Test (F.A.C.T®) 301.
RESULTADOSNão existiu diferença estatisticamente significante entre as medidas em ceratoplastia penetrante e ceratoplastia lamelar anterior profunda.
CONCLUSÃOSensibilidade ao contraste foi similar entre os pacientes submetidos à ceratoplastia penetrante e à ceratoplastia lamelar anterior profunda para tratamento do ceratocone.
The keratoconus is a bilateral corneal disease that attacks 1 out of 2,000 people throughout the world1. It typically appears in late adolescents and young adults whose mean age is 22.4 years old.2 It is a progressive disease3 and the main cause of keratoplasty in young adults.4–5
Recent advances in surgical techniques have encouraged an exchange of treatment methods for corneal disease surgery. Many types of lamellate techniques are replacing the technique of penetrating keratoplasty. This is primarily because lamellate techniques keep the healthy tissue uncut and replace the modified tissue.6
Deep anterior lamellar keratoplasty is a safe method to treat keratoconus surgically. It is also similar to the penetrating keratoplasty method in terms of the visual acuity results and the lack of risk of endothelial rejection.7–9
Snellen visual acuity is used for a long time as a successful method of checking the result of surgeries. However, during the last two decades studies have shown that there are different aspects of visual function, not solely the acuity aspect, which is compromised in patients who suffer from vision opacity and corneal irregularity.10–13 Another of those aspects consists of contrast sensitivity, which has been widely accepted as a visual quality indicator.14
This study used the contrast sensitivity method to identify and analyze differences in quality of visual function for patients who had either undergone penetrating keratoplasty or deep anterior lamellar keratoplasty surgery to treat keratoconus.
METHODSSubjects for this study voluntarily agreed to participate after the purpose of the research had been explained to them.
Inclusion criteria were as follows: a best-case spectacle-corrected visual acuity of ≥ 20/30 in patients over 14 years old who had undergone keratoplasty and had no post-operative complications for at least 12 months.
The keratoconus diagnosis was based on refraction and the computerized topography of the cornea.
Exclusion criteria were as follows: a best-case spectacle-corrected visual acuity <20/30, other previous ocular surgery, or complications during or after surgery.
The patients were split into two groups:
Group I – Patients submitted to penetrating keratoplasty,
Group II – Patients submitted to deep anterior lamellar keratoplasty.
The corneas were kept and well-preserved in Optisol®.
The deep anterior lamellar keratoplasties were carried out through a deep dissection technique with air. The Descemet membrane and the corneal endothelium were kept intact.
Snellen visual acuity (VA) and the contrast sensitivity (CS) were measured in one eye of each of 15 patients in each group.
The Functional Acuity Contrast Test (F.A.C.T.® 301, Stereo Optical, Chicago, IL) was used to perform the contrast sensitivity test. The distance was set at 10 feet (3.05 m) and the light between 68 and 240 cd/m2. The test was performed with spectacle correction. The test, which is based on a table with grades, measures the contrast sensitivity of five different spatial frequencies: 1.5 cpd (cycles per degree), 3.0 cpd, 6.0 cpd, 12.0 cpd and 18 cpd. The results can be evaluated by the Snellen Functional Acuity Equivalent or assessed separately in each spatial frequency.
The measures of each spatial frequency and the Snellen Functional Equivalent values were compared between the two groups. The Student's t test was used to verify if the mean values of the groups were different. The level of significance was 5% for the statistical analysis (p < 0.05).
Demographic data were also considered.
RESULTSThe age of the patients in Group I (penetrating keratoplasty) varied between 14 and 34 years old, with a mean of 25.5 ± 6.64. Group II (deep anterior lamellar keratoplasty) patients’ ages varied between 14 and 49; the mean age was 28.3 ± 13.2 (Table 1).
Group I had eight (53.3%) female patients and seven (46.7%) male patients. Group II had eight (53.3%) male patients and seven (46.7%) female patients (Table 1).
All patients were accounted for at 12- and 24-month follow-ups.
The best spectacle-corrected visual acuity in Group I was 20/30 in seven (46.7%) patients, 20/25 in seven (46.7%) patients and 20/20 in one (6.6%) patient; For Group II, this distribution was 20/30 in eight (53.5%) patients and 20/25 in seven (46.5%) patients. The mean values of visual acuity were 0.74 (± 0.09) for Group I and 0.72 (± 0.07) for Group II (p = 0.48) (Table 2).
Table 3 shows the refraction values and visual acuity with spectacle correction in each case.
Refraction and Visual Acuity
| Patient | GROUP I Refraction | VA | Patient | GROUP II Refraction | VA |
|---|---|---|---|---|---|
| 1 | + 2.00 - 3.00 40° | 20/30 | 16 | +3.00 -3.00 15° | 20/30 |
| 2 | −3.50 - 3.00 180° | 20/30 | 17 | −0.50 -3.50 120° | 20/25 |
| 3 | −2.25 -3.75 90° | 20/30 | 18 | −2.00 -3.00 85° | 20/30 |
| 4 | −1.00 -1.75 55° | 20/25 | 19 | −6.00 - 3.50 85° | 20/30 |
| 5 | +2.00 -3.00 60° | 20/30 | 20 | −0.50 -2.00 150° | 20/25 |
| 6 | −2.00 30° | 20/25 | 21 | −5.00 -2.00 25° | 20/30 |
| 7 | −1.50 -3.50 90° | 20/30 | 22 | +3.00 | 20/30 |
| 8 | −3.00 -2.00 20° | 20/25 | 23 | +0.50 -3.00 40° | 20/30 |
| 9 | −2.00 -2.00 35° | 20/25 | 24 | −0.50 -2.00 10° | 20/25 |
| 10 | −0.50 -3.00 185° | 20/30 | 25 | −2.50 5° | 20/25 |
| 11 | −0.50 -2.00 170° | 20/25 | 26 | −2.50 -1.50 75° | 20/30 |
| 12 | −1.00 -1.50 10° | 20/25 | 27 | −1.00 -1.00 35° | 20/25 |
| 13 | −1.00 -2.00 80° | 20/25 | 28 | −2.00-1.00 180° | 20/25 |
| 14 | −2.00 -1.00 30° | 20/20 | 29 | −1.00 -1.50 60° | 20/25 |
| 15 | −6.00 -2.25 60° | 20/30 | 30 | −0.50 -2.50 30° | 20/30 |
VA: Visual Acuity.
There was no statistically significant difference in contrast sensitivity in any spatial frequency evaluated between the groups. The mean value and the standard deviation presented for all frequencies were. (Table 4 and Figure 1).
Comparison of the results in each spatial frequency.
| Spadai frequency | Group I | Group II | |||
|---|---|---|---|---|---|
| Mean Score | Standard Deviation | Mean Score | Standard Deviation | Significance | |
| 1.5 cpd* | 6.0 | ± 1.15 | 6.2 | ±0.79 | p = 0.65 |
| 3 cpd | 4.2 | ± 1.55 | 4.2 | ±1.55 | p = 0.40 |
| 6 cpd | 3.1 | ± 1.79 | 3.1 | ±2.23 | p = 1.00 |
| 12 cpd | 1.9 | ± 1.37 | 1.2 | ±0.42 | p = 0.14 |
| 18 cpd | 1.6 | ± 1.07 | 1.1 | ±0.31 | p = 0.19 |
For to the Snellen Functional Acuity Equivalent, Group I showed a mean value of 0.317 (± 0.177) and Group II, 0.290 (± 0.133; p = 0.644). There was no statistically significant difference (Table 5).
DISCUSSIONMany studies have reached the conclusion that deep anterior lamellar keratoplasty yields great visual results in treating keratoconus; further, it risks neither endothelial failure nor endothelial rejection.7–9,15
Others have concluded that the best spectacle-corrected visual acuity results are similar between penetrating keratoplasty and deep anterior lamellar keratoplasty.8,17
Studies have shown how useful the contrast sensitivity test is in assessing the progress of keratoconus, while also providing a successful evaluation method for keratoplasty.16,19
Recent studies have revealed no differences related to contrast sensitivity at a distance when comparing penetrating keratoplasty patients against deep anterior lamellar keratoplasty patients. Results have also shown that visual acuity after deep anterior lamellar keratoplasty is dependent on the thickness of the residual recipient stromal bed, with a better visual acuity in cases with less residual stromal thickness.19
This study has shown that further contrast sensitivity had similar statistical values in all spatial frequencies evaluated (1.5 cpd; 3.0 cpd; 6.0 cpd; 12.0 cpd and 18.0 cpd) between Groups I and II.
CONCLUSIONFor tests of contrast sensitivity at a distance in one-year-post-operative surgery patients, the deep anterior lamellar keratoplasty procedure has shown similar results to the penetrating keratoplasty procedure for treatment of keratoconus.