Diagnosis/Therapy in Ophthalmology

Central corneal thickness andcorneal diameter in prematureinfants

Caitriona Kirwan,1 Michael O’Keefe1,2,3 and Susan Fitzsimon1

1Children’s University Hospital, Dublin, Ireland2Rotunda Hospital, Dublin, Ireland3University College Dublin, Dublin, Ireland

ABSTRACT.

Background: Central corneal thickness is significantly greater in full-term infants

than in adults. Very little is known about corneal thickness in premature infants.

Methods: Measurements of central corneal thickness and horizontal corneal

diameter were carried out in 35 premature babies (70 eyes) undergoing screening

for retinopathy of prematurity. Initial measurements were taken at � 31 weeks

gestational age and at intervals until term was reached.

Results: Babies born at � 31 weeks have very thick corneas which show a

progressive and statistically significant decrease to term. Conversely, horizontal

corneal diameter shows a progressive significant increase to term. A very strong

inverse correlation was found between these two parameters.

Conclusion: We demonstrate that premature infants have thick corneas and

small corneal diameters. Central corneal thickness decreases dramatically from

� 31 weeks to term and is mirrored by a significant increase in corneal diameter.

Key words: central corneal thickness – corneal diameter – premature infants

Acta Ophthalmol. Scand. 2005: 83: 751–753Copyright # Acta Ophthalmol Scand 2005.

doi: 10.1111/j.1600-0420.2005.00559.x

Introduction

A number of studies have demon-strated that central corneal thicknessin full-term infants is significantlygreater than in adults (Ehlers et al.1976; Autzen & Bjornstrom 1991).Furthermore, a previous study of cor-neal thickness in premature infantsdemonstrated a decrease in cornealthickness from 33 weeks gestationalage to term (Portellinha & Belfort1991; al-Umran & Pandolfi 1992). Theaim of this study was to record central

corneal thickness and horizontal cor-neal diameter in infants at 31 weeksgestational age, to document thechange from this time to term and todetermine if a correlation existsbetween central corneal thickness andcorneal diameter.

Methods

A prospective study of changes in cen-tral corneal thickness and horizontalcorneal diameter in premature infants

undergoing screening for retinopathyof prematurity was carried out. Eyeswith other abnormalities such as catar-acts were excluded from the study.Screening commenced in all infantsbetween 30 and 32 weeks gestationalage at which time initial measurementswere taken. Subsequent measurementswere taken at 2–3-week intervalsas appropriate until full-term wasreached.

Central corneal thickness measure-ments were recorded using a handheldultrasound pachymeter (DGH 55; DGHTechnology Inc., Exton, Pennsylvania,USA). This pachymeter utilizes a soundvelocity of 1640 m/second. Threerecordings were taken in each eye andthe pachymeter was programmed so thateach recording represented an average of20 measurements. The recording withthe lowest standard deviation waschosen to represent the central cornealthickness. Horizontal diameter wasdetermined using callipers and takingwhite-to-white measurements. Allinfants had lid speculae inserted andmeasurements were recorded at thesame time as funduscopy was performedwhen screening for retinopathy ofprematurity (ROP).

Measurements were recorded atvarying gestational ages: 30–32 weeks,34–35 weeks, 37–38 weeks and then atterm (39–41 weeks). Using a singledata point from each baby, the meancentral corneal thickness values in eachgestational age group were determinedand compared using the two-tailed

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t-test. Similar analysis was conductedon the mean corneal diameter in eachgroup, again utilizing one data pointfrom each baby in each age group.The correlation between central cor-neal thickness and corneal diameter ineach group was determined using thePearson product moment correlationcoefficient.

Results

There were 70 eyes of 35 babies (20boys, 15 girls) in the study. The meangestational age at birth was 28.3 weeks(range 23–32 weeks) and the meanbirth weight was 1006 g kilograms(range 490–1380 g). Initial measure-ments were recorded at a mean gesta-tional age of 31 weeks and at intervalsuntil term. Mean central corneal thick-ness at the initial measurement wasfound to be 691 mm (Table 1). Thiswas associated with a mean horizontalcorneal diameter of 8.0 mm. Centralcorneal thickness measurementsshowed a progressive decline from theinitial to the final measurement atterm, at which time a mean of 564 mmwas obtained (Fig. 1). Conversely, hor-izontal corneal diameter showed a con-tinuous increase over the same periodto a mean value of 9.6 mm at term(Fig. 2). Determination of the Pearsonproduct moment correlation coefficientrevealed a very strong inverse

correlation between central cornealthickness and corneal horizontal dia-meter from initial measurement toterm (� 0.97); decreasing central cor-neal thickness was very strongly asso-ciated with increasing corneal diameter(Fig. 3).

Discussion

The issue of corneal thickness hasattracted increasing attention since theOcular Hypertension Treatment Studyidentified central corneal thickness asimportant in the diagnosis of glaucoma(Brandt et al. 2001). It concluded thatmeasurement of central corneal thick-ness should be an essential part of thework-up of patients with ocular

hypertension. Thinner corneas havelower intraocular pressure readingsand thicker corneas have higher read-ings. Central corneal thickness variesamongst racial groups and in thosewith glaucoma syndromes (Shimmyoet al. 2003). Increased central and per-ipheral corneal thickness in newbornsis thought to be due to prolonged eyeclosure (al-Umran & Pandolfi 1992).Decreasing thickness after birth isthought to be due to improved hydra-tion control. Thickness decreases invalue from that found in prematureand term babies to an adult value inchildren aged 2–4 years. A previousstudy in 1991 examined central cornealthickness in 13 eyes of prematureinfants born at less than 33 weeksgestational age (Portellinha & Belfort

Table 1. Gestational age, central corneal

thickness and horizontal corneal diameter at

30–32, 34–35, 37–38 and 39–41 weeks gesta-

tional age.

Gestational Central Horizonta

age corneal corneal

(weeks) thickness diameter

(mm) (mm)

30–32

Mean 691 8.0

SD 87 0.2

34–35

Mean 648* 8.5*

SD 72 0.3

37–38

Mean 605* 8.9*

SD 59 0.3

39–41

Mean 564* 9.6*

SD 34 0.5

* Statistically significantly at p < 0.05.

500

550

600

650

700

750

800

Gestational age (weeks)

Mea

n ce

ntra

l cor

neal

thic

knes

s(m

icro

ns)

30–32 34–35 37–38 39–41

Fig. 1. Graph showing the change in mean central corneal thickness from 30 weeks gestational

age to term.

7.5

8.5

9.5

10.5

Gestational age (weeks)

Mea

n ho

rizon

tal c

orne

aldi

amet

er (

mm

)

30–32 34–35 37–38 39–41

Fig. 2. Graph showing the change in mean horizontal corneal diameter from 30 weeks gestational

age to term

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1991). It demonstrated a progressivedecrease in thickness from 33 weeks toterm. It found no correlation betweengestational age, birth length and weightand central corneal thickness.

The exact mechanism that deter-mines central corneal thickness has inour view not been fully elucidated.Premature infants of less than30 weeks gestational age have hazycorneas and in most infants this pre-cludes fundal examination. However,in the vast majority of infants there issufficient corneal clarity after 31 weeksto permit funduscopy. This findingindicates that central corneal hydrationplays an important role in determiningcorneal thickness in babies up to31 weeks gestational age. After this webelieve that other factors influencethickness. This study shows that adecrease in corneal thickness was clo-sely correlated with an increase in cor-neal diameter. This finding suggests

that growth of the eye, with possibleremodelling and stretching of collagenfibres, plays a significant role in thereduction of central corneal thickness.The mandatory screening for ROP ofpremature infants born under 31 weeksgestational age and under 1500 g pro-vided us with a population of prema-ture infants for this study (Cryotherapyfor Retinopathy of PrematurityCooperative Group 1996). We wereable to measure central corneal thick-ness and corneal diameter at varyingintervals from 31 weeks to term. Therecent introduction of a predictablehandheld pachymetry instrumentenabled easy measurement of centralcorneal thickness.

In conclusion, this study demon-strates that premature infants at31 weeks gestational age have thickcorneas and small corneal diameters.They undergo a dramatic shift betweenthis time and term, with a reduction in

corneal thickness that is mirrored by anincrease in corneal diameter.

Referencesal-Umran KU & Pandolfi MF (1992): Corneal

diameter in premature infants. Br J

Ophthalmol 76: 292–293.

Autzen T & Bjornstrom R (1991): Central cor-

neal thickness in premature babies. Acta

Ophthalmol (Copenh) 69: 251–252.

Brandt JO, Beiser JA, Kass MA, Gordon MO

& Ocular Hypertension Treatment Study

(OHTS) Group (2001): Central corneal

thickness in the Ocular Hypertension

Treatment Study (OHTS). Ophthalmology

108: 1778–1788.

Cryotherapy for Retinopathy of Prematurity

Cooperative Group (1996): Multicentre

trial of cryotherapy for retinopathy of

prematurity: Snellen visual acuity and

structural outcome at 5.5 years after

randomization. Arch Ophthalmol 114:

417–424.

Ehlers N, Sorensen T, Bramsen T & Poulsen

EH (1976): Central corneal thickness in

newborns and children. Acta Ophthalmol

(Copenh) 54: 285–290.

Portellinha W & Belfort R Jr (1991): Central

and peripheral corneal thickness in new-

borns. Acta Ophthalmol (Copenh) 69:

247–250.

Shimmyo M, Ross AJ, Moy A & Mostafavi R

(2003): Intraocular pressure, Goldmann

applanation tension, corneal thickness and

corneal curvature in Caucasians, Asians,

Hispanics and African Americans. Am J

Ophthalmol 16: 603–613.

Received on February 22nd, 2005.

Accepted on July 12th, 2005.

Correspondence:

Professor Michael O’Keefe

Suite 5

Mater Private Hospital

Eccles Street

Dublin 1

Ireland

Tel: þ 353 1 885 8626

Fax: þ 353 1 885 8490

Email: mokeefe@materprivate.ie

550

600

650

700

7.5 8 8.5 9 9.5 10

Horizontal corneal diameter (mm)

Cen

tral

cor

neal

thic

knes

s (m

icro

ns)

Time

Fig. 3. Graph showing a strong inverse correlation between mean central corneal thickness and

mean horizontal corneal diameter from 31 weeks gestational age to term.

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